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Tube gear opinions

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SIY

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Amps can be accurate or they can be amplified tone controls, depending on the design.

FTFY. Really, you can get whatever coloration you want in an amp regardless of the particular active devices used.
 

egellings

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Tube sound comes about when the tube amp's high-ish output impedance forms a voltage divider with the speaker's impedance, and you hear how the speaker's frequency-dependent impedance alters what appears across its terminals.
 

MakeMineVinyl

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DimitryZ

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Tube sound comes about when the tube amp's high-ish output impedance forms a voltage divider with the speaker's impedance, and you hear how the speaker's frequency-dependent impedance alters what appears across its terminals.
At one time, it was popular to drive 8 Ohm speakers from the 4 Ohm tap, trading power for lower output impedance.
 

MakeMineVinyl

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At one time, it was popular to drive 8 Ohm speakers from the 4 Ohm tap, trading power for lower output impedance.
I still do that.
 

H-713

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Wow, that's ummm interesting. :oops:

Interesting tube choice... the FU32 is basically a clone of the 832, which bears some similarity to the 829. It's a VHF tube, so oscillation could be a bit of an issue.

Both the 832 and the 829 are interesting tubes, though pretty impractical for any sort of audio amplifier. They were designed to be useful for VHF service, or for radar service. From what I remember, the 3E29 is a modified version of the 829B that could stand off higher voltages, which made it more useful for radar pulse generators.
 

Sal1950

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Tube amps can be accurate or they can be amplified tone controls, depending on the design.
And a much higher proportion of them have a tonality and voice. Hence tube amp sound, and the myth of tube sound.
Both very true posts. I'm not tuned into todays tube market but I do know the offerings are all over the place in the sound they will bring to a system. Also depending on the amps output impedance, ecach can sound very different in any particular system depending on speakers impedance.
I still miss my VTL amps, I chose them back then on various reviews but mainly on JA measurements and comments in Stereophile
"On the test bench, you could have been forgiven at first for thinking that this VTL was a solid-state design,"
https://www.stereophile.com/content/vtl-100w-compact-monoblock-power-amplifier-measurements
David Manley was a recording engineer and his early HiFi amps were designed to be as accurate as possible. Later he started bending to market demands by first adding pentode/triode switching to the line and later other non-accurate tricks.
Everyone is fully entitled to pursue their chosen preferences but personally I've always first wanted to be able to hear what the source was intended to sound like. The VTL's quite high input sensitivity allowed me to also run a McCormack pure passive preamp that had absolutely no sound, noise, or distortion of it's own. The very bottom in that rig was handled by 2 huge HSU subwoofers and 2 NAD SS monoblock amps. IMO the perfect marriage.
I'm getting all nostalgic here for the ole days, my listening room was large so the 2 channel rig was set up on the north wall and the multich-video rig was on the south. With my chair in the middle, all I had to do was swivel 180 degrees to entertain my choice. Life was good :)
 

Capitol C

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I've done both.

I would suggest that the hallmark of what is loosely called "tube sound" may be attributed to limited Global Negative Feedback.

I have heard some lower power transistor amps which had similar "character" but they were terribly expensive. The Pass Aleph 0 sounded great and similar to well made tube amps of the day.

It's my opinion that the best tube amps have genuine triode output stages, limited global negative feedback and heavy iron transformers.

Such designs restrict loudspeaker choices to only the most efficient designs.

I wish that there were a way to explain negative feedback simply enough so that people who are not engineers or mathematically-inclined scientists could understand it. It is really not a difficult idea, just one that needs some math.

I've attached a file which goes through the math for a (generic) amplifier with what is called an open-loop gain of A. This is the gain you would get if you just compared the input to the output without any other circuitry. This might not be practical to do, and it is not how you would use any amplifier. Note this is a general idea, not just applicable to op amps, it also describes a tube, a single transistor, or an entire circuit such as a preamp, power amp, an integrated amp, or the radio-frequency amplifiers in my lab. Note also that A can depend on frequency and amplitude, ie, it does not need to be linear itself.

The circuit drawn in Fig. 4.2 has a gain that is modified from the open-loop gain. It is useful to define a quantity B=R/(R+RF), which tells how the ouput voltage is divided by the resistors. In this circuit, the overall gain G, what you would measure by comparing output to input, becomes
G=A/(1+AB). Note again that this works no matter what the amplifying element is. If it is a complex multi-stage circuit, this is called global feedback, if it is a single transistor or tube, it is called local feedback.

