Hello Roger, I've purchased your tubes several decades and liked the quality and longetivity.
Funny how people denigrate my Marantz 7T although I only use it for 78 rpm phono stage. It sounds much like a 7C.
My Dynaco ST70 on my second system has magnificent bass as it was modified from its ultralinear design to a voltage regulated design (taking off the 2nd transformer tap). Added very large storage cap, ss rectification but kept the tube for soft start. Just a wonderful low powered amp.
My friends and I have found some early ss receivers with low power are superior to higher power receivers in the same line. E.g. Yamaha CR 620 is superior to the CR 1020 and higher power receivers. The Sherwood 7100 is superior to the 7200 and 7300. They have fewer stages on the low powered units. I use the Yamaha for video/audio systems although a friend uses them on his Legacy Focuses. Even the Sherwood brings out great low and tight bass on Legacy Signature IIIs (its shocked the seller when I used it to audition them).
I really like your answers on many of this forums questions.
There only place where I strongly disagree is in the use of premium fuses. My amps had standard fuses replaced by SR Blue fuses. The difference in SQ was very substantial. The manufacturer of my big amps went one step further and replaced his fuses with circuit breakers. Now his amps sound nearly identical (we can't tell the difference) from my amps with the SR blue fuses. He is a huge skeptic and this is his only tweak to his system.
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.
I heard those Jadis amps on new Magico speakers (maybe the S3 or Q3). I wondered why the highs were rolled off and soft sounding. Probably due the loss of power in the highs. Terrible sounding.
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Hello Roger
Many people believe that SET tube amplifier give more mid range magic than Push pull tube amplifier.
Do you agree on the notion as designer of tube amplifier?
If so, could tell me why it is so?
thanks in advance
Thomas |
@unreceivedogma
The triode mods actually have more power somehow. I know Jon put a tiny little transformer in there somewhere, he explained what it is for and that it’s not in the output circuitry but I’m not technical enough to remember.
I have built both triode and pentode Futtermans with the same tubes you have and I cannot agree that triode has more power. I did triode for simplicity in a low power Futterman I offer with a built in Autotransformer. It does about 3 watts into 8 ohms direct but 30 watts into any load via the Autoformer. I plan to make more OTL/autoformer amplifiers. Including the Autoformer in the amplifier feedback loop is far better than having it outside the loop. Did you happen to see the measurements before and after? There are several builders offering fancy cabinets for the classic speakers like the 604. Who can say what a piece of fine furniture should cost? Of course for that money there is better sound to be had. I would like someone to tell me why spend big bucks on cone speakers when there are better technologies. |
@musicpod
Slew rate. Some people feel that this is a significant amp spec. Would you please give your thoughts on the importance of slew rate.
Slew rate is another way to look at the power bandwith of an amplifier. The Jadis 200 had horrible slew rate (intentionally it seems) and this 200 watt amplifier could make less than 5 watts at 20Khz. It was not broken! Like any spec, some manufacturers will focus on this and get a geat number. If the amp can make full power without turning the sine wave into a triangle at 20Khz then thats good enough. 10V/us is enough though you will see numbers much higher.
At what db level do you consider a speaker efficient? At what level inefficient?
Would it be possible to provide context to where Mr. Levinson may have been coming from regarding the 400-watt optimum power level?
I have discovered in speaking with many audiophiles that almost everyone has way too much power and too much gain. People overestimate their listening level typically by 10 dB which means they are using 1/10 the power they think they are using. I will not advise anyone on power unless they know their speaker sensitivity and have a Radio Shack or better SPL meter. Quoting listening level without and SPL meter is pure foolishess.
The range of listening levels is much wider than the range of speaker sensitivity. Therefore one must know their listening level. I would be really impressed if someone quoted their peak voltage at the speaker terminals. So far this has not happened. Mr Levinson does not design amplifiers. However his engineers have made everything from 25 watts to whatever. Where he comes up with 400 watts I have no idea but I would say thats is a crazy high number for most people. |
@fsonicsmith \\
Roger, I have two questions though the second is a doozy.
1) What do you think of the Tungsol KT150?
2) What are your top 5 criticisms of the ARC Ref series components (i.e. the Ref 75SE or Ref 150SE amp and the Ref 6 preamp)?
I ask because I own and am proud to own the Ref 150SE and Ref 6 and more importantly, they deliver untempered joy and because while you said some negative things about Bill Johnson, you passed over the fact that Ward Fiebiger was the mind behind the latest designs.
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...He wasnt too happy about the output impedance. I have tested the KT-150 but as yet not interested in using it as it has a single source. It is expensive, It is cool looking in some ways, the data sheet is way off and there are no curves. #2 What do I think of ARC. No tech likes to work on their equipment. I won't any longer. I did a repair on the M200 that had been back to the factory for expensive repairs that did not fix the problem. The problem was a regulator transistor installed backwards. So much for QC. Since the same mistake was made in two mono amps, how many other amps off that run had the same problem. It was intermittant, very hard to find. Bill Johnson got way over the top with complicated circuits, never learned how to make a proper power supply that was short circuit protected. The first SP-6 took the regulator transistor out of safe area every time you turned it on. So the 6A had a little zener board to bypass the turn on. I mean really, this is the solution of a child. Since the power supply problem never got fixed he finally put a tube in place of the transistor... and called it a sonic improvement, of course. They made too many versions of everthing collecting $$ everytime you passed go. Most of the mods were called "sonic improvements" but all the mods on the SP-6 (which went to E) were reliability mods not sonic. Their build quality is lovely sadly their circuits are not. I have not met Ward. I see that things are departing from Bill's complexity back to something reasonable. Yet why send an amp to JA that is not going to test well? The IM on that amp is pretty high. It doesn't meet its own spec. The new power amps have the power tubes on the PCB which is a horrible thing to do. If not for Harry Pearson they might have died on the vine. Harry, the self claimed "Audio Pusher" got in bed with them and profited from a lot of loans never returned. When I visited Harry at Sea Cliff there was a ARC preamp standing on its side in the bar sink. The meters are cool looking, the price is high, I can see why people buy it but I cannot recommend it. Im sorry, but you asked. I'm sorry to be so negative about ARC, but I was a dealer for them from 1975 to 1980. If you have not heard about the "pink papers" thats a story in itself. ARC treats dealers with a heavy hammer, large opening order and threats if you do not follow the party line. Bill called us up one day because he heard we were doing A/B comparisons for our customers. He said "stop immediately or I will pull the line" |
@prof
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? I don't know what "classic tube-amp sound" is. I mean I don't design for it. I just make a good amp and I like to use tubes rather than transistors. Though I see some amps intentionally colored like this Cary SLI-100 Most of us designers dont do that.Good performance is not a mystery. I am tempted to call Cary and ask them what are they thinking. I read the review and the manufacturers comment. This is a sad turn for a company that was making some good stuff. I will be sad if anyone buys that amplifier, however someone will like it. There always someone. With low damping the response modification will simply follow the impedance curve. I set up an A/B this past week and we did some listening today. We could easily hear the differences, levels matched, carefully set up for instant comparison. If I were simply swapping amps not by a relay, I doubt the difference would be as apparent. I did one other thing that astounded me when we went from the QUAD 57 to a competent Alan Jones monitor I said... Why do people listen to little monitors when they can have a nice, room filling ESL? |
@unreceivedogma
What you are doing sounds fine to me. Shows are shows and rarely a good place to judge a system. I'm lucky to fiind one system I like. |
@rost
I´m using a balanced configured Pass SS XP20 pre with output impedence stated at 1K/leg, balanced and 200 ohm, single ended (according to manuel) driving tube monoblocks with rated input resistance at 47K.
