Does anyone care to ask an amplifier designer a technical question? My door is open.

@bdp24 

@ramtubes, I finally got around to reading the review by Herb Reichert of the Cary SLI-100 in the December Stereophile. Damn, what a piece of junk! Cary specs the amp at 100w/ch from a pair of KT150 power tubes per channel; John Atkinson, using 1% THD and noise as the definition of clipping, measured the amp’s output from the 8 ohm tap into an 8 ohm load as a mere 3.2 watts! Out of a pair of KT150’s! You have to work REALLY hard to make an amplifier that bad. Whomever designed this boat anchor should find a new line of work; amplifier design is obviously beyond his abilities. 3.2 watts/ch for $5995? Not a "very good value" ;-) .

And what does this tell us about Herb Reichert, who very much likes the sound the amp produces? That Herb apparently likes distortion, I would say. You are now justified in completely disregarding anything and everything Reichert has to say about hi-fi. If one "likes" a power amp this bad, what doesn’t one like?

RM: "He (Harry Pearson) was an idiot." At an instore talk in the 1980’s at a S. California hi-fi shop to introduce a new product, Bill Johnson told this story about Pearson: Bill had sent Harry a new pre-amp for evaluation and review, and soon received a call from HP, saying the pre was defective. Bill had Pearson return the pre to ARC, where it was tested and found to be operating perfectly. A phone call and questions revealed the source of the problem; Harry had installed shorting plugs, not into the pre’s unused input jacks, as they are intended to be used, but into it’s output jacks. Well duh! Should anyone that ignorant really be considered a "reviewer", and empowered as such?

Its good to have  voice of reason here. I do know Herb and he listens at low levels. Remember he was in the Single Ended camp for many years so he doesn't need much power. 

As I have said before, at very low power, less than a watt, that amp and many others will sound just fine. Its in its class A range as far as distortion is concerned. However if someone has Maggies and listens loud it will not be pleasant. If they truly need a 100 watt amp this is not the one to get.

Now HP is another matter. While he created a lot of the language we now use, some good some bad, he was essentially ignorant of electronics, amplifiers, anything technical. I am amused at the story about the shorting plugs. 

While I would enjoy having Jon Atkinson's job I would not enjoy being a reviewer. They have to come up with all sorts of drivel on everything they test. I only read the subjective review if the measurements are way off. 

We did some testing the other day with the QUAD 57. Both myself and my friend listen around 80-90 db. At those levels the 57 required only 10 volts peak. Sometimes 20 V on loud passages. Almost any amplifier can provide that. 

I plan to write up our listening session sometime soon. It is a laborioius project to make a strict, level matched A/B, not blind test. The listener knows which amp he is listening to. Its not a test of the listener, its a test of the amp. 

I have had many responses, good questions, no Trolls. If I missed your question please re-ask it again.

@mrdecibel

I will be the first. I never owned an amp of yours. I have owned other tube amps by several other manufacturers. I gave up on them, and this has been through a pair of modified and tweek’d pair of Klipsch Lascala. Why did I give up on them ? Noise, microphoncs, pretty often biasing, warm up time ( I leave ss amps continuously because of the superior sq ). and " timing " in the bass ( muddy ). I go passive through a Dac. Should I try an amp of yours, and why ? I listen loudly to rock and jazz. Thank you... Enjoy ! MrD.

First I’m not using this post to sell amplifiers, that is up to you. However I can understand and appreciate your frustration with the tube amps you have owned. Here is why.

Noise is simply due to designer who doesn’t hear or mind the noise, probably has no internal limits for what is low noise, or doesn’t know how to measure noise. It could be a noisy tube.

Microphonics are generally created in the first tube of the amp, the input tube. You just have to find a good one. I do grade tubes for noise and microphonics.

A good amplifier needs to have its bias adjusted perhaps twice a year or when you hear something change radically.

Good amplifiers warm up and are 99% there in about 5-10 minutes. There is no good reason to warm them up or leave them on. They play in the first 30 seconds and don’t sound bad as they come up slowly.

Muddy bass is generally due to low damping factor. Get a damping factor of at least 8-10. More than that wont make much difference and high damping tube amps are often unstable due to too much feedback.

BTW, I am believer in both pcs and fuses. Enjoy ! MrD

Thats fine with me. Just don't use premium fuses in the B+ circuit of any power amp. There is a lot of energy stored in the filter caps and it has to go somewhere. A high interrupting fuse does the proper job of leaving most of the energy in the filter caps rather than tearing a path of destruction through your amplifier..

@djones

 I have never owned a tube amp , always used SS and this doesn't come up if it's rated for 8 and 4 Ohm. I have what is I am sure a novice question. My speakers are 6 Ohm and I notice most tube amps have 4 Ohm or 8 Ohm taps and sometimes 2 Ohm. Where would I connect a 6 Ohm speaker?

Here is where experimentation will produce very real and obvious results. Always use the lowest tap that gives you enough volume without distortion (clipping). You will then get the most damping and the speaker will have frequency response as close as possible to the designers voicing. If you want more detail on why that is ask me. Its long.

Also experiment with the taps at low listening levels where clipping will not be an issue. Listen for tonal changes and peaky or mushy bass. The bass is most affected. 

FInd an impedance curve for your speaker and send me a link. Impedance variations are the largest cause of response variations with most tube amps and tap choices.

@frogman An extremely generous offer. Thank you.
What is it, from a technical standpoint, that allows good tube amplification to reproduce micro dynamics in a way that is much closer to what I hear in live music? I refer to the ability to reproduce the seamless dynamic gradations in volume (especially very subtle gradations) that give music a sense of aliveness; not simply the ability to play very loudly. I know some will disagree, but to me tube amps generally do a better job of this than solid state. The attributes of tube amplification are often described in terms of tonality, dimensionality, staging, but to me the thing that draws me to tubes more than anything is the way they reproduce dynamics. I generally hear more dynamic nuance (realism) from tubes. Thoughts?

Transistors have a very abrupt turn on. A silicon transistor starts conducting with 0.6 volts on the input (base) and is fully on by 0.7. With MOSFETS the numbers are just as bad 3.1 to 3.5 or so.

Tubes, on the otherhand, have in input range of many volts. A preamp tube might go from -10 to 0 on the input. A power tube -50 to 0. The - sign occurrs because tubes want to be on till you cut them off, so the grid (input) always starts out negative.

So input range has something to do with producing microdynamics and dynamic range as the devices themselves inherently have more range.

