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Tube Preamp Question

levimax

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I can't say I agree because my own experience is that a tube preamp can and usually does make a difference the sound that comes out the downstream amp, including class D amps such as my own Purifi-based amp. (Granted you will likely get more "tube sound" from a tube power amp but you'll probably get more of what's bad than what's good.)

What tubes in general do that people like is added 2nd and/or 3rd order harmonic distortions. These distortions do to sound, as some people describe the effect, is to make it more "musical", "full-bodied", "organic", "liquid", or similar descriptor. What's equally important, IMO, is that these distortions also serve to mask unpleasant higher-order harmonics that would otherwise make the music "harsh", "etched", "glassy", etc..

Again IMO, it you want to used tubes to insinuate these happier distortion, the best place to do it is at the preamp stage: you get dose of the goodies without the compromises of a tube power amp in terms of lack of power, impedance sensitivity, etc.
I have played around with both tube pre-amps and power amps but only older ones engineered to be Hi-Fi and operating correctly. To me, outside of being limited in power, I don't find they sound any different than high performance SS amps (when evaluated level matched and blind). I am firmly in the "Tube amp sound is a myth camp".

On the other hand I have experienced and seen first hand the psychoacoustic power of tube amps and it is indeed very powerful. To maximise this effect large tube power amps, preferably mono blocks and ideally OTL, are the way to go :)
 

fpitas

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I have played around with both tube pre-amps and power amps but only older ones engineered to be Hi-Fi and operating correctly. To me, outside of being limited in power, I don't find they sound any different than high performance SS amps (when evaluated level matched and blind). I am firmly in the "Tube amp sound is a myth camp".
I grew up hearing good tube amps, and I agree. As for the myth, it could have been a self-fulfilling sort of thing born of equal parts nostalgia and snake oil.
 

Gorgonzola

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d around with both tube pre-amps and power amps but only older ones engineered to be Hi-Fi and operating correctly. To me, outside of being limited in power, I don't find they sound any different than high performance SS amps (when evaluated level matched and blind). I am firmly in the "Tube amp sound is a myth camp".

On the other hand I have experienced and seen first hand the psychoacoustic power of tube amps and it is indeed very powerful. To maximise this effect large tube power amps, preferably mono blocks and ideally OTL, are the way to go :)
Humm .... all just psychoacoustics??

I call on @atmasphere to comment. He makes large, monoblock OTL tube power amps such as this MA-3 ...

atmasphere.jpg
 

fpitas

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Blumlein 88

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I can't say I agree because my own experience is that a tube preamp can and usually does make a difference the sound that comes out the downstream amp, including class D amps such as my own Purifi-based amp. (Granted you will likely get more "tube sound" from a tube power amp but you'll probably get more of what's bad than what's good.)

What tubes in general do that people like is added 2nd and/or 3rd order harmonic distortions. These distortions do to sound, as some people describe the effect, is to make it more "musical", "full-bodied", "organic", "liquid", or similar descriptor. What's equally important, IMO, is that these distortions also serve to mask unpleasant higher-order harmonics that would otherwise make the music "harsh", "etched", "glassy", etc..

Again IMO, it you want to used tubes to insinuate these happier distortion, the best place to do it is at the preamp stage: you get dose of the goodies without the compromises of a tube power amp in terms of lack of power, impedance sensitivity, etc. There are a few so-call power amps that have a tube input or 1st stage, but these are effectively the same as a tube preamp.

For fun, here's a pic of my tube preamp which is fully differential and all-tube apart from the chip-based volume control. As mentioned, it's driving my class D Purifi power amp ...

gi.mpl
I don't know I believe the common knowledge about 2nd and 3rd order harmonics. Play with Pkane's Distort and you'll find those have to be very high to make a difference. I've used or owned some that were somewhat smoothing like one of the Carey's but they had a rolled response, no feedback and could get up there in distortion. I forget who, but one of the companies used to make an FET preamp with no feedback which could sound similar. Among other things they had a low pass filter just above 20 khz to prevent it trying to amplify higher frequencies and causing IMD down in the audible band.

I knew someone with a Sonic Frontiers Line 2 preamp. It was a good preamp, but it didn't sound different than say a good Classe or Spectral unit. Some tube pre's have way more gain than you needed. So with some sources a nearly audible noise could be there. I wondered how much that played into the sound being different.

