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
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.
rrog
1,958 posts
 
I think John probably knows better than to change those adjustments.

If it was my preamp and I suspected adjustments have been changed I would ship it to Audio Research, so I know it is working properly.

I think a lot of audiophiles try equipment that isn't working properly or not broken in and decide they don't like it. These hybrid preamps take a few days of warm up to start sounding their best.
jazzgene OP
145 posts
 
I don't know John Rutan but have heard good things about his business. I don't think he's a tech though. All this is what I heard from the previous owner. Not that I don't trust him but I just want to make sure the amp is working properly.

Found a schematic for the LS25 mkII. I think I got it now so I will check the voltage tomorrow. Right now, I am going to enjoy the Yanks bash the Rangers again!
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