Octavia Not Working Properly

[flyguy]

I am building an Octavia by the General Guitar Gadgets instructions (here's a link).  I bought the PCB from them, and used exactly the parts specified (parts list) except for the intensity pot which is still a 1K linear pot, however it "notched" so that instead of turning freely it has little places where it stops. (hope that makes sense).

The effect works fine when bypassed, however when I engage it, there is an awful crackling noise, and the guitar cannot be heard at all. I've tried moving the circuit board around, jiggling the wires on the input/output jacks to see if it's a short, but I don't believe it is a problem with the wiring.

Here are the voltages:

Power: 8.99v

Transistors:

Q1:

C - 1.88v
B - 1.6v
E - 2.25v

Q2:

C - 8.98v
B - 2.4v
E - 2.0v

Q3:

C - 3.5v
B - 2.7v
E - 2.1v

The two diodes are also getting a few hundred millivolts a piece.

Anyone know what's going on here?

[10acErnie]

Hi,

I'm new here too. I'm guessing from your post you already read the thread "What to do when it doesn't work"

I'm new at the diy stuff (well after taking about 15 years off!) and I can't really help you much except to say that I built the Octavia from the same PCB about two weeks ago and it sounds great. So be assured that there is hope!

Oh, there was one project I did recently (can't remember which one) where the input and output jacks were reversed on the layout that was online. Try plugging into the output and out from the input. That may not be it but it'll only take a second to try.

[flyguy]

Hi Ernie,

Thanks for the tips (and yes I've read that thread!), but unfortunately it still does not work. I've taken the entire thing out of the case and made sure nothing is grounding out, and like I said, when bypassed, my guitar sounds perfectly normal, but when I engage the effect and turn up the volume pot, there is this horrible scratching noise (no matter what I set the intensity too). Voltages look right as well. I'm thinking it's one of the components on the board, but I really don't know how to go about finding which one.

Any suggestions would be really appreciated!

[KORGULL]

I think the voltages for Q1 are not right. The emitter shouldn't be higher than the base and collecter. Check the resistors around Q1 for correct values for a start. Maybe you mixed up the 220 ohm with the 220K?

[flyguy]

I think the voltages for Q1 are not right. The emitter shouldn't be higher than the base and collecter. Check the resistors around Q1 for correct values for a start. Maybe you mixed up the 220 ohm with the 220K?

I checked the resistors around Q1, and they are all the appropriate values. So I guess that isn't it.

Any other ideas?

[bluesdevil]

Here's what I do when something doesn't work for me:
Double check component values AND placement.
Check wiring to pots and jacks. Make sure footswitch is wired correctly.... sometimes it is better to remove bypass switch and just wire jacks directly to input/output.
If that doesn't do it, check for shorts or bad solder joints. Get out your DMM (digital multi-meter) and set it for "continuity" in beep mode... look in your manual on how to set it.  This will help you find traces that are shorted together. IF you find a short, use a utility razor (be careful!!) and run it between the traces.
   If you've done all that and it still doesn't work, chances are it's a cold solder joint. Check for any wiggling components and reheat solder until it flows smoothly over the connection.
      If you don't have a DMM, you can still use the razor and reheat suspicious looking joints. Hope that helps you get it up and running.... good luck!!!

[petemoore]

You need to figure out Q1 bias, maybe the transistor pinout...
 I use a DMM for checking actual values of resistors, in circuit thought this can take thinking through the current paths, doing math, or pulling one end of a resistor to see what it's value is. I'd just check points from V_ and V+ to see what resistances Q1 is seeing from those points, and generally check resistances around Q1.

[flyguy]

This morning I resoldered all of the components, as well as changed out two caps that I thought might have been buggy, and I also resoldered the switch, input jack, pots, and double checked all components (continuity and all).

And... the pedal worked for maybe a minute or two after that, but then it went right back to what it was doing before with the buzzing and no guitar signal.

Anybody else know what this could be?

And what's transistor biasing? Would this still apply even if the effect worked for me before?

[bluesdevil]

Good to hear you got it to work for a short bit.... you're almost there!! Check your ground wires.  It sounds like a loose wire connection to me.