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Tube Preamp Question

NoxMorbis

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I'm confused about tube preamps. Shouldn't the tube be the last stop before the speakers in order to benefit from the tube preamp?
 
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NoxMorbis

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What do you consider a benefit?
Yeah. I guess another way to state it is will you get the same thing from a dedicated hybrid D amp as you would from plugging in a tube preamp to a nonTube class D amp?
 

LTig

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I'm confused about tube preamps. Shouldn't the tube be the last stop before the speakers in order to benefit from the tube preamp?
If by benefits you mean tube distortion it does not matter where in the chain you add it, as long as the devices following the tube stage are linear.

Edit: Hence it makes more sense to use a comparably cheap tube preamp feeding a solid state poweramp than the other way round because powerful tube poweramps are very expensive.
 

sergeauckland

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If by benefits you mean tube distortion it does not matter where in the chain you add it, as long as the devices following the tube stage are linear.

Edit: Hence it makes more sense to use a comparably cheap tube preamp feeding a solid state poweramp than the other way round because powerful tube poweramps are very expensive.
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.
 

JiiPee

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I think the primary benefit of the tube preamp is that the knowledge of listening a tube preamp makes the owner experience the vaunted tube sound even if there are actually no audible differences compared to SS preamps. Then there is of course the image : A guy who owns a tube preamp is naturally more interesting person than an average Joe with ordinary consumer electronics...
 

fpitas

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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.
Ah, but the new eBay breed are run starved plate voltage with miniscule current to get the full advantage of grungy sound.
 

anmpr1

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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.

I suspect that is generally the case with modern tube gear. An exception is likely the old stuff--vintage.

I have a homemade 'updated' PAS (totally new circuit boards and SS power supply; phono stage is a JFET amplified by dual 12AY7; Alps volume pot and Bourns potentiometers). You can turn it up to 1 or 2PM, and you won't hear phono noise (as long as the ground remains intact). Line level digits sound as clean as my SS preamps. This is all from casual listening, of course. I haven't measured anything. FWIW.

However, amplifiers are Dyna Mk IV, with period circuitry (1960), but new tubes. Unless it is my imagination (which I honestly don't think it is), the sound of these 60 year old vintage amps is muddy and 'soft' (if those descriptions make any sense). Definitely not as 'tight' as either my 30 year old SS Yamaha, or four year old Benchmark amplifier.

Loudspeakers are relatively sensitive, easy to drive 8 ohm, so I don't think that part of the chain is making a difference for the amps.

I wouldn't advise anyone to use a sixty year old tube amp in a contemporary setting. Unless they invest in a soldering iron, and don't mind the expense of tubes, and the heat. That said, I find the listening experience as enjoyable as with the SS stuff.
 

Blumlein 88

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Generally tube preamps don't have tube sound. It is tube power amps that do. Now yes those starved plate designs have a sound though not like a tube power amp. And that illustration is why just having vacuum tubes doesn't guarantee "tube sound".
 

fpitas

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Generally tube preamps don't have tube sound. It is tube power amps that do. Now yes those starved plate designs have a sound though not like a tube power amp. And that illustration is why just having vacuum tubes doesn't guarantee "tube sound".
I'm not sure actual tube sound is important. Frankly, it seems like joining a club sometimes.
 

anmpr1

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Frankly, it seems like joining a club sometimes.

I think that's a lot of it. Historically, tubes where meant to be heard but not seen. If you look at designs from the '50s up through the introduction of mass market SS, early to mid '60s, tube gear most always had covers, open in the back for access. But the actual tubes themselves were hidden. It wasn't something anyone wanted to 'show off'. Separate power amps all used cages which mostly hid the tubes, and those units were mostly hidden anyhow, inside consoles or cabinets.

Someone, somewhere, decided that tubes could be used for cosmetic purposes, and started sticking them in open air.

You wouldn't know this Fisher was a tube amp, unless you looked at the back. McIntosh makes sure you know you bought tubes, using green LEDs to highlight the sockets.

fisher.jpg
fisher2.jpg
mac.jpg
 

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fpitas

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I think that's a lot of it. Historically, tubes where meant to be heard but not seen. If you look at designs from the '50s up through the introduction of mass market SS, early to mid '60s, tube gear most always had covers, open in the back for access. But the actual tubes themselves were hidden. It wasn't something anyone wanted to 'show off'. Separate power amps all used cages which mostly hid the tubes, and those units were mostly hidden anyhow, inside consoles or cabinets.

Someone, somewhere, decided that tubes could be used for cosmetic purposes, and started sticking them in open air.

You wouldn't know this Fisher was a tube amp, unless you looked at the back. McIntosh makes sure you know you bought tubes, using green LEDs to highlight the sockets.

View attachment 274629 View attachment 274631 View attachment 274632
Yeah, back in the day the only tube items that had more or less exposed tubes were high-end amps. In high school a friend and I had the job of changing the dual KT88s/channel and adjusting the bias in a friend's dad's stereo. Oddly, that amp did not have the warm fuzzy muddy sound often associated with tubes. We got to keep the old tubes, too.
 

sergeauckland

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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.