Amps have both RCA & XLR (only + phase) inputs. So my question is what input is preferable and why ?
Your response will be greatly valued and appreciated.
If I understand your correctly the XLR is unbalanced + only. If that is the case there is no difference which input you use. |
Is there a particular Direct Drive Amp you can recommend to drive the panels? (Again I’m in a 240V 50Hz country). I dont know of anyone making DD amps but myself. It a rather special thing.
|
@russellstone Hi. I was turned off tubes when a Mac 2275 couldn’t properly drive my ML Summit X’s (yep, ‘soft’ bass’). After some searching I found an Accuphase E-600 matched beautifully. My question is: how can Accuphase make a class A amp that runs cooler than many A/B amps, and substantially cooler than other class A amps that can give you serious burns when touched? The Mac could not handle the low impedance. The Accuphase has lots of current. I looked it up, its 30 watts at 8 ohms, therefore low voltage supplies. A 30 watt class A amp can run cool, but not a 100 watt Class A. thats the difference. Here is a great example where 30 watts at 8 ohms is better than 75 watts from the Mac. Did you try the 4 ohm taps on the Mac? |
Roger, I have two questions though the second is a doozy.
1) What do you think of the Tungsol KT150?
2) What are your top 5 criticisms of the ARC Ref series components (i.e. the Ref 75SE or Ref 150SE amp and the Ref 6 preamp)?
I ask because I own and am proud to own the Ref 150SE and Ref 6 and more importantly, they deliver untempered joy and because while you said some negative things about Bill Johnson, you passed over the fact that Ward Fiebiger was the mind behind the latest designs.
|
analogluvr,
I’ve been curious about the Atmospheres.
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. I have yet to listen to it in the new environment with the sub. Maybe it will sound better.
As for setup, I run the signal through the preamp, then into the Velodyne servo, which splits the signal and sends above 70 to the Futtermans and below 70 to a 300 watt ss amp within the servo and then to the sub, which is also connected to the servo by another line that as I believe they say in their literature “digitally corrects for phasing” in order to reduce distortion from that source.
By cutting off the signal to the Altecs below 70, it gives them much less work to do and they sound clearer.
When I go to shows, the way I would put it is that I almost never hear anything that I would prefer, and never ever hear anything that I would prefer that’s within 300% of what I have spent on my system.
Nice to meet you. It’s nice to know that there is somebody out there who thinks and hears similarly. By hearing, I mean that my ears, from an early age, grew accustomed - maybe trained is the word - to hearing audio a certain way. My system no doubt sounds very colored to many, but it suits me fine. |
@unrecievedogma I also have settled on a remarkably similar system. I use Altec 604E’s run full range from a pair of atmosphere M60s. Then off of a second Output on my preamp I run a dahlquist crossover to a pair of 12 inch subs. I usually have it set at about 60 hz.
I also have a pair of fostex T 900 super tweeters augmenting the top end.
I have owned a lot of gear including high end Tannoy‘s, apogee Divas, reference 3a grand veenas. I find this to be the most enjoyable and best for me. No plans on changing anything.
When I go to the shows I find my rig to sound better than pretty much everything there, to me. |
Since you listen at such low levels both amps are playing no power at all and thus both have very little distortion.
Are there some yes/no questions I could answer. It hard for me to see exactly what you are getting at. Thanks for the reply! I’m still trying to understand: 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? You write that the low damping factor will come in to play across various speakers, so it seems that’s at least part of the factor. But does it explain everything? I’ve always associated low damping factor mostly with audible effects in the bass region. But with the tube amps there is also a sort of thickening and slightly softening of the mids and upper frequencies - it seems an across the board effect on the sound, not just in the lower frequencies. What other deviations may be coming in to play to alter the sound, even at low volume levels? Also, I thought that impedance difference in speakers could cause audible issues in the high end as well - e.g. audibly rolled of highs etc.Which never really seems to occur that I can detect, across a broad range of speakers with very different impedance/sensitivity profiles. If you can get a low impedance amp then you can hear what the speaker designer intended you to hear. Ha! You trying to nudge me towards accuracy? How dare you! ;-)I’m more concerned with ending up with the sound I like, not in satisfying whatever the speaker designer may like. Normally when I audition a speaker it’s hooked up to solid state amps and I can get a very good indication as to the general sound and character of the speaker. Then I just nudge it a bit more in the direction I like. I’ve found the CJ amps preserve what I like about a speaker, while adding a bit more of what I like in to the equation. As mentioned, I’ve used amps like the Bryston 4B ST, which would provide the type of low impedance/damping performance I presume you are alluding to. Every time I’d switch to the Bryston I’d hear that slightly more tight, taught, precise sound and think "well, that does some things differently and strikes me as more ’accurate.’ But I always found over time the whole system still had a sonic signature anyway, and I found the sound overall more organic, easeful and believable with my tube amps. Such is personal preference. Thanks again. |
PS:
the speakers could have have been changed to 8 ohms at re-coning. I kept them at 16. They are rated 101 dB efficiency.
