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Topic: Peachtree Nova and its tube pre-amp (Read 11799 times) previous topic - next topic
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Peachtree Nova and its tube pre-amp

I have had a Peachtree Nova (integrated DAC, pre-amp and amp) for about a year now.  I use it exclusively for computer audio playback via either an optical connection or usb/coax.  (The speakers it drives are BW CM7).  It sounds reasonably good.

There is a remote-control switch for the pre-amp that enables you to toggle between a solid-state pre-amp circuit and one that has a 6922 tube.  There is an accompanying blue LED glow that illuminates the tube when the circuit is activated.

Naturally, I have periodically experimented (both sight and blind tests) to see (so to speak) if I could hear a difference.  Briefly, I can't.  Not a hair.  Ever. In blind tests I do no better than random guessing.

Other people claim they can hear a difference (not just those who can hear differences between files with identical checksums), although I have no idea if anyone has ever passed a blind test.

This leaves me wondering if I swapped out the tube for a different one, whether that might make an audible difference.  (The whole tube idea is new to me, and strikes me as a whole new vista of audiophoolry, but at the same time I am slightly curious...).  These things are expensive.  To get a tube that the tube experts tell me would be an unambiguous improvement might be $150 or more.  Doubtess you can pay more.

That brings me to my main questions:

(1) Has anyone identified an audible difference with any tube in a Nova?  (i.e., something more solid than anecdotal sighted testsing?)

(2) Are there readily available any blind test results for different versions, makes, etc. of a particular kind of tube? Or ones that definitively demonstrate that this whole tube business is BS?

Peachtree Nova and its tube pre-amp

Reply #1 –
  I'm not a fan of 1950's technology...  (I do understand why guitar players like tubes, because they like the way they sound when driven into distortion.)

I don't know if changing the tube will help/hurt....  But I do know that it's possible to built a tube circuit that's fairly immume to tube variation, or a circuit that's sensitive to tube variations.    Tubes age and eventually die.  If changing a tube changes the sound, it's likely that a different sample of the same tube-number (same manufacturer) will sound different, and that the sound will change over time...  Generally not a good thing with audio equipment!

It's hard to improve the sound, if there's nothing wrong....  And I doubt there's anything wrong with the solid-state output.

For a very low cost, you can build a solid-state circuit that has very low distortion, very low noise, and very flat frequency response...  Especially a circuit in a DAC, which doesn't need any gain.  A similar circuit with tubes is going to cost much more to build.  (Tube power amplifiers require an output transformer, which makes it even more difficult & expensive to match the performance of a solid state amp.)

Peachtree Nova and its tube pre-amp

Reply #2 –
"I'm not a fan of 1950's technology..."

Me either, but bad things happen when I pull out the transistors.

I wanted a good DAC and an integrated system.  The optional tube stage just struck me as a marketing gimmick, but I thought as long as I have it, it might be interesting to play with.

As far as "improvement," the claim (not mine) is that the second-harmonic distortion introduced can be pleasing to the ear, even if it is less accurate.

Peachtree Nova and its tube pre-amp

Reply #3 –
Quote from: wgscott on
As far as "improvement," the claim (not mine) is that the second-harmonic distortion introduced can be pleasing to the ear, even if it is less accurate.


That can be true.

If universally true, then the distortion could be added in the mastering process.  Even if the DAC is the proper place to add even harmonic (more the point than just second order) then it would likely be cheaper to do it digitally than to put in a tube stage.


Peachtree Nova and its tube pre-amp

Reply #4 –
Hi wgscott,

From what I understand, tubed power amplifiers usually have a (much) higher harmonic distortion than solid state amps.  The inter-modulation distortion of an tube amp is usually (much) lower than a solid state amp.

Harmonic distortion is usually (but arguably) regarded as more a favorable distortion (i.a.w. people like it; it gives that "warm" sound to an amp) while harmonic distortion is usually regarded as an unfavorable distortion.

Having said that, I am not sure if (and if so, to what extend) that goes for pre-amps. 

I know 2 persons that can ABX their tube power-amp against any solid-state with 100% accuracy every time (until this day, on their own setup!).  But again, this is about power-amps, not pre-amps.

It looks like you have already established the fact that you can not distinguish solid-state from tube pre-amp mode.  If you are up for an experiment and have $ 150 lying around that you have no use for, you can check a replacement tube yourself.

But honestly (and despite my postings on this forum) I believe that the $ 150 would be better spend on (for example) buying flowers for loved ones.  I can almost guaranty it will not make your setup sound better, but it will put a smile on your face :-)

If you want to improve sound quality, you can also do a Google on "golden rule loudspeaker placement".  You will get a number of hits that explain loudspeaker setup in your room according to "Phi".  I believe you to have quite a bit more knowledge about that thanI do!  It it's possible for you to do so, it is well worth trying it out.  And if it did not give any results, you did not spend money on it.  This is a rather difficult improvement to ABX test though, so you will have to decide for yourself if it works.

