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Old 13th August 2003, 04:32 PM   #1
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Default Buzzing in A40

the a40 is a monoblock design but sharing the same chasis
on the left channel buzzing is high but on the right channel buzzing is very high. Both their ps are soft regulated by a caps multiplier. BUt a sawtooth waveform on the caps is present
buzzing is really loud. For the jfet current source, only the resistor option is used .any ideas to help solve the problem
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Old 13th August 2003, 05:51 PM   #2
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Have you tried caps across the current source resistors?

However, if the buzzing is "really" loud this may not be the problem.
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Old 13th August 2003, 06:22 PM   #3
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It was quite common for people to get an N channel Jfet
(used in the current source which biases the two diodes
which in turn bias the main current sources) which has a different
pinout than the one used in the project. If this is the case,
there will be excessive current through the Jfet and lots of
ripple voltage will appear at the output of the amp. Check
the current through the resistor Gate to Source on this Jfet
and see if the current exceeds a few mA. If it does, replace the
Jfet and confirm the proper current < 5 mA or so.
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Old 13th August 2003, 08:35 PM   #4
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Don't know if you have the same problem, but i had a hum too, untill i used 2 bridge-rectifiers per PS.

Good luck

Grtz
Nick
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Old 13th August 2003, 11:24 PM   #5
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tried caps across current source, used 2 bridge rectifier per ps must now try jfet current source, snubber network across the diodes, and try cap compensations. Does that help? i understand that is for low pass filter, changing to something bigger would roll off high frequency when feedback, can that reduce the buzzing
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Old 13th August 2003, 11:48 PM   #6
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So, I do understand you correctly that you are currently using a resistor in place of the JFET?

If so, definitely try the JFET first.

What's the amplitude of the sawtooth?
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Old 13th August 2003, 11:56 PM   #7
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sorry i meant the sawtooth on the rectifying cap. is around 0.2volts. Ripple after the caps multiplier is 25mv but sine wave.
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Old 14th August 2003, 12:35 AM   #8
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If you are running 2 transformers you might start with disconnecting power to one of them. I say this because
I had a simmilar problem when I used 2 transformers
in the same chassis the other times I used a singlr transformer
with no problems. If this stops the hum you may have some
weird ground loops. If you still have the hum why not try the
amp without the cap multipler ?

Good luck,
bob12345678
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Old 14th August 2003, 03:00 AM   #9
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without the cap multiplier buzz was there aready. Same level after inserting cap multiplier. would try disconnecting 1 trans. I have tried different grounding scheme, Inserting base resistor on the pin of output trans,lift and isolate ground via 10ohm and 0.1uf. When connecting cd player and preamp, buzz and hum increases. Could be bad wiring layout.
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Old 25th August 2003, 11:42 AM   #10
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Default Ground loop noise

I have (also) build a40 using two separate toroidal
transformers.

Didn't work to use on ground
point for the both power supplys.
Very irritating buzzle noise appeared.

So i builded them as two separate blocks
in the same chassis. Works very fine.
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