Does anyone care to ask an amplifier designer a technical question? My door is open.
I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.
I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer. . Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.
I like to tell true stories of my experience with others in this industry.
I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.
On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.
I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.
Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.
Cary has had notoriously bad measuring amplifiers for as long as I can remember. They have long been the poster-boy amps when people want to argue the "measures awful, but sounds great" stance. Personally, it’s been far too long since I last heard a Cary amp for me to have an opinion on the sonic performance.
I just read the Stereophile review of your amp. Congratulations, it really does impress upon the reader that you know what you are doing!To see JA actually impressed with the measurements of a tube amp is really something.
As for this comment you made to someone else:
I would like someone to tell me why spend big bucks on cone speakers when there are better technologies.
I’m wondering which "better technologies" you are referring to.
Do I infer correctly from your comment to me about the QUAD 57 vs the Alan Jones monitor, that you are speaking of, for instance, electrostatic speakers?
If so, I can tell you why I prefer cone speakers.
I first fell in love with electrostatics in the 90’s and first owned the Quad ESL 63s. As did another audio pal. The shock of not hearing any box sound, and that amazing transparency and "hearing in to the recording" sensation were at first intoxicating. But after a while I found the sound too disembodied, too ghostly, like peering through a window in to another room where the music was happening, but it wasn’t "moving air" in the room I occupied. When I’d play my little old Thiel 02 monitors there was such a difference in palpability, aliveness and "thereness" that it just re-enforced what I was missing. That was the case even after I added the Gradient dipole subwoofers to the Quads. Still among the best sub/panel matches I’ve heard.
I still love to "visit" electrostatics (the Quad ESL 57s being my favorite), for their unique qualities. But every time I listen to an electrostatic, of any make, I come away happy to have moved on to cone speakers.That includes every hybrid I’ve ever heard: The cones seem to add some body, but only within their frequency range. As the frequencies climb up to where they are handled by the panel, the sound character changes to my ears to that ghostly quality, so I am always aware of this discontinuity.
I’m not sure if this problem is solvable. Though, one brand I find intriguing is the JansZen speakers, using the electrostatic panels in more of a sealed box design. I wonder if those might maintain the palpabiity and body in the sound, but I’ve never heard them.
My bad. I rarely go to shows. I meant showrooms. Audio store showrooms I presume are set up to show the gear at some approximation of optimability.
By “more power” I’m just going by where I set the volume control before and after. It was a surprise, as I thought there would be less, and I was pleased because in my layman’s view it meant less stress on the tubes and circuitry.
There wasn’t much more volume, as the goal was simplicity, as you say; stability, as I have observed; and even more transparency in the mids, as I have also observed, though the Jensen caps also had something to do with the transparency eventually.
So, if you are building OTL triodes too, Jon is not correct. There are more than three. But are you using the same design approach? You guys should talk to each other!
Also, I’m not sure what you mean by better technology than cone speakers. First off, the Altec is a horn/cone hybrid. That aside, while electrostatics have their virtues, they don’t move air the way a cone does, as someone here also observed. That’s what I mean by the dynamic punch of the Altecs. I’ve heard some great horn speakers, with prices in the stratosphere.
The serial number on my Altec dates them as 1954, the year I was born, lol. If it ain’t broke...
All
OTL amps like high impedance because they have lots of voltage but
limited current. Since current is the limit use the forumla
Power
= current squared x impedance. The amplifier max current is the same
for both speakers but 16 ohms gives you twice the power of 8.
@ramtubes Roger, I think if you revisit the above comments you will find them to be incorrect. An OTL has to be able to drive real world loudspeakers and so can produce the same currents at the output as any other amplifier. FWIW, the output tubes in most OTLs can easily blow a 10 amp fuse in certain situations without damage to the tubes.
Your use of the formula is not accurate. As an example (I think you have clio9's M-60s on hand) look at the output power at clipping into 4, 8 and 16 ohms. Now this is a smaller OTL, but I think you can see that its output power does not behave as you stated above. The half power of 16 ohms occurs at 4 ohms, not 8.
Two versions of the Futterman circuit. East coast/West coast. Harvey was
a hoot. I visited him and his gang around this time. Sadly or not, he
folded too. Is there a Futterman curse?
There most certainly is! Every manufacturer that has made a Futterman amplifier has had to go out of business. This is because there is more to the circuit than meets the eye, and no-one was able to do the execution such that a reliable amplifier resulted. The reliability problem is what drove them out. Of course, there are notable exceptions- the Fourier company simply under-rated parts and used sloppy construction, to the point where it would not have mattered what they made- they would have failed and gone out of business anyway. Harvey used surplus and unreliable capacitors in his amps (unreliable because they were not used in the right application).
Since I dont believe wire has a sound I prefer colors. I use all 9
colors in my amplifiers. With colors you can actually start to see the
circuit without a schematic.
If you look carefully you will find some long wires repeated so you could simplify things there.
Our wire is custom-built. Because of that we have to buy a lot of wire at any one time. The long wires repeated is so that all the power tubes have exactly the same series resistance involved (although the cathode resistors dominate that aspect) and transmission line effects are minimized (the output section has bandwidth to several MHz so stability is important). Once you understand how the dielectric behaves you find no need for Teflon.
If my amps are being run at levels that do not bring on distortion, why
do they still have that classic "tube-amp" character even at those low
listening levels? If it’s not the clipping characteristics that are
coming in to play...what is it that produces that classic tube sound as I
described it?
@prof The fact of the matter is that the amps make audible distortion, which is the coloration you hear. Below a certain low power level they can often be making more distortion than at higher levels!
I have a 3 disc LP set of Theodorakis’s “Canto General” that Atmosphere
produced, and I found the engineering to be disappointing. It has been
muddy, and there has been no bass to speak of.
@unreceivedogma There is plenty of bass on that recording! We had the biggest bass drum in the state at the time. But it is very deep, and some systems don't play it very well. Since I recorded it, I can use it as a reference and I can tell you that many tone arms don't play that bass right either.
first thanks for the input on Ralphs amp, speakers likely the dead ESL-63 I mentioned in another post. I am away from them but I am assuming with ago all the panels are toast, the limited fault tree look I have done so far indicates EHT power supply issues. I am away from them so do not know on panel color, will check that when home next. Thanks all for inputs on rebuilders.
I am away from my toolbox also but I will get DMM peak voltages measured today, SPL at 1 M
fun, real data will set you free was our mantra at work for 30 years...
Hears what JA had to say in Stereophile.. The Audio Research Reference 75 measures well for a classic tube amplifier design with a single pair of output tubes for each channel and a modest degree of loop negative feedback. Its output transformers are also of good quality, the only proviso being that the amplifier should not be used with loudspeakers whose impedance drops significantly below the nominal value of the output transformer tap Read more at https://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements#jbpCd1H...