The Futtermans are now about 45 Watts each. . |
Roger,
Thanks for your offer
of help. We met about 3 to 5 years ago at Brooks Berdan's retail store. You made a
presentation that included your background, your audio philosophy and one of your amplifiers. It is nice to reconnect with you.
I have several
questions for you:
Amp
power. You mentioned 100 watts should be adequate unless the user listens
at loud levels or has inefficient speakers. I read an interview with Mark
Levinson. In it he stated that when he was
designing amplifiers he conclude that 400 watts was the optimum power
level. (Unfortunately, I do not remember the context for his comment).
At what db level do
you consider a speaker efficient? At
what level inefficient? Would it be possible
to provide context to where Mr. Levinson may have been coming from regarding
the 400-watt optimum power level?
The
return of tubes (in terms of popularity and use) to audio. I own some McIntosh products and note that
they actually, at one time, had a marketing campaign focused on denigrating
tubes and praising solid state. Within
the McIntosh world, the lore is that it was their Asian owners – Clarion – that
pushed them to bring back tube-based products.
Thank
you.
|
Hi Ramtubes,
”Are we talking about NYAL Futterman? Perhaps I have missed something in this thread? Do you mean Jon Snyder?”
You will be sorry you asked!
Let me fill you in on my setup.
When I was 14 years old (that’s many many years ago. It was the Summer of Love), I started out with a Dyna 70, a Dyna PAS, a Garrard table, a Stanton cartridge, and a pair of Lafayette two way speakers.
Around the late 80s, I had built up to the configuration that I more or less have today:
Altec Lansing 604Cs and 604Ds
Mastering Lab crossovers
New York Audio Lab (NYAL) OTL3s (Futterman)
Beard P505 preamp
Sumiko MMT arm
VPI HW table (MK II then, MK IV with SAM today)
Koetsu cartridge (Black then, Onyx today)
and just this month, I added a Velodyne 15 inch sub that keeps anything below 70 or 75 hz from reaching the Altecs.
The speakers have have been re-coned three times, most recently three years ago, each time by Gabriel Sound in NJ. They do a lot of pro stuff: stadium work for Pink Floyd for example.
Jon Specter, not Snyder, is his name. I found him accidentally when I was following an Ebay listing for a pair of Futtermans. After many weeks with not a nibble, I “contacted the seller” - Jon - and suggested he add search words like Macintosh, Conrad Johnson, etc because “outside of a small circle of friends” as the late great Phil Ochs said, nobody knows what a Futterman is.
Not yet knowing who the seller was, I asked him how he came upon them, and he says he built them himself when he was at NYAL.
How serindipitous. Recently, a tube in one of my Futtermans blew up - literally, glass shattered - and seemed to have taken out half the circuitry. Until then, George Kaye had done my repairs, and while he does excellent work, he lives up in Brattleboro and it’s a schlep (he has his own company, btw, Moscode) and it turned out that Jon lives in Staten Island! So I asked him if he could repair the amp. He said yes but suggested that I listen to his pair - which had the triode mod - and if I liked them to just swap.
So we tried that, and they sounded great, but cosmetically they were a different iteration which I didn’t like so I declined the swap and had him do the mod on my pair and relied on my Dynas while I waited. He relisted his pair per my suggestion and sure enough he found a buyer - in Austin Texas, I believe - in three days.
John did another mod for an old Cooper Union alumni colleague of mine last year: he says that to date, those are the only three OTL3 Futtermans that he is aware of with the triode modification. I know George was involved because I was at Jon’s shop a couple times when he called George to consult on some issues, and I was still keeping in touch with George myself.
The triode mods actually have more power somehow. I know Jon put a tiny little transformer in there somewhere, he explained what it is for and that it’s not in the output circuitry but I’m not technical enough to remember.
I think you said that you dont believe in “audio grade caps” but Jon put a bunch of them in the Futtermans, the Beard, and the Mastering Labs. Jon said they would take about 100 hrs to break in and I didn’t hear anything at 100 hrs. At 150 I still didn’t hear it and I was beginning to wonder if I wasted some money, but at 200 they kicked in and I did in fact hear a difference, nothing dramatic, it was subtle: the sound became silkier and more open.
Btw, Jon also plays a great blues guitar in a band that he has, and is a cousin of Al Kooper.
The result of this configuration of components and the work put into them is a very, very lifelike presentation. I have heard equipment - some of it quite expensive, eg speakers that cost three times as much as my entire system - in audio showrooms that sound more accurate in terms of the timbre/texture of voices, instruments, etc. And you must know that for decades audiophiles would sneer at Altecs. I’m sure there are many in this forum. But I am telling you, I have never heard anything that comes even remotely close to having the lifelike acoustical space, nor the absolutely incredible dynamic punch that this configuration does. With some recordings - I’m thinking of the Frank Sinatras in particular, both Capitol and Reprise era, even the mono presses - the effect is of a startlingly present and holographic sound. The one weakness had been the bass was sometimes wimpy. With my new listening room and the Velodyne, that problem is gone.
As for Pearson: I sometimes read reviews in Stereo Review of components costing $30K to ... what is that pair of horn speakers (funny how horns are back!) for $600K? Magico? I would regularly post the comment “Is the Law of Diminishing returns somehow made obsolete in the audio world? Where is Haffler now that we really need him?”
One anecdote with regard to expensive speakers and irresponsible audio designers/manufacturers and then then I will look forward to your reply:
I was walking home one day, when I was still in NoHo in NYC, and I saw a pair of speakers through a storefront window in an audio showroom that caught my attention. I went in for a closer look.
The cabinet was about the same same size and proportions as mine were. The speakers had no grille cloth, so I could see the coaxial driver, identical to mine. The only thing different was the cosmetics of the cabinetry, which had a beautiful brick colored wood finish. I looked at the price tag, and then asked for a salesperson. I asked him what went into the $33,000 cost of the speakers.
After about 10 minutes he more or less concludes, and I say “that’s all interesting. Now could you tell me if that is a 604C or a 604D driver in there, or did the manufacturer copy it from scratch?” He looks a little confused. I continue “I know that’s an Altec 604C. I’ve been using them for almost 40 years. In your presentation, however, you did not once mention that fact. What distinguishes this speaker from the 604?” He then goes back to the crossover design, and I interrupt “I heard you the first time. It sounds like the Mastering Lab crossovers, by Sachs. You did not mention him. Everyone knows that the stock crossover in the Altec wasn’t what it should be, and Sachs came up with a two shelf design. I see similar knobs on the back of the cabinet.”
