Mark III Questions. R130 and R133/C28

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jrb32
Mark III
Posts: 173
Joined: Wed Jan 31, 2018 8:32 am

Mark III Questions. R130 and R133/C28

Post by jrb32 » Tue Apr 10, 2018 6:01 am

Hi Guys, I've finally finished tracing my III Black Stripe and drew up a schematic.

(well about 95% done technically! Some final things to finish off and double check) Everything with a R, C or D, LDR etc number has been verified and traced by me. This includes LDR supply, EQ etc and should give you an idea about how things work exactly! I also finally understand how the R2 circuit works! Hooray!

However, I have some questions regarding a few weird things that don't make sense to me. I'm not an electronic or amp design guy so apologies! My questions are:

1. Why do people use R130 instead of R109 for the R2 mod? I know people say to replace R130 with a 250K Pot or Trim Pot, but wouldn't R109 be a better candidate for overall R2 volume for the attenuator? Or would this reduce the overall effect of the R2 channel instead?

2. What is the point of R133 and C28? If they were removed in R1 mode the preamp would be basically the same as a IIC+ apart from some component value differences. It just seems odd and I don't understand why they are there!

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PDF Link https://drive.google.com/open?id=1Hwhcz ... 9XKAcg0aeT

Thanks,

Jon

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