Long time listener, first time caller... (Muroidea

O

Orson Anton Welleson

New member
How-D,

I've been reading the discussions across the PPCB forums for quite some time, but haven't posted for a number of reasons (family, family and family) so I am familiar with all the regulars here, although I'm new to you all.

So I assembled a Muroidea the other day, curious what a Rat sounds like after all these decades. It sounds great, but I'm really bothered by the way the tone/filter and drive pot behave. The drive pot opens up fairly quickly and by halfway, that's it - no further distortion, harmonics, etc. What's more, trying to get the sweet spot of the lower gain portion of the drive control is hard to nail on the head. The filter pot has *all* of the high end in the first 10% of it's rotation. I've experiemented with different values and tapers for both, but nothing resolves these behaviors/performance of the pots.

I'm thinking I need to try to Fuzz Face trick of using anti-log pots, or this: https://www.freestompboxes.org/viewtopic.php?t=8270

Any thoughts? Anyone else experienced this and found a satisfying solution?

Thanks,

Orson
 
Welcome!

Experimenting with pot values and tapers is a good first step. Instead of reducing gain, you could also increase headroom. R6 dictates when the hard clipping starts, you could try increasing this value (maybe 10k?).

This might have an effect on the Filter control, and you may need to reduce or jump R7. That would give you more highs at the highest setting. It won't help much with spreading out the action. A Log pot is the best option already. Another option would be to decrease C8, which will move the corner frequency up.

Good luck!
 
Im glad you posted. Got my thinking about how disappointing the rat filter is. I might head to the bread board and try a notch filter or something drastic in there. 🤔
 
Are you feeding it a particularly hot signal?
Once you extend the opamp as far as it can go, you won't see much change. This will happen way sooner in the rotation with active or hot pickups or most basses
A parallel resistance with the pot could help this and is easy enough to test with a pair of alligator clips.

What chip are you using?
It's possible a fake 308 (386/741 etc) while functional could exhibit unexpected behaviors.

The tone pot sweep sounds off. Double check your values, if you haven't already.
 
Last edited:
Aleph Null said:
Experimenting with pot values and tapers is a good first step. Instead of reducing gain, you could also increase headroom. R6 dictates when the hard clipping starts, you could try increasing this value (maybe 10k?).

This might have an effect on the Filter control, and you may need to reduce or jump R7. That would give you more highs at the highest setting. It won't help much with spreading out the action. A Log pot is the best option already. Another option would be to decrease C8, which will move the corner frequency up.
Click to expand...
My first thought was "breadboard", and we dread the bread. I suppose I can install some sockets and play with values if nothijng else works.
jwin615 said:
Are you feeding it a particularly hot signal?
Click to expand...
Nope, just Lawrence Wilde noise free tele bridge pickups.
jwin615 said:
A parallel resistance with the pot could help this and is easy enough to test with a pair of alligator clips.

What chip are you using?
It's possible a fake 308 (386/741 etc) while functional could exhibit unexpected behaviors.

The tone pot sweep sounds off. Double check your values, if you haven't already.
Click to expand...
Okay, I'll start with the parallel resistance. I have plenty of clips, so there's that.
I'm using an Asian LM308 I bought from Synthrotek, so yeah, fake. I'm going to get some of the metal can LM308 from PPCB when I have money tomorrow.

Checking values, thank you!

Thank you everyone, I appreciate your input.
 
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