I lack 99% of your engineering expertise, but I don't read the measurements as being as bad as you seemingly do. It seems to me that JA has a tendency to disagree with his own reviewer's perceptions as to which output tap is best rather than criticizing the design of this amp and it's output tap measurements per se. In some ways, this entire discussion is premised upon design expectations; should the amp designer account for every possibility or to some degree, is the end-user responsible for matching the amp to a suitable loudspeaker? It seems to me that you adopt the former view, which is somewhat quizzical given your avowed distaste for dynamic coned speakers and your view that ESLs/Planars are the only form of speaker that makes musical sense. For better or worse, at Stereophile high-dollar tubed amps seem to be always matched up with various iterations of Wilsons, none of which present graceful impedance curves. I find it curious in general, Roger, that you defend measurements of tube amps as meritorious in a vacuum (pun intended). You seem to imply that the measurements may not tell the complete story, but that just the same any mediocrity in the measurements that are utilized is sure to correlate with deficiencies in sound. In other words, I interpret your posts-not just in this thread but in others too-to be consistent with a person who adopts only the first half of the golden oldie phrase, "not all things that count can be measured and not all things that can be measured count". This may dismay you quite a bit from an engineering standpoint, but I take measurements of tube amps to be very analogous to measurements of DAC's; the best measuring DAC's don't often sound the best. They don't even necessarily render the so-called "musical truth" the best. Is there a known measurement of tubed gear that can predict a tube amp's ability to render the texture of a violin or the blat of a trumpet, the subtlety of David Rawling's plucking of a Martin acoustic, let alone sound stage width or depth? I do agree with you that for the price charged, ARC has no excuse for mounting tube sockets directly onto the PCB. But to my knowledge, that is a reliability issue and not a performance issue. I also agree with you that ARC gear is unnecessarily complex and hard to service. The same could be said for BAT and Lamm and yet they have great reputations. The sheer number of capacitors in both my ARC Ref 150SE and Ref 6 is either alarming or impressive depending upon one's point of view. Again, BAT and Lamm seem to adopt the same approach. Your own decision to go hybrid with your higher powered amp and to go true balanced with your higher powered amp but not your lowered power amp is a head-scratcher. If-as you state-monos are more susceptible to hum than stereo amps, why do you implement RCA-only vs. offering true balanced in the opposite direction? And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn't it indisputable that it is cheaper to produce and less complicated? You on the one hand have little good to say about Rogue and yet when it comes to hybrid tube amps, I think of Rogue (and Musical Fidelity though I don't count their "tubes" as tubes).
I would like to hear how each of you figured out how much power you needed to buy in watts?
Never bought by power. Always purchased by sound. Currently have 100 and 150w SS and 40w tube
84db 1w / 1m. min 3.2Ω, max 16Ω, mean 7Ω
Loud level is 90db C weighted slow measured with REW at seating pos 13ft from LS. Don't have low level. Each selection is listened at optimum for type. Sonic wallpaper is MP3 over internet in MONO, MP3 is intolerable in stereo.
On several occasions with lackluster sound at higher SPLS, I ended up purchasing more power elsewhere and that has worked.
HI, Roger here with a question.
I would like to hear how each of you figured out how much power you needed to buy in watts?
I would appreciate the following information in your response.
Your listening level LOUD SPL (preferably measured at 1 meter from the speaker with a REAL SPL meter. Your low listening level. If you are using a cell phone app then you have confirmed it?
Your speaker sensitivity?
Listening Distance from speakers?
How many watts at your load is the amp is rated to supply?
I figured it out by listening and trial and error over time and based essentially on those parameters as a guide. However specifications alone seldom tell the whole story. The devil is always in the details much of which is never specified. Detailed measurements like those in Stereophile help a lot but I have found there may still be surprises playing real music even with very comprehensive test measurements at ones finger tips, though if done correctly, measurements certainly help with the decision making process of what to try next or not.
Thanks for a lovely simple question. Preamps are much easier and to me not so interesting as power amps. In my career I have designed two major preamps, the RM-1 a very high performance preamp that was not at all easy and then the RM-5 which was quite easy.
With power amps I could go on forever. They are challenging because one has to consider the wide variety of loads they will encounter, there is a lot of energy so if things go *BANG* lots of stuff can be destroyed. I have designed dozens of power amps and only produced the ones I feel will perform well in a variety of systems.
Preamps are much easier and to me not so interesting as power amps.
From the heart, I don't want to tease you out and set you up for some type of audio sparring, a form of website f-erism I despise. I respect you and am willing to do my best to listen/read with an open mind. But that said, you can't possibly mean that preamps are easier in general and I am unaware of any accolades for your preamps (whereas you are lauded for your amps). Obviously you mean that for your tastes and purposes, preamps are easier than amps. Few would argue that the audio world is full of great amps and that there are a dearth of great preamps. I have an opinion that is not subject to proof-that the easier a loudspeaker is to drive (in terms of both impedance curve and sensitivity) the more a great preamp's sonic attributes are appreciated. A great preamp does more than attenuate a signal. It breathes life into music. A great preamp is quietly powerful, while a great amp simply provides grunt. Once again, purely resorting to engineering and lab measurements is a sure way to fail when it comes to preamps. A great preamp needs a great PSU section, preferably outboard. Lab measurements don't explain why a great PSU is so important to the performance of a preamp.
Your own decision to go hybrid with your higher powered amp and to go true balanced with your higher powered amp but not your lowered power amp is a head-scratcher. If-as you state-monos are more susceptible to hum than stereo amps, why do you implement RCA-only vs. offering true balanced in the opposite direction? And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn’t it indisputable that it is cheaper to produce and less complicated? You on the one hand have little good to say about Rogue and yet when it comes to hybrid tube amps, I think of Rogue (and Musical Fidelity though I don’t count their "tubes" as tubes).
I do not understand the first sentence at all. Where is the head-scratcher?
Sound, reliability, completeness of design, ease of service are all pretty equal in my mind. Sound is subjective. The other are objective and will bite you in the butt.
I think you misunderstand the RM-200 and RM-10 so lets get this straight. I dont like the term hybrid at all. In a good design we use the parts and circuits that do the job best. I wanted the RM-200 to have good CMRR (hum rejection in simple terms). One cannot do that with a tube at the input. One needs two active devices that are critically matched and stay matched. So I used a "supermatched pair". That is not a made up term but a technical term for a pair of transistors where each transistor is 100 transistors in parallel. I can trim the CMRR to 90 dB or better and it will stay that good for a very long time.
The RM-200 has many other special characteristics such as, fully balanced input to output, taps down to 1 ohm, reasonable damping, good power bandwidth. It also has something few amps do not have which is the abilty to drive a dipping load with increased power rather than decreased power. Neither CJ, Rogue, ARC or anyone else I can think of has done that.
The RM-10 is a sweet little EL84 amp that appears to delight QUAD owners, can be switched to mono or stereo with a unique driver circuit that does not require gain matching or summing resistors like the Stereo 70 and others do. You can look this up as to how stereo tube amps are converted to mono. BTW they are not bridged.
For a small amp like the RM-10 I saw now need and have not had even one request for balanced. The RM-10 is unique in that is produces 35 watt from one pair of EL-34s where most produce 17.5 watts. I spoke about this application at Burning Amp 2018. Perhaps you might watch the video. http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/
Monos are generally suseptible to hum because of power cord grounds. Not much else. I dont understand your point of "going in the opposite direction" The RM-10 is a very affordable amp. It is one of a very few tube amps that has no PCB. Its hand wired start to finish.
It seems to me that JA has a tendency to disagree with his own reviewer’s perceptions as to which output tap is best rather than criticizing the design of this amp and it’s output tap measurements per se.
