In a FWct +/- supply, can the + and - rails draw slightly different currents?

keto · 2721

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Offline keto

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on: October 24, 2011, 03:16:50 AM
Hey all, I've got the + and - HV supply for an active crossover platform up and running. At the moment I've referenced the caps and bleeder resisters to ground, but not the 0C3 "center tap" (which now sits at about 5vdc). If I ground the 0C3s, they will draw slightly different currents from the + and - rails of the FWct supply, right? Is this okay? Thanks! --keto

Tom Jones

Offline Paul Joppa

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Reply #1 on: October 24, 2011, 09:21:29 AM
They can draw completely different currents.

Paul Joppa

Offline keto

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Reply #2 on: October 24, 2011, 07:22:26 PM
Great! I've got the VRs' "center-tap" grounded now.

After trying a bunch of 0C3s and 0D3s and getting varying AC readings at their +/-115vdc and +/-153vdc nodes, of between 7mvac and 12mvac, I decided to try adding a choke-input (MQ BCM-8 12H/75mA) to the PSU and using 0B3s.

That seemed to work better, yielding a consistent 5.5mvac at their +/-84vdc nodes. And only with the 0B3s did I get a consistent reduction in mvac readings as I progressed from L to C1 to C2 to VR. So the 0B3s are smiling.

Well, I think I'll go ahead with my initial 4-tube circuit (a pair of LR4 300hz low-passes, and two pairs of CF buffers) using the 50K resistors I've got on hand, and see if I can get away with the relatively low +/-84vdc.

Many thanks!

--keto

Tom Jones

Offline xcortes

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Reply #3 on: October 25, 2011, 04:50:51 AM
Suddenly the "wasted psu space" became filled.

Looking good so far!

Xavier Cortes

Offline Grainger49

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Reply #4 on: October 25, 2011, 04:55:26 AM
How about a bypass cap at the output of your OD3/OC3 as used on the FP III?  I like KK Teflons, I think I remember that Dock did too.
« Last Edit: October 27, 2011, 12:11:00 AM by Grainger49 »


Offline keto

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Reply #5 on: October 25, 2011, 09:33:06 AM
I meant to say that there wasn't enough space and that the leads were too long. It would also be useful to have more lateral space between pairs of 12AU7's, for the filters. I tried the bypass cap, from 10 to 47nF and it didn't measure any differently. But I'll come back to that.

Tom Jones

Offline keto

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Reply #6 on: October 25, 2011, 04:37:44 PM
I've taken a step back and am using the original CRC filters and the 0D3s, which at the last check measured 10mvac on their +/- 150vdc nodes. Well, I hooked up a pair of cathode followers, 56K loads, -6Vg, 3mA and the circuit is passing signal and no noise. Whew!

Tom Jones

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