Cetus preamp - adding a "tight" switch

[maertz13]

it's a great circuit. borderline good enough to not need any boost, but sometimes you just need that low end shaved off. where in this circuit could I sneak a HPF to clean up the low end a bit? any chance I could use C2 and just run a 100k (or close value) resistor to ground and put that on a switch?

 

[jesuscrisp]

You could try smaller C6, somewhere from 10-22n.

 

[maertz13]

that had a really positive effect, thank you. it also got me wondering, how would I wire up a pot instead of R9? if I got a 5k pot and a 5.1k resistor, I could vary the resistance from 10 to 5k, sweeping the cutoff frequency between the stock 480hz and approx 1000hz, right?

 

[jesuscrisp]

Yes but it will also affect the amount of gain a fair bit.

 

[Feral Feline]

Use the pot instead to bleed in extra capacitance.

Have J.Crisp's 10n cap in the stock C6 position with wires running off it to a pot with 22n cap. The resulting 32n lets you get dang close to the stock 33n, probably enough you wouldn't be able to tell the difference.

 

[AxelKay]

Use the pot instead to bleed in extra capacitance.

Have J.Crisp's 10n cap in the stock C6 position with wires running off it to a pot with 22n cap. The resulting 32n lets you get dang close to the stock 33n, probably enough you wouldn't be able to tell the difference.

View attachment 54522

Very interesting experiment!
In your schem above, is the "C1" where the 10nf goes or the 22nf?
Also what value pot would you recommend?

 

[jesuscrisp]

C1 is the smaller cap (10n) as the pot adds resistance in front of the cap, thereby usually creating a blend.

However, by adding a pot like that in the specific configuration of this kind of op amp stage, you're creating a second order filter like on the Timmy overdrive, which usually results in a different low end character as well. No harm in trying though.

 

[mdc]

You could also try reducing C3 or C4 and see if you like the results? If you find a few values that work you could fly leads off of the PCB and put a few caps on a switch.

 

[Feral Feline]

Very interesting experiment!
In your schem above, is the "C1" where the 10nf goes or the 22nf?
Also what value pot would you recommend?

As JesusCrisp said, C1 in the schem I posted is your Cetus C6. I'm still learning about this stuff, so couldn't have told you it's a 2nd-order filter.

Schem-snippet I posted is from Joe Gore's Bulk Fuzz (his take on the Bazz Fuss), and the pot-value is right on the schem — B100k.

So have you tried it yet?

 

[AxelKay]

@Feral Feline Yes, and I think it needs a tad more gain when maxed. Maybe a 300k pot for the gain?

P.s. no I haven't tried your mods yet.

 

[jesuscrisp]

For more gain increase R4, making the gain pot bigger won't do much.