One other thing that has drawn me to tubes. Only with tubes can you make a minimal circuit that sound good. Transistors require many stages and lots of feedback. Now feedback is not inherently bad but a lot of feedback gets people in trouble with oscillations (instability). I also like the fact that tubes need no protective circuitry, last long if well treated, are nice to look at.

Transistors don’t last forever and transistor amps are much harder to fix than most tube amps. (not ARC) :(

In the new year, time permitting, I will put up some videos to show people how easy it is to fix a tube amp. The other day I fixed one over the phone in Germany. With proper knowledge and a little advice its not hard.

@uberwaltz 

 Now a novice question.

i have zero tube amp experience.

a lot of my equipment runs xlr connections

i have not seen many tube integrated amps sporting xlr inputs.

is there a good reason for this?

Balanced inputs take a lot of extra stuff. Most integrateds are going to turn the balanced into unbalanced right off because of volume control issues. The extra stuff in SS amps is a 50 cent op amp. In tube amps it would another tube or transformer. Much more expensive.

Balanced makes more sense on power amps where it is actually easy to do because of the absence of a volume control. 

Keep in mind just because a unit has a XLR input that is no assurance that the input is balanced.

@mrdecibel 

Roger, thank you for the response. I have to disagree with you as to warm up time of a component ( which is relative to break in time ). For me, 5-10 minutes is never enough. " Don't sound bad when they come up slowly ". For me it takes much more time. I am not talking measurements, I am talking " listening ". I would like to leave it at that, as this, too, could wind up being a very controversial discussion, and not new to Audiogon. Enjoy ! MrD.

Was that MY amp that took hours? Not all tube amps are the same. However you are welcome to warm up as long as you like. There is no controversy. 

To help solve the warm up problem I put a forming switch on the RM-200 MK II at the suggestion of Richard Vandersteen. This switch keeps the caps formed beyond operating voltage. We both feel that cap forming is the most obvious reason for long warmups.  

One might also consider warm up time on their ears and other senses. When we first sit down we are not in the same state as some time later when we have relaxed and shut out the noise of the outside world.

@bdp24 

Roger, I assume the balanced/XLR-only input on your RM-200 is accomplished with a transformer. Do you wire it in accordance with AES File 48 (pin 1: ground, pin 2: non-inverted signal, pin 3: inverted signal)? Thanks---Eric.

Actually it does not though I do use th AES standard for the pins. 

The balanced input is a differential pair with feedback right to the input so that the characteristics of the amplfier are determined largely by 4 high quality resistors.. and of course the rest of tube magic.

The CMRR is very high at 90 db and the amps works and sounds the same if driven unbalanced (single ended)

@rego Where do I begin when considering an Amplifiers Characteristics?

The first thing people are hearing, whether they believe it or not, is the difference in amplifier output impedance that will affect some speakers more than others. An amplifier with an output impedance greater than 1/10 the tap impedance will start to modify the frequency response of a speaker. The frequency response modification will simply follow the impedance curve of the speaker. 

There are some tube amps out there, that people love, that have an output impedance greater than the tap impedance and those will make very obvious changes in frequency response. The bass will always have a peak, the mids may have a dip, the highs may be accentuated or reduced, all dependent on the impedance curve. 

I purposely did not use the term "damping" because that term implies controlling the woofer which is actually not what is going on. However 1/10 the tap impedance or 1/10 the speaker impedance is a damping factor of 10.  I firmly believe that we should retire the term damping factor or get a better understanding of what is really going on. One has to remember that an 8 ohms speaker has typically 6 ohms of DC wire resistance in the voice coil. This makes the output impedance rather unimportant.

I expect some flack on this. So just be kind and logical and I will blow your mind about damping.

@rocknss
 Curious on how you have trained your ears.

Time, attention to distortion, frequency response variations, lots of A/B testing... lots of that. I set up one today to use a QUAD 57 to compare a stock with a modified amplifier that has come to interest me and may become a product.

One experience I would share is a listening session with 5 rather proud golden eared audiophiles and myself. They were all lined up on the couch in pretty good position to hear the system. I was 90 degrees off axis having some wine and cheese. I heard a horrible rendition of a stand up bass.

I first said, thats the worst bass fiddle I have ever heard, is this some horrible recording, no its a well respected recording. Then I asked, "what do your guys hear" They said audiophile things like, poor imaging, no depth, yada yada yada. I said, What i hear is a lot of distortion, like 30%.  The source was a tube modified OPPO player. I said, hey got some more 6SN7s around? So new tubes made everything fine. The host, a good friend, quickly brought up his tube tester and we found the old tubes were down to 20% emission.

The point of this story is that audiophiles rarely hear distortion as distortion. That word is not popular. They were listening to and judging a system that was simply broken. So the first thing people need to know is when their system is broken. I think many systems are.

In closing I think time, confidence (which is hard to get depending on who you hang with), and the Harman link are all good things. I know that Harman has developed some very good listening procedures and selects their listeners carefully. The qualification process to become one of their listeners is long and many people are eliminated. What Harman wants to get out of all this is to have listeners tell them if they are going in the right direction with changes in speakers and other components. Of course they use measurements also. Any sane person would.

@stereo5 

I have a question for you Roger:
What are your thoughts on Class D amps? I have listened to quite a few and always came away unimpressed with my ears aching. I am a Mac guy at heart marrying a Mac solid state amp with a Mac tube preamp. Perhaps I like a more mellower sound?

I heard your tube amps back in the 90’s at Sound II in North Dartmouth, Ma. Leo (RIP) was a huge fan of tubes and carried your line as well as VAC and Audible Illusions. I did a lot of listening and buying in that store. An added plus was there was a fantastic strip Joint right across the street from the store on Route 6. Really fun times!

I was making class D amps in 1990, before they were hardly known. Mac Turner brought me in to consult on his. What disturbes me about them is that they all get their sound from the IC in the front end. Perhaps some are discrete front ends but I have not seen any. 

The biggest problem is the output choke that is necessary to filter the switching waveform. If you look at Stereophile reports you will always seen one impedance that is flat while the others either peak or droop. 

They are going to be popular due to size, low cost, ridiculously high power that hardly anyone needs. I was interested back then as an engineering exercise but no desire to make any. Over 100 watts is only justified by either high listening levels or insensitive speakers or both together. Excess headroom is a myth. 

I have some Mac gear to be quite excellent. I have a post about that here. Just go to my profile to find it.

@terry9  I build solid state amplifiers, and like to match output transistors. At first I matched for HFE, then VBE at constant current similar to operating spec. Only later did I realize how much this parameter drifts over the first hour of warmup.