As far as JA is concerned. The reviewer writes what he writes, JA measures and comments and sometimes wonders why the reviewer didn’t hear distortion or damping or whatever. He is trying to make sense of sometimes disparate opinions as I would. The reviewer does not see JAs measurements or comments till publication.
Read MIke Fremers lead in to the RM-200. To paraphrase, "I know I wont get caught with my pants down when JA measures this amp" In other words, he knows it will measure well. I am still amused at manufacturers like Cary where the marketing guy really got caught with his pants down.
I am far more interested in JA’s measurements than the fluff about this record and that CD sounded. The reviewers rarely tell us anyting about how much power they are using, what the speaker and amp interaction might be. IMO most of them listen around a watt. Should JA only measure up to a watt on a 100 watt amp where someone might really need 100 watts?
This may dismay you quite a bit from an engineering standpoint, but I take measurements of tube amps to be very analogous to measurements of DAC’s; the best measuring DAC’s don’t often sound the best.
This dismays me not at all. How does this analogy apply? A DAC drives no load at all. A speaker drives a host of loads and will sound different into each of them, with output impedance being the most obvious factor and distortion the next. How can you make such a statement?
Now if you think speakers should be matched with a particular amp then your are faced with the problem of changing both at the same time or hunting for another speaker that likes your amp or amp that likes your speaker.
I am proud to say that my amps sound damn good on a wide variety of speakers and that is what good engineering is all about.
Just to lay your mind at ease. Your ARC is not a bad amp at all. Im glad you like it. Its just not up to my standards.... or John’s as he warned in the end of his measurements.
What is intereresting is that current ARC power amps are not up to Bill Johnson’s standards. All of Bill’s amps were very low distortion, high damping. I dont particularly like the way he went about it but it is crystal clear that he valued those two parameters in all his amplifiers. The current designer has an entirely different set of values. I appreciate that he has gone to simplicity. Now all he needs to do is get the performance up a bit. What do we know about his background?
While I agree that not all things can be measured I am writing about things that can be measured and their effect can be understood.
May I ask since the RM-200 had both excellent sound according to Mike Fremmer and excellent measurements at half the price 33% more power, why did you not buy and RM-200?
I still love to "visit" electrostatics (the Quad ESL 57s being my favorite), for their unique qualities. But every time I listen to an electrostatic, of any make, I come away happy to have moved on to cone speakers.That includes every hybrid I’ve ever heard: The cones seem to add some body, but only within their frequency range. As the frequencies climb up to where they are handled by the panel, the sound character changes to my ears to that ghostly quality, so I am always aware of this discontinuity.
The term "visit electrostats", the 57 in particular is apt as I "visited" mine today. I am in the process of modifying a OTL amp to improve its "specs", cure offset drift and increase reliability and life of the tubes. I am using the 57 in that test because of its widely variant impedance and revealing nature. The differences are palpable.
I do not like all ESLs. Beveridge made a great one but it is very hard to place. The 57 as it was called. is truly "Walker's little wonder". I owned 63's and do not miss them. I like line sources. I like the wide dispersion and center fill that line sources produce. So perhaps its the line source I like the most. I have heard some large cone line sources and I would say they approach ESLs. But the drivers will never do what ESL drivers do.
I have been around ESLs all my life and sometimes when I hear cone speakers I just want to run out of the room. As far as moving air a 12 inch cone has to go a lot farther than a 4-8 sq ft piece of 1/2 mill mylar that has virtually no mass. Be aware, a cone speaker is a "mass loaded driver" by its vary nature. This cannot be disputed. An ESL is an "air loaded driver" Id rather have air than mass to move around.
In closing, and not to be a tall poppy, but it takes knowledge of both acoustics and electronics to make an ESL. One has to make his own drivers, step up transformers, polarizing supplies and at voltages that scare most people. Cone drivers are bought off the shelf, the good ones have already published curves that you can count on, no high voltage and not much knowledge to hook them up. Red wire, Black wire, cap, choke nothing dangerous, nothing EXCITING.
I figured it out by listening and trial and error over time and based essentially on those parameters as a guide. However specifications alone seldom tell the whole story. The devil is always in the details much of which is never specified. Detailed measurements like those in Stereophile help a lot but I have found there may still be surprises playing real music even with very comprehensive test measurements at ones finger tips, though if done correctly, measurements certainly help with the decision making process of what to try next or not.
Today I compared two identical amplifiers, level matched, A/B switch in hand. I played Willy Nelson (raspy male voices are very telling), I played Bach Organ works, piano, lots of things. Sometimes listeners bring in music to these tests that they like, but will not expose differences.
All I had done is add 12 dB of feedback to one amp and left the other stock. i didnt change any caps, didnt replace resistors with naked ones, didnt put in premium wire or fuses.
Both had been measured and were in proper operating condition. 12 dB of feedback will reduce distortion by a factor of 4 and increase damping by a factor of 4. It was not hard to hear the clairty, dynamics, and defined (rather than one note) bass.
This is the story that the specs told and the listening confirmed. Come on over and have a listen. Lets not worry about comprehensive measurements when even the basic ones arent even good. The stock amp has a damping factor of less than 1 and 4% distortion at full power and I played it at full power.
These tests are not easy to do even for me. It can take a whole day to set it up, and ive only been doing it for 40 years. Very few people set up these tests.
Why do audiophiles try so hard to ignore, object to, claim that measurements are irrelevent? Why is one reviewers impression more important? Many readers of Stereophile dislike measurements so much they say its a waste of space?
I don't design by measurement but I know what minimum performance is required to make a good amplifier. Of course some designers loose sight of balance in design and drive one spec to the limit. That often results in a bad sounding amplifier.
What are you going to say to the poor lad who buys the Cary SLI-100 hooks it up to a pair of Maggies, turns it up loud and smiles. If you have a good sense of clean sound you will not enjoy 10% distortion, compression, muddy bass. Without JA's measurements there would be no warning. His reviewer did not use more than a few watts of a 100 watt amplifier, what happens when someone does?
By “more power” I’m just going by where I set the volume control before and after. It was a surprise, as I thought there would be less, and I was pleased because in my layman’s view it meant less stress on the tubes and circuitry.
This is a popular thought, however where you set the volume control has nothing to do with power or stress on the tubes and circuitry. A volume control controls gain, not power. You an be at full power anywhere on the control setting depending on the gain of other parts of the system.
Also, I’m not sure what you mean by better technology than cone speakers. First off, the Altec is a horn/cone hybrid. That aside, while electrostatics have their virtues, they don’t move air the way a cone does, as someone here also observed. That’s what I mean by the dynamic punch of the Altecs. I’ve heard some great horn speakers, with prices in the stratosphere.
The Altecs were designed to get a lot of SPL with not a lot of power. When they were designed 20 watts was a lot of power, now its not. I have not heard any good horn speakers, though one of my students has the Avantgarde 3 way. We are having a demo this coming week. Horn speakers tend to have peaks in the response. They are very efficient, however I am not running a movie theater.
Actually ESls couple better to the are and are virtually massless. A cone speaker is a "mass loaded driver" whose motion is totally controlled by the mass. The problem with mass, as we well know is how to start and stop it.