Here are measurements of the SFL2 (they noted it measured little different from an SFL1) in Stereophile.

Up to 2 volts distortion is around -85 THD+N balanced. It was worse using RCA outputs. I don't see how such low 2nd and 3rd harmonics are masking much. As we are less attune to 2nd and 3rd at such a low level it is the same as not being there I would think.

As for power amps, my use was with electrostats. Those combined with the output transformers (higher output impedance) and the wildly varying with frequency impedance and phase would give them a sound. Quite a few transformers would end up resonating mildly near 20 khz giving a bit of 'air' to the sound. Once I started doing room correction with a Tact unit I didn't use tube amps anymore. Having done series amp testing I believe it was more than FR effects only, but that was much of it.
 

OldHvyMec

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The reply from post #20 is very close to my own thoughts. A good preamp adds a flavor of perfect imperfection to the chain that WILL be
amplified through the tone circuit, power amps and finally speakers. A SS pre vs Valves depending on who did what seldon sounds anything
like an older valve preamp. If you clean up an old Mac C11, 20, 22, there are few preamps that sound like them. They have a flavor with certain
valves. Telefunken or well tested RCA BPs.

I can take those same valves (12AX7) and put them in my newer Mac preamps (C25,2600) and there is a completely different outcome.

I like a C11-C22 in front of class D, NC500s for my summer time listening. I've hooked those power amps to everything I own. The preamp
makes or breaks the sound of all my power amps. There has to be 45 different power amps and at least 25 preamps at my home.

I have one valve linestage I like, Cary SLP-05. I seldom have to EQ anything. It's usually in the bass region of an LP.
9 out 10 times I had a rumble filter flipped on or off.

Yea, you could call me a tube snob, a reel to reel snob, an LP snob, a Mcintosh snob, yep I'm a snob all right. Proud of it too.
Oh, I like my eggs sunny side up. Citizen Kane and Forrest Gump are my favorite movies. Val Kilmer in Tombstone is the best of
all time. Though "The Island of Doctor Moreau" and Marlon Brando was a great one too.

No, I don't get out much.

Regards
 

egellings

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Maybe. I've used them with ESLs, and the amps certainly have a sound with those. The various preamps I've used were clean sounding. SETs certainly have a sound. Too much of one for my tastes.
I think that tubes can work with ESLs if the amplifier is a high voltage design using high voltage tubes that are directly connected to the stators with no intervening transformer. The resonance caused by the transformer's leakage inductance and the stator capacitance of the ESL can be nasty. Dump the transformer, I say. I heard a pair of Acoustat ESLs set up that way and they were downright spooky in their accuracy.
 

Blumlein 88

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I think that tubes can work with ESLs if the amplifier is a high voltage design using high voltage tubes that are directly connected to the stators with no intervening transformer. The resonance caused by the transformer's leakage inductance and the stator capacitance of the ESL can be nasty. Dump the transformer, I say. I heard a pair of Acoustat ESLs set up that way and they were downright spooky in their accuracy.
Oh sure, but those are hard to come by. I had some Acoustats, but not the directly connected amp version. Class D amps seems to handle the ESL panels better than most amps.
 
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NoxMorbis

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Whilst I agree with the above, I'm confused by the whole 'tube sound' business, as the tube preamps I've known and measured have had low distortion, decently wide frequency response, and at line level, adequately (i.e. inaudibly) low noise, albeit all worse than most SS preamps. Consequently, apart from the looks of the glowing tubes, which with preamps won't be much, I've not understood the audible benefits of a tube preamp.

S.
That's how I understand it, too, but it's a kind of asthetics and subjectively 'different' sound thing.
 

LTig

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I think the main reason why people prefer tube power amps, and especially
  • those with SE output stages, and/or
  • those with reduced or no global feedback
is the high output impedance (up to several Ohm). With most speakers the resulting frequency response has more bass (around the impedance peaks of the woofer) and more highs (due to the rising impedance of the tweeter's voice coil).

To get the same result with a SS amp simply add a suitable resistor between power amp and speaker. I remember having read about someone who did it and found out that the SS amp did sound very close to the tube amp. Of course you can use suitable tone controls to get the same effect.
 
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NoxMorbis

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Just to confirm my credentials, here's a photo of my study system, recently changed from 'modern' i.e. 1980s SS to vintage valves.