However, my latest amps are Class A, and I suspect that a more realistic match is obtained by culling outliers by HFE, then match from VBE using the bias at constant potential and sufficient to generate the operating current. Finally, instead of using matched emitter resistors, I use emitter resistors tailored to the output devices, so that each emitter resistor sees the same potential drop.
Your thoughts? Any advice appreciated.

Kudos to you for building your own gear. I have often said that the best amplifier is the one someone builds for himself. It brings along with it the joy that it is your creation not someone elses.

Of course you match HFE at operating current?

What is the spread of emitter resistor values? That part concerns me a little.

How many transistors in parallel?

Yes transistors are very temperature sensitive. VBE varies at -2 mV per degree C. Thus a 40 degree rise will be 80 MV and that is a lot to deal with. Do you have a VBE multiplier in the bias circuit?

@geek101    Hi Roger, thanks for the great offer. I would like to know what are all the measurable variables does one consider when manufacturing an amplifier.

I am guessing this list is most exhaustive then the spec sheet typically posted?. If not correct me.

For most of the lesser informed people buyers like me we only have spec sheet and most amps almost are always good with stated specs. So it is really hard to differentiate and choose.

Good Question. One thing to do is follow John Atkinson's measurements of amplifiers. If you dont get Stereophile its a good mag and only $12-15 a year. If I get 10 new subscribers I get a toaster... :).. Just kidding

I find most amplifier specs to be missing something that should be there. Perhaps because that particular spec is not so good. So here is the list.

Distortion from 0.25 watts to full power over 20-20,000 cycles. This spec came from the FTC.

Damping factor can be most important thing if it is below 8-10. However much more than 10 doesnt make much difference. In other words, some SS amps have damping over 100. Thats ok, but at what sonic cost.  Damping factor will have a great effect on frequency response if your speaker has a widely varying impedance curve. Dont be impressed by super high damping. Its not going to matter.

-3dB power bandwidth. Jadis did not publish this because the spec would be horrible. Heres a 4 chassis amp that can do 200 watts but not to 20Khz. The spec 20-20Khz is more like 5 watts. I have measured it.

Noise often specified in db below full output. Not a good way to spec this. I would prefer a simple statement in noise in mV both wideband and A weighted. Good luck on that one. 

Power consumption will give you some idea of how much this thing is going to heat your room. 

That pretty much covers it. MTBF (mean time between failures) is speced on all parts of your computer, industrial power supplies and many things. Unfortunately I have never seen this spec on an amplifier. The number for most amps would be very low. MTBF for things like hard drives is 300,000 to 1,200,000 hours

 http://knowledge.seagate.com/articles/en_US/FAQ/174791en

The MTBF of amplifiers varies widely and is only known by those of us who fix them. I am very proud of the MTBF for my amplifiers. I can only state it in years and its at least 30 years. 

If you want to buy an amplifier that will not trouble you, use the internet and find what people have experienced.

@bdp24 

Thanks for the balanced info Roger. 4 resistors > transformer! I've been running the RM-200 with a balanced pre-amp, but if connected to an unbalanced source (First Watt B4 x/o), what is your recommended method of converting the RM-200's XLR jack for use with an RCA plug, or put another way, connecting an RCA plug to the XLR jack? I've seen a cable with XLR's at one end, RCA's at the other. Acceptable?

Yes any proper converter or cable that grounds pin 3 (signal -) is fine. I purposely made the amplifier perform the same either way. Balanced helps in situations where people have ground loops. 

@terry9 

I was measuring HFE with a handheld, not warm, not at operating current, and only using the result as a first cut to cull outliers.

Emitter resistors are 0R1 +/- 0R02, so not much.

4 x PNP and 4 x NPN.

No VBE multiplier, but then I leave my amps on most of the time, and they stabilize below 50C.

50 C/122F is nicely cool, only 25 C above ambient in a standard room. You either have big heat sinks or not so much idle current.

Do you mean resistors from 0.1 ohms to 0.02 ohms? I like the American system of resistors.  That is a large range. Do your account for this and make the idle currents equal in each transistor?

HFE for a power transistor at low current is rather meaningless. Why not do all of it at operating current?

A VBE multiplier is a very good thing and easy to add. How much does your total idle current vary from cold to hot and how long does it take to get there? What is the idle dissipation?

Roger, thank you again for your response. My ears have required long warm up times for almost all of the gear I have had over the years. Solid State as well as tubes, dacs, tuners, tape machines, etc. I suppose R. V. knew what I was talking about, the warm up problems. Is the forming switch the same as an amp having a stand by mode ? I assume it is this capacitor thing that I have been responding to. I am glad you are here posting, as I am greatly enjoying the information. Enjoy !

Glad you know your ears, many people dont. 

SS equipment can be very temperature sensitive because transistors themselves are much more sensitive than tubes as I have written here to another question. Therefore there may be a lot of variation over time. 

The forming switch is not like a standby switch. A standby switch, such as on a guitar amp, keeps the tube heaters on but cuts off the B+ to let the amp cool and extend tube life. However it is intended to be used by the player on breaks not longterm. Turns out long term, tubes do not like to have only their heaters lit without B+. Cathodes tend to get lazy. They learned this in the tube computers. So even overnight standby can start to be a problem and really has no sonic benefit. Standby on a Fender is so the player can go get a beer.

I designed my amplifiers to warm up to optimum pretty fast. I have worked on other amps, expecially ones with SS devices in the power supply, that take quite a while to come up to optimum.

@cakyol

Can you please tell me the purpose of resistors R1 -> R8 in the power supply shown below in the URL ? Is it to reduce the resonant frequency in case the supply oscillates with the stray inductance of the smoothing caps ?https://www.passdiy.com/project/articles/burning-amplifier-1

They are part of the RC filter of the power supply, to reduce ripple. A choke would be better but expensive and bulky. He is likely using multiple resistors to spread the heat and often reduce cost.

It is nothing to do with resonance or stray inductance. Those arent problemsl. Its simple AC ripple filtering.

They could be replaced by a single power resistor of sufficient wattage at 1/4 the value. They appear to be 1 ohm each which is rather low to do much. Nelson is a good guy we spoke together at Burning Amp 2018. http://http//berkeleyhifischool.com/having-fun-at-burning-amp-2018/  

In his earlier presentations he talks about the Amp Camp. It is once again available at DIY audiostore. Its not my kind of circuit but it is interesting.

@assetmgrs Roger; How do you feel about the design characteristics of hybrid amps, say with a tube preamp and a solid state power amp like the Rogue Pharaoh? Does this approach offer advantages of both tube and SS, or does it compromise the best of both sides? Thanks in advance.