The really cool thing happens when the open-loop gain is large. To see this, imagine that A is 100, then G=100/(1+100B), so that if B is not too small, this becomes approximately G=1/B=(R+RF)/R. (If you are rusty on algebra, try it out for various values of B on a calculator). This is wonderful, it says you can take a real device, where G depends on frequency, amplitude, how hot the circuit is, etc., and as long as A is large enough, it doesn't matter: The overall gain depends only on the value of two resistors which you can choose!

There is, of course, much more to it than this, but in the end, negative feedback, local or global, is necessary to get good linear amplifiers. Far from being the villain that it is portrayed as in some audio discussion groups, it is your best friend.
 

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Wes

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There is a way to explain negative feedback simply enough so that people who are not engineers or mathematically-inclined scientists can understand it.

You simply analogize it to someone moving a thermostat on a heater/AC to maintain a given temperature.
 

Sal1950

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I would suggest that the hallmark of what is loosely called "tube sound" may be attributed to limited Global Negative Feedback.
It's my opinion that the best tube amps have genuine triode output stages, limited global negative feedback and heavy iron transformers.
Along with the highest output impedances, the biggest FR variations into a actual speaker load,
OH and the highest measured distortion.
Not something to have if your interested in hearing the true sound of the source, they are in no way representative of a High Fidelity system.
No thanks
 
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jsrtheta

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Both very true posts. I'm not tuned into todays tube market but I do know the offerings are all over the place in the sound they will bring to a system. Also depending on the amps output impedance, ecach can sound very different in any particular system depending on speakers impedance.
I still miss my VTL amps, I chose them back then on various reviews but mainly on JA measurements and comments in Stereophile
"On the test bench, you could have been forgiven at first for thinking that this VTL was a solid-state design,"
https://www.stereophile.com/content/vtl-100w-compact-monoblock-power-amplifier-measurements
David Manley was a recording engineer and his early HiFi amps were designed to be as accurate as possible. Later he started bending to market demands by first adding pentode/triode switching to the line and later other non-accurate tricks.
Everyone is fully entitled to pursue their chosen preferences but personally I've always f.rst wanted to be able to hear what the source was intended to sound like. The VTL's quite high input sensitivity allowed me to also run a McCormack pure passive preamp that had absolutely no sound, noise, or distortion of it's own. The very bottom in that rig was handled by 2 huge HSU subwoofers and 2 NAD SS monoblock amps. IMO the perfect marriage.
I'm getting all nostalgic here for the ole days, my listening room was large so the 2 channel rig was set up on the north wall and the multich-video rig was on the south. With my chair in the middle, all I had to do was swivel 180 degrees to entertain my choice. Life was good :)

Those McCormacks were idiosyncratically sweet preamps. I'd love to have any of the Micro Line Drives I owned back now. I had the TLC and the ALD, too, at various times. But the Micro was, in its way, perfect
 

jsrtheta

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The problem is with disclosure. Most of those designers claim transparency (Nelson Pass is the exception.) They all claim to have finally solved the crossover distortion problem, or the clipping problem, or the current supply problem, or the this problem or that problem, and finally their amp is the one that truly provides transparency other amps are lacking. They claim other amps are "harsh" and "fatiguing", without explaining what those amps do that makes them so. They claim that their amps provide "pace and timing" consistent with the original music, which other amps do not transparently provide, without demonstrating what pace and timing actually mean in terms of waveforms.

If they said, "our amp sounds great because we left in a healthy dose of even-order harmonic distortion, so forget the high distortion measurements and just listen to figure out what you think of it," nobody would complain. But they don't. They say only they have made a product that captures the true essence of the music, while others have not.

Rick "measured against their own claims" Denney

Huh. I never accused a power amp of being harsh or fatiguing. I always blamed the preamp.

Have I been framing the wrong man?
 

KA7NIQ

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Tubes add a little seasoning to the sound.
Once, I had a stereo friend switch my amplifiers behind a room divider, so I could not see what amplifier was playing. We tried to match levels as best we could. I had a Conrad Johnson Tube Amp, well known for it's warmth, and a Sumo Andromeda Solid State amp to compare. Surprisingly to me, I identified the solid state amp as being more warm! Just to mess with me, he said "Here is the Tube Amp" Immediately, I said "Yeah, there is the warmth" He invited me behind the room divider, and the Sumo Solid State amp was playing! He never switched amps, but just the fact that he TOLD me I was listening to the Tube amplifier, influenced my perception of the sound! Sean Olive was right. He told me about double blind testing, and I doubted him, until I actually tried it for myself.
 
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