How do I adjust the symmetry on my mono amps

MiL · 1st March 2011, 10:01 PM

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

nigelwright7557 · 2nd March 2011, 12:37 AM

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.

MiL · 2nd March 2011, 07:04 PM

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

sreten · 2nd March 2011, 08:04 PM

Hi, I would assume it adjusts output dc offset, very simple, rgds, sreten.

MiL · 2nd March 2011, 08:08 PM

Hi Sreten,

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

Thanks/Mike

sreten · 2nd March 2011, 08:35 PM

Hi, not all, you simply use a DC voltmeter, rgds, sreten.

MiL · 2nd March 2011, 08:41 PM

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

richie00boy · 2nd March 2011, 09:05 PM

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.

MiL · 2nd March 2011, 09:12 PM

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

2nd March 2011, 12:37 AM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	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. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

2nd March 2011, 08:04 PM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, I would assume it adjusts output dc offset, very simple, rgds, sreten. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

2nd March 2011, 08:35 PM	#6
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, not all, you simply use a DC voltmeter, rgds, sreten. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

2nd March 2011, 09:05 PM	#8
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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2nd March 2011, 07:04 PM	#3
MiL diyAudio Member Join Date: May 2010	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

2nd March 2011, 08:08 PM	#5
MiL diyAudio Member Join Date: May 2010	Hi Sreten, Well I am not too knowledgeable in this area. Is it still the same measurement as suggested by nigelwright? Thanks/Mike

2nd March 2011, 08:41 PM	#7
MiL diyAudio Member Join Date: May 2010	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

2nd March 2011, 09:12 PM	#9
MiL diyAudio Member Join Date: May 2010	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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