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

@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?

@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"

@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. 

@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. 

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