I continue “So, it seems like, excepting for the craftsmanship of the cabinet, which is extraordinary beautiful, these are the exact same speakers as mine - drivers, crossovers, cabinet geometry. Except that I put $3,300 into acquiring mine and getting them to perform at their best, while you are asking for ten times that amount. Are you suggesting that the cabinet aesthetic is worth the $29,700 difference? Or is there some other magic that this manufacturer has put into the performance - which is where the rubber is supposed to meet the road - of this pair of speakers? Could we remove the back panel, maybe, and see inside, see what has been put into this?”
By this time, I had attracted a small crowd. I concluded by saying “Sorry, I have an appointment to make and I’m already late, maybe another day! Thank you for your time!” I left, figuring that some dumb Wall Street sucker who doesn’t know what to do with his money will pick them up. They did, in fact, sell within the month. |
With some affinity for The Dead, corporate or not
in the old days before they had to feed the wall of sound monster, they used 4 x MC240 in bridged mode to run the PA
those are 50# each, so that was an ungainly bit of plywood all four were attached to....
Roger - one of my first memories is also at age 4 watching the MC240 and Bozaks arrive in my parents house
no $ for furniture, plenty for music and HiFi
i still have the 1961 MC240 / MX110 Z
have you measured a 240 ??????
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My name has zero to do with Jerry Garcia...I borrowed the last names of two people in my office (Tom Garcia and Dave Wolf) around 20 years ago for an open mike thing I was doing, and I kept the name for professional use and to disguise my identity as an international celebrity. As far as the Dead goes, I recently found a ticket I didn't know I had kept (I don't keep stuff like that) in a bag of papers from my late mother's stuff...3 bucks for a Dead show I saw in Honolulu on Jan 3rd 1970...framed it! There's a recording of that show someplace that I should try harder to find, just to complete the set.
I like the fact that my Dennis Had amp is relatively "unmeasured," although I'm sure somebody has looked into that...if measurements for the thing were available, I still would not care one iota as the thing simply reproduces music so beautifully among my gear pile it's earned its place several times over. |
@cakyol I predict that these capacitors will be in a vicinity with a temperature of about 60 - 65 C most of the time - Definitely use 105°C parts.
- Cap ESR goes up with age, so while the C may still be good with old parts, the increased ESR will play havoc with Z.
- Dielectric degrades with time and more so when not charged.
- A small DC fan could cool the temperature by 30°C. 12VDC fan on 3V is inaudible from 6 inches. Two 60mm fans operating push pull will keep things very cool.
You may find this link interesting. "Determining end-of-life, ESR, and lifetime calculations for electrolytic capacitors at higher temperatures" https://www.edn.com/design/components-and-packaging/4326347/Determining-end-of-life-ESR-and-lifetime... |
If I am a good guesser I would have to say that since wolf_garcia plays guitar and he has mentioned the Grateful Dead in a few of his posts the reference would be to the Doug Irwin Wolf guitar (known for the Dire Wolf inlay) made for Jerry Garcia. I’ve seen Garcia play it a number of times and the current owner of the guitar has made it available to be played by others, most notably Steve Kimock who Garcia really respected as a guitarist. You can see it here: https://liveforlivemusic.com/features/a-brief-history-of-jerry-garcias-five-most-well-known-guitars/[Side Note: Upon Garcia’s death some of the Irwin guitars made for him were auctioned off to help pay for Doug Irwin’s medical expenses, and it got a little gnarly with the Grateful Dead asking for a piece of the action since they contended none of the equipment ever belonged to Garcia, but was purchased under the Grateful Dead corporate umbrella. In essence the guitars weren’t Garcia’s to give away. So the band got to keep a couple of the guitars in the legal settlement. So much for that community thing.] As for the Dennis Had Inspire amp, I have a lot of respect for Dennis having owned and enjoyed very early Cary equipment, but knowing someone that measured one of these amps I couldn’t ever bring myself to buy one. If anyone wants to have their amp measured Roger is game to do it (even brought his equipment to Burning Amp one year to measure amps). He keeps notes on all the amps (and some preamps) he has measured. I think Roger has measured most of my equipment and even I was surprised at some of the results. |
Roger - What brand of speaker wires and interconnects do you use ?
|
Thanks Roger for offering to answer questions.
I´m using a balanced configured Pass SS XP20 pre with output impedence stated at 1K/leg, balanced and 200 ohm, single ended (according to manuel) driving tube monoblocks with rated input resistance at 47K.
Amps have both RCA & XLR (only + phase) inputs. So my question is what input is preferable and why ?
Your response will be greatly valued and appreciated.
|
Speaking of member names, I particularly like wolf_garcia's, as Howlin' Wolf is big in my house. Ain't that a man?! Mine comes from my preferred drum finish and bass drum (kick drum, if you insist) size; bdp for black diamond pearl (not the current lame version, but the old stuff, which became unavailable after the 1973/4 oil crisis), 24 for 24" diameter (also Buddy Rich's preferred size). |
@prof What a terrific thread! Thank you Roger!
I hope you can answer a couple questions that have long baffled me about the sound of some amplifiers - in this case, using my own as example.
Earlier in the thread, you mentioned how the impedance interaction with a speaker is a significant factor in how one amp might sound different than another, depending on the design.
I’ve always understood (or not understood?) this to mean that if the amps performance varies with impedance swings presented by the speaker, you will start to get contoured sound around those impedance swings - e.g. more or less bass here, more or less highs there etc. Like a tone control.
And if I have that right, and one is using an amp that is very susceptible to altering the signal based on the impedance character of a speaker, then the "tone control" variations ought to vary as you switch between speakers. So one speaker may sound fairly neutral (if it doesn’t present a tough impedance load with said amp), another may sound rolled off, another boosted in the bass, etc.
The thing is, in my subjective experience, the character of an amplifier (at least the ones I own) tends to seem more constant than that.
So take my Conrad Johnson Premier 12 tube monoblocks - for reference, measurements here:
https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurements
I have had a ton of speakers of varying designs - Quad 63s, big Thiel speakers, transmission line bass, reflex, sealed, tough impedance curves, easy ones....
And I’ve tried numerous amps, including some solid state (Harmon Kardon, Bryston 4BST, and others), and the thing is, the "character" I hear when I implement the CJ amps seems to remain constant: a slightly more rounded sound, that classic bit of "golden glow" in the upper mids/high frequencies, rounded but taught bass, etc. I just don’t seem to hear the tonal variation I should think may happen.
