2. amps-preamps
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ARC LS25 mkII adjustment

Does anyone know the procedure to adjust the LS25 mkII preamp? I am considering swapping tubes with new ones and would like to know how to adjust the 2 trimmers that looks like sets the voltage for the tube bias.

I don't have any documentation on where to measure and what to set to. Anyone have any experience with this preamp?
jazzgene
jazzgene OP
145 posts
 
Gmuffley,

I see. Do you know what to look for to confirm the trimmers are set up correctly? I am the 2nd owner of this preamp and want to make sure everything is set up right. I suppose you are to measure at some point on the board and use the trimmer to set it to a specifice voltage. Do you know the specifics?
gmuffley
132 posts
 
There are no voltage readings on the ARC schematic, but you could check the voltage drop across the 1 K source resistor; it should be approximately equal. Unless you know someone fooled with it, I would not worry.
rrog
1,958 posts
 
Jazzgene, Did you change the adjustment?
jazzgene OP
145 posts
 
I know someone did swap and adjust the amp. I was told it was John Rutan at Audio Connection.

I do want to confirm it is all good.
jazzgene OP
145 posts
 
Gmuffley,

R10 and R11? Or the 1k trimmer itself? I guess I can measure the voltage drop at RV1 and see if the 2 channels are similar.
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