So this would be a integrated. I looked at a picture. I would be concerned about tube noise. I have heard their tube phono stage is unusable due to noise. I see the line stage is a 12AU7, thats a poor choice as quiet ones are hard to find. Might be a problem on sensitive speakers.

I dont see a noise or distortion spec on their literature. Thats a little bothersome. The damping factor of >1000 is very hard to verify and will be cut in half with even a heavy speaker cable. So its kind of silly.

I worked on older Rogue amplifiers and was not impressed. Too many things done strange, like DC heaters for the output tubes and running them way too hot. When I see that kind of stuff I have to wonder. There was no way to reduce the idle current (bias) so I had to put in the most expensive output tubes to be able to guarantee any reasonable life.

I hope their new stuff is better and wish them success if it is. Keep in mind it is a value product, not necessarily high end.

@geek101  @ramtubes with Class D switching freq over 450/500 KHz these days do you still think output filtering is an issue?. How do I educate more about this ?. If the issue of filtering not a function of switching freq please correct me. Thanks again.

One would want to see the measurements John Atkinson style. There is no other way to know but measure it. If these things interest you Stereophile is your best bet and its a good deal at $14 or so.

The filtering is easier the higher the frequency. That does not mean its done right. JA recently reviewed a D amp that had what I assume is pre EQ to make up for the drop. I think it was NAD.

Of course there are flaws in that idea because it EQ's for a resistive load. At least one can play with it and choose by ear.

@terry9 

Thanks for the nod ... I guess the takeaway is, "Don't be so lazy. Match HFE at operating temperature and current." Thanks!

Have you measured the idle current of each transistor at operating temp in the amplifier? You of course know just to measure the Emitter drop divided by R. How well is it distributed? Then you could put a scope on them at full power and see how equal those are. 

Dont spread the emitter resistors too much because they might not track and share over full swing. I would make all the emitter resistors the same and do good transistor matching. You might make them a little higher like 0.22 ohm. You won't loose much output.

The concept of varied emitter resistors is a thought I have not had. :)

@blueranger

Thanks for your expertise. I have a question about damping. You said a heavy gauge speaker wire would actually decrease damping. So a speaker gauge around 16 might exert more control over the woofers for deeper bass?

What I wanted to convey that a damping factor of 1000 will never reach or be appreciated by your speaker. Above 10 is generally enough, hard enough to obtain on a tube amp. SS amps will have higher factors but to no avail at the listening end.

You want low resistance cables. For a few meters 16 ga is fine. Double the length and you should subtract 3 from the ga to get the same resistance, therefore 13 ga. Isn’t it interesting that every 3 ga doubles the resistance over the entire range of wire...Bet people dont know that one. You can only learn that at a traditional school like UVA. Any alumni here?

But here is the worst news to many is; Damping does not really control a woofer. Im sorry as this will disturb many. Paul Klipsch spent his lifetime trying to put this across. I dont know why it ever started being called damping. Perhaps someone here will do a little research. My clue would be to see when pentodes replaced the 45 triode in radios of the late 1930s.

We have to keep in mind that these radios and phonographs had single 8-12 inch speakers and an open back cabinet. In that case one could say we are damping the woofer by providing it a low impedance so that the resonant peak will not be so big.

Modern speakers dont require damping, they are already damped in their cabinet. They really are. Go tap on the woofer, you will hear the resonant bass frequency. Short the terminals and see how much your tap changes in level. I expect not much. You can even do this with your speaker connected. Tap it with the amp off then tap it with the amp on. The amp will be the short if it is high damping. its not quite fair to do this with a tube amp as the transformer may damp the speaker more with the amp off than on. HUM, isnt that interesting.

The resonant frequency of the woofer determines the low frequency cutoff and will not change with wire, damping or anyone's good wishes. It will however go a bit lower with time as the woofer loosens up, but only a few Hz. 

What modern speakers need is a low impedance drive to deal with their often widely varying impedance. A 8 ohm speaker can easily go from 50 ohms down to 4 or 3 or 2 ohms. That’s quite a range. Then damping makes a difference because it provides constant voltage to the varying impedance.

Of course some speaker makers keep their impedance rather constant, which is a very good thing if you want to play with a wide variety of amplifiers.

Maybe an open minded university, interested in electonics history, would let me do PhD research on such an arcane topic. Offers accepted. Though I hardly have the time for anything so rigorous.

@terry9 

In case you are wondering, the 25V rails are to accommodate Quad ESL's. With 75:1 step up transformers (Plitron), the amps can only punch the panels to 3750V, exactly half the level which engages the protection circuit. So I can bypass the protection circuit with impunity, and get a remarably refined ESL sound.

You have my ear. Tell me more about what you are doing. Which QUADS? I am guessing 63s.

@enobenetto  I own your RM-10mkii, which is a mysteriously addictive amp. How did you approach low-frequency response? I ask because the bass the amp produces is punchier than any 100-watt solid state I've owned.

I have zero knowledge of electronics, so my other question is a simple one of your opinion on newer Russian tubes and their sonics/quality. I might be the only person in audiophile land who actually likes the JJ brand. They seem the most linear and balanced, albeit with a dry top end.

I am pleased how many people love the bass of that amp. I think I just lucked out. I designed and prototyped all the transformers myself. The application is unique. Very high voltage, perhaps its that. I gave a talk about it at Burning Amp2018 that outlines the application and compared it to the typical applications 

 http://berkeleyhifischool.com/having-fun-at-burning-amp-2018/

I stock several brands and vintages of EL84s. I do not stock JJ so I can't say much. Im glad you like them.

@terry9  Idle current diminishes from 1600mA to 1200 mA, in the course of one hour. Rails are +25V and -25V, so dissipation 80W reducing to 60W.

Sounds like a nice amp. High idle, reasonable rails. Congrats.  Its for more sensible than some 200-1000 watt monster or a bridged amp.

I am puzzled why the idle current goes down rather than up as it warms. Usually its the other way round because of the negative temp coefficient of transistors.

@terry9

I would use a dual trace scope, make sure the two channels have identical gain, use one emitter resistor on channel 1, call that the reference. Then use channel 2 to see how the others (one at a time) match up at various power levels. I would find the results interesting.

Have you also looked at the output transistor current driving the speaker at high levels, high frequencies? Trumpet music, thats a killer? Have you measured the impedance of the primary side over frequency? I have found some stepups have so much capacitance that more of the energy goes into the transformer than the panels. FYI, the 57 and 63 transformers, though different, are very cleverly wound. A torroid typically has lots of shunt capacitance that you have to drive. The QUAD transformer does not.

