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Same Thing I'm Doing

24.27.41.140

Triode_Kingdom

In Reply to: RE: Choke for Music Reference RM-9 posted by audioeyedoc on April 07, 2021 at 13:41:38

The amp projects I'm starting now are all doublers. I'll be using a Hammond 155T after the doubler caps, then a reservoir cap. The choke is rated 0.5H, 300 mA, 30 ohm. This might not seem like much inductance, but it significantly reduces ripple and presumably noise. The second cap doesn't need to be too large. The doubler caps each pass 60 Hz current, but the reservoir cap is operating at 120 Hz. Also, because the doubler caps are in series, the load only sees half the capacitance of each in terms of storage and output impedance. In any event, a single 500V cap (or equivalent) will work well in the second position. As an aside, you might consider redesigning the bias supply to eliminate the Zener diodes. If the bias voltage can "track" B+ changes, potential fluctuations in output stage bias current will be minimized.

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Buy Chinese. Bury freedom.

Edits: 04/09/21

Follow Ups:

RE: Same Thing I'm Doing - rage 07:22:04 04/20/21 (0)
TK - would you say there are any advantages to 30 ohms DCR vs 10 ohms DCR given the same amount of inductance? I know you typically say the supply impedance is set by the final cap - so maybe the DCR isn't terribly important?
RE: Same Thing I'm Doing - audioeyedoc 14:49:28 04/15/21 (1)
What should the value be?I've read if the capacitance is too high in this position-the B+ may go too high.I have a 100mf/500v and a 470mf/500v.
- RE: Same Thing I'm Doing - Triode_Kingdom 12:14:30 04/16/21 (0)
  "I've read if the capacitance is too high in this position-the B+ may go too high."
  
  The voltage won't move substantially higher, but it will sag less under load. That's what we want for an AB1 amplifier, because it tightens the bass response and reduces IMD. There's a point of diminishing returns, of course. I suspect most of these power supplies reach an optimal value when the capacitance after the choke roughly equals the capacitance ahead of it. IOW, if the doubler consists of two 200uF caps in series, about 100uF after the choke would be appropriate. That's not any sort of rule, just my own gut feel for all this.
  
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  Buy Chinese. Bury freedom.

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