Rather than defend cone speakers, lets open our thoughts to why they are so popular and do they belong in the home? Fine for cars and portable radios, but that is not HiFi.
There was a time when the best and most expensive speakers were ESLs. But then came along Wilson and the world changed. We made a $4,000 ESL with DD amplifier at Beveridge when wilson was still working in his garage. He won, we lost. What happened?
Speaking of Maggies... I would like use a quality, lower powered tube amplifier to drive mine. What is your idea of an appropriate amount of “tube” power for them? I sit about 9 1/2 feet from the speakers in a 14’ x 21’ x 8’ room, and typically listen at 80-85 dB (measured with a RS meter; C weighting/slow response). They’re rated for 86 dB/ 2.83v/ 500 hz. My preamp volume control is almost always around to 9:00. I really appreciate the idea of simple circuit design for both the amplifier and the preamp. I just feel like I’m not using the power in my amp (200w/ch), and also that I’m not using the gain in my preamp (12 dB). Power is expensive, and I’d rather put the money into the quality of the amp if I don’t “need” the hundreds of watts.
you can’t possibly mean that preamps are easier in general and I am unaware of any accolades for your preamps (whereas you are lauded for your amps). Obviously you mean that for your tastes and purposes, preamps are easier than amps.
I mean precisely that. You might want to do a little more reading on the RM-1 and RM-5. Perhaps you are new to this hobby.
This has nothing to do with my tastes and purposes. The RM-1 (1976) was lauded for its RIAA EQ accuracy, was the first popular preamp to use the 6DJ8/6922, has the lowest noise possible for that tube. Has 5 fully regulated, short circuit proof power supplies. Built in two chassis and weighs 55 pounds ! It is the only tube preamp to my knowledge that id DC coupled throughout with servos, relay protection and no output coupling capacitor.
That was a lot of work, But once you make a good preamp what is there left to do?
Power amps, on the other hand are a world of variety. Circuit topoligies, output transformers, protection, tube life. These are really difficult things to do.
Granted most people who dont design preamps will agree with you, but they dont design preamps, now do they?
A great preamp does more than attenuate a signal. It breathes life into music. A great preamp is quietly powerful, while a great amp simply provides grunt.
A preamp does not attenuate a signal, it amplifiers a signal, provides selection of sources and control of volume, accurate phono EQ. But these are easy to obtain. There are only about 3 ways to make a preamp gain stage. There are an unlimited distinct ways of making a power amp and a good one is a challenge.
I will say that many preamps fail because of poor power supplies. My power supplies are among the finest and they dont break like ARC power supplies. You can short my power supply, go to lunch, come back, remove the short and all is well, doesn’t even get hot. One millisecond short on an ARC power supply and you wont have time for lunch or dinner. Ask any tech.
A power amp is the finess in a system, certainly not the grunt.
May I remind you this is a thread to ask a technical question.
using a few of your own words, perhaps you did veer into “ tall poppy “ turf a bit...
in my inteactions w very talented engineers over the years - and there have been many , many outside of audio, ego is also an essential design ingredient... there are some speaker people doing a bit more than just buying off the shelf cones...some of them make amplifiers..
” I was about to write that the M7-HPA measures well for an amplifier with zero loop-negative feedback. Actually it measures well period. John Atkinson.....
I think he liked how it sounded also with cone speakers ;-) I think there are several paths the enlightenment....
and on the RM-10 can you talk about 35 WPC vs the class A 25 wpc version w hand wound transformers?
I think either one could drive my 85 DB, 6 Ohm (+/- 3 ) speakers. Loud is 90 db C weighting, slow on the venerable R-Shack analog most of my listening is done low 80’s....
current amp is a NAIM SS class A/B solod state...it has plenty of grunt.....
Was the preamp you mention above marketed by Beveridge Audio, I searched it and the only preamp that came up was RM1 and RM2 by Beveridge. I'd be very interested in getting one of them.
Funny that the latest ARC amps I've heard sound greyish, muted dynamics, etc. My friend has an ARC 75 which is no match for his Classic 60s or my voltage regulated amps. Worse, his amps, Ref 5 preamp and $10K CD player all have had significant break-downs after only a year or two. Yuk!
My question remains, I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers. They sounded great wherever I heard them and they appear to be conventional designs well executed. They must have good impedance outputs to make them adaptable to drive many types of speakers like your own amps.
I’m gonna take a wild guess: sound pressure level?
I think the debate between cone and electrostatic is reminding me of the great cable interconnect debate. Could it be that this is just personal preference? Or even that my ears are just trained and accustomed to whatever cones do to the ears? I’ve listened to my share of electrostatics. Some were very impressive. Some were better than my Altecs in many respects. But none moved me.
Back to SPL. I do get the bit about moving air as opposed to mass. In theory, that is more efficient. But then if true, there would be an electrostatic subwoofer. ? Maybe there is?
@krelldreams, though you asked Roger for a recommendation of a low-powered tube amp for use with Maggies, I hope he doesn’t mind if I chime in on the question. As a long-time Maggie owner (my first bought in 1973, the original Tympani T-I; I now own Tympani T-IVa’s), I can assure you a typical low-powered tube amp is about the worst kind you can partner with a Maggie. But what do you consider a "lower" powered tube amp? Under a hundred watts? Under 50? Maggies are very insensitive speakers, and benefit from a "higher"-powered amp. Another factor working against tube amps with Maggies is that the speaker present a 4 ohm and lower load to an amp, and almost all tube amps prefer a higher-impedance load, producing less power at higher distortion into lower impedances than into higher.
While this may strike some as inappropriate in an answer to a question posed to the designer/manufacturer of Music Reference amps, I’m doing it anyway ;-) . There is one tube amp I can suggest for use with Maggies, the one I use: the Music Reference RM-200 Mk.2. Unique amongst tube amps, it produces slightly higher, not lower, power into a 4 ohm load than into an 8 ohm one. About 100 watts/ch into 8 ohms, a little more into 4. Most 100w tube amps produce only 60 or so watts into 4 ohms. The RM-200 is also a real good amp in general terms. Low distortion ("clean" sound, including at bass frequencies, The Achilles heel of many tube amps), low output impedance (no tube amp colorations, such as added "warmth" and/or "soft" highs), stable into reactive loads (usable with ESL’s and ribbons), long tube life (some popular tube amps burn through a set of output tubes in as little as a couple thousand hours, and a replacement set are not cheap), and tasteful, classic styling, all at a reasonable price. Review, both subjective and objective, available on the Stereophile website.
Thanks for the compliment and notes on the RM-200.
I was also introduced to the Tympani speakers in 1973-4. At the time this product could only be bought from ARC dealers and was essentially a speaker that Jim made for Bill. Both were just starting out. At the time the largest amp ARC made was 75 watts/ch. Bill also required you buy his electronic crossover for the 3 way system which was a total of 8 panels. Those were the days. Great sound at nothing like today's high prices. Marketing took a back seat to engineering not its the other way round.
SE amps are often great with sensitive speakers. The 805 tube is an interesting transmitting tube. These types of tubes often exhibit low distortion over their entire power range. It takes power to drive them hense the 300 B is actually doing some work here. We used a 300B in a single ended amp to drive an 833 output tube. The 833 is a monster of a tube, requiring 10 volts at 10 amps of very clean DC for the heater. That part was quite challenging. I think we went for 100 watts of audio power, all transformer coupled.