BTW, I am not impressed at all with the Plitron audio transformers. Van Der Veen’s paper seemes flawed to me. He is a great speaker promoting his idea of automatic bias. He believes you can use a gapless tube output transformer to make a practical amplifier. I take great issue with that. I think there are some unasked thus unanswered questions. I would ask him, "what happens when there is a DC offest in the output stage. It will happen when the amp is pushed?"

Similarly if you have any DC across your primary the core flux will be off center. I cant say how many mV is ok, but i think at 50 it could be noticed and at 100 mV it might be a real problem.

Here’s how to set up your test:

Scope ground goes to hot output terminal of course. Im assuming the output stage is emitter follower.

Dont forget to float the AC power on your scope. Othewise you will be shorting your output.

On my bench I only have one piece grounded. Everything else floats. Even my soldering iron floats because sometimes I solder amplifiers while they are on. There are parts of the circuit that dont much mind. Dont do that with SS amps, the are unforgiving.

@terry9 @atmasphere 

Actually this is pretty common with bipolars. They can get into a phenomena known as 'thermal runaway' if this is not well controlled

.

Ralph, did you perhaps mis-read this. He said the idle goes down not up as the amp warms. This is the opposite of thermal runaway.

Terry, do you still hold your idle current goes down as it warms?

If so I want to see your circuit. Hey, I'd like to see it anyway. This is unusual. 

@bdp24 

Roger, here’s a question about light loading with the RM-200 Mk.2 amp: With a loudspeaker given a nominal 8 ohm load rating by it’s designer/manufacturer (it measures between 10 and 20 ohms from 20Hz to 20kHz save for the 60Hz-180Hz band, where it dips down to 7 ohms, centered at 80Hz), the RM-200 will of course put out at least it’s rated 100w/ch when connected to the amp’s 8 ohm taps. If it is instead connected to the 4 ohm taps (light loading), what will the amp’s output wattage be?

Because of the speaker’s relatively high and even impedance curve, it is not for the flattest frequency response I am interested, but rather the lowest distortion and longest tube life. I realize that with light loading those will be achieved at the cost of less power output from the amp. I have a modestly-sized room, and don’t listen at very high SPL, so am willing and able to accept that.

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. 

I still prefer US, European or Japanese vintage production over the new stuff!

Is a 1980s RM-9 in good working condition vintage enough? :) They just going like the Energizer Bunny

@terry9

I see you have jumped on the bandwagon of expensive parts. I have not yet found them to be superior and they are costly and often fragile. Those resistors especially. I dont see the benefit.

As far as dialectric, i understand it well. Let me ask your a question. How much AC voltage (changing voltage) is across a coupling cap in any amplifier?

I am still curious about your falling idle current with rising temp.

How do you drive the capacitance of all those QUADS. Have you done some measurements on what the combined impedance of the whole setup is?

How do you arrange them?

@roberjerman

So Roger: new production tubes from our old Cold War rivals. Can the Russians really make and sell quality tubes at such low prices? A quartet of 12AX7's for $18 (shipping free!). We did that ourselves back 50-60 years ago. But that was when US tube production was in the millions for the radio/television market! Do Russian mfgr's have to compromise on material quality and less vacuum- pumping to sell at a low cost?

They are doing better and better. Sometimes I send back a whole batch but not so much lately. Low noise 12AX7 are hard to make. Where do you get 4 for $18? Im sure they are not tested for noise or microphonics. Luck of the draw like poker.

Sadly the USA makers never got the noise as low as the Europeans. However USA makers were very good at power tubes.

Vacuum pumping is not a problem, cathode coating is. They told me when I visited the EI factory. "All we know is we mix up the cathode coating in a tin pail with whatever water and let it sit overnight, its better that way. However we don't know if thats because it sits overnight or perhaps the night watchman takes a leak in the bucket."

Im not kidding and that came via Dragona, our translator, right from the head of production. I spent 10 days at that factory. Sad its gone, they were on to something and I wanted to help by offering noise testing which they could not do. I passed on their offer to make me $100,000 worth of tubes, prepaid. they were broke, Good luck seeing those.

@quincy

I have always wondered if vacuum tube technology was abandoned prematurely (for solid state), and never fully exploited to its full potential?

Vacuum tubes were not abandoned but slowly pushed aside.  However the majority of reciever manyfacturers like Fisher, Sherwood, Marantz, Pioneer, Kenwood, Heath, Knight and Lafayette all went to SS sooner than they should have. Of that list I would say only Marantz made good on the change-over in that their early SS gear. Their early SS gear is quite good where the other early SS gear was quite bad. Kudos to Sid Smith who did a very good job to make the Marantz 7T sound as the 7C. However the current value of each does not reflect this because tubes are favored. Both 7s are quite good.

Other early SS designers were Dawson Hadley of Marantz, Jim Bongorino of SAE then GAS, Quatre was horrible, Bob Carver offered power and value but not good sound. Crown was ok, Mac Intosh made some great Autoformer SS amps (see my link via my profile)

In the early ARC preamps up to and including the SP-6 Bill J stole the Marantz 7 circuit topology, added a very unrelaible, poorly regulated power supply. Bill Johnson did nothing I find interesting and just made things worse in every way as time went on. CJ, I'm sorry, never impressed me. Two Economists do not make an EE. Getting them to talk about circuits is a non conversation. Their amps are pretty classic circuits. Its not that you have anything bad but frankly a Marantz 8 is hard to beat. Really really hard to beat. I cant even say I beat it with the RM-9 but I did give more power. I don't want to over do it but Sid Smith was a far better engineer than any of his contemporaries. A lovely man. I met and interviewed both him and Saul Marantz. Perhaps I should publish the tapes. The tube HK Citation amps have some serious flaws. 

Who else shall we talk about? The RM-1 was way ahead of its time and I would love to have it reviewed if anyone wants to review legacy products. It is the first preamp to use the 6DJ8, is DC coupled, No output capacitor, response down to 0.1 HZ. Sadly ended by the folding of Beveridge ESLs. I have considered re-introducing just the line stage to sent to John Atkinson. He has never measured a line stage that does what the RM-1 does. Pardon my enthusiasm, but its really special.

If you want to give me a list of companies for a yes/no I would be happy to go down it. Some of the no’s will be no, no, no. like Counterpoint who rightly went bankrup. Sometimes the world takes care of itself. Counterpoint was a group of nasty people making a horrible product.

In short, some companies made a good transition some not. Current tube amps have some interesting ideas but none that really impress me.