IMG_20230115_131349578.jpg
 

DVDdoug

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I'm not s fan of this 1950s technology...

If a tube amplifier has a "tube sound" it will sound different than another tube amp. If you want a tube sound you need to choose the particular amp you like.

Shouldn't the tube be the last stop before the speakers in order to benefit from the tube preamp?

Probably... Guitar players often prefer tube amps but guitar amps are not supposed to be high fidelity. They have a particular sound and they are "part of the instrument". And guitar players tend to like they way tube amps sound when over-driven into distortion, so yes, that's (mostly) the output section. (You wouldn't want the whole band to sound like that!!!) Usually they are all-tube, including the preamp section. And usually, the guitar player has a favorite amp and a favorite guitar.

- Tube power amps need an output transformer which makes them harder & more expensive to design and build. And the transformer can be a big reason for the "tube sound" (distortion). But even with a transformer a well designed tube amp can be low-distortion like a solid state amp. And although tube amps tend to soft-clip when overdriven, they can be designed to hard-clip just like a solid state amp when pushed into distortion. A guitar player would want the opposite... So solid state guitar amps are designed to soft-clip so they sound similar to a tube amp when overdriven. With a high-fidelity amplifier we want to completely avoid driving the amp into distortion so that characteristic isn't important.

- You can build a preamp without a transformer (in the audio path) so it's not as difficult or expensive to build a good one. (Solid state is still more economical.)

- Unless you have a turntable and a phono preamp, a home "preamp" isn't really a preamp... It's a "control center" and although it may have some available gain, 90% of the time the signal through the preamp is being attenuated, not amplified.

- Recording studios sometimes use tube microphone preamps for their "tube sound" characteristics. But the effects are subtle... A different microphone or a different microphone will make more difference. There's a lot of "mythology" in the pro world, but they aren't quite as crazy as audiophiles. ;) They might use a particular vintage preamp (and mic) because Frank Sinatra used it, or whatever Lady Gaga used on her latest Grammy winner, etc. You won't find a tube power amp in a modern recording studio. They might have some vintage tube compressors or other processing/effects equipment. And some studio condenser mics have tubes. ...Condenser mics have a built-in "head amp" and most are solid state but the mic still connects to a preamp. (Dynamic mics don't have any active electronics inside.)

-
 

DSJR

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Quad II's to drive a subwoofer? Mine (sensitively rebuilt some time back by Glenn Croft r.i.p. are delightfully 'musical' and charming on vocals, but extended bass isn't at all a part of their portfolio really ;)

Speaking of Glenn, he had some excellent valve/tube preamps in the 'Micro 25' series (his hybrid Series 7 power amps measured just like a valve amp with high distortion and 2.4 ohm output impedance, arguably deliberately) and certainly on the line inputs, were arguably transparent and with low noise.
 

egellings

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I think the primary benefit of the tube preamp is that the knowledge of listening a tube preamp makes the owner experience the vaunted tube sound even if there are actually no audible differences compared to SS preamps. Then there is of course the image : A guy who owns a tube preamp is naturally more interesting person than an average Joe with ordinary consumer electronics...
Placebo effect, mostly, if the tube amp is an audibly competent one.
 

notsodeadlizard

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Everyone should do what they can do best.
Tubes (especially triodes for audio frequency range) are very good for voltage amplification. Solid state devices are good for the power amplification.
So, what you are asking about is called "hybrid amplifier".
Of particular interest are hybrid amplifiers with a unity gain output buffer.
I've made several of such beasts and they are formidable.
Tube voltage amplifier allows for high amplitude and very characteristic soft clipping.
And the output buffer replaces the output transformer.
This works quite well without global feedback at all.
In general, it is a very exciting area for an exciting hobby.
 

Blumlein 88

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I'm not sure actual tube sound is important. Frankly, it seems like joining a club sometimes.
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.
 

sergeauckland

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Quad II's to drive a subwoofer? Mine (sensitively rebuilt some time back by Glenn Croft r.i.p. are delightfully 'musical' and charming on vocals, but extended bass isn't at all a part of their portfolio really ;)

Speaking of Glenn, he had some excellent valve/tube preamps in the 'Micro 25' series (his hybrid Series 7 power amps measured just like a valve amp with high distortion and 2.4 ohm output impedance, arguably deliberately) and certainly on the line inputs, were arguably transparent and with low noise.
Yes, bridged into a single sub. Works fine for desktop use. They are flat to 20Hz, so extended enough. Output impedance somewhat high, but as the amps are set for a 4 ohm load, output impedance is OKish.

S
 

Gorgonzola

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Generally tube preamps don't have tube sound. It is tube power amps that do. Now yes those starved plate designs have a sound though not like a tube power amp. And that illustration is why just having vacuum tubes doesn't guarantee "tube sound".
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
 
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