I think the debate between cone and electrostatic is reminding me of the great cable interconnect debate. Could it be that this is just personal preference? Or even that my ears are just trained and accustomed to whatever cones do to the ears? I’ve listened to my share of electrostatics. Some were very impressive. Some were better than my Altecs in many respects. But none moved me.
All debates with audiophiles come down to personal preference. If you like your system then great. My friend Bruce DePlama used to say. "You go to Roger's house you hear Roger's sound. You come to my house you hear my sound".
The Altecs are loved by many. Nothing wrong with them. No one is overcharging you for them. They are efficient and work well with smaller tube amps.
I would hope we all agree that speaker differences, speaker/amplifier interactions, are far more obvious than cables.
I hope we all have decent systems, without un-intended peaks, without horrible distortion, without noise. If you have one of those problems lets fix it.
@ramtubes, Roger I happened to make my first visit to a new hi-fi shop just opening in Livermore, CA in 1973, Audio Arts. It was a 1-man shop, that man being Walter Davies, now the maker of the great Last Record Care products. And as luck would have it, that was the same day Bill Johnson was delivering and installing a complete ARC system in his new dealer Walt’s listening room; a Thorens TD-125 MK.2, a Decca Blue mounted on a prototype ARC arm (it never went into production), an ARC SP-3, and Tympani T-I’s (as you said, at the time distributed by ARC) bi-amped with a D75 and D51.
I was just a kid, and spent a couple of hours getting an education in high end hi-fi. A couple of months later I had that exact system (with a Decca arm) in my own room. All set up and connected, I pushed in the power switch on my SP-3, and immediately heard a "poof" and smelled the aroma of something burning, which turned out to be a resistor in the power supply. Welcome to the wonderful world of using under-rated parts! High End? Not by my definition!
Funny that the latest ARC amps I've heard sound greyish, muted dynamics, etc. My friend has an ARC 75 which is no match for his Classic 60s or my voltage regulated amps. Worse, his amps, Ref 5 preamp and $10K CD player all have had significant break-downs after only a year or two. Yuk!
That is how I would expect the ARC amps to sound given their measurements. Sometimes there is a correlation. I see we still have reliabiity issues. I feel for ARC and the many people who work there. When Bill was selling the company he had 10 requirements of the buyer. One was to not move the company. Bill did some nice work, however he left a few things undone. He never made a short circit protected power supply. That makes techs and the owners who pay them really unhappy. He had a thirst for new products which resulted in many mods because the first releases were unfinished designs. When a preamp goes from SP-6 all the way to SP-6E thats a lot of mods.
My question remains, I'd like to know what you opinion is of the VAC IQ (continuous autobias) amplifiers. They sounded great wherever I heard them and they appear to be conventional designs well executed. They must have good impedance outputs to make them adaptable to drive many types of speakers like your own amps.
VAC seems to be doing some good work these days. I have worked on one of their big preamps, it was nice but picked up hum from a power amp 2 feet away. We were surprised.
Autobias can be done many ways. The problem with many autobias schemes is that they shift bias in the wrong direction when the music gets loud (above the class A region). If Kevin worked it out well Kudos to him. I still prefer a bias pot and meter. My bias is so stable as to be checked only a few times a year.
However many are looking at amps that dont need adjustment as my newer RM-10. We have found that many of the new tube generation do not like the though of having to use a meter and adjust something.
I am very happy that I put the LEDs in the RM-9 in 1985.The bias circuit lended itself to them and balancing the DC coupled driver was important. When I did the RM-200 bias LEDs were a complicated option due to the circuit and the driver needed no balancing.
I feel in some ways I'm punished for putting a supermatched pair of transistors at the input and thus entered the "Hybrid" land. As always I choose the parts to do the job best. A tube in the input would have gone back to Driver Balancing pots, CMRR pots, tube selection. Sometimes doing an audiophile a favor does one no good.
Roger I happened to make my first visit to a new hi-fi shop just opening in Livermore, CA in 1973, Audio Arts. It was a 1-man shop, that man being Walter Davies, now the maker of the great Last Record Care products. And as luck would have it, that was the same day Bill Johnson was delivering and installing a complete ARC system in his new dealer Walt’s listening room; a Thorens TD-125 MK.2, a Decca Blue mounted on a prototype ARC arm (it never went into production), an ARC SP-3, and Tympani T-I’s (as you said, at the time distributed by ARC) bi-amped with a D75 and D51.
I was just a kid, and spent a couple of hours getting an education in high end hi-fi. A couple of months later I had that exact system (with a Decca arm) in my own room. All set up and connected, I pushed in the power switch on my SP-3, and immediately heard a "poof" and smelled the aroma of something burning, which turned out to be a resistor in the power supply. Welcome to the wonderful world of using under-rated parts!
Thank your for the walk back in time. Anyone who is not old enough to have your experience I encourage to read every word above. Thats exactly how is was back then. My store in Richmond VA was called Audio Art and is still in business. Manufacturers visited us. Nakamichi flew in on their private Mitsubishi plane. We ate, we drank, Bob Fulton told the story how the monkeys behaved when they heard sounds carried by different speaker cables.He said bad cables confused them. No kidding. In his Fulton J system, one of the best things going back then, he used Ford solenoid coils for woofer chokes. He was delightful.
The J was cool because you made it in pieces as your funds allowed. First you bought the bookshelf speaker which was a fine speaker in itself. Did what a good "monitor" should. Then you could either buy the 8 Cu Ft woofer box or the RTR ESL tweeter. When you were done you could please the missus with a dark brown cloth and wood "hat" that covered the whole thing. Stood about 4-5 ft tall. Marvelous. No bullshit, even the monkey story is better than most cable claims today. He made some good wire when this current crowd of cable makers were babies. I think some of them are still babies the way they rant and bend science.
As to your "POOF of smoke" thats is simply an unprotected power supply. Bill didnt seem to get the point that the down side filter capacitor looks like a short every time you turn on the preamp. Rather than take the time to discover how to make a Short Protected power supply he just added band-aids. It was always claimed to be some "sonic improvement" to make it easier to swallow. Most times it was a fixing a failure mode in an unfinished design. Power supply failures were never mentioned. As I recall the SP-6A upgrade was $150 for a little circuit board with two diodes and a resistor. He always kept the price you paid plus the upgrade cost equal to the price of the newer unit. Of course you had to send the preamp back, wait 6 months and some claim they got someone elses preamp back. ARC database has lots of information, though no stories. http://www.arcdb.ws/ It is the work of a group of dedicated ARC fans. Good place for ARC info on prices, modification dates, some schematics.
Back then the joke was. If you buy an ARC preamp you have to get two because one will always be in the shop and by the time you get that one back its aready one or more behind the latest version. People like Harry Pearson turned that inconvenience into a virtue.
If you dont believe me ask bdp24. He has obviously been around the block. Im sad for the horrible choices newbies have to make. The pressure to buy expensive cables and power cords and fuses and products that do nothing. Those did not exist when I got into this. We had to make real stuff. However we had coloful fellows like Bob Fulton, Jim Whiney, Matt Polk and Co, Arthur Jansen was still alive and I interviewed him as well as Saul Marantz and SId Smith. And last but not lease Harold Beveridge, my mentor.