@tomic601

My question is what tube testers are you recommending at sane portable prices..

The B&K Dynajet series is fine and still under $100 or less on eBay. The 601 is the one I have. Although I have the big Hickok I find it heavy and slow to set up. ALL you need is an emission tester, not a transconductance tester.

I hope to release a curve tracer/tube tester for around $1000 that will do far more than the Hickok standard. It will connect to your computer, draw graphs, match up tubes and measure a whole bunch of things I have found to be important.

@terry9 

Each Quad has its own mono block. Two Quads facing ahead, and two Quads at one radian angles, facing in. A bit like one of Walker's experiments. Think of two sides of a hexagon on the left, mirror image on the right. And two at the back of the room, attenuated, but important.

Its ok, ive seen plenty of SS amps. The negative temp coefficient is interesting. 

You sure have a lot of stuff there. It would still like to know what kind of capacitance you are driving at 10Khz and up. 

As to the capacitor question. In the passband there is 0 Volts of signal across the cap. 

I'm still in the Polypropylene camp. Best thing for the money. Remember any part I buy is 5 x cost to the final buyer. So I cant buy too many $50 caps expensive resistors. I also appreciate manufacturers who make relaible parts. I have found CJ, Jensen, and others to fail. There is no reason for a coupling cap to fail in this day. The problem with premium caps it the people make them do not have the years of experience that the old timers have.

While I could make an amp with all premium parts, sell it for a lot more, I just dont find anything special about these parts. I would only do it to reach into the buyers pocket.

@terry9

Are you aware that the secondary capacitance of this transformer is 800 pf and the input capacitance of the speaker panel is many times lower? If I multiply that times turns ratio squared i get a primary load of 45 Microfarads. For the transformer alone.  Are they kidding? Thats a lot to drive. The QUAD transformers are quite good and much lower capacitance. 

I dont get these Plitrons at all. Tell me what is wrong with the QUAD transformers?

The primary of the Plitron is 0.1 ohm. How low is your dc offet?

I have bought a set of 4 Gold Lion (Russian) KT-66's for use in my pair of Heath W5's. $35 a tube! Originals sell for $200+ a tube (UK). They sure do look real nice! I still have the original US Tungsol 5881's in use. I wonder if the Russian ones can stand up long-term to the plate and screen voltages in the W5's

How high is the plate voltage? I didnt think the W5 ran the tubes hard? The Russian KT66s are fine and the Chinese looked good to me. Lifetime will be an issue compared to the NOS Genelex.

Originals are expensive due to supply / demand and how high someone will go.

You know the 5881 is a small 6L6 and neither has the plate area of a KT66. Are you having any problem with tube life? What do you think you get out of a pair before the silver gettering is all gone?

@terry9

What I see in Plitron (theoretically) is two things: first, the two plates of the ESL are driven by the same core, so they can be precisely balanced; and second, they offer 75:1 step-up instead of 250:1. Since I committed to 75:1 with 25V rails, going back to 250:1 would involve re-engineering the protection circuits.
Rather than that, I would try to build high voltage amps to drive the Quads directly. Wish me luck - and long life!What I hear (subjectively) is that the Plitron 2905’s are much brighter than the remaining stock 2905, without sounding harsh. Piano on vinyl sounds quite similar to the instrument upstairs on the modified units. The unmodified unit sounds mellow but imprecise compared to the Plitronned. In fairness I must add that this was accomplished with the help of nichrome wire and a small inductor to equalize primary impedance over the frequency band, as per the Vandersteen data sheets.My DC offset used to be 50mV or less. What it is now is a good question, one that you have prompted me to ask. Thank you.

Terry, all of this is intended to help, so have a seat and let me inform you of some things going on. These things may alarm you. You may like what you have created better than the original, however you may not if you go back. Here are the problems I encourage you to look into... deeply, with meters, oscilloscope, numbers.

1. 50 mV offeset on 0.1 ohms is 1/2 amp, a considerable problem for both the Plitron and your amp. 500 mA is a significant portion of your 1200 ma idle current. Later we can talk about how saturated your core may be.

2. There is NO advantage in having the two stators driven from the same core. I can almost promise you the leakage inductance on either side of the center tap of the Plitron is far from equal. It would almost have to be unequal if the thing is done in two winds. You do know how torrids are wound? Great videos on YouTube for those who want to see.

3. The two QUAD transformers are likely more matched at high frequencies than the two halves of your torroid. You can easily confirm this by driving them from 10K-20KHz with a dual trace scope, any low level is fine. I believe you will see the two stator drives rise and fall opposite to one another as you sweep the audio range. See at what frequency this starts. Dont judge those transformers on how small they are and how they look. Nor judge the Plitron on its looks, size or marketing. 800 pf in the specs is a red flag for me. That is 45 uF on the primary, which is like 1/4 ohm at the top frequencies. 

4. I have built many DD amps and I am listening to a 5200 volt DD now on my ESLs. Perhaps we could talk about a kit for you.I stil make small production runs if you are interested. DD is the way to go then all that other stuff like parallel capacitance, leakage inductance, core saturation all disappear with the transformers which have always been the weak link of ESL speakers.

5. I think you mean the Vanderveen data not Richard Vandersteen.
I sincerely doubt there is anything special going on in that torroid. I would have to say that a torroid is a flat out wrong way to make an ESL stepup. I make my own, but not that way. One has to reduce the capacitance not increase it. Torroid winding is the highest capacitance on earth.

If you do all this, you will learn a lot. I have been building ESLs since 1976. If you dont know who Harold Beveridge was I suggest you do a little research.Peter Baxandall wrote an entire chapter (in some large general speaker book) just about the QUAD 57 and 63. Well worth reading. I have his chapter in my file and refer to it often. After reading it many times I think Baxandall had a lot to do with, or entierly did the electronics while Walker had the concept of the rings and delay line. Baxandall gives a compete model of both drive systems.

Perhaps I shouldn’t say which speaker is the work of art.

Please take all this as education, Im just reviewing your good work and adventure so far. I admire you getting as far as you have.

BTW 5,000 volt amps are not so difficult as what you have gone through so far with your SS amps. They dont need protection circuits and I wonder why you are still using yours?

Do you live anywhere near SF, CA?

@georgehifi 

Hey George, did you see the review of the Cary SLI-100 in the lastest issue? Why would they be so dumb to send an amp that is going to look so bad on JA's well documented test procedure? 

