AD30TC channel 2 68k ohm resistor

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Farrerdale Records
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AD30TC channel 2 68k ohm resistor

Post by Farrerdale Records » Fri Apr 28, 2017 4:09 am

It's been some time since I've posted, it was under another name that has since lost the login but my fascination with the AD30 continues.

I had a power scale mod done from London Power done a few years back that was improperly installed and I got back into the working of my amp and fixing it. Its lead me to revisit a mod I've always wanted, to make CH1 and CH1 as identical as possible.

Looking at the schematics for the main board the capacitors on V1a/b are in different order than V2a/b, with C2 being wired different than C16. Depending on what schematics you find, there should either be two 47K (R3/44 and R23/45) resistors in series with a 100K (R4 and R24), for 194K, or a single 91K (R5 and R30) in series again with a 100K for 191K.

It appeared that two 47K resistors were wired in series and inserted into R5 and R30, as I don't have two resistor spaces on my PCB. Not sure if this was factory or the guy who modded it thought he was following the schematics found online.

I changed it to 91K.

Specifically to CH2 I changed R1 from 68K to 91K to match R2 of CH1, seeing that as the major difference. CH2 now seems to be noisier and actually have higher gain than before.

Do I also need to move C2 to match C1?

Will this quiet the noise I'm now getting?

CH1 is fine, no new noise at all, although darker than before. I have gone from JJs to Mullards at the same time and I'm thinking that this is the tube selection as opposed to the resistance change from 194K to 191K.

I want both CH1 and CH2 to be as close as possible, using CH1 for humbuckers guitars and CH2 for single coil guitars, should the question of why be asked.

Please let me know!

Curtis
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