Roger, funny you mention the Fulton J, as that was what I replaced my Tympanis with! After having lived with the T-I’s for a year, in ’74 I heard the Model J at John Garland Audio in San Jose, powered by Fulton’s own mono tube amps (a modified Dynaco Mark III, I believe). I had heard ESL tweeters before (in the ESS Transtatic I---they had used the same RTR tweeters as did Fulton in the J, 3 of them to the 6 in the J), and the Infinity Servo-Statics, and those tweeters made the Tympanis sound SO veiled. I also was hearing and feeling the bottom octave, which was missing in the Tympanis. The J’s midrange (provided by the available-separately Model 80) was great by itself (unusually transparent for a cone speaker), but adding the RTR ESL tweeters and Fulton’s transmissionline-loaded woofer box made it a very full range loudspeaker. I no longer have the Fultons, but I picked up a pair of Transtatics in 1982 for 400 bucks.
Bob Fulton was also a great recording engineer, and his ARK label LP’s are fantastic; very alive (immediacy, like a Decca/London cartridge), transparent, and detailed, with extremely natural vocal and instrumental timbres. He recorded local Minnesota choirs and orchestras, which in their amateurishness are charming.
first thanks for the input on Ralphs amp, speakers likely the dead ESL-63 I mentioned in another post. I am away from them but I am assuming with ago all the panels are toast, the limited fault tree look I have done so far indicates EHT power supply issues. I am away from them so do not know on panel color, will check that when home next. Thanks all for inputs on rebuilders.
The fault tree should have the panels at the top and EHT at the bottom.
The EHT power supplies are usually NOT the problem in the 63's. The problem is dried out contact cement. All the panels fail over time and temperature cycling is their worst enemy. My friends died in a hot room one summer day. There are many videos on YouTube that show how the glue lets loose and how to rebuild them. Its not for the faint of heart. It is indeed sad that the 57 panels last forever and the 63 panels have a very limited lifetime due to.... GLUE!
I am away from my toolbox also but I will get DMM peak voltages measured today, SPL at 1 M
fun, real data will set you free was our mantra at work for 30 years..
As I listened to the modified and unmodified OTLs the other day on the 57s (that story is told in an earlier post of 11/26), I had the 57 terminals hooked up to the scope. I was constantly monitoring voltage. Music is fun to watch and anyone can get a good scope on eBay for under $100 and learn to use it if nothing else to look at music, look for oscillations, look for offset drift Its really not hard, really. I suppose I sould make a video.
I could see certain things the amps were doing. It takes a lot of experience to see and hear music and correlate, but indeed I could see current clipping and hear the mud is produced. I could see bass peaks due to low damping (that took a oscillator or sweep CD). I could hear that the low damping amp produced a boomy one note bass while the one with 4x the damping produced actual bass tones.
Years ago in the Stereophile "As we see it" column the writer asked several people what they listen for. His daughter said she listens to the "beat". Someone else the tonality, someone else the separation of instruments, someone else the soundstage, yada yada yada.
I think this is important for listeners to think about what they listen for when they judge a system. If his daughter puts on a recording where she likes the beat it might not reveal any of the other things. But she just wants the system that gives her the "beat"
I particularly wanted to hear high level high frequencies where the low impedance of the 57 would tax the amplifier. If I had Miles Davis I would have used him, but I dont have Miles. I do have Bach organ works with trumpet enchmade. Thats even toughter. https://en.wikipedia.org/wiki/En_chamade
I could see and hear the current clipping. More hear than see. But I also knew I was in the 3% and over distortion area of the amp and 12 dB of simple feedback made a big difference in the clairty of this organ stop. I had a brief experience of being mentored by an old German organ builder so I knew and was facinated how organs worked. This music was chosen precisely to provide an audible test. It was done with levels matched by pink noise and immediage A/B switching.
BTW the 57 has a dc resistance of 0.5 ohms. If an amp has even 50 mV of offset that is 100 mA of output current which is also similar to the bias of most SS amps so at idle either the top or bottom transistors are turned off. This is not good for the speaker or amp. The 57 was meant to be driven by an amp with an output transformer where there is never any offset.
This is the stuff I think people should know that is never talked about. If you doubt me go measure it for yourself.
Thank you for your reply. Roger commented on your reply, but my question remains somewhat unanswered. Your advice, which is common (though not universal), is why I’ve never tried a 25-50 w/ch “quality” tube amp. I’d love to be able to try some amps at home, but the few dealers within reasonable distance don’t have much to choose from. One guy carries Line Magnetic, but I’m not interested in buying one of those, and don’t want to try something I’m not planning to buy, just to see if it has enough power. I’ve had five different pair of Maggies in the past 32 years, among other types of speakers. I always end up going back to them after trying something different. I don’t listen very loudly, and I don’t feel like I’m using anywhere near 200 watts per speaker, so I asked a tube amp designer what he thought would be an appropriate power output for my speakers. I have a Dynaco st 70 in my weight room system, but it isn’t a “high end” amp, so I’ve never used it in the main system, as I don’t think it would represent what a really good amp could do. I had a VAC 100 w/ch amp in the past. It was plenty powerful, but ended up losing out to a Krell KSA 250 (purely on sound quality) when I was able to do a side by side comparison. I also had CJ Premier 5’s, but they’re very powerful, so not what we’re talking about here, and ultimately proved problematic, so I replaced them with the hotrodded CJ Evolution 2000 tube input/mosfet output amp I have now. I do know that in the late 80’s/early 90’s, iirc, Magnepan had a 1960’s tube integrated playing into their speakers in their lobby... I think it was a Scott, @ 20 w/ch. I’m sure it was played at a very low level. Roger’s RM 10 looks interesting to me, as does the Decware Torii Mk IV. From an electrical stand point, would these drive MG 1.7i speakers playing music at 80-85 dB ? That’s what I’d like to know before I buy something without the benefit of hearing it first.
At your listening levels an RM-10 would do the job. I need to talk with my salesperson about arranging an in home demo.
The RM-10 now has a beautiful but expensive wood base which I would not like to have go back and forth.
The RM-10 is very light weight (15# i think) and thus can be shipped economically. What would you say to getting the amp in a simple base and if you decide to keep it buy the newer base or take a discount on the amp with the simple base?
Roger, I think if you revisit the above comments you will find them to be incorrect. An OTL has to be able to drive real world loudspeakers and so can produce the same currents at the output as any other amplifier. FWIW, the output tubes in most OTLs can easily blow a 10 amp fuse in certain situations without damage to the tubes.
I still find that OTLs at low impedance are current limited. As to 10 amps without damage. When I put a 6AS7 on the curver tracer and go just a bit above the peak rated cathode current I see flakes of cathode coating coming off like sparks from a sparkler at much less that one amp. WIth the grid being so close they can easily fall into the grid wire and POOF. Horizontal output tubes that Futterman and I use are specified for high peak current about 1 amp.
I will measure the power of the M-60 at the impedances you suggest. What numbers should I find? At what level of distortion? The amp is now working well with fresh tubes and all DC voltages confirmed to be in line. I have always liked the WIggins circuit and if I ever produce one it will be with transformer of course.
