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RE: Is this regulated filament supply any good?

Posted by Alex Kitic (A) on October 25, 2014 at 05:45:11

In Reply to: Is this regulated filament supply any good? posted by Nickel Core on October 25, 2014 at 01:28:16:

With all sincerity I don't believe ANY of the mentioned regulator solutions (voltage regulation by means of LM317 or similar) actually has that feedback/correction problem.

If the regulator could act against the musical signal, it would cancel it, if not 100%, than to a very high degree (let's say 60dB cancellation). This would be obvious as a much attenuated power output and audible even to those with poor hearing abilities. As an illustration, take the LM317 CCS example and remove the bypass cap: the output will be almost totally attenuated i.e. cancelled by the action of the regulator (setting a constant current).

The problem with voltage regulators is the same as for all other DC heaters solutions: the fact that the filamentary cathode is not on the same potential throughout, and there is a difference in operation from one end of the cathode to the other. This is the reason why AC sounds better, the cathode being at the same potential.

AC of course has one major issue, hum. Another issue related to AC is intermodulation. One has to weigh the two alternatives and decide on the compromise he is willing to make.

High frequency AC generated by means of modified electronic transformers (half-wave bridge) is most probably the best in terms of sound (AC, thus cathode at the same potential) as well as noise/hum (even if 30kHz, the 2nd harmonic, much attenuated, is 60KHz, which cannot be effectively reproduced through output transformers, nor reproduced without enormous attenuation by the tweeters, let alone heard by humans). The frequency is too high for audible heterodyne effects, although some claim irregularities may be observed on a scope using sine wave signals: but music is not a sine wave, rather a series of impulses differing in frequency and magnitude as well ss decay and duration...

The main issue with HF AC is effective measurements and the relatively difficult calculation/adaptation. But once one surmounts the initial difficulties it is both great sounding and reliable.

Now the usual inquisition can do it's best trashing me and my suggestions/design work/achievements - while I am going to exercise a new skill: ignoring bashers and haters ;)


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