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Toroid transformer noise
Toroid transformer noise
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Old 30th January 2018, 02:09 AM   #41
liquidair is offline liquidair  United States
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Join Date: Aug 2005
Quote:
Originally Posted by SemperFi View Post
So its not the toroid! No need to spend time on that... It must be the rectifiers or something in the supply circuit. Are u using full wave rectification on all windings? If half wave u may build dc bias on the core since its not a symmetrical load. How many secondary windings? Is there a winding being used to supply several rectifier/circuits?
Ya, and I even wonder about the rectifiers since I've tried rotating the entire unit and even gotten below it. I would think (and could be wrong) that the rectifiers would be more of a electrostatic issue, so a huge chunk of grounded steel in the way would mop that up.

No, only fullwave on 3 windings and only 3 rectifiers. The aux winding supports relays and then a digital uC section, so I step the voltage down from 12V (relays) to 5V (uC) with a regulator to isolate. The ground takeoff for this supply is at the output cap of the 5V regulator.
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Old 30th January 2018, 02:50 AM   #42
liquidair is offline liquidair  United States
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Join Date: Aug 2005
Quote:
Originally Posted by esl 63 View Post
c92 c118 c125 put 10ohms in series
c97 c121 c126 remove...
c137 10 ohms in series
10 ohms in series with F1
0,2 ohms in series with F2 and F3
And dc blocker on the primary
Now it will be dead quiet!!
Thank you! I tried most of this.

Removing c97, c121 and c126 made a huge difference to the 1-5kHz range. Improvement could have been 10dB or more in that frequency range.

10 ohms in series with the slug caps did very little, potentially an improvement in the 3-7kHz range.

The rest were destructive so I was hesitant, but I did put 10ohms in series with F1 and it may have helped a bit but nothing super obvious.

Interestingly, I tried removing C120 and C128 based on trobbins' idea, and it seemed to lower the 120 and 240 Hz range, but it also seemed like I was getting more upper harmonics and that the noise seemed to modulate more. I then tried removing C94 and C96 ("series cap 2 in the HV supply) and the noise was 10dB higher across the entire range....which makes me wonder.

Then I tried swapping the XFMR leads on the Aux supply to see if I could possibly use phase of the charge pulses to cancel at least the LV supplies, no improvement.

But I went back and compared to the professional unit and we are actually beating or tied with it on the spectrum analyzer test. So I'll take this as a victory so far.
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Old 4th February 2018, 04:24 PM   #43
esl 63 is offline esl 63
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Join Date: Aug 2010
More improvements?
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Old 10th February 2018, 06:58 AM   #44
basreflex is offline basreflex  Spain
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Join Date: Oct 2007
I just unwound a 2kw german made toroid power transfoermer of an audio power amp. it had a screen between primary and secondary, it had a magnetic screen made of the same toroid magnetic strip material , wound 2 turns around the whole transformer. impressive. a custom built sedlbauer ..
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