1176ln rev.7 help

fuzzbox

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Jun 4, 2004
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95
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Montreal, Canada
I was trying to adjust it according to the manual I downloaded from jbl.
Problem is my 20:1 and 12:1 don't work. When I depress one of those 2 it seems to bypass the limiter. I noticed C4 is alittle discoloured.(silver mica)
could this be what is causing the 2 ratios not to be functioning? I checked the voltage on the 2 test points in the manual. collector of Q8 should be +30v +/- 0.5 I'm getting +33v, neg voltage -10 +/-0.5 tested at case of IC1 I'm getting -9.8v.

Anyone have Idea's?
 

gyraf

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Aarhus, Denmark
C4 should not have anything to do with that.

The ratio switches in 1176 does two things: It step-attenuates signal going to the rectifier (setting rectifier gain, thus ratio), and it adds a DC offset to the Q-bias (altering threshold so average compression stays more or less the same over different ratios).

My bet is that the ratio switches are either broken or dirty. Try cleaning them, and use your Ohm-meter to check that they work right. And while you're at it, check that connections to the main PCB are alright.

Jakob E.
 

fuzzbox

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Joined
Jun 4, 2004
Messages
95
Location
Montreal, Canada
Thanks Jakob,
It was a broken jumper on the switch. Not an easy find. The wire is a covered in a yellow plasic jacket, the jacket was stuck to the pin but the wire was broken. Thanks for the help.
 
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