How do I adjust the symmetry on my mono amps - diyAudio
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Old 1st March 2011, 10:01 PM   #1
MiL is offline MiL  Sweden
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Default How do I adjust the symmetry on my mono amps

Hi All,

I recently refurbished my Ion systems monoblock with new contacts, electrolytes etc. I am not an expert in amplifier construction though I know how to use a soldering iron. In the pictures you can see that I managed to change the bias trim pot and that one is very easy to adjust. However if you look at the symmetry trimpot, I did not dare to change it because I do not know how to adjust it. I would like to change it for a Bourne trim pot like I did for the bias adjustment hence the old trimp pot settings where all over the place. Any one on this forum who know how to adjust the symmetry?

Any advice is greatly appreciated.

Please see attached images of one of the mono amp boards 2 x after re furbish and 1 x before solering all the new components.

Thanks/Mike
Attached Images
File Type: jpg mono amp board 1.jpg (106.3 KB, 80 views)
File Type: jpg mono amp board strip.jpg (109.8 KB, 76 views)
File Type: jpg Monoampboard_2.jpg (265.4 KB, 76 views)
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Old 2nd March 2011, 12:37 AM   #2
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I would have guessed you put a scope on the output, apply a sine wave and check for symetry. i.e. +/- phases are equal in amplitude.
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Old 2nd March 2011, 07:04 PM   #3
MiL is offline MiL  Sweden
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Hi,

Thanks for the input! So feeding the low level inputs with a sinus signal will do it, perfect.
I am pretty sure these old trim pots are totally off its settings just like the ones for the bias were.

Cheers/Mike
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Old 2nd March 2011, 08:04 PM   #4
sreten is offline sreten  United Kingdom
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Hi, I would assume it adjusts output dc offset, very simple, rgds, sreten.
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Old 2nd March 2011, 08:08 PM   #5
MiL is offline MiL  Sweden
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Hi Sreten,

Well I am not too knowledgeable in this area. Is it still the same measurement as suggested by nigelwright?

Thanks/Mike
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Old 2nd March 2011, 08:35 PM   #6
sreten is offline sreten  United Kingdom
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Hi, not all, you simply use a DC voltmeter, rgds, sreten.
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Old 2nd March 2011, 08:41 PM   #7
MiL is offline MiL  Sweden
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Hi Sreten,

I managed to measure over the resistance for the bias setting due to that it is marked on the circuit board but symmetry, no. Though I guess it is enough to measure the voltage of each output when the low level input is feed by a tone generator?

Thanks/Mike
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Old 2nd March 2011, 09:05 PM   #8
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No, just connect a voltmeter to the amp output with no speaker or load connected and no input or source connected. Adjust the pot to give as close to zero as you can get it.
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Old 2nd March 2011, 09:12 PM   #9
MiL is offline MiL  Sweden
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Hi Richie,

Well, thanks for the corrections and instructions as you understand I do not know much about these things, I'm a chemist This seem to be a very easy adjustment to perform!

Many thanks/Mike
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