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In Reply to: RE: Al is on the money ... posted by Naz on October 16, 2014 at 04:15:22
Hi,
I generally do not like sand in my amps, especially not in the current loops.
I'm not using just 'any' filament bias resistors (see pic). These are silver wire wounds from AudioConsulting (Switzerland) I use for the first stage. I use a Kiwame resistor in the second stage.
Yes, its still a bit noisy, but not more so then the $250K Kondo M10 I once had. My records are generally noisier ;)
Quick question. When using diodes in the cathode... Am I correct that this will not influence the Zout of the stage? That would be a great benefit compared with cathode/auto bias.
Thanks,
NC
Follow Ups:
for biasing gain stages such as this I've found no better way than Schottky diodes, SiC providing greater voltage drop. They sound better than anything I've tried, particularly for phono applications and I've spent serious time evaluating the options. Although I've not tried every other diode possible Schottky diodes generally sound way better than silicon diodes to my ears.
Since they have very little dynamic resistance local nfb is minimal so they don't have to be bypassed. Therefore OP impedance is almost as good as running a piece of wire in the cathode circuit.
Serious resistors you are using btw, very impressive looking!
Cheers,
Naz
I have tried diode bias on a CCS parafeed line stage, and am very pleased with the results. Not sure what effect that diode bias has on output impedance with a conventional gain stage. With parafeed, you can take advantage of the Western Electric output topology (parafeed cap returning to the top of the cathode), which I believe, would not increase the output impedance of the stage, since the AC signal path is restricted to just the tube, parafeed cap, and the OPT.
The benefit is that you can eliminate the cathode bypass cap. I know, we've just substituted a parafeed cap for a cathode bypass cap, however the parafeed cap is much smaller, and can therefore be of higher quality. I preferred this over battery bias as well.
twystd
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