Where to put high pass filter on MXR Micro Amp boost pedal

[Joe_Shroe]

I'm building an MXR Micro Amp pretty much matching the exact schematic. However when there's enough gain, bass gets a bit too distorted for my liking. Where should I put a high pass filter to smooth out the bass distortion? I tried putting it after R3 and before the noninverting input, but it made the audio very crackly and poppy.

[thermionix]

What about a smaller C1?

[Joe_Shroe]

Okay I'll test that later. Quick questions though, are R1 + C1 + R2 forming both a high pass and low pass filter together? How does the 4.5v bias voltage on R2 affect the filter if any? And what would be the lowest recommended value of the input decoupling cap C1? Could I go as low as 470pF for example, or does it only affect the high/low pass filters?

[Elijah-Baley]

My Micro Amp has the bass a bit boosted, though not distorted.
I'll try to decreas the C1 just a bit, you could use a 0.082uF (82nF) to reduce a little the input bass.
Then you could try to decrease C3 from 4.7uF to 2.2uF. I never do it, but a sort of Fat mod should be to increase C3 to 10uF, so I assume decreasing it you can get the bass cut.

Let us to know!

[Kipper4]

What they said ^

C1 try as low as 10nf.
You'll probably find somewhere in the parish of 22-47nf will do.

It largely depends on what's down the line obviously. Gear and amp wise and your taste.

Rich

[Joe_Shroe]

Thanks for the replies. Changing the value for C3 is doing the trick for the low end cutoff, I'm using 0.22 uF right now. One last follow up, what would I need to change for the high end distortion cutoff?

[thermionix]

To roll off some of the top end?  Try a bigger C2.  I think I'd grab 220pF first, then more or less.