Buzzing and oscillation with upgrade

[edwin]

I just installed a dual preamp pan pot and added a q switch to the electronics in my Modulus with Alembic pickups. It's a bit noisy and when the q switch is in the highest q position, it oscillates with a ferocious racket. I'm sure it's a ground problem, but I'm wondering if anyone has a clue about where to start before I dive in.


Boy, does it sound good though!


TIA

[rv_bass]

Edwin,

This might be a place to start:

http://club.alembic.com/index.php?topic=22092.0

[mica]

Is the electronics cavity shielded?

[moongerm]

Would like to hear it once you get her fixed Edwin?

[mica]

Also, does the oscillation happen only in a certain position of the filter? It may be a case of "it's easier to send it in for Ron to fix it"

[edwin]

The oscillation happens regardless of the position of the frequency control, but only when the the q switch is in the highest position.

Is it possible that it does this because it's an older filter module "borrowed" from a Strat Activator?

OTOH, the bass is shielded, but I wouldn't say it's a stellar job. I could spend some more time paying attention to that.

Thanks!

[mica]

Nah, that shouldn't really matter as far as I know. When I told dad about it he's pretty sure that it's going to need his direct attention to figure this mystery out.

[edwin]

Sigh. I'll double check all my connections, but if this is what has to happen, this is what has to happen.

[hieronymous]

Sigh. I'll double check all my connections, but if this is what has to happen, this is what has to happen.

Oh well, you'll just have to make another trip out here!

[edwin]

Sigh. I'll double check all my connections, but if this is what has to happen, this is what has to happen.

Oh well, you'll just have to make another trip out here!

I'd have to set up a go fund me for that.

I'll yank the electronics and see if it happens without the pickups and if it does, just send in the harness.

[edwin]

Update: I sent the circuits to the mothership, got them back about a week later with a couple mods to the filter board, and the oscillation is gone. I kinda miss it in a perverse way. Not really, but it was fun through delay and reverb!

The buzzing was still there, but a bit of copper shielding tape and that was taken care of. I don't understand why Modulus did such a poor or nonexistent job of shielding back in the day.

Thanks, Mica and crew for the quick turnaround! The bass sounds fantastic now!

[mica]

You'll notice there is an option on the upgrade page to specify for GUITAR or BASS. You heard the bass values on the guitar filter! Le ooops!

[edwin]

Now I'm confused. I grabbed a filter out of a guitar and put it in a bass. Is this wrong? Sounds pretty good to me.

[mica]

You can do that with no problem. However, the values of the components when we add a Q-switch are specific to bass or guitar.