Especially when you are unhappy about your sound quality (I can not see any problem with your speakers), it is also worth looking into adjusting the room itself.  There are quite a few products that have a positive influence on room acoustics, but I do not have any experience with those.  I am fairly sure that someone with knowledge and experience can help you with that on this forum. 

Hope this helps, and if you have any questions please ask!

Regards,
Peter

Peachtree Nova and its tube pre-amp

Reply #5 –
First off, let me say I don't know the specifics of your setup. However, if (and it is an IF) the designer has done his job properly, the pre-amp should be designed to cope with the drift and component tolerances for the specific "tube" (to me it's a valve, since I'm in the UK) within its useful life. That being the case, there will not be an audible difference if you change the tubes for the same type unless you buy a sub-standard one that's out-of-spec. Changing to a different one isn't a good idea unless you really know your tubes well, it's far more likely to degrade than improve performance. As for buying outlandishly priced tubes, cryogenically treated ones and so on - try reading the pages of drivel written saying that the 1958 version of the tube sounds much more open or warmer and so on (that's not a quote but I see comments of that type). That ought to tell you enough! Perhaps someone can point me to a substantiated claim but I've yet to see one.

It is perfectly possible to build tube pre-amps of high audio quality but nowadays it's a lot cheaper to do it in solid state to a higher quality still. If you're lucky enough that the tube-version you have is well designed and is not sonically different (to you) from the solid-state one built in, play away - you only have your money to lose by it!

I also admit, like the poster above, not to be a fan of '50s technology where modern is demonstrably superior. Progress has ensured that we can beat the old techonology, on cost grounds even if no other.

Peachtree Nova and its tube pre-amp

Reply #6 –
Quote from: thesurfingalien on
Hi wgscott,

From what I understand, tubed power amplifiers usually have a (much) higher harmonic distortion than solid state amps.  The inter-modulation distortion of an tube amp is usually (much) lower than a solid state amp.

Harmonic distortion is usually (but arguably) regarded as more a favorable distortion (i.a.w. people like it; it gives that "warm" sound to an amp) while harmonic distortion is usually regarded as an unfavorable distortion.

Having said that, I am not sure if (and if so, to what extend) that goes for pre-amps.

The first bit is true, but not the complete picture. Power amps in tube form can be built to an acceptably high standard. They do have lower intermodulation distortion, true but when it can be reduced to inaudibility in either solid-state or tubed amps it becomes irrelevant. Only the spec-obsessive need pursue perfection.

As for the difference between power and pre-amps, no they don't have the same set of problems. The largest source of distortion in a tubed power amp is the output transformer, something that has to be used in a practical amp. For a pre-amp, there's no power requirement (relatively) so there's no output transformer needed. With careful design, a pre-amp can be tubed and of a perfectly adequate performance. It's just costly, and no, I'm not talking of exotic components - just good electronic and physical manufacture.

Peachtree Nova and its tube pre-amp

Reply #7 –
Solid-state pre and power-amps can be easily built such that all sources of distortion and noise are below the threshold of audibility (at least with music - sine waves are a bit less forgiving).

The only way a tube stage can improve the sound is by adding distortion that you happen to like. Personally, I want my playback chain as accurate as possible and if I want to mess with the sound I'll do it in software.

Peachtree Nova and its tube pre-amp

Reply #8 –
Quote from: lessthanjoey on
Solid-state pre and power-amps can be easily built such that all sources of distortion and noise are below the threshold of audibility (at least with music - sine waves are a bit less forgiving).

Not wishing to be too pedantic here but isn't music a complex collection of sinewaves? We have someone called Nyquist to thank. He showed that any waveform can be analysed as a collection of sinewaves. An amp that can't cope with sinewaves can't cope with music, in the strict sense. Whether the distortion is audible is, of course, a different matter. I'm assuming that's what you were alluding to.

Quote from: lessthanjoey on
The only way a tube stage can improve the sound is by adding distortion that you happen to like. Personally, I want my playback chain as accurate as possible and if I want to mess with the sound I'll do it in software.

+1 on that bit

Peachtree Nova and its tube pre-amp

Reply #9 –
Quote from: antz on
Not wishing to be too pedantic here but isn't music a complex collection of sinewaves? We have someone called Nyquist to thank.


I'm a natural-born Pedant:  It was Fourier.

Thanks everyone for the insights.

I did read something called Joe's Tube Lore which is quite entertaining.  I was just wondering if any such claims have ever been subjected to a test (i.e., can you really tell an Amperex 6922 from a Sovtech)?  I suspect if I am unable to tell whether the tube circuit is engaged or not, subtle differences, even if they are real, might escape me any my cynical ears.  Still, if I could test it for $10, I would...