An even worse example is my Eico HF81 14W integrated. I’m sure you know this infamous little "classic" amp. It sure didn’t seem to measure well:
https://www.stereophile.com/content/eico-hf-81-integrated-amplifier-measurements
And, if I understand the implications of those measurements at all, it would suggest the amp would be susceptible to sonic variation, as speaker loads vary.
And yet, the little guy just seems to "sound the same" no matter what speaker they drive: from easy to drive monitors I own, all the way to MBL radialstrahler 121 omnis (a brutal load), to even my big Thiel 3.7s. They always have that same sound - a sort of lush, thickened, sparkly not "dark" sound, with a swollen bottom end that makes any speaker sound "bigger." (My hunch had always been this was some "low damping factor" in the performance of the amp that gives it this character across speakers, but now you’ll slap me upside the head for that).
So my questions are:
1. Why might I be perceiving that the amps have the same essential character even when used across a wide array of varying speaker loads?
2. Even more confusing to me: We are often told that the distortion signature of an amp tends to give it a sound. But for the most part, this arises only when power is under high demand, clipping etc, correct? If so, why do the amps seem to retain their specific character no matter what volume I play them at?
I don’t tend to listen loud. Often topping at around 75 dB or so. As I understand it, at least when I’m not listening to music with dramatic dynamics, most amps should essentially be cruising in terms of distortions. So if they are not going in to the type of distortion that starts to distinguish amp distortion profiles, why do they still sound different even at lower volume levels? All those "tubey" characteristics seem to be there no matter the volume.
Now, of course a confounding variable here is listener bias. But, if I’m hearing what I think I hear, I’d appreciate your unraveling my confusion.
Thanks! First I noticed that the conrad and the Eico both have similar damping factors. As I have said before that is the first thing we hear. Therefore they will modify the speaker frequency response in the same way. If you can get a low impedance amp then you can hear what the speaker designer intended you to hear. Since you listen at such low levels both amps are playing no power at all and thus both have very little distortion. Are there some yes/no questions I could answer. It hard for me to see exactly what you are getting at. The Eico has the added problem of the tone controls which are hard to make flat. One has to remember, the world of hi fi when the Eico was built is nothing like what we are dealing with today with your Conrad. Pre war the frequency range for good music was 80 Hz-8Khz. Post war it became 20-20K, thanks to DNT Williamson. 78’s were replaced with vinyl, Prerecorded tapes had a fair market and were excellent. Some record companies got serious about RIAA and getting things right. The Eico is just on the cusp of all that. Heath, Fisher, Lafayette, Knight and Scott all became very hot. The progress made then far surpasses the progress in amplifiers we are making now, if we are making any at all. Now its alll about a pretty face isnt it. I am blessed that my dad built a Heathkit preamp, amp and tuner when I was 4 years old. Mom says I watched all of it,though I cannot recall the images. The W2 is an excellent amp. Very open chassis, not expensive on eBay. Rather unknown. I mean what could be better than a Williamson. :) |
You cleverly dodged my (lame and silly) question so I STILL don’t know when I can get my beer, but the answer you provided to the question I didn’t ask is, of course, still relevant. Also, having carped (that’s right...carped!) here about how silly Magic Fuses are for years and engendering some resistance (to put it mildly) from athletic supporters of the things, your reasoned response about them was much appreciated. |
@hearincolor
Hello.
I am very slowly learning how power amplifiers work and have a hybrid car amp with low voltage 12ax7 tubes for the input signal that got hot and melted the plexiglass cover and some nearby hot glue. Do they normally get warm enough to cause these symptoms? It is a USamps Ax-Tu1000. They use what is called "vacuum tube current sync drive" and cannot find any info or a more universal name regarding it. I purchased it used and the previous owner claims his speakers got ruined but find it hard to believe.
Thank You.
Cool member name, I get it. A few things. A 12AX7 is not a low voltage tube. It likes to see a 300 volt power supply. A 12AX7 is the coolest running twin triode. It should not get so hot. So they are doing something wrong. Perhaps a few holes in the plex are in order. Sync drive is a totally made up term. Marketing talk, there is no universal name. You do realize that the 12AX7 has no business being in a car amp. Its just another piece of bait. At 300 watts it can ruin lots of speakers, Im not surprised the previous owner blew his up.. Can yours take it? |
What a terrific thread! Thank you Roger! I hope you can answer a couple questions that have long baffled me about the sound of some amplifiers - in this case, using my own as example. Earlier in the thread, you mentioned how the impedance interaction with a speaker is a significant factor in how one amp might sound different than another, depending on the design. I've always understood (or not understood?) this to mean that if the amps performance varies with impedance swings presented by the speaker, you will start to get contoured sound around those impedance swings - e.g. more or less bass here, more or less highs there etc. Like a tone control. And if I have that right, and one is using an amp that is very susceptible to altering the signal based on the impedance character of a speaker, then the "tone control" variations ought to vary as you switch between speakers. So one speaker may sound fairly neutral (if it doesn't present a tough impedance load with said amp), another may sound rolled off, another boosted in the bass, etc. The thing is, in my subjective experience, the character of an amplifier (at least the ones I own) tends to seem more constant than that. So take my Conrad Johnson Premier 12 tube monoblocks - for reference, measurements here: https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurementsI have had a ton of speakers of varying designs - Quad 63s, big Thiel speakers, transmission line bass, reflex, sealed, tough impedance curves, easy ones.... And I've tried numerous amps, including some solid state (Harmon Kardon, Bryston 4BST, and others), and the thing is, the "character" I hear when I implement the CJ amps seems to remain constant: a slightly more rounded sound, that classic bit of "golden glow" in the upper mids/high frequencies, rounded but taught bass, etc. I just don't seem to hear the tonal variation I should think may happen. An even worse example is my Eico HF81 14W integrated. I'm sure you know this infamous little "classic" amp. It sure didn't seem to measure well: https://www.stereophile.com/content/eico-hf-81-integrated-amplifier-measurementsAnd, if I understand the implications of those measurements at all, it would suggest the amp would be susceptible to sonic variation, as speaker loads vary. And yet, the little guy just seems to "sound the same" no matter what speaker they drive: from easy to drive monitors I own, all the way to MBL radialstrahler 121 omnis (a brutal load), to even my big Thiel 3.7s. They always have that same sound - a sort of lush, thickened, sparkly not "dark" sound, with a swollen bottom end that makes any speaker sound "bigger." (My hunch had always been this was some "low damping factor" in the performance of the amp that gives it this character across speakers, but now you'll slap me upside the head for that). So my questions are: 1. Why might I be perceiving that the amps have the same essential character even when used across a wide array of varying speaker loads? 2. Even more confusing to me: We are often told that the distortion signature of an amp tends to give it a sound. But for the most part, this arises only when power is under high demand, clipping etc, correct? If so, why do the amps seem to retain their specific character no matter what volume I play them at? I don't tend to listen loud. Often topping at around 75 dB or so. As I understand it, at least when I'm not listening to music with dramatic dynamics, most amps should essentially be cruising in terms of distortions. So if they are not going in to the type of distortion that starts to distinguish amp distortion profiles, why do they still sound different even at lower volume levels? All those "tubey" characteristics seem to be there no matter the volume. Now, of course a confounding variable here is listener bias. But, if I'm hearing what I think I hear, I'd appreciate your unraveling my confusion. Thanks! |
@unrecievedogma Hi ramtubes,thank you for that and here’s a followup. If triodes are low impedance and OTLs like high impedance, what was Jon doing then when he switched the OTLs to triode?i can tell you that the amps sound better after the conversion, and they are more stable too. The bias and the balance don’t drift anymore. Jon Specter made the conversion with some guidance from George Kaye of Moscode. Both formerly worked at NY Audiolabs.
