Quietest tube amplifier brand?

[Boomzilla]

To the best of your knowledge, does (or has) anyone done a comparative noise study for different brands of vacuum tube power amplifiers?

I've got a high-sensitivity pair of speakers coming in this week for review, and I suspect that my "Heathkit Frankenamps" may have too much hum and hiss for the speakers. I have a friend who can loan me tube amps for the duration of the review, but all of his speakers are far lower sensitivity, and he would therefore have no idea as to which might be the lowest noise. He has multiple brands and models to choose from, but I don't want to burden him with asking to measure all his amps. Among the brands I'm sure he has:

Dynaco
VTL
Quicksilver
and a couple of others

Any idea who makes really QUIET tube power amps?

Thanks - Boom

[audiobill]

This is a little difficult - two main ways to reduce noise in tube amps with very high sensitivity speakers:

-Use very high quality parts - metal film resistors, film caps in power supply, Teflon coupling caps, simple signal paths, low noise tubes - think Conrad Johnson

-Use differential balanced circuits - think Audio Research or Balanced Audio Technology - but remember twice the parts count equals twice the cost, and they certainly don't cheap out on parts quality.

And certainly no digital hash producing switching power supplies.

Each of these paths can be very expensive.

Or, just build a VTA ST70, ST120 or M125s with the best parts you can afford. As you've written, the most cost effective path available.

Stock vintage dynacos may not plumb the depths of noise reduction (they used carbon comp resistors, selenium rectifiers, electrolytic caps etc), but the VTAs can.

Also talk to Rogue Audio - like the Quicksilver, good value in assembled amps.

Of your friend's choices, I think I'd pick the VTL then the Quicksilver

www.stereophile.com/content/quicksilver-audio-horn-mono-monoblock-power-amplifier-measurements-part-2

Bill

[Boomzilla]

Thank you kindly, audiobill - Just what I needed to know.

And I've done this: "Use very high quality parts - metal film resistors, film caps in power supply, Teflon coupling caps, simple signal paths, low noise tubes" to a Dynaco PAS preamp before that (at that time) measured quieter than a new Adcom solid-state preamp. So this method DOES work. My friend applied the same modifications to his Dynaco Stereo 70 power amp and got the same noise reductions. But his main noise reduction came from converting the filament heaters from AC to DC. But the result must have been tied to the design, because the new (and VERY quiet) Audio-gd tube preamp I just reviewed used AC on the heaters! Go figure...

In any case, I think that somewhere down the line, I might purchase a somewhat more powerful pair of tube amps than my 12-watt Heathkits. Amps I'm considering are the Rogue Audio Atlas (the original version with EL-34 output tubes - not the newer Magnum version), the Dynaco Mk. III mono blocks, or the conrad-johnson MV60. The other (more work) option would be to build the M125 amps with my choice of parts.

[audiobill]

Fyi, I had the CJ MV60 se (w/6550s) for a time - very nice, and can obtain reasonably used.

Here's the EL34 version  for $1,650.


www.usaudiomart.com/details/649580991-conrad-johnson-mv60-amplifier-el34-tubes/

[garbulky]

Oh boy. Well I think with tube amps, their distortion can be so high, that you have to define what you consider as adequately quiet. For instance the quick silver's have a massive harmonic distortion spike at -55 db which puts it in "potentially audible territory" at 0.2% THD.
Conrad Johnson's $9500 as pair tube amp LP125 M has a THD of 1% from 30hz upwards, which means they didn't even rate to 20hz. It has a -50 db harmonic spike which is potentially audible.

www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements

In comparison
Here is a sub par implementation of Hypex's Ncore module. THe IOM ncore ($800)


Audio Research's ref 150 tube amp does better at 1 watt with a (reasonable) measured result of -72db harmonic distortion spike. Which I suppose is amazing for tubes as they are approaching the average distortion of a solid state amp. But then as you've noted a AR amp sounds a lot like a solid state amp, which may not be what you're looking for.

So are you talking about measured distortion or are you talking about hum or buzz that is audible from a listening distance or perhaps only audible with ear next to tweeter? If so, then your choices are probably better as there's probably several nice sounding tube amps out there that don't buzz all that much.
The Schiit tube preamps have been very quiet. But I don't think their tube amps are quiet.

[audiobill]

Schiit doesn't make tube amps.

And tubes require listening with your ears, not a distortion analyzer.  For some folks, that's not possible to do.

As I've counseled @keithl, it's pretty easy these days to make equipment that measures great, but much, much harder to make equipment that sounds great.

Not necessarily the same thing......

[garbulky]

Jun 1, 2020 9:39:35 GMT -5 audiobill said:

Schiit doesn't make tube amps.

And tubes require listening with your ears, not a distortion analyzer.  For some folks, that's not possible to do.

Everything requires listening with your ears. There's nothing special about tubes that require ear listening more than solid state. Both amps need to be auditioned to see what one likes.

But he is looking for quietest, so if one wants the quietest, one has to look at measurements as the measurements can measure distortion and noise that the ears can't. They will show what the quietest is.
Schitt makes several tube headphone amps but no tube power amps.

[AudioHTIT]

I assume you’re referring to background noise — typically hiss, sometimes hum when no music is playing, or during quiet passages (not distortion which accompanies the signal). My old Dyna Mark IIIs were ‘reasonably’ quiet with my JBL D131s or LE8Ts (the only high sensitivity speakers I used them with), but some hiss could be heard with your ear up to the speaker. My VTL MB450s are very quiet (especially given their power), but the Maggies @ 86 dB SPL / 2.83V don’t give a fair representation to answer your question.

[DYohn]

Just don't buy cheap crap and you'll be fine. And don't obsess over measurement porn. It's usually meaningless in the real world at the levels in the above post.

