Dynaco Pas 3 Hiss from HV regulator - Page 3

SY · 29th April 2008, 10:32 AM

Yes, that ripple is almost certainly grounding. That's the rectifier charging the caps. Time to get out the soldering iron!

Dietz's paper was called, "Understanding and Reducing Noise Voltage on 3-Terminal Voltage Regulators." Originally appeared in EDN. Somewhere on the forum, I posted an exact reference...

edit: Werner Ogiers showed some nice plots:
http://www.tnt-audio.com/clinica/reg..._noise2_e.html

rollo22 · 6th May 2008, 06:10 PM

Sy

I am making tests to find the origin of the problem, incidentally I now use R5 = 120R to get 10mA, but it does not change much.

>> Dietz's paper was called, "Understanding and Reducing Noise Voltage on 3-Terminal Voltage Regulators." Originally appeared in EDN. Somewhere on the forum, I posted an exact reference... <<

Do you have a copy of that article ?

Regards

Rollo

SY · 6th May 2008, 07:57 PM

No, bringing up the current won't help a grounding/layout issue. If you have any pics and/or diagrams, perhaps one of the eagle-eyes can spot the problem.

rollo22 · 18th May 2008, 06:43 PM

Hi
I made some progress, I changed the lower resistor of the reference with 2 150 V Zeners + 1 18 V Zener, a 10 uF 350 V cap across them and it is much much better, hiss and ripple is only about a few mV, looks like random distribution, visible with a 100 gain opamp only.

The noise is noticeable only 30 cm from the loudspeakers and is proportional to the volume position.

I guess now I have to add some cap at the B+ point and start to upgrade the caps/resistors on the line amp one channel at a time.

I cut off the tone control and I will later go with the Spice upgrade (add 1 valve as a buffer) mod but only after I get some decent sound from the standard caps/resistors upgrade.

Any suggestion ?

Regards
Rollo

29th April 2008, 10:32 AM	#21
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	Yes, that ripple is almost certainly grounding. That's the rectifier charging the caps. Time to get out the soldering iron! Dietz's paper was called, "Understanding and Reducing Noise Voltage on 3-Terminal Voltage Regulators." Originally appeared in EDN. Somewhere on the forum, I posted an exact reference... edit: Werner Ogiers showed some nice plots: http://www.tnt-audio.com/clinica/reg..._noise2_e.html __________________ If there's a sucker born every minute, where do the rest of them come from?

6th May 2008, 07:57 PM	#23
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	No, bringing up the current won't help a grounding/layout issue. If you have any pics and/or diagrams, perhaps one of the eagle-eyes can spot the problem. __________________ If there's a sucker born every minute, where do the rest of them come from?

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6th May 2008, 06:10 PM	#22
rollo22 diyAudio Member Join Date: Nov 2005 Location: Milano	Sy I am making tests to find the origin of the problem, incidentally I now use R5 = 120R to get 10mA, but it does not change much. >> Dietz's paper was called, "Understanding and Reducing Noise Voltage on 3-Terminal Voltage Regulators." Originally appeared in EDN. Somewhere on the forum, I posted an exact reference... << Do you have a copy of that article ? Regards Rollo

18th May 2008, 06:43 PM	#24
rollo22 diyAudio Member Join Date: Nov 2005 Location: Milano	Hi I made some progress, I changed the lower resistor of the reference with 2 150 V Zeners + 1 18 V Zener, a 10 uF 350 V cap across them and it is much much better, hiss and ripple is only about a few mV, looks like random distribution, visible with a 100 gain opamp only. The noise is noticeable only 30 cm from the loudspeakers and is proportional to the volume position. I guess now I have to add some cap at the B+ point and start to upgrade the caps/resistors on the line amp one channel at a time. I cut off the tone control and I will later go with the Spice upgrade (add 1 valve as a buffer) mod but only after I get some decent sound from the standard caps/resistors upgrade. Any suggestion ? Regards Rollo