Are we talking about NYAL Futterman? Perhaps I have missed something in this thread? Do you mean Jon Snyder? This may help. Triodes are low impedance at the plate. The Futterman circuit doesnt care about that. Ive made some triode and some pentode. One gets more power with pentode and I can image they drift more in pentode. |
This is not in a bad way. " First I'm not using this post to sell amplifiers, that is up to you. " Exposure, soft selling, putting the puppy in my arms. Genius ! All good. Love the thread ! Enjoy ! MrD. |
Hello.
I am very slowly learning how power amplifiers work and have a hybrid car amp with low voltage 12ax7 tubes for the input signal that got hot and melted the plexiglass cover and some nearby hot glue. Do they normally get warm enough to cause these symptoms? It is a USamps Ax-Tu1000. They use what is called "vacuum tube current sync drive" and cannot find any info or a more universal name regarding it. I purchased it used and the previous owner claims his speakers got ruined but find it hard to believe.
Thank You. |
No one has said this yet, except Roger, in his response to my 1st question. If this isn't a form of advertising and exposure, and yes, to sell some amplifiers, I do not know what is. Awesome Roger ! Enjoy ! MrD. |
First I wonder what happened to the speakers? Were they repanelled at the factory? Did some fool with the crossover?
Thats a hard speaker to drive and a 100 watt integrated mignt not be up to the task. The Perreaux is much larger and probably more tollerant of the low impedance.
An RM-200 will drive your speakers from the 2 ohm tap to some reasonable level. How loud do you listen, at what distance and what is the sensitivity of the speaker?
The best amp for you would be a Direct Drive to the ESL. Thats what I use.
I have a keen interest in ESL speakers and have measured many. What I have found is that the hard part of driving them is often the transformer, not the panel. Going direct to the panel makes a big difference. My DD amplifiers produce about 1200 VA into a
capacitive load. Thanks for your reply. The original panels had lost their top end, sounded rolled off, tried washing them as per instructions, the ML SL III clearspan replacement panels were just too bright with the Plinius 9100, (which for a 120W intergrated is pretty robust, but may have been stretched driving the unpowered subs as well as the electrostatic panels), plus I notice you say torroidal transformers are not ideal for electrostatics, which this amp has, (there was no futzing of the cross-overs), it really did make sense to bi-amp. The old Mos-fet Perreaux looks like a PA amp, XLR inputs and limiters (volume controls) on the front, which assisted the bi-amping. Is there a particular Direct Drive Amp you can recommend to drive the panels? (Again I’m in a 240V 50Hz country). I don’t generally drive my stereo too loud, and have been using the pre-amp in the Plinius to feed the Perreaux it all sounds pretty sweet just hankering for that tube sound. |
Hi. I was turned off tubes when a Mac 2275 couldn’t properly drive my ML Summit X’s (yep, ‘soft’ bass’). After some searching I found an Accuphase E-600 matched beautifully. My question is: how can Accuphase make a class A amp that runs cooler than many A/B amps, and substantially cooler than other class A amps that can give you serious burns when touched?
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Hi ramtubes,
thank you for that and here’s a followup.
If triodes are low impedance and OTLs like high impedance, what was Jon doing then when he switched the OTLs to triode?
i can tell you that the amps sound better after the conversion, and they are more stable too. The bias and the balance don’t drift anymore.
Jon Specter made the conversion with some guidance from George Kaye of Moscode. Both formerly worked at NY Audiolabs. |
@cakyo Use electrolytic capacitors with a 105°C rating over the 85°C versions.
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@rsf07
I wish I could tell you more on the specs of the speaker but there's little info. Roger Sanders does use a dbx Venue360 DSP unit he modifies (there are no crossovers or transformers in the speakers that I'm aware of). When you say "direct drive" amps since I'm non-technical what are you referring too? Can you send links to your own direct drive amps?Much appreciated.
I will soon publish something about my amp, but as you can see without your information my specs will do you no good. I can build up to about 5,000 volts. Beyond that its like building a radio transmitter. My speakers work at that peak and 2,500 V polarizing. I contend running the polarizing high for sensitivity causes air gap saturation. Ive heard it! Once again try to get some info on your speakers. Look at the DIY and ESL forums. Call the manufacturer. Here is the essence of direct drive. A direct drive amplifier is a bridge where each electrode goes to one side of the bridge. One side goes up while the other goes down. The problem with step-up transformers has been covered widely. What is not ever discussed is how much capacitance they have compared to what they are driving. There are very few people designing or making step ups these days and my objection to the Plitron has been covered here in depth. The problem is that designing such transformers is close to a lost art. Without some numbers I cannot say if the King transformers are good or not. I found this link. The minimum is 1.8 ohms at 25 Khz, sensitivity 83 db http://kingsaudio.com.hk/D001.jpg. Not horrible, but choose your amp wisely. Its strange that none of their amplifiers will drive this speaker at all. I havent looked at the rest which are rather Martin Logan style. |
@ramtubes,
Thank you for the input and highlighting what’s actually happening in the market. I’m enjoying the thread and learning a ton.
