Boss CH-1 and BF-2 distorted signals

[rburgosnavas]

Hello, this is my first post, and I hope this is the right place to ask this.

I have a Boss CH-1 and BF-2 that are giving me a nasty, distorted or buzzy signal when the effects are enabled. Both pedals sound clean when on bypass. About 8 years ago or so, I got the DIY bug and decided to open both of these pedals up and see their guts. I ended up adjusting the trim pots they had and I was pretty happy with the tweaks. Now I notice this ugly fuzz sound coming from both of them, the BF-2 way less usable than the CH-1.

Any leads on how I can fix them?

[Mark Hammer]

When the bias trimpot is adjusted, there is a zone where the delay signal is optimal.  A little higher or lower bias than that, and you will still get delay signal passing, but it will be distorted.  A little higher or lower than that, and you get no signal.

Sounds to me like you need to adjust the bias better.

If I can offer a bit of advice, if you don't have a scope to help with this task, then I would suggest temporarily lifting one end of the resistor that mixes the dry signal with the delay signal so that you ONLY hear delay.  If you have a way of doing so, listen with headphones so that ALL you hear is the delay signal from the pedal and nothing else.  That will help to set it by ear.  Once you've got that down, simply resolder the resistor end you lifted.

[rburgosnavas]

It sounds like I would have to turn the bias trim pot in tiny increments, is that about right?

[rburgosnavas]

Aright, pulled out the pedals, tried to make some adjustments, and here are the results:

For the BF-2 I was able to adjust the bias and it cleaned up really well, but the wet signal is very slightly dirty, I would say a 1 out of five in amount of dirt. The distortion guess away when I play the neck humbucker of my Les Paul; it distorts when I use the bridge pickup.

The CH-1 is actually distorted in both wet and bypassed signals, and I can't tell what the bias control does when I change it because of that.

I read somewhere else in the forum about a possible blown transistor or opamp. Could that be what is happening here?

[Mark Hammer]

I'm not going to venture a guess about the CH-1, because we'd need more information.  But I will say that the BF-2  actually includes a soft clipping circuit to keep the feedback signal in check and not overload the delay chip.  If you look at the schematic for the pedal, you will see a pair of diodes in the feedback loop of the op-amp where input and regen are combined.  The resistor in series with those diodes serves to soften the clipping, but I would still turn the regen/feedback all the way down when trying to figure out why the bridge pickup sounds dirty, because the pedal may well be doing exactly what it was designed to do when getting a hot signal.