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In Reply to: Relevance at AF posted by Mark Kelly on September 02, 2002 at 16:39:49:
In fact, the signal current loop includes the power supply, so a shunt-regulated stage does have signal current going through the regulator. The few I've heard sound better than an electrolytic cap at the end of the power supply... but I don't think Ive heard enough different implementations to call that a general rule.
Follow Ups:
I'm currently using a glow diode as the upper half of the voltage divider in a quasi-ultrapath circuit, and it appears to perform really well.Partly why I took umbrage at the suggestions made in palomarjack's post.
Thanks for posting that, it is a valuable experiment that I've not seen done before.Here's a random thought, which I've not yet tried since I don't have a glow diode based amp or preamp on hand. If the glow tube's impedance is 100 ohms in series with 4mH, then you could bypass it with 0.4uF in series with 100 ohms. The combination would have a constant 100 ohm impedance at all frequencies; it looks topologically like a first order crossover. Crossover frequency approximately 4kHz. It should help reduce power supply noise intrusion in the high frequencies, without upsetting the audio operation. Hopefully the 100 ohms will be enough isolation to prevent the glow tube from going unstable, as it probably would with just the capacitor.
As you note below, the bypass trick is established. It does not result in as flat an impedance as you suggest - there's a nice hump at the resonant frequency of the LC parallel filter.I have found that this and the phase behaviour of the shunt need to be taken into account when designing the bottom half of the voltage divider in the quasi ultrapath circuit I mentioned. Haven't nailed it yet, will post when (if) I do.
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