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@tomic601
i have been considering the 60 wpc kits Ralph puts out...thanks also for your participation here also.. The M60 is a nicely laid out amplifier, spacious inside, easy to build for even a first times. Chassis and parts are nice. One suggestion. Ralph uses all one color wire, blue, I would suggest you get a few colors it makes troubleshooting much easier. Red for B+, black ground, blue plates. This can be looked up as there is a standard. I would also use teflon stranded wire I find his solid wire a little hard to work with. If you nick a solid copper wire it will easily break at the nick. You will need a 50+ watt iron for all the terminal strips and there are many. Use low melting 37/63 solder. 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. Of course once its built who cares. Just dont bring me an amp with one color wires all bunded up. First thing I do is cut them free. Also make sure you speaker will be happy with high output impedance (damping is less than 1). Amp loves 16-32 ohms, an Autoformer is a good idea in some cases, no all. |
@maplegrovemusic
Roger - I own a pair of king sound - King v1 and a pair of King sound ks17 . This direct drive amp you spoke of , how does that work ? do I have to bypass the step up transformers , and do the speakers need to be modified to use that amp ?
The advantage of a DD amp on ESLs is to completely remove the enormous step up transformer and use it as a doorstop. As I have written here before, I have found cases where the step up is more than half the load. Try to find the previous posts where I get more into it. If one plays most large ESLs on reasonable volume trumpet music they need 1500-2500 watts per channel. Roger Sanders knows this, I have measure this, there is no doubt about this. Beveridge, Acoustat and Sanders use full panel rather than segmeted panel like QUAD. Thus a QUAD can be driven by 100 watts. So you see not all things are the same. What technical data can you provide me on your speakers, Capacitance, impedance, polarizing voltage...... |
@wolf_garcia On another note, neither of my current fave tube guitar amps has a "standby" switch as they’re relatively low powered (18 and 15 watts respectively), so the question is: When can I get my beer? Another question I’ve asked elsewhere is how do Premium Fuses work? What do they do and why? Thanks in advance for the answer (or answers). The standy switch on a small amp doesnt save enough to pay for it. When you have 4 x 6L6s and a 5U4 then it makes sense. Premium fuses don’t work. They don't protect wery well. They have caused a great deal of damage in DC circuits like the tube fuse in my RM-9. Hi Fi TuningFuses demonstrated their complete lack of knowledge by putting the fuse wire in a teflon sleve to "reduce microphonics"... Fuse microphonics, how cleverly stupid. The teflon containes the plasma which is the opposite of what a sand filled fuse does. The writers of the literature come from the bottom of the barrel with no knowledge of electronics. Just ask them sometime.. I have. Read my first sentence in the OP. I had to shut down a fuse thread because we were not getting anywhere. I realized there is no logical argument that will sway them an inch. The Fuse evidently makes them feel a certain way. My advice stick with Buss and LittleFuse. They know what they are doing and won’t rob you like those Premium fuse peopls. They are all theives preying on the unwashed audiophile. Fuses bring out trolls perhaps thats how they work. I am truly sorry anyone ever thought of Premium fuses. |
@cakyo .. I am building a symmetric plus/minus 70 volts dc (2 x 50 volt ac secondaries) power supply for an amplifier I am building. Mechanical issues are giving me more trouble than electronics such as drilling holes accurately etc. To this end, I want to build this so I do not have to change the smoothing capacitors for a LOOOONG while so I dont have to re-drill holes etc if and when they break. I am concentrating on those specific capacitors since they are large electrolytics and hence are most likely the least reliable of the components.
In your experience & opinion, which make (and series/types) of such large electrolytics are the MOST reliable in the long term ? I am considering about 40 to 80 milli farads at 100 volts per each side of the supply, depending on the price & physical dimensions. I predict that these capacitors will be in a vicinity with a temperature of about 60 - 65 C most of the time. Some sellers are asking big money, just wait for an auction like this. eBay item number:192627561898 Just an example. I had some 49,000 at 75 V, look for something like that. Do you have your power transformer yet? Hope its at least 6-10 amps. How do you intend to use this power? 10,000uF 100V Sangamo Electrolytic Capacitor Computer Grade Crown Power Amp BGW. These went for $8 each. No problem with age or use, they last forever. Get a few extra at this price and never worrry. Besides the diameters are pretty standard in only a few sizes so there is a lot of interchangeability. Mallory, Sprague and other US makers made these. Its sad how many of these I had to thrown away. Tried to sell them on eBay, no luck. Which is good for you as there are people who will let them go for nothing. I see one for sale now fot $380.. he's a newbie. :) |
@bdp24
Roger, I think you provided this information somewhere, but I can't remember where, and can't find it. So let me ask you: what is a good output impedance number to shoot for in a power amp? How low does it need to be to prevent frequency response peaks and dips due to the speaker impedance/amplifier output impedance interaction? I know the figure will be different for a speaker with a wild impedance curve (the original Quad ESL) than for one with a fairly even curve.
Great Question... Damping of 10 which is an output impedance of 1/10 the load is a nice number and about all one can achieve in a tube amp and maintain staility. Quad achieved 20 on the model II for the ESL57 because Walker wanted 20, he said so in the speaker spec. The II is a fairly low power ampifier, yet a great one. Futterman had a damping factor approaching 100 perhaps more. It has lots of well applied feedback which it can tollerate due to no transformer and its excellent internal bandwith (open loop bandwidth). I think it is clear that he was interested in low output impedance. The open loop response of a tube amp is almost entirely dependent on the output transformer. When you see those peaks after 20Khz in JAs measurements that is all from the transformer actually reversing phase and making the feedback positive. Great indication of an amp that will oscillate into certain loads. Ringing on the square wave shows the same thing. Since you brought up the Quad 57, Walker or Baxandall did a very smart thing in the transformer to keep the impedance from going to infinity in the bass. They put 3 shorted turns of #16 wire, very loosely coupled inside the transformer. I only know because I melted the wax of one. *(by accident)* This clever idea helps tame the bass if an amplfier had very high output impedance. Even protecting the amp from overvoltage at low F so as not to arc the amp's transformer. This may take some further explanation. I had to sit down when i saw it. Of course SS amps can have much lower output impedance, approaching that of a heavy speaker cable or even lower than that cable. JA measures with a few feet if realistic cable. As I write this, every time I write "damping factor" I have to back and change it to either output impedance or regulation. I think I left it twice in the hope of shifting the tide a little bit. The Futterman is an amazing amplifier I hope to cover in depth in the future. Waiting for questions to arise. |
Hi ramtubes,
Thanks for answering my previous question. I appreciate it.
