Meng volume pot problem

agithegreat · 05:38 PM

Ok, so i bit the bullet last weekend and pulled apart my chinese meng amp (6n1 and 6p1) and i point to pointed it, exactly as it was on the board.

Now, however, i get a high pitched whine everytime i release the volume dial. If i then press the pot again it instantly goes.
There is no DC offset present on the signal lines anywhere that i can see.

With speakers in it also goes quite when the volume dial in not pressed, when it is pressed it acts exactly the same as it did prior to me messing

.

The tubes also seem a little warmer than usual but i measured heater voltage at 6.2v (6.3 is recommended) so i'm happy with that. B+ voltage starts at 300v and drops to around 285v by the time the heater has got warm enough to allow current flow. When i touch the pot this drops to 283v. So 2v drop just as i touched the pot?

Can anyone help?

Frank Berry · 13th August 2010, 05:45 PM

Make sure that the frame of the volume pot is grounded.

agithegreat · 13th August 2010, 06:25 PM

Ermm....... Fixed it

.

Thanks

.
I neglected that the PCB when screwed to the chassis earthed it.
So i just put the signal ground to the chassis and the pot was obviously attached to the chassis.

13th August 2010, 05:30 PM	#1
agithegreat diyAudio Member Join Date: Jun 2008	Meng volume pot problem Ok, so i bit the bullet last weekend and pulled apart my chinese meng amp (6n1 and 6p1) and i point to pointed it, exactly as it was on the board. Now, however, i get a high pitched whine everytime i release the volume dial. If i then press the pot again it instantly goes. There is no DC offset present on the signal lines anywhere that i can see. With speakers in it also goes quite when the volume dial in not pressed, when it is pressed it acts exactly the same as it did prior to me messing . The tubes also seem a little warmer than usual but i measured heater voltage at 6.2v (6.3 is recommended) so i'm happy with that. B+ voltage starts at 300v and drops to around 285v by the time the heater has got warm enough to allow current flow. When i touch the pot this drops to 283v. So 2v drop just as i touched the pot? Can anyone help? Last edited by agithegreat; 13th August 2010 at 05:38 PM.

13th August 2010, 05:45 PM	#2
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	Make sure that the frame of the volume pot is grounded. __________________ Frank

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13th August 2010, 06:25 PM	#3
agithegreat diyAudio Member Join Date: Jun 2008	Ermm....... Fixed it . Thanks . I neglected that the PCB when screwed to the chassis earthed it. So i just put the signal ground to the chassis and the pot was obviously attached to the chassis.

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