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Old 2nd November 2004, 03:28 AM   #1
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Default Help me design pre-amp PS

Been trying to get rid of hum in my pre-amp (6sn7 transcoupled to a tango np126)

I have on hand two chokes from Hammond, a 20H and 12H, and Black Gate wkz 100uf+100uf 500v. I tried LCLC (20H, 100uf, 12H, 100uf) and the hum is terrible.

I tried CLCLCR (1 uf, 20H, 100uf, 12H, 100uf, dropping resistor of 20k to reach 260V), hum was not too bad but still heard from listening position

Any suggestions on how to improve my filtration? Been thinking of doing CLCLC (10uf, 20H, 47uf, 12H, 47uf) then split into two RCR (1k, 100uf, drop R of 20K)

Thanks in advance
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Old 2nd November 2004, 08:12 AM   #2
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Default Re: Help me design pre-amp PS

Quote:
Originally posted by hardcore
Been thinking of doing CLCLC (10uf, 20H, 47uf, 12H, 47uf) then split into two RCR (1k, 100uf, drop R of 20K)
Try just 10uF--20H--100uF
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Old 2nd November 2004, 03:28 PM   #3
mcs is offline mcs  Denmark
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With all those chokes and big caps, I very much doubt that power supply ripple is your problem.

Have you tried DC on the tube heaters?
Have you tried moving the power supply transformer and chokes far away from the output transformer?
Have you tried shielding the amp/tube (if it isn't already)?

Best regards,

Mikkel C. Simonsen
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Old 2nd November 2004, 04:42 PM   #4
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Quote:
With all those chokes and big caps, I very much doubt that power supply ripple is your problem.
I agree.

Your hum problems may be from other porpuses.I have some humm problems with my amp.Notice that my ripple on filtering is tooooo small.But hummmmmm.
Try to put away the power tranny from the circuit.And be careful with the position of chokes,interstage tranny and power tranny.Keep the safely 90 degrees placement at each other.
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Old 2nd November 2004, 08:58 PM   #5
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Default Re: Help me design pre-amp PS

Quote:
Originally posted by hardcore
Any suggestions on how to improve my filtration?
10uF, 10H (2H would do it), 100uF. CLC. Ground the first stage properly and bias heaters with a hum balance control.

Tim
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Old 2nd November 2004, 10:17 PM   #6
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Hi,

I'd rather check earthing/grounding and heater current cables. Simply - check cabling. You can find good papers on earthing/grounding.
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Old 3rd November 2004, 01:46 AM   #7
Enzo is offline Enzo  United States
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And make sure the ground returns for the gain stages are not sharing copper or chassis with the power supply or other circuits. The star ground approach.

Isolate the problem. is the hum 60Hz or 120Hz? Ripple will be 120Hz - assuming full wave rectification. 60Hz is hum picked up from the tranny, the heaters, or poor shielding.
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Old 10th November 2004, 07:32 AM   #8
Blue is offline Blue  Cayman Islands
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As Resident says orientate the iron work to prevent magnetic coupling, and as Enzo says in his US centric way 120Hz or 60Hz which I understand also makes sense in the Philippines, if ripple is the problem, but I doubt it is with the size of chokes, you could resonate them with parallel capacitors but make sure they are well rated as the current in them could be high.
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