I do have another question please...
I am building a symmetric plus/minus 70 volts dc (2 x 50 volt ac secondaries) power supply for an amplifier I am building. Mechanical issues are giving me more trouble than electronics such as drilling holes accurately etc. To this end, I want to build this so I do not have to change the smoothing capacitors for a LOOOONG while so I dont have to re-drill holes etc if and when they break. I am concentrating on those specific capacitors since they are large electrolytics and hence are most likely the least reliable of the components.
In your experience & opinion, which make (and series/types) of such large electrolytics are the MOST reliable in the long term ? I am considering about 40 to 80 milli farads at 100 volts per each side of the supply, depending on the price & physical dimensions. I predict that these capacitors will be in a vicinity with a temperature of about 60 - 65 C most of the time.
Thanks
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Dennis Had (alive and well in Apex or Cary or someplace) hand built the best sounding amp I’ve owned over many decades of owning things. The amp’s 2nd birthday happened recently (he signs and dates these things), and I rewarded it by giving it a new tube. Although mine is one of the extremely high powered versions of his "Firebottle HO" (it’s a HO...says so right there) SEP at a massive12 watts pc (hide the children, batten down the hatches), his stuff, other than the well regarded headphone amps he makes for Moon, is subject to his whim of making one a week maybe and only selling ’em on Ebay. He currently seems to be making only a 2 to 4 watt SE version (8 watts with KT150s?), but I hear he might make something else if you ask nicely. There are no specs published by him for the Ebay stuff, and he’s nothing if not enthusiastic. I am consequently tied to highly efficient speakers, but the bondage works for me.
On another note, neither of my current fave tube guitar amps has a "standby" switch as they’re relatively low powered (18 and 15 watts respectively), so the question is: When can I get my beer? Another question I’ve asked elsewhere is how do Premium Fuses work? What do they do and why? Thanks in advance for the answer (or answers). |
If a system is not broken and has serious deficiencies cables will likely not correct the problem. How can they? I'm not suggesting cables can cure a serious deficiencies. However, since cables interact with the amplifier and the loudspeaker, they can ameliorate slight deficiencies be it amplifier, loudspeaker or environment. Some amplifiers are nearly immune to cables, but loudspeakers are not. |
I would like to know the capacitance of the panel itself, the electrode spacing and the polarizing voltage.
Direct Drive is the best way to go. I have found many cases where half the power goes into the step up transformer and other EQ components. How does he EQ the speaker these days? I just started reading the
speaker description. Sounds like its an entire system.
I wish I could tell you more on the specs of the speaker but there's little info. Roger Sanders does use a dbx Venue360 DSP unit he modifies (there are no crossovers or transformers in the speakers that I'm aware of). When you say "direct drive" amps since I'm non-technical what are you referring too? Can you send links to your own direct drive amps? Much appreciated. |
Hello Roger, I'd like to come back to tube testers. I'm not sure I understand correctly about your recommendation for a simpler device, to measure emissions. Is this for the basic purpose of monitoring for tube failure? Would I need a tester with more capacity in order to check prospectively for tube matching? Thanks, Mark |
Thank you for posting this. I have a question specific to a tube tester I own and use. It is a Weston 981 Type 3; it incorporates a line check adjustment where the line voltage is adjusted to a mark on the meter. When I test 6550 or KT88 tubes with the tester is in Gm test mode and the line check is done the voltage drops. The voltage holds steady when testing less powerful output tubes. Should I compensate by readjusting the line voltage or use the reading with the lower line voltage? Or do I have a problem with the tube tester?
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Roger, You posted the following "As I tell everyone. Light loading can be done on any tube amplifier. If you dont play above 80 dB go to the lowest tap. If you play 90 go one higher, if you play more than 90 you may have to use the high tap to get the volume you desire. This change should be far more apparent than a cable change. 7 ohms on the 8 ohm tap is no problem for the amp but lower taps always perform better technically though how it sounds to you is more important. "4 ohms on the 4 ohm tap produces 100 watts. 8 ohms on the 4 ohm tap around 60 watts. As you go down in taps you spend more time in the class A region. The distortion and damping are much improved. "Would be nice if you had a way to measure the peak voltage you require, then much better advice can be given. You can also get at that with a SPL meter at one meter at listening level. Then with speaker sensitivity we can compute it "Everyone needs an SPL meter. For $50 its an execellent investment. People spend more than that on a poorly designed high end fuse. Please do not buy premium fuses, TuningFuses are the worst and the others I have not dissected but the people who sell them should be dissected."
******* Just an anecdotal experience. I own an ARC Ref 150SE. It has 3 output taps: 4, 8 and 16. I settled on using the 4 ohm tap for many of the reasons you mentioned above. John Atkinson reviewed an earlier version of the a few years ago and made the following comments: "As expected, the Ref150's output impedance varied according to the transformer tap selected. The 16 ohm tap measured 1.4 ohms at low and middle frequencies, rising to 1.9 ohms at the top of the audioband. The figures for the 8 ohm tap were 1 and 1.4 ohms; for the 4 ohm tap, they were 0.55 and 0.87 ohm. All three taps offer quite a low source impedance for a transformer-coupled design; as a result, the modulation of the amplifier's frequency response, due to the Ohm's Law action between that impedance and that of our standard simulated loudspeaker, was relatively mild." See Atkinson report here: https://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements
So, in my experience, the Ref 150 SE, on balance, sounds best when light loaded off the 4 ohm tap. At times, I thought the 8 ohm taps sounded better, but after a while, I found the sound bright, probably because there is a 20++ ohm peak at the midrange cross over point. And as you predicted, bass is tighter when played off the 4 ohm taps, although I think speaker impedance in the bass region bounces around quite a bit but has a 3.8 ohm saddle in the 50 to 200 Hz range. As far as loudness is concerned, my speakers are rated at a 92db sensitivity and the amp has plenty of power to drive the music to uncomfortable loudness levels, albeit with little perceive distortion or signal scrambling. So the bottom line is that there seems to be something to be said for light loading. Bruce
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