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Son of Screamer - low output help please


 
6/12/2004 3:14 PM
Dave Zeryck
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Son of Screamer - low output help please
Fired up my Son of Screamer (Tubescreamer without the input & output buffer stages, as per Jack O's schem) today. Quiet, no hum or hiss.  
 
BUT - though I get a signal, it is weak.  
Gets stronger as you crank up Drive or level, but weak as a kitten.  
Gets less trebly as you crank down treble, so the pots appear to be connected correctly.  
 
All grounds check OK - input sleeve to output sleeve, to pot bodies, all grounded. Grounds on board check OK. Checked the IC in another stompbox, it works  
 
Voltages  
 
JRC4558 pins:  
1 - 4.5v  
2 - 4.5v  
3 - 4.5 v  
4 - 0 V (ground checks OK to output sleeve)  
5 - 4.5 v  
6 - 4.5 v  
7 - 4.5 v  
8 - 9 v  
 
R1 and R2 both at 4.5 v  
 
POTS  
 
Tone 1, 2, 3 lugs all 4.5 v  
Level 1 & 2 - 0 v  
Level 3 (goes to ground & checks OK)  
Drive 1 & 2 - 4.5 v  
 
What makes sense is no DC on the Level pot as the 1 uF C6 cap couples that.  
 
What worries me is the 4.5v in the feedback loop (pins 1 & 2, first stage of the opamp). Shouldn't the cap C2 off the feeback loop to Vr (I use a .1mF though Jack specs a .05) block the DC into the feedback loop?  
 
Any hints?  
I got the schem from an article on GEO but you can quicklink it here:  
 
http://www.geocities.com/CollegePark/Quad/1290/scream.gif  
 
thanks in advance
 
6/13/2004 1:16 AM
Dave Zeryck
email

Fixed...no action needed.
 
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