@almarg Correspondingly, at my 12 foot listening distance I have measured peak SPLs on those recordings of close to 105 db, with the softest notes being in the vicinity of 50 db. I used a Radio Shack digital SPL meter for these measurements, set for C-weighting and fast response.
My speakers (Daedalus Ulysses) are rated at 97.5 db/1w/1m, and have a very flat impedance curve with a specified nominal impedance of 6 ohms. My 12 foot listening distance corresponds to 3.66 meters. Putting aside room effects for the moment I assume that SPL produced by a box-type dynamic speaker such as those falls off at 6 db per doubling of distance, which means an 11 db reduction going from 1 meter to 12 feet. I conservatively add in 3 db to reflect the presence of two speakers (as I understand it that figure will actually be closer to 6 db at my centered listening position when both speakers are producing similar signals), and I add in perhaps 3 db for “room gain.”
97.5 -11 + 3 + 3 = 92.5 db at the listening position for 1 watt per channel. Let’s call it 93 db.
I add in about 3 db of margin to the 105 db I want my amp/speaker combination to be able to produce at the listening position. So the required minimum amplifier power (into 6 ohms) is:
105 + 3 - 93 = 15 dbW (decibels above 1 watt)
15 dbW = 32 watts.
Thanks for your measurements and math. I think the math will leave most with their head swimming. Perhaps you could add some details to the steps so that others, less math inclined, might work things out. it is nice for people to know how different speakers fall off with distance. Perhaps you could write that up for us. :)
I ask for SPL both at listening position and 1 meter for two different purposes.
I want to get to know the listener and measuring at 1 meter leaves out all those other calculations. One just works off the 1 meter speaker spec and adds or subtracts. If one is 3 db higher than the speaker spec he is at 2 watts, 6 db is 4 watts, 10 db is 10 watts, 20 db is 100 watts.
@krelldreams, you should definitely try your Dynaco ST70 with the MG1.7, just to see if that gives you enough power. The RM-10 is a far better amp than the ST70, but their power output is about the same (right Roger?). But remember, a 35 watt tube amp puts out less power at the Maggies’ 4 ohm (and lower) impedance. The RM-200 doesn’t.
Another option is to have Roger make you an autoformer (maybe even build it into the amp!), to raise the impedance the RM-10 sees.
@almarg
. I recently changed to a Pass XA25, which is specified as a class A amplifier rated at 25 wpc into 8 ohms and 50 wpc into 4 ohms. Per JA’s measurements, though, it is capable of 80 and 130 wpc into those impedances. I presume that most of that increase represents the amp’s capability after leaving class A, although per JA’s comments some of the increase apparently reflects differences in the distortion percentages the ratings and measurements are based on.
I have a different take on the reason for the power disparity... simply heat. The amp got hot at 1/3 specified power of 25 watts. At 1/3 of 80 is would have shut down. I think I saw a "more later" on that from JA, but cannot now find the quote. Perhaps you can.
I think what Pass Labs did is a sensible way to get around the FTC power test procedure. Perhaps 25 watts is the class A region however the amp does just fine out of class A and I cannot see anything in the distortion plots that concerns me when the amp leaves class A to AB.
Too much has been made of Class A amplifiers. Most dont know what class A involves. You could call this amp a 25 watt class A amp though its really an 80 watt, high bias AB amp that just wants to get around the FTC rule.
@bdp24
The J’s midrange (provided by the available-separately Model 80) was great by itself (unusually transparent for a cone speaker)
Thanks for reminding me the model number of the 80. For others who dont know the 80 was a full range speaker, woofer and tweeter as I recall, doing its best at being a full range, small, economical speaker. Fulton made good sounding stuff. I don't know how but I always assumed him to be a compentent engineer with great listening skills.
He told the monkey story with a totally straight face like, Hey this really happened. We bought his wire.
It appears you have owned some fine equipment. Nothing like we are faced with today, which is mostly marketing, jewelry and auto body finishes. oh and bad specs.
@fsonicsmith
And while a solid state input stage may very well offer better measurements, where is the proof that it sounds better? At the end of the day, isn’t it indisputable that it is cheaper to produce and less complicated?
Are you saying a solid state input stage is not a good idea, or doesnt sound as good, or you would not buy an amp with one?
@bdp24 That's actually a good suggestion, and easy for me to do, and I have no good reason why I haven’t. I had a Forte model 4a for awhile as well (50 w class A), but never tried that on Maggies either. I have different systems in different areas of the house, and typically don’t mix them (?). I did try a passive preamp in the main system recently and did Not like how it made the system sound. Maybe my preamp isn’t too bad after all... I will try the Dynaco with the Maggies this weekend. Thank you for taking an interest in my quest for sonic nirvana! Lol
@kellydreams
. I did try a passive preamp in the main system recently and did Not like how it made the system sound
Not knowing the passive and what is was driving, including cables I would say this:
I have no problems with passives. If one thinks of it as the volume control on an integrated that is somewhat separated physically the question becomes: What is in the way? What might be loading the passive? Generally the problem is cable capacitance or output/input impedance problems (I wont say mismatch).
Heres the way I look at it. In an RM-10 the input is right to the grid of the tube. In a preamp its the same thing. Why should it sound any different?
People do like preamps for other reasons, many of which may be imaginary. I made lots of preamps. Of course you need one for phono.
Bill Johnson told me they sell twice as many preamps as power amps. Seems people like to play with preamps more. Some say because its the thing you touch.
In my system i got tired of the cables from the pre to the crossover. I wanted something really simple.
Because the RM-3 crossover has two knobs for high and low output I decided I needed only one, the bass and so made the treb pot into a volume control. Reduces cables and connector problems.
Now I think the way to make a crossover is with several line inputs, volume and bass level. So simple. I adjust the volume and sub level (100 Hz and down) on most every CD.
If you care to share the specs on the passive, cables and power amp we might figure out what was happening?
For full range speakers in particular, aren’t speaker efficiency ratings only useful for determining power needed if they cover the lower frequencies, which is by far where the most power is needed to deliver flat frequency response and avoid clipping?
Don’t power requirements for flat frequency response increase exponentially with lower frequency?
Also FWIW it has been bandied about that manufacturer published speaker efficiency ratings are often let’s just say not completely accurate. True?
Also for that matter do some otherwise highly regarded amps cheat by not even attempting to deliver flat frequency response down to the traditional benchmark low frequency limit for hifi, ~ 20 hz or so?
I’m not ready to abandon passives from one less than favorable experience. The passive I have is a Luminous Audio Axiom... one input, one output, and volume pot. I listen to vinyl 95% of the time, so I was feeding it from the output of a phono preamp. To my surprise, the output with the pot at about the 10:00 position was approximately the same level as my tubed linestage at 9:00. The sound was bright.. too bright, and the deeper bass sounded more prodigious, but a layer of midbass was missing, and female vocals, which had sounded natural minutes before (through the preamp) were almost painful to my ears. It was like someone made the old eq smiley face curve on my system. The cables I’m using are old Tara labs solid core... 1/2 m from the ‘table to the phono pre, and 1 m from the phono pre to the amplifier. The amp sensitivity is rated at 900 mv, the cartridge has an output of 2.5 mv, and the phono stage is 42 dB/47k. I was going to question you about preamps, but didn’t want to stray too far from the thread topic. However, as I have found, others may be interested in your answers. I read forum threads that interest me frequently, but rarely write in. This one caught my attention more than usual because it was started by someone who actually builds this stuff... and is known to do it successfully. No offense to anyone else! I read all opinions and add them to my mental database. One thing I’ve learned is, what appears to make sense on paper is not always the case in practice. Thank you for your time. Truly
Thanks for your measurements and math. I think the math will leave most with their head swimming. Perhaps you could add some details to the steps so that others, less math inclined, might work things out. it is nice for people to know how different speakers fall off with distance. Perhaps you could write that up for us. :)
I ask for SPL both at listening position and 1 meter for two different purposes.
