Boss RX-100 spring reverb clipping before unity gain: what can I try out ?

[frank_p]

I have this big spring reverb box but one thing that annoys quite a bit is that it clips slightly at unity gain.  Now, I don't know if changing the electro caps or putting some more modern transistors/ICs in there could improve the situation.  I already posted about this box a way back; but right now I have found the service manual.  There it is:


http://manuals.fdiskc.com/flat/Boss%20RX-100%20Service%20Manual.pdf


Do someone have an idea about what could perhaps yield to positive results about the clipping or point me to what measures to be taken on the board to have insight to what is happening.

I can scope and measure, no problems.

Thanks.

[Joe Kramer]

Hey Frank!

Nice reverb unit!  Thanks for posting the schemo too.  To help reduce input clipping, probably the first and simplest thing would be to increase the value of R68.  Try something like 100K.  If that doesn't solve the problem, you could lower the gain around IC1A/IC1B by increasing the resistance of R10 and R29.  Also looks like the clipping diodes around IC2B could be investigated.  You could either use a pair of two diodes in series (four total) instead of that pair of single diodes, or you could increase the series resistances of R14 and R15.  If the clipping is at the xstr input stage, you can reduce xstr output gain there by increasing the resistance of R7, but this will shift the bias point of the xstr, and may make clipping worse until you adjust the values of R3 and R4 for proper bias.

Hope that helps!

Joe

[frank_p]

Hey Frank!

Nice reverb unit!  Thanks for posting the schemo too.  To help reduce input clipping, probably the first and simplest thing would be to increase the value of R68.  Try something like 100K.  If that doesn't solve the problem, you could lower the gain around IC1A/IC1B by increasing the resistance of R10 and R29.  Also looks like the clipping diodes around IC2B could be investigated.  You could either use a pair of two diodes in series (four total) instead of that pair of single diodes, or you could increase the series resistances of R14 and R15.  If the clipping is at the xstr input stage, you can reduce xstr output gain there by increasing the resistance of R7, but this will shift the bias point of the xstr, and may make clipping worse until you adjust the values of R3 and R4 for proper bias.

Hope that helps!

Joe

That is a really good start.  Thanks for the input Joe!  .

Think that the first thing I'll do is probe along around with a sin wave untill I see where it's starts to look strange.  Then I' ll go with your advice.  I would really like that this box could take a bit more input amplitude.

HF