Help me design pre-amp PS

hardcore · 2nd November 2004, 02:28 AM

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

Geek · 2nd November 2004, 07:12 AM

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

mcs · 2nd November 2004, 02:28 PM

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

resident · 2nd November 2004, 03:42 PM

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.

Sch3mat1c · 2nd November 2004, 07:58 PM

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

yagoolar · 2nd November 2004, 09:17 PM

Hi,

I'd rather check earthing/grounding and heater current cables. Simply - check cabling. You can find good papers on earthing/grounding.

Enzo · 3rd November 2004, 12:46 AM

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.

Blue · 10th November 2004, 06:32 AM

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.

2nd November 2004, 02:28 AM	#1
hardcore diyAudio Member Join Date: Jul 2003 Location: Philippines	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

2nd November 2004, 02:28 PM	#3
mcs diyAudio Member Join Date: Aug 2003 Location: Denmark	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 __________________ My personal electronics website Remote control kits website

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2nd November 2004, 09:17 PM	#6
yagoolar diyAudio Member Join Date: Oct 2004 Location: Mazowieckie, Jozefoslaw	Hi, I'd rather check earthing/grounding and heater current cables. Simply - check cabling. You can find good papers on earthing/grounding.

3rd November 2004, 12:46 AM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	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.

10th November 2004, 06:32 AM	#8
Blue diyAudio Member Join Date: Nov 2004 Location: Grand Cayman	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.