Read Dec, pg 91. Read pg 153 for Cary's response. In there their response they say measurements are not everything and an amplifier should sound "intoxication and emotional". "A degree of second order harmonic texture gives the midrange a certain musical.... and expands the soundstange". Pure marketing drivel. Where is Dennis Had when we need him?

The whole argument about 2nd harmonic distortion being "benign" totally ignores Intermodulation distortion which is far worse and always higher. If you are listening to a small group, singer, solo guitar a little THD isnt bad. It just creates the octave. My question is "what is the 2nd harmonic of Beethoventh's 9th:". In a full orchestra, with chorus. there is no fundamental to do much with. Some people must think the amplifier has the intelligence to go find the fundamental note and create the octave. Amplifiers arent that smart. They just amplify a time/voltage varient signal. Its not like they are following the score.  :)

All the specs on this amp are horrible, shameful, disgusting, who designed this? Please go do something else.   By John's standard this 100 watt amp reaches 1% THD as 3.2 watts, 3% at 22 watts, finally reaching its 100 watt rating at 10%. 

You all get this in addition to poor damping, noise and rising distortion even at one watt on both ends of the frequency range. 

If you want a comparson look at the review of an RM-200 II, an amp at virtually the same price.

@georgehifi

I think that one comes later for free on line, as I’m such a tight arse, I only read the ones Stereophile drip feeds online for free.

But it must be bad to beat the Leben CS300, check out the HF boost because either the output transformers are ringing or the circuit is oscillating. And it’s shown in the 1khz square waves as well.
To me another one, that should not be passed on final inspection to be sold.

https://www.stereophile.com/images/1111Lebfig01.jpg

https://www.stereophile.com/images/1111Lebfig02.jpg

Yea thats all pretty bad and if they were smart that is a good one not a failure on inspection. That kind of response is simply a result of poorly applied feedback. Strangely, given that the damping factor is horrible there isnt much feedback and they didnt manage to pull off even a little. Certainly the work of someone who doesnt care or couldn’t do any better.

Notice that the top rings longer than the bottom in the SQ wave. That is because the two halves of the primary do not have the same coupling to the secondary.

What a mess, their standards of performance are rather low. Might sound ok at low levels on easy speakers but the low damping will certainly modify the response of the speaker. The bass rolloff is bad too Probably everything is bad. I’ll go read what JA said.

Hey, do you have a link to the complete review? I got 29 hits for Leben. A lot of mention for a poorly performing amplifier.

Heres another poor performer from Jadis..https://www.stereophile.com/content/jadis-orchestra-reference-mkii-integrated-amplifier-measurements

He was kind to measure the distortion vs frequency at just 2 watts on a 50 watt amplifier.  Imagine how bad it would be at 10,20,30 watts.

Great posts in here!

i get my info directly from Steve McCormack,
im watching this convo like a hawk.
thak you

 say hi to steve for me

@terry9

Thank you for your interest, Roger. I take your comments in the helpful spirit in which they were given.

You have motivated me to look again at the stock Quads, and think about driving them with my current amps. These amps have proven themselves to be very stable over the years, and don’t really need protection circuits in the speakers. I think. So I just may continue to do without. To be clear, I am not using the Quads’ protection circuits.

I would be interested in a DD amplifier, but I am somewhat frightened of the high potentials. The one thing I know about super-KV work is that it’s qualitatively different from sub-KV work. Perhaps you could point me to your website?

They are not on my website, not really a Music Reference product. More of something I make when someone interesting who is doing something interesting contacts me. We made 4 for a guy in Australia and his friends. I also sold them 8 Acoustat panels and advised them how to set them up. He had been playing with Acoustats for many years and appeard very comfortable with high voltage. Acoustat panels are very useful and flexible and not expensive.

The high potentials bother me not at all. Perhaps because I was a TV tech from age 16 through college. 25,000 volts DC in a color tv is just not a big deal. One should be attentive no matter what the voltage. Ive blown up more things with current than voltage.

@amb3cog

I’m willing to bet that Burning Amp alone will help. I know you can’t just spend, spend, spend, but maybe some directed advertising on Facebook towards people that are very interested in learning electronics would help. You might pick up done young people struggling to afford College? Something different should be tried, either way. Because if the word doesn’t get out. No one will ever know. It’s that simple. I only found out about the school, because I was on your site, for instance. I think it’s a great thing you’re offering, either way, and bless you for doing so sir.

Thanks for the complilment and advice. I have never looked into advertising and that is a good idea. I might give FB a try but I am not happy with what Mr. Z had done and how he is handling it. Horribly irresponsible. Ive bought puts on FB. I think FB has been a miserable failure. I think the stock price is reflecting that. 

Does anyone have suggestions on an alternative site to use for adverts? There must be lots.

I put up flyers all over the EE department at UC Berkeley. They have a total of 1000 undergrad and grad students. The flyers stayed up for several months, i checked. I got not one response. I know what is going on there and its sad. I have visited the labs, lectures, was invited by one prof to announce my school in front of his class of 150 students. I think I got one from the 150 to visit.

College students these days just want to get a diploma. Its their ticked to a high paying job. I like the Asian students, they are bright, however they might get a better education back home. They come here for the prestiege of a UC or Stanford degree. I went to Stanford, it was disappointing. UVA was far better.

The grad students who write the labs keep using the negative input of an op amp. This is not what we do in industry and it only takes a minuite to show why we dont, its noisy. Whats the chance of me correcting that? Similar labs are going at UC Davis and perhaps all UC. Thats a lot of students.

@terry9  

Thanks for all your help, Roger. You really have opened up a stack of stuff for me to do. Much, much appreciated.

Hate to be pedantic, but I think that the 45uF figure should be 4.5uF, which is less of a problem: (75**2)  *  (800  *  10**-12)  = 4.5  *  10**-6. Your other concerns with the Vanderveen (got it right this time?) transformer remain an area of intense interest (and research!) to me. Thanks again!

You are indeed correct, it is 4.5 uF and still too much.  What raised my flag was that when i measured my speaker was at 80 pF for the 3.5 sq ft panel and I managed to make a transformer with about the same 80 pF capacitance and at 200 to 1 step up. Not much point in going further than that as half the power is in each. However had I used the plitron the numbers would be 90% of the energy absorbed by the transformer and 10% to the speaker. Thats a bad deal. 

Have you measured your drive capacitance? It is simply what you get stator to stator with a cap meter. I knew it when I was Direct Driving my 63's but that was 10 years ago. 

Not sure they still do but the 63's have a big 220 UFelectyrolytic cap in series with the hot speaker terminal to block DC. Do they still have this in some or all models? I could never understand why so large when 10 uf PPN would do.

