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Old 31st August 2012, 01:26 PM   #2881
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Quote:
Originally Posted by ashok View Post
Is it on one of the pages of this thread ?
Yes, and you will find many detailed photos of this exceptional realization too.
Look this post and before:
Simple Symetrical Amplifier
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Old 3rd September 2012, 01:20 AM   #2882
shaan is offline shaan  India
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Today I put my ear over the speaker and...

Click the image to open in full size.

There is HUM!

Faint, but present... normally not detectable... but head too close and "mmmmmrmrmrmmmrmmrmrmrrmrm".

I increased the fb current-feed resistors from 1k2 to 1k5, and the hum almost vanished. But, Iq is now 70mA; and only 3mA through the VAS.

I suspected the PSRR. Off to my PC and simulated the following, a 15V capacitance multiplier. Seems okay in the sim. I was wondering whether others have experience with it, there. As it is known that the +-15V must be as clean as possible. Please. Or should I just double parallel-to-zener capacitance?

Thanks in advance.

P.S.- NO complaints about the music. It's as good as it was. With 1k2 current-feed resistor of course.
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Old 3rd September 2012, 01:38 AM   #2883
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Originally Posted by shaan View Post
There is HUM!
Are your grounding well designed (star) ? Did this hum stay the same when no source connected ?A capacitance multiplier is a good (very good) soundig choice for main power. For +-15 v, i would prefer a low noise regulated circuit.
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Old 3rd September 2012, 02:11 AM   #2884
shaan is offline shaan  India
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My grounding is star. The hum is there with no source connected or input short to ground or zobel at the output. Otherwise the amp is very stable and sounds superb.

I think I will start with doubling the capacitors first.
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Old 3rd September 2012, 03:07 AM   #2885
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My grounding is star.
Return line from speakers direct to the common point of the PSU? Input grounds isolated from chassis and amps et direct to this point too ? Experiments for the best grounding point on the chassis ? No oscillation ?
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Old 3rd September 2012, 04:25 AM   #2886
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I use a cap multiplier on my TSSA. Without it there was a small hum but with the multiplier it is dead quiet.
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Old 3rd September 2012, 05:37 AM   #2887
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Quote:
Originally Posted by shaan View Post
[LEFT]There is HUM!
The power supply is common to the two channels? If so, in each case it is necessary to look for other connection point ground.
This can be time consuming.
To avoid this, apply a separate power supply. For each amplifier left and right channels of their own, independent.
Increasing the capacity of the filter capacitors will not help.

Last edited by Svjatoslav; 3rd September 2012 at 05:50 AM.
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Old 3rd September 2012, 05:56 AM   #2888
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My build is double mono.
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Old 3rd September 2012, 07:02 AM   #2889
shaan is offline shaan  India
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Quote:
Originally Posted by Esperado View Post
Return line from speakers direct to the common point of the PSU? Input grounds isolated from chassis and amps et direct to this point too ? Experiments for the best grounding point on the chassis ? No oscillation ?
Yes.

Quote:
Originally Posted by Svjatoslav View Post
The power supply is common to the two channels? If so, in each case it is necessary to look for other connection point ground.
This can be time consuming.
To avoid this, apply a separate power supply. For each amplifier left and right channels of their own, independent.
Increasing the capacity of the filter capacitors will not help.
I built only a single board. I am talking about the capacitors parallel to the zeners. Thanks.

Quote:
Originally Posted by Joachim Gerhard View Post
My build is double mono.
I plan to do the same.
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Old 3rd September 2012, 07:03 AM   #2890
shaan is offline shaan  India
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Quote:
Originally Posted by Joachim Gerhard View Post
I use a cap multiplier on my TSSA. Without it there was a small hum but with the multiplier it is dead quiet.
I was wondering if a cap-mult could help with the feedback current supply, in Class-AB SSA.
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