Peachtree Nova and its tube pre-amp

Reply #11 –
Quote from: DonP on
Quote from: wgscott on
As far as "improvement," the claim (not mine) is that the second-harmonic distortion introduced can be pleasing to the ear, even if it is less accurate.


That can be true.

If universally true, then the distortion could be added in the mastering process.  Even if the DAC is the proper place to add even harmonic (more the point than just second order) then it would likely be cheaper to do it digitally than to put in a tube stage.


It can't be *universally* true since the same nonlinearity that creates harmonics also creates IM. IM is generally inharmonic and therefore usually ugly to listen to.

Note that most demos of SETs and other tubed amps are done with solos and small groups, where the IM problem is naturally less.

Commercial production equipment that adds nonlinear distortion such as the Aphex Aural Exciter is generally used on just one mic, the soloists.

Peachtree Nova and its tube pre-amp

Reply #12 –
Quote from: wgscott on
Quote from: antz on
Not wishing to be too pedantic here but isn't music a complex collection of sinewaves? We have someone called Nyquist to thank.


I'm a natural-born Pedant:  It was Fourier.

Thanks everyone for the insights.

I did read something called Joe's Tube Lore which is quite entertaining.  I was just wondering if any such claims have ever been subjected to a test (i.e., can you really tell an Amperex 6922 from a Sovtech)?  I suspect if I am unable to tell whether the tube circuit is engaged or not, subtle differences, even if they are real, might escape me any my cynical ears.  Still, if I could test it for $10, I would...


About as close as the original ABX developers of that came was a DBT comparing a tubed amp to a SS. After the first (positive) test session the amps owner found that the amp needed its output stage balanced and if memory serves, new output tubes. The second test session had negative results.

Peachtree Nova and its tube pre-amp

Reply #13 –
Quote from: antz on
Quote from: thesurfingalien on
Hi wgscott,

From what I understand, tubed power amplifiers usually have a (much) higher harmonic distortion than solid state amps.  The inter-modulation distortion of an tube amp is usually (much) lower than a solid state amp.

Harmonic distortion is usually (but arguably) regarded as more a favorable distortion (i.a.w. people like it; it gives that "warm" sound to an amp) while harmonic distortion is usually regarded as an unfavorable distortion.

Having said that, I am not sure if (and if so, to what extend) that goes for pre-amps.

The first bit is true, but not the complete picture. Power amps in tube form can be built to an acceptably high standard. They do have lower intermodulation distortion, true but when it can be reduced to inaudibility in either solid-state or tubed amps it becomes irrelevant. Only the spec-obsessive need pursue perfection.

As for the difference between power and pre-amps, no they don't have the same set of problems. The largest source of distortion in a tubed power amp is the output transformer, something that has to be used in a practical amp. For a pre-amp, there's no power requirement (relatively) so there's no output transformer needed. With careful design, a pre-amp can be tubed and of a perfectly adequate performance. It's just costly, and no, I'm not talking of exotic components - just good electronic and physical manufacture.



I stand corrected.  It looks what I know about tubes is outdated.  Thanks for the info!

Regards,
Peter

Peachtree Nova and its tube pre-amp

Reply #14 –
Quote from: antz on
Quote from: lessthanjoey on
Solid-state pre and power-amps can be easily built such that all sources of distortion and noise are below the threshold of audibility (at least with music - sine waves are a bit less forgiving).

Not wishing to be too pedantic here but isn't music a complex collection of sinewaves? We have someone called Nyquist to thank. He showed that any waveform can be analysed as a collection of sinewaves. An amp that can't cope with sinewaves can't cope with music, in the strict sense. Whether the distortion is audible is, of course, a different matter. I'm assuming that's what you were alluding to.

Quote from: lessthanjoey on
The only way a tube stage can improve the sound is by adding distortion that you happen to like. Personally, I want my playback chain as accurate as possible and if I want to mess with the sound I'll do it in software.

+1 on that bit


You're correct. I meant to say that problems may be more audible with a single sine wave (although it's true that IM products will be most audible with a pair of sine waves). I'm very much aware that signals (including music) are fundamentally composed of sine waves

Peachtree Nova and its tube pre-amp

Reply #15 –
 Lots of good thoughts here - to add some specifics....I certainly can understand the seduction of tubes! My opinion is that its good not to be "seduced" by them unless you are willing to part with some major amounts of cash. I, so far, have avoided them. As others have stated, there are free methods available to "experiment" with tube like plugins through VST tube simulators. I have about a dozen of them in my foobar VST wrapper (ex. Ruby Tube).

I find it interesting that the tube in the Peachtree stage was difficult to differentiate from the SS stage. My gut feeling is that you could experiment with "tube rolling" but you may end up frustrated by the cash outlay without much to show for it.