I want to get to know the listener and measuring at 1 meter leaves out all those other calculations. One just works off the 1 meter speaker spec and adds or subtracts. If one is 3 db higher than the speaker spec he is at 2 watts, 6 db is 4 watts, 10 db is 10 watts, 20 db is 100 watts.
Thanks for your comments about my post, Roger.
I guess the first thing I should emphasize is that the dynamic ranges of the two recordings I referred to in my previous post, while being applicable to MY determination of minimum required amplifier power, are VASTLY greater than the dynamic ranges of most or all of the recordings most others listen to. And in fact are much greater than the dynamic ranges of most of the recordings I listen to. So my bottom line of a 32 watt minimum power capability, for my purposes, is likely to be considerably less for those who listen at comparable average volume levels (average SPLs say in the 70s at the listening position) **if comparably efficient speakers are used.**
This is consistent, btw, with statements I believe Roger made earlier in the thread to the effect that many listeners require less power than they tend to believe.
I’ll also say that the point to going through the kind of calculations I described in my previous post is of course NOT to make any kind of final determination of what amp to choose, which of course should be made by listening, assuming that is possible. The point is to narrow the field of candidates that are to be considered, and to minimize the likelihood of making an expensive mistake, that would perhaps work for some of the listener’s recordings (especially those having narrow dynamic range), but would not work (or at least would not work well) for other recordings (especially those having wide dynamic range).
Another important point to keep in mind is that speaker sensitivities are often specified as the SPL produced at 1 meter in response to an input of 2.83 volts, rather than 1 watt. For an 8 ohm speaker (that is truly 8 ohms) 2.83 volts corresponds to 1 watt, so the two kinds of specifications will be identical. But 2.83 volts into 4 ohms corresponds to 2 watts, so for example a 90 db/2.83 volt/1 meter/4 ohm speaker is really just an 87 db/1 watt/1 meter/4 ohm speaker.
Regarding measurements at 1 meter, I haven’t done that (aside from during the unique speaker calibration processes that are required to utilize the capabilities of my DEQX HDP-5), mainly because it wasn’t necessary for my purposes, and because at least in my case making the determination from the listening position and performing the necessary calculations isn’t difficult. Also, while 1 meter measurements would simplify the calculations somewhat, as Roger mentioned, one would still have to somehow address the effects on SPL of having two speakers, as well as addressing room effects in some manner.
... it is nice for people to know how different speakers fall off with distance. Perhaps you could write that up for us. :)
In general the SPL provided by a box-type dynamic speaker (meaning a speaker that is non-planar and is not a line source) will fall off at 6 db per doubling of distance, **neglecting the effects of room reflections.** (As can be seen in my previous post, I added 3 db to my calculations as a rough guess of "room gain" as perceived at the listening position). The fall-off of planar and line source speakers as distance increases will be significantly less than that, as those speakers tend to throw their sound forward. The reason being, I believe, that as listening distance increases the angle between the listener’s ears and central part of the speaker and the upper part and the lower part of planar and line source speakers decreases to a greater degree (pun intended) than in the case of typical dynamic speakers having drivers that are spaced relatively closely. Making the sound emitted by those parts of planar or line source speakers more able to contribute to the perceived SPL than at smaller distances.
A fall-off of 6 db per doubling of distance can be extrapolated to any combination of distances based on the formula 20 x log(D1/D2), where “log” is the base 10 logarithm. If D1 is greater than D2 the answer will be a positive number; if D1 is less than D2 the answer will be the same number except with a minus sign in front of it. One can perform this calculation with a scientific calculator, or with the calculator that is built into Windows if it is set to scientific mode, or with various online calculators. In my case my listening distance is 12 feet. 12 feet is 144 inches; 1 meter is 39.37 inches; 144/39.37 = 3.66 meters. 20 x log(3.66/1) = 11 db, rounded off. So the SPL produced by a single box-type dynamic speaker at 12 feet will be about 11 db less than at 1 meter, neglecting room effects.
The conversion of dbW to watts that I showed in my previous post is based on the ratio of two power levels, expressed in db, being 10 x log(P1/P2), where “log” is again the base 10 logarithm. If P1 is greater than P2 the answer will be a positive number; if P1 is less than P2 the answer will be the same number except with a minus sign in front of it. So it can be calculated that 32 watts is 10 x log(32/1) = 15 db greater than 1 watt, which can be expressed as 15 dbW. Converting in the opposite direction (15 dbW to 32 watts) is a bit trickier mathematically, but no doubt there are online calculators which can facilitate that.
@maplegrovemusic
Roger - What brand and model subwoofer do you use ?
Its of my own design. It is very smal,l less than 1/3 cu ft. Therefore its corner frequency is 100 Hz and falls off at 12dB/octave. In the crossover I EQ it up at 12dB/octave so it comes out flat. I can start the bottom EQ wherever I want. Typically 30 Hz. It could be 20 Hz, Works the same way.
This may be hard to understand because its no longer a mass loaded driver. It is operating in the region where regular woofers do not. It is now an air spring drive and I call it the "Air Spring Woofer". It is not longer working under mass load physics. It is working under spring physics.
The amp is any old SS 100+ watt amplifier. Currently a nothing special Denon. The woofer level control is on the crossover.
This solves a lot of problems with powered subs. Unless they have a remote (do they now?) it is difficult to adjust the level for different CDs, I find when the woofer control is right next to the volume why not trim it. I use a range of about 3 db for myself but always bump it up depending on what I think the listener might like. Generally Im playing to a under 35 croud and they like how the bass sounds .. and more of it, sometimes I give them 6-10 dB more. The bass control is marked in dB so I know where I am.
Plate amps have short life if played loud. The solder joints just fall apart from vibration. Some just have a short life!
In my system the only cable going to the woofer is a speaker cable, shamefully 16 ga lamp cord. The woofer is already well damped and above the range it plays. The amplifier sits on the rack with everything else.
Do you know that most people do not hook up subs properly? I can sympathize, to do it right takes miles of wire. You have to run the preamp to the woofer and back to the main amp which may be far from the woofer. Theres cable capacitance issues, potential noise pickup, grounding, and the incredible cost of premium long cables. I presume 4 meter cables cost heaps more than half meter.
In either case, if you dont use the crossover you do not get the benefit of taking the bass workload off the satellites. I bet 90% of the subs out there do not use the crossover for that and the reason audiophiles dont trust putting their sound through the XO and rightly so. The electronics in most subs is not great.
Why dont sub makers put the amp and xo into a nice chassis to put on your rack? If this is such a great idea why doesnt everyone do it? Two good questions for sub makers :)
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