Tubes Begone!

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OK

The page is really “Valves Begone!” since those “little bottles with lights in” (thank you Robert) are not “tubes” but “valves”! “Tubes” ought to attract more hits from tube wankers though.

Preface

A past life in Audiofoolsville (via Chickasaw Falls) sees me in custody of a plethora of C-J valve gear – most of which comprised incompetent power amplifiers that were decommissioned some time ago in favour of simple DIY solid state amps which are superior by orders of magnitude in all respects.  However a very expensive and much hyped “Premier Ten” preamp remained in my downstairs system as I considered it innocent enough and I needed an input selector and some gain, or so I thought. Turns out the thing is guilty and works better when handcuffed – turned off and used as a passive input selector with no gain – which is more than I ever used when it was plugged in anyway!

It’s the big one.  The rest is switched off too.  All rubbish.  The more recent models look a lot fancier but have exactly the same kind if GARBAGE inside!

The hype

Well it read in part like this (poor grammar, punctuation and spelling verbatim):

  • “The zero feedback circuit insures temporal accuracy and spatial detail.”
  • “The volume control is a 23 position switch selecting among 23 pairs of resistors ­ never more than a single-pair of resistors are inserted in the signal path by this control. The balance control is an 11 position switch that is electrically out of the circuit in the centered position. There are no carbon-track or conductive plastic resistive elements to degrade the audio signal in the Premier Ten.”

The reality

  • It’s a noisy line stage that added no gain, injected lots of distortion and did nothing to improve anything .  “Temporal accuracy”? “Spatial detail”?  What do these bogeyman terms mean anyway?  Are such things measurable?  NO!  Perhaps they’re just used in an attempt to scare children.
  • No carbon tracks?  No conductive plastic resistive elements?  So what?  Perhaps they mean “We prefer to leave the dirty work to the tubes themselves”.

What happended?

Short story.  The stepped attenuator went very noisy in one channel yet again.  I don’t turn it anyway.  It was left at 1 click past 12 o’colck.  So I looked at the schematic to see what I might find and found that after the input selector, the two direct outputs called “Rec 1” and “Rec 2” bypass the attenuator and everything else.  No buffers.  No nothing.  These were designed for connection to a tape deck so that any one of the inputs could be recorded.  I could use Rec 1 instead of the “Main Outs” (via the little bottles with lights in) to the active crossover and just leave the thing switched off.  A superior 64 bit digital volume control is built into the playback software anyway and the surround processor (on anoher input) has a volume control too.  I’d just have to check that the voltage gain through these “bypasses” (i.e. a gain of 1 = nothing) was about the same as what it was through the valves at one click past 12.

REW sweeps

The red sweep is basically the response of a Focusrite 2i2 sound card used to make the measurement through the preamp’s Rec Out.  The blue sweep (also including the 2i2) shows that the valve preamp’s amplitude reponse is basically OK from 20Hz to 20KHz.  The “unity gain” achieved via the Rec Out 1 is 1dB higher.

But here’s the rub:

THD at 100Hz is almost 10 fold when the valves are in circuit.  It only gets worse below that.  NOS Sylvania 6GK5 valves that measure “as new” are installed.

It inverts phase which despite their “advice” to reverse the speaker cables, is inaudible.

Individual harmonics and noise:

Valves in (cursor at 100Hz):

Which shows very clearly that there is no predominance/emphasis of so-called “nice” even harmonics!  Just the usual hash of harmonics both odd and even.  Noise at 100Hz is 0.01%

Rec Out 1 (cursor again at 100Hz):

Noise at 100Hz 0.002% – that’s basically the 2i2 sound card.  5 times better!

Is this fair?

Maybe not without a comparison, so here’s one.  An extremely inexpensive op amp based DIY preamp which includes one of those “dreaded” carbon track pots and also includes an active crossover and a Linkwitz Transform circuit measured with the same 2i2 sound card.  This is the midrange output:

I’ve moved the cursor to 200Hz since 100Hz is out of band, but as is plainly clear, THD is basically level from 100 to 200Hz anyway and the noise is actually higher at 200Hz – so this favours the valves.  THD 0.006% (6 times better than the C-J).  Noise 0.004% – somewhat better than the C-J.  And this is far more than a mere preamp!

Conclusions

  • Valves were an early fumbled attempt at electronics a hundred years ago and have absolutely no place in any competent modern hi-fi system (just like vinyl).
  • That the imbeciles at duiaudio.com and other lunatic asylums are discussing them, building new circuits with them and generally revering them is affirmation of their ignorance and stupidity.
  • Proponents of commercial valve stages are playing on buyer nostalgia, house them up in fancy boxes, have all sorts of solid state electronics lurking behind them trying hard to keep them in check, but their products are all fundamentally incompetent.
  • The C-J valve preamp was a pathetic shame and works better as a mere input selector – turned off!
  • Valve power amps are orders of magnitude worse than pre-amps – even if they’re push-pull.
  • The C-J preamp might as well have been wired as a passive attenuator with no power cord.  Right up to several clicks beyond 12 o’clock (where it never went), it provided no gain whatsoever and inserted nothing but distortion and noise over the signal!  For what?
  • There are no longer any valves in service in my life and that can only be a good thing.
  • Valves BEGONE!

Oh but what about “temporal accuracy”?  Measure it and show me!  In the meantime I’m happy to miss out on it (whatever it is)!

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