Help with Noisy Guitar Pedal PLEASE....

[sonolink]

Hello all
I would appreciate your help with this one please. Here’s the story:

I built a Valvewizard Glass Blower Booster (http://www.valvewizard.co.uk/glassblower.html) on vero board following the SabroTone Layout not long ago (http://www.sabrotone.com/?attachment_id=2218). I ran into some problems and followed Midwayfair’s suggestion to make some changes (http://groupdiy.com/index.php?topic=61496.0)

I tested the pedal on my 100w Engl Sovereign guitar amp and all was fine…
A couple of months later a friend borrowed the pedal to try it out and reports back that it doesn’t work !!!

He is plugging it into a 18w Plexi clone and basically the symptoms are that the pedal doesn’t let the sound through and the sound is heavily distorted and cut. I got the pedal back and checked it on my amp again and noticed that if I put it at the END of the pedal chain or on its own everything is ok but if I put it at the BEGINNING of a pedal chain, when I engage it or another pedal is engaged the sound is awful, kinda distorted and destroyed...

So I went with the pedal back to my friend's to check it out on his gear. Surprinsingly, on his amp the pedal sounds awful all the time and the amp has barely any output unless strung hard and even so the sound is crap.

I checked with another pedal I built without the mod suggested by Midwayfair and this one works fine but I’m not sure that the problem is in the mod since the mod was relevant to switching…

I’ve attached a clip with the crappy sound here:
https://soundcloud.com/thesoundkitchen/gtr-booster-ocd-amp

Any ideas please?

Thanks
Sono

 

[CJ]

replace Q3-J112

 

[midwayfair]

replace Q3-J112

I think he removed the JFET switching IRRC.

OP, measure voltages on everything; also measure voltages on the input and output. What you describe can be a symptom of having DC on the input or output.

Also, verify the value of the 100R on the output. Make sure you didn't use 100K.

 

[sonolink]

Thanks for your quick replies

I did take J112 out following Midwayfair's suggestion

I'll check and report back.
Thanks again
Cheers
Sono

 

[sonolink]

Hi again

Opamp voltages are:

P1: 5.22vdc
P2: 5.22vdc
P3: 2.6vdc
P4: 0v
P5: 5.22vdc
P6: 5.22vdc
P7: 5.22vdc
P8: 8.77vdc

Voltages are the same in on or off switch position.

Output resistor (r11) is 100R.
Output jack has 5v between Tip and Sleeve pins.

Maybe that's the problem?
Anything else I should measure?

Thanks for your help
Sono

 

[midwayfair]

Your output cap is bad, shorted, or missing.

 

[sonolink]

That would be C7  right Jon?

 

[sonolink]

You were right
C7  wasn't soldered right.
Now it seems to work ok

One question: why on my 100w it worked ok at the end of the chain but not at the beginning?
And why didn't it work AT ALL on my friend's amp?

Thanks a lot for your help
Cheers
Sono

 

[midwayfair]

You were right
C7  wasn't soldered right.
Now it seems to work ok

One question: why on my 100w it worked ok at the end of the chain but not at the beginning?
And why didn't it work AT ALL on my friend's amp?

Thanks a lot for your help
Cheers
Sono

Not all amps have an input capacitor. Maybe yours does. If you get DC on the grid you can make no sound come out (and potentially damage the amp).

I have no idea what else was in your pedal chain to know why it didn't work there.

 

[sonolink]

A Fulltone OCD...