Runoffgroove brittania help needed

[Jordash]

Hey guys, I'm sorry I only ever seem to post on here when I have problems! I'm just finishing off a runoffgroove Britannia pedal, which I can't wait to try, but I'm having some issues.

The overall volume I get at the output is very quiet with no over drive. I'm also having issues biasing q4, I can't get the voltage anywhere close enough. Here are a couple of gut shots along with the voltages:





Input voltage - 8.98

Q1:
G - 0
S - 0.62
D - 6.01

Q2:
G - 0
S - 0.67
D - 4.99

Q3:

C - 8.51
B - 5.54
E - 4.95

Q4:
D - 6.49
S - 6.42
G - 5.94

U1:
1 - 4.21
2 - 4.21
3 - 3.83
4 - 0
5 - 4.17
6 - 1.43
7 - 7.91
8 - 8.51

The only part sub I can think of is using clear red leds, could this be causing issues?

Any help would be really appreciated.

[GibsonGM]

Hi, don't worry about posting looking for help, everyone starts there!   Then later you can help others.  Nice to see you using perfboard - i do everything with it, for good or bad.

Your FET voltages look good except for Q4 (as you noticed)....something is probably not wired right there. I'd expect your source to be closer to zero, and you show 6.42v!!    Maybe that 1K isn't going to ground, but somewhere else?  Gotta go over it with a magnifying glass, and use your meter to be sure how it's wired up.  Maybe a solder blob has caused a short.

**The LEDs are there to clip when the signal goes above a certain threshold...all a sub would do is either clip earlier (more dirt) or not clip (less dirt).  If you DO clip and get dirt, the signal will be quieter; if you don't clip, you get more volume.  Just how it works.

Check all connections to Q4, let us know what's up.

Here's the schematic:  http://runoffgroove.com/britannia.html

[PRR]

> Here's the schematic:

Thanks.

> I'd expect your source to be closer to zero

Gate also.

I can't see any single wiring error which could cause both voltages to be way high. Even if source is not tied through the 1K to ground, and the gate has back-broken, still there are the two diodes on the gate so that can't go over 0.6V.

Bright light, clear mind, good look.

[Jordash]

Guys,

Thanks for the advice. A fresh look this morning and I spotted a missing link from q4 to ground, fixed that and I get sound! It's pretty good although I struggle to get unity volume, it's pretty quiet unless the gain is up high. Also the crunch isn't very smooth, maybe I'll try swapping out the less and see if there's much of a difference.

Again, thanks for the help.

[GibsonGM]

Glad you got that sorted out!

Going back to the LEDs now seems to make sense.  Their forward voltage will determine when you clip, of course.

Have you ever used an audio probe?  (Search on this forum if not).  Lets you hear what each stage is doing; very useful.

[duck_arse]

hey jordash!

I think you might be missing a connection from the 8k2 to the 22nf at pin 7. that may well account for your wrong IC voltages posted.

[Jordash]

Amazing spot! That's it, it sounds great! Cheers guys you're awesome.

[GibsonGM]

Good eye, DA!     Yup, tons of great help on here!   
Enjoy the pedal, it looks like it sounds nice (lol). 

[duck_arse]

excellent.