Two amps on the left are GEC 912 amps DIY built as monoblock power amps. They drive a pair of JR149s out of shot. The two on the right are Quad II amps, bought as 'Spares or Repair' and repaired. They drive a subwoofer under the bench, crossover is a spare Behringer DCX2496 just to remove below 85Hz from the JR149s, and drive the sub.
Turntable is a Goldring Lenco GL75 with Ortofon MC15 Super carrtidge, and as a preamp, I use my small Behringer mixer as it was doing nothing otherwise.

View attachment 274648
Nice. I felt like I just walked back in time. One thing for sure, case design has come a long way -- lol.
 

mhardy6647

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I think that tubes can work with ESLs if the amplifier is a high voltage design using high voltage tubes that are directly connected to the stators with no intervening transformer. The resonance caused by the transformer's leakage inductance and the stator capacitance of the ESL can be nasty. Dump the transformer, I say. I heard a pair of Acoustat ESLs set up that way and they were downright spooky in their accuracy.
tubes and ESLs go well together when one thinks about voltage(s) and impedance(s). Dave Slagle did a pretty nice rendition of purpose-built amplification for the Quad "ESL-57" (more or less Quads, I suppose).
I heard a variant of this exercise and the results were mighty fine.

 

Gorgonzola

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Well, if you want a subjective comparison of SS and an Atma-Sphere amp, here ya go:


Long story short: they sound about the same.
That's fair. I haven't heard either of these amps but 'First Watt' amps are relatively high distortion 'cause Nelson designs the that way. He is a believer in low feedback because higher feedback produces the high-order harmonics which I alluded to.

Anyway despite showing folks my tube preamp I'm not necessarily advocating them. As for power amps, I would never consider at tube power amp nor a First Watt. I leave the choice of preamp open but I definitely recommend S/S power amps of the ultra low distortion variety. Were I looking for a new, low wpc power amp, I'd first look a the Topping LA90.
 

atmasphere

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Humm .... all just psychoacoustics??

I call on @atmasphere to comment. He makes large, monoblock OTL tube power amps such as this MA-3 ...

View attachment 274687
I don't know I believe the common knowledge about 2nd and 3rd order harmonics. Play with Pkane's Distort and you'll find those have to be very high to make a difference.
According to Pkane, his simulation does not include rising distortion with frequency, which has been very common in amplifiers using feedback going back since feedback started being used- about 70 years. This is caused by the amplifier circuit having insufficient Gain Bandwidth Product to support the feedback used. So when the circuit reaches its limit, feedback decreases with frequency on a slope, thus the rise in distortion, usually this is happening inside the ear's most sensitive range (Fletcher-Munson). The devices and circuits needed to get around this problem didn't exist until sometime in the 1990s.

I am assuming the distortion harmonics of lower notes also see an increase with frequency in an amplifier with this problem; if you measure the harmonic spectra at 50Hz as opposed to 1KHz you'll see what I mean.

You can get around this problem by not using any feedback at all. Then you can get a nice straight line when graphing distortion vs frequency. Or you can have enough GBP to support the feedback, which we're seeing now in self-oscillating class D amplifiers with the same result- a nice straight line. I'm of the opinion that this property is important.

Regarding the tubes/transistors thing, IME of fifty years of amplifier design and manufacturing, it is entirely psychoacoustics; interacting with how the ear/brain system perceives sound. This is most noticeable in SET amplifiers, which, if driven too hard (past about 20-25% of full power, which is very easy to do since they don't make a lot of power in the first place...) where higher ordered harmonics will show up on transients (where most of the power is needed to reproduce music), thus lending the amplifier a 'dynamic' quality. But its really distortion interacting with the ear to create that illusion. IMO 'dynamics' should arise from the recording, not the playback electronics.
 

fpitas

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That's fair. I haven't heard either of these amps but 'First Watt' amps are relatively high distortion 'cause Nelson designs the that way. He is a believer in low feedback because higher feedback produces the high-order harmonics which I alluded to.

Anyway despite showing folks my tube preamp I'm not necessarily advocating them. As for power amps, I would never consider at tube power amp nor a First Watt. I leave the choice of preamp open but I definitely recommend S/S power amps of the ultra low distortion variety. Were I looking for a new, low wpc power amp, I'd first look a the Topping LA90.
The J2 has about 0.008% distortion at 20mW where I run it. It rockets up to 0.025% at 1W, mostly 2nd harmonic:

 
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