Help please - low output from SOS, check voltages...

[Dave Z]

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

[R.G.]

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?

Nope, having those at 4.5V is correct. With C2 blocking the - input and output from Vr, the output is driven to the DC voltage level of the + input, which also happens to be Vr. That's all correct.

I don't see anything in the DC voltages that is a flaw. I would check other things - wiring, soldering, bad pot, bad jack, etc.

[Dave Z]

OK thanks RG, that I will do....

[Dave Z]

Fixed, used a magnifying glass, missed aconnection right at the start by a tad (pad-board).

Sounds awesome! Time to sell the boutique OD box...