freestompboxes.org

Hey guys,

I've run into a spot of trouble and am struggling to find a way to resolve it.

Basically I have a Fuzz War and OCD in one box with a switch to select between circuits and a main bypass switch, the problem occurs when the Fuzz War is selected I get a high pitched oscillation from the OCD (I presume it's the OCD as the oscillation stopped when I pulled the IC out to kill the circuit). The squeal is there albeit quietly when the pedal is bypassed and increases in volume considerably when the pedal is activated. When the OCD is selected there is no oscillation, everything fine. The Fuzz War works fine when selected but as soon as you stop playing you hear the oscillation.

This is how I have it wired up currently;



Any ideas why I'm getting the oscillation from the OCD? It only happens when both circuits are wired to the selector 3PDT, both work fine when wired independently.

I have tried wiring the bypass switch to ground the PCB input on bypass, PCB output on bypass and also neither, got the same oscillation problem with each method. Have also tried wiring all the grounds to input among various other ground wiring combinations and just can't get rid of it.

I'm at a loss now, any advice would be greatly appreciated!

Cheers,
Graham

Hi Graham,

The wiring diagram looks OK.

Assuming you've wired it exactly as shown, only one of the circuits has its input grounded in bypass mode (depending on the state of switch B). As there's a bit of breakthrough squeal from the OCD, try stepping on switch B (while the unit is still bypassed) and see if the squeal stops.

When you play through the OCD, it is fine, as its input is effectively grounded through your guitar pickups, but when you go to the Fuzz, the OCD squeals. It could be that its input is not grounded. Have you got a pull-down resistor (1-2.2M) across the OCD input ? If not, try one.

Good luck. Keep us posted.

Lucifer wrote:Hi Graham,

The wiring diagram looks OK.

Assuming you've wired it exactly as shown, only one of the circuits has its input grounded in bypass mode (depending on the state of switch B). As there's a bit of breakthrough squeal from the OCD, try stepping on switch B (while the unit is still bypassed) and see if the squeal stops.

When you play through the OCD, it is fine, as its input is effectively grounded through your guitar pickups, but when you go to the Fuzz, the OCD squeals. It could be that its input is not grounded. Have you got a pull-down resistor (1-2.2M) across the OCD input ? If not, try one.

Good luck. Keep us posted.

Hi thanks for the reply

The squeal does stop if you select the OCD with switch B and the pedal is bypassed so as you say perhaps it's input is not being grounded?

I'm not sure about a pull-down resistor as it's a pre-fabbed board, here is the schematic for it though, it looks as though there is one there to me (R1)? I'm not the best at reading schematics though tbh!

Hi Graham,

You have correctly identified R1 as the pull-down resistor in that diagram (not bad for someone who claims he can't read schematics . It might be worth checking that you have this resistor in place and that it is soldered properly.

The other thought that struck me was that you may need to de-couple the power supplies for each circuit. It could be that the fuzz is getting onto the power rails and into the OCD. The OCD should have adequate filtering of its supply, if you have built it exactly as per the schematic, but I don't know what your fuzz has got, so it might be worth checking that.

Do you have any gutshots that we could look at ? We might be able to spot an out-of-place wire or something.

Good luck.