[brubacca]

Boomzilla,

One thing to know about Rogue Audio is that they make running changes to their circuits. Its not just major version changes. Mark O'Brian told me on my plant tour that they do running revisions as needed.

So one Atlas EL34 amp isn't necessarily as quiet as another. In fact, your chances are much better for the newest KT120 based amps to be quieter. The Atlas hasn't been sold with el34 for at least 5 years (by my terrible memory).

Edit: I read that you can use el34 tubes in the newer kt120 based units. Check with rogue to be sure, but I believe you have to turn the bias pots way down, something like 10 revolutions. I found this years ago when considering el34 for my Cronus Magnum. I'm sure a call to Rogue would get the exact number.

[pedrocols]

I bet none of us can hear that noise unless of course you have teenager's ears...😂

[Boomzilla]

As many of you have already posited, I'm not so much concerned with % distortion in conjunction with program, but more with background (no signal) hum and hiss. If I have to put my ear to the speaker grill to hear the background hum or hiss, no worries. But if I have to hear it from my listening position, I'll not be happy. Since I listen at low volumes anyway, a quiet background is more important to me than to some. An amp that is "quiet from the listening position" with 90dB-efficient speakers may not be so at all with 102dB-efficient ones. On a bad day, I can occasionally hear some hum and hiss from my Heathkits without any signal at the listening couch (using my Emotiva T2 speakers). My gut feeling is that when I put in the much higher sensitivity speakers in the mix, the previously-marginal background noise will become unacceptable.

I can use my Emotiva PA-1 amps, that are as quiet as a mouse, but I'd also like to hear the review speakers with tubes. And since I don't need to spend the money for now, I might as well borrow some tube amps for the audition. If my friend is generous enough, I may well borrow two or more of his tube amps at a time and just see which is the quieter of them with the review speakers.

The good news is that high power is going to be completely academic with the review speakers. I'll NEVER be running them at even a single watt of amplifier output. So any tube amplifier (even a SET one) would be more than sufficient. In fact, never having heard a SET amp, now might be a good time.

Thanks kindly to all in the thread - I profoundly appreciate your feedback!

Boomzilla

[Boomzilla]

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

Oh boy. Well I think with tube amps, their distortion can be so high, that you have to define what you consider as adequately quiet. For instance the quick silver's have a massive harmonic distortion spike at -55 db which puts it in "potentially audible territory" at 0.2% THD.
Conrad Johnson's $9500 as pair tube amp LP125 M has a THD of 1% from 30hz upwards, which means they didn't even rate to 20hz. It has a -50 db harmonic spike which is potentially audible.

I understand. I suspect that my 12-W Heathkits would measure terribly as well.

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

...Audio Research's ref 150 tube amp does better at 1 watt with a (reasonable) measured result of -72db harmonic distortion spike. Which I suppose is amazing for tubes as they are approaching the average distortion of a solid state amp. But then as you've noted a AR amp sounds a lot like a solid state amp, which may not be what you're looking for.

You're EXACTLY right - If I wanted solid state, I've a number of other amps that sound that way.

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

...So are you talking about measured distortion or are you talking about hum or buzz that is audible from a listening distance or perhaps only audible with ear next to tweeter? If so, then your choices are probably better as there's probably several nice sounding tube amps out there that don't buzz all that much. The Schiit tube preamps have been very quiet. But I don't think their tube amps are quiet.

The latter - No hum, buzz, or hiss from the listening chair is the goal.

[garbulky]

Jun 1, 2020 14:25:43 GMT -5 Boomzilla said:

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

Oh boy. Well I think with tube amps, their distortion can be so high, that you have to define what you consider as adequately quiet. For instance the quick silver's have a massive harmonic distortion spike at -55 db which puts it in "potentially audible territory" at 0.2% THD.
Conrad Johnson's $9500 as pair tube amp LP125 M has a THD of 1% from 30hz upwards, which means they didn't even rate to 20hz. It has a -50 db harmonic spike which is potentially audible.

I understand. I suspect that my 12-W Heathkits would measure terribly as well.

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

...Audio Research's ref 150 tube amp does better at 1 watt with a (reasonable) measured result of -72db harmonic distortion spike. Which I suppose is amazing for tubes as they are approaching the average distortion of a solid state amp. But then as you've noted a AR amp sounds a lot like a solid state amp, which may not be what you're looking for.

You're EXACTLY right - If I wanted solid state, I've a number of other amps that sound that way.

Jun 1, 2020 9:18:55 GMT -5 garbulky said:

...So are you talking about measured distortion or are you talking about hum or buzz that is audible from a listening distance or perhaps only audible with ear next to tweeter? If so, then your choices are probably better as there's probably several nice sounding tube amps out there that don't buzz all that much. The Schiit tube preamps have been very quiet. But I don't think their tube amps are quiet.

The latter - No hum, buzz, or hiss from the listening chair is the goal.

In that case, I think most decent tube amps would probably fit the bill. You may have some sort of ground loop issue because you've noted hums and buzzes in the past. Once you've figured out how to isolate that out of the way -no easy task - it should work well.

[mfeust]

A relatively quiet tube amp in one person's system may not be quiet at all in your system. I have 2 Jolida 502p running in mono mode. Very little hiss in tweeter with ear inches from speaker.

Mark

[Boomzilla]

Thanks, mfeust - I'd been wondering about the Jolidas...

[klinemj]

I love my Prima Luna. I don't know how it measures, but it sounds amazing.

Mark

[DYohn]

Right now I have two tube amps in my systems, one from Butler and one from Audio Valve. No detectable hiss or other noise in either.

[audiobill]

No noise whatever from my Mcintosh MC275s into 92 db PBN Montana EPS speakers. Just oodles of sonic goodness.