45 said:
Since Don is measuring at the plate of the preamp tube, the power amp, much less a speaker, isn't even required for the electronic baseline - just a resistor. The tube is not in a chassis, so no mechanical form of the input should be present. That's the trivial case. If tubes resonated with merely a signal input they wouldn't be useful for much.
The question is one of quantity and quality. When listening to music, how much is audible/desirable/undesirable? What kind is audible/desirable/undesirable? Level is easy to modulate, to a first approximation in a linear way, with distance.
Sheldon
Sheldon said:
It is not trivial as you think. You have to demonstrate by physical methods you have no mechanical noise.
The tube is not floating in the vacuum and has at least one mechanical coupling anyway.
The acoustic branch (i.e. part of the dispersion law which regulates the wave propagation in solids) is active from 0 Hz and a continuum in energy.
Given that people are sensible to things like THD down -60dB, typically, a picture showing no more than 20db dynamics is questionable.
45
What's wrong with just using the headphone test?
Trying to isolate the tube looks like trying to prove a negative to me. "If we only had 20 more dB isolation" From what I have seen, it's nearly impossible to prevent the resonances from firing up. The tiniest little airborne or wire lead borne signal is all it takes. Resonant detectors are among the most sensitive detecting devices, NASA uses them to capture satellite signals.
What I plan to try is putting the tube and speaker in an old heavy fiberfilled speaker cabinet with some plywood over the speaker openings (and a brick on top). With close proximity between speaker and tube, one doesn't need much speaker volume. The headphones can be cabled out to the next room. Then I will listen to some string music with the speaker on or off. If it sounds better with the speaker on, then "case closed", at least for me.
One caveat I see with this approach, is that "better sounding" may require full room acoustic reverberations to be detected by the tube. In which case, out of the box they come for testing.
If this test does turn out positive for the speaker on case, then the next logical test would be to use a microphone pickup in place of the DHT, for summing in some reverberation. This might clear up whether the effect is from tube resonances or just microphone effect.
I also want to try out that magic gong tube section I found earlier to see what that sounds like in a preamp. I wouldn't be surprised if the resonances there have amazing effects on the sound. But that may be a different deal altogether, since I don't see that extreme effect with the other DHT tubes I've tried.
Still waiting for my Hammond 124B xfmr to show up.
Don
Trying to isolate the tube looks like trying to prove a negative to me. "If we only had 20 more dB isolation" From what I have seen, it's nearly impossible to prevent the resonances from firing up. The tiniest little airborne or wire lead borne signal is all it takes. Resonant detectors are among the most sensitive detecting devices, NASA uses them to capture satellite signals.
What I plan to try is putting the tube and speaker in an old heavy fiberfilled speaker cabinet with some plywood over the speaker openings (and a brick on top). With close proximity between speaker and tube, one doesn't need much speaker volume. The headphones can be cabled out to the next room. Then I will listen to some string music with the speaker on or off. If it sounds better with the speaker on, then "case closed", at least for me.
One caveat I see with this approach, is that "better sounding" may require full room acoustic reverberations to be detected by the tube. In which case, out of the box they come for testing.
If this test does turn out positive for the speaker on case, then the next logical test would be to use a microphone pickup in place of the DHT, for summing in some reverberation. This might clear up whether the effect is from tube resonances or just microphone effect.
I also want to try out that magic gong tube section I found earlier to see what that sounds like in a preamp. I wouldn't be surprised if the resonances there have amazing effects on the sound. But that may be a different deal altogether, since I don't see that extreme effect with the other DHT tubes I've tried.
Still waiting for my Hammond 124B xfmr to show up.
Don
smoking-amp said:
The response is the same Don. You are not putting in yourself 100% away from systematic errors. Moreover, you should also take into account that once selected one type of tube - say the 19 - microphonic effect does not show up at the same level for each individual 19.
It is not impossible, you can do much better!smoking-amp said:
In fact you could just see some attenuation in your experiment because you were attempting to damp and not going for true inertial confinement (i.e. best possible insulation).
That is what I meant here (post 173):
Damping (in its literal meaning) is not the right thing to do.
An elastically suspended object at subsonic frequency works by means of
inertia reaction for our purposes.
Basically the (big) difference is: damping the resonances means that you are attenuating a negative effect that is already masking and irreversibly degrading your sound, while inertia reaction simply does not make it happen, not only as consequence of speakers acoustic feedback but anything of the outer world that can excite your components!
smoking-amp said:
The NASA resonant detectors I know are mounted on the satellites and take electromagnetic signals from the Earth (lightning) and from space.
smoking-amp said:
With the speakers and the room things get much more complicated.
Even more if we consider the listener, the only thing that has never been properly included in the chain by acoustics and the other hifi reproduction theories.
Big mistake!
Music and its execution have been developed solely according to the listener.
We need to talk about many other things to get there and for the purpose of this thread it is OT. If you like we talk about it elsewhere.
45
"Any progress?"
I got my 124B Xfmrs in, but I haven't gotten around to putting a DHT pre- amp together to try out yet.
Been too busy lately with modding a Tek 576 curve tracer for tubes and working on a toroid winder project. I'll get around to this eventually. I also just got in a split bobbin filament xfmr suitable for the pre-amp. (high common mode isolation)
Kayaking tomorrow though. Oh, and the darn hard drive on my computer is hitting 1 out of 4 successful boot-ups lately, gonna have a big problem to fix soon.
Don
I got my 124B Xfmrs in, but I haven't gotten around to putting a DHT pre- amp together to try out yet.
Been too busy lately with modding a Tek 576 curve tracer for tubes and working on a toroid winder project. I'll get around to this eventually. I also just got in a split bobbin filament xfmr suitable for the pre-amp. (high common mode isolation)
Kayaking tomorrow though. Oh, and the darn hard drive on my computer is hitting 1 out of 4 successful boot-ups lately, gonna have a big problem to fix soon.
Don
If we are reviving a dead thread, DHTs have outlived Kodachrome -- Dec 30th 2010 is the last day for processing if you have any laying around.
Good call!! I still have my Leica lenses, though I use them on my Canon digital body with an adaptor.
Must be two years since I used film. I'd sell all my camera bodies except they still have bits of film in them and I can't be bothered to finish the films off and process them!!
Anyone want a load of camera bodies - Leica R, Contax etc?
Andy
Must be two years since I used film. I'd sell all my camera bodies except they still have bits of film in them and I can't be bothered to finish the films off and process them!!
Anyone want a load of camera bodies - Leica R, Contax etc?
Andy
It's sad that they never came out with digital backs for some of these. I thought that was going to happen with the Contax G at least.
At any rate, my DHT's have been replaced by transformer coupled differential MOSFET followers, which I must say sound (and measure) better
Jumping back in the discussion, and I am just at post 128, I like to note I had a 6J6 for an input in a differential preamp and used that for about ten years, excellent sounding, but also microphonic and it could enter in strange oscillations, induced from strong jumps in passages, giving a metallic ringing of several seconds.
Note the 6J6 is a IHT, with just one central heater.
So I guess it is the mesh wires of the grid that do give this effect.
I gave up on this pre-amp because of the microphonics (with a stepped att this is not practical). For the record.
I built a 3A5 linestage, but never took it in production either. [I am now with Aikido for how long that lasts]
albert
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