Tube DIY Asylum

RE: Increase L in pi network

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This Post Has Been Edited by the Author

In Reply to: RE: Increase L in pi network posted by Sidewinder on September 22, 2017 at 00:15:20

If you are looking for more speed: "tighter" dynamics, a sense that complex music does not turn to mush, and a more delicate sense of touch, I don't think that in your case increasing the inductance and DCR will deliver. Actually, it will probably slow you PS recovery - exactly what you don't want and your B+ would drop a little. You are running small final capacitor values so I think recovery will be very important.

When I was designing the PSU for my next SET amp - a few years ago now - I digested a lot of info from here, elsewhere and various articles, deciding that a Pi filter would be the way to go for a SET amp (putting aside flywheel, LSES etc. for now). The PS would have low impedance down to frequencies of interest, fast but critical-ish damped recovery, and sufficiently low ripple (which is not as low as most provide); these objectives affect one another. From memory, I calculated the final capacitor size to give me low enough impedance to my output tube, then calculated roughly the resistances I'd need for sufficient recovery times (40mS or so). Once I had some constants to work with (PS TX resistances, rectifier types, choke L and DCR etc.) I simulated and refined in PSUD... a lot. I was able to meet my criteria, but could not do it with off-the-shelf parts... the choke being perhaps the most important component. I ended up with 5U4G - 10uF (metalised film) - 7Hy (<10 Ohm DCR) - 120uF (metalised film) per channel.

When selecting a choke for use in a Pi filter, use sufficient Hy to keep your ripple under control (in combination with cap sizes etc.) and go for the lowest DCR you can, while still being satisfactory in other parameters. Problem is, such chokes can be expensive.

As an aside, I ran PS calculations and simulations for a range of commercial and DIY SET pre and power amplifier designs... most were pretty horrible, with cLCLC PS being some of the worst. Weird resonances, poor recovery, (what would be) audible ripple, ringing, glacial recovery...

Apologies if some of the info is vague - it was over a year ago and I've forgotten much!

Cheers,
91.

"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein

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