@donjr 

A friend of mine loves Accuphase. I have seen inside and its beautifully built, measures well but its just too many parts. Their preamp has something like 600 transistors and 1200 diodes. Im into simple circuits. 

Sure would love to see the specs and a review but only with measurements.

@ieales A balanced input is no guarantee of better sonics. The devil is in the details.Every audiophile should read Bill Whitlock’s AES paper"An Overview of Audio System Grounding and Interfacing" available here https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Thanks for the link.. Its 212 pages of slides. Power point :( I hope he takes breaks with refreshments. This could take hours. Id need 3 cocktails and a sandwich.

Can you direct us to a few pages with some meat on the bone. Im sure there is some wisdom there.

@almarg 

It would help to quote the original question so we can follow this. 

It appears to be an answer but im not getting it.

@pryso

Roger, really appreciate your efforts with this post. But, a question -

"Over 100 watts is only justified by either high listening levels or insensitive speakers or both together. Excess headroom is a myth."

I and many others find headroom seems to relate to clean (undistorted) dynamics. Would you expand on your myth statement, why you feel that is the case? Maybe the key is "excess"?

Thank you for bringing this up. Ive been waiting for this.

Answer is I cant say what you are hearing. I dont know if you are clipping sometimes or not. If you have a scope or peak reading voltmeter you could find out.

Now here is what i DO know. A 1000 watt amplifier played at 1 watt is likely overkill, though I had one Japanese man express this headroom is necessary. I responded, large amplifiers played at low levels may not be as good as smaller amplifiers. Many people feel small amplifiers sound better when they are enough.

Amplifier designers have to commit certain "sins" when making really big amps. High power tubes amps are enormous with enormous transformers. Take the JA200 for instance. Theres a big sin in that amp. It plays 200 watts cleanly up to 500 hz or so. As you go up the power bandwith is reduced every octave. At 20 KHZ it does just a few watts. I have measured it. Go look at the 4 chassis of that amplifier. Yet this ampifier has good reviews and hardly anyone knows about this problem. Did JA get hold of one? IDK?

Tube amplifiers scale up pretty much pound for pound for watt. 500 watts is 5 times heavier than 100 watts. Again look at the Jadis. BTW that power rolloff is entierly intentional. I could easily modify that amp to have full power to 20KHZ. The transformers are excellent. Why they chose to roll off the power I dont know, I dont speak French. Im happy to fix one up for anyone interested.

So i ask you, how many watts do you have and how many are used at your average listenting level. The headroom on CDs is well defined and easy to measure. The ones that play loud likely have 10 db. Good ones have 20dB not much more or they sound too soft.

There is a lot to this question so lets hear back from you and others.

@mapman 

Lifelike SPL for me is that what one might hear at a similar live performance in the good seats, not too close but not too far away.

I want my gear to be able to handle it all including perhaps sitting close to the percussion at the symphony or in small club proximity to a rock band. I want to be able to hear it all. I might not be able to in reality but if I can be convinced its very close in my own unique room then that is good enough.

At the same time I want to preserve my sense of hearing so most of the time I would strive to avoid SPLs higher than the mid 80s or so. But I want my system to do it all and never break a sweat no matter what I may ask of it at any given time. That was a key design goal in putting together the setup I’ve had now for several

Ok, some would say mid 80's is lower than a symphony close up. What are your peaks?

My system doesnt sweat but i know its limits via an oscilloscope on my equipment rack. It lets me see how close I get to clipping on various music. 

Would you like to share what you have put together along with some important numbers like speaker SPL/watt, Amp power, Listening distance, anything else?

@bdp24 

@jcder, everyone is going to recommend his own pre in answer to your question. Here are a couple to consider: There is a Hovland HP-100 listed on Audiogon right now (at an asking price of $2350), a fine line stage (I heard it in Brooks Berdan’s reference system for quite a while). The EAR-Yoshino 868L line stage, another good one, occasionally pops up for around $3,000. The 868 has one true balanced (via transformer) XLR input, if that matters to you. EAR Designer Tim de Paravicini very much strikes me as the UK’s equivalent of Roger Modjeski; old school EE’s with good ears and lots of knowledge and talent.

Happy Thanksgiving. May I remind everyone the purpose of this thread is to ask a technical question, not to discuss whose preamp is better.

This is the only time I will say this and I will ignore future preamp comparisons. 

@georgehifi

https://www.stereophile.com/content/leben-cs300-integrated-amplifier-measurements

JA does make mention of the ultrasonic resonance, but "maybe" because they’re an advertiser, didn’t make too big a deal of it.

Thanks for the link. When saw the picture again my mind went.. Ah, is this Luxman? Looks like Luxman. Does perform like Luxman. Must not be Luxman.

This amplifier is a strange combination of thoughts and performance. While the bass rolls off with out the boost, the boost is enormous when used and nothing in between.

Of course it didnt do the Quads well, "no bass grip". What did you expect when the output impedance is so high and I did not say damping. I want the word damping to go away as it is a most misleading term.

Look at horrible distortion curves at even low power. The only reason anyone could like this amp is on high sensitivity speakers like Art’s and at low levels. After a watt this amp is a mess.

I have been waiting someone who really wants to know ask me why damping is such an outdated term.

@mapman 

Back in the 70s selling most popular receiver lines from Pioneer to sansui to Tandberg the more powerful models in a line  (generally up to 120 w/ch or so) ALWAYS sounded better at least at moderate or higher levels.
Clipping is always public enemy #1 to good sound. Avoid at all costs. Better to have overkill than clip on that great sounding full range dynamic recording.
Modern louder recordings are more prone to clip as well being louder overall so that ups the ante even more when it comes to how much power might be needed.
Also music not reproduced at lifelike volumes is not accurate reproduction rather a scaled down one. Nothing wrong with listening at lower levels but one is not even attempting to reproduce real music accurately that way.

I agree with you. I worked on a lot of pioneer and such. Receivers are value products. I respect them, have worked on possible 500 in 3 years as a busy beaver. After about 80 watts I see no good reason to buy a big receiver, thats the time to go separates. 

I have found the following. Using a scope to determine clipping I find that most people do not hear clipping till it reached 10 % of the time and those are just little Millisecond clips. Longer clips are more notiable because they block the signal for a long time. So how much overkill is needed? Recievers are not designed for overkill. I use a nice Marantz 2235 in my lab for background music. Way more than I need for my Rogers LS3/5As.

I would say louder recordings are prone to less clipping because they are more compressed. Your ideas?

What is a lifelike SPL for you? On what music?