Interstage HPF and LPF in amplifiers

[Vivek]

I'm trying to wrap my head around AMP IN A BOX type of pedal

I decided to first try 2 stages and maybe see if adding a 3rd stage brings anything sonically pleasing to the design.

Recently RECKLESS wrote that 700hz is a magic number for LPF as well as HPF in stages in an amp

However I want to have knobs to adjust these filters

Suppose my schematic is

Buffer > HPF1 > Clipper1 >LPF1 > Clipper2 > LPF2 > tone control > Buffer

and I want to have these filters variable

Q1 : What should be the  frequency range of each of these  variable filters  ?

Q2 : Would it be useful to have a 6db /12db switch for HPF1 ?

Q3 : is there a need for another HPF after Clipper1 ?

Q4: I understand that clipper1 normally does less clipping than clipper2. Please comment.

[iainpunk]

1>
for the HPF, i recommend having a variable passive first order filter. stacked with a 2nd fixed hpf (at the lowest frequency you want to cut off with the first hpf)
50Hz - fuzzy
100Hz - less but still fuzzy (think the difference between a fuzz face and big muff)
300Hz - thick desert rock distortion (think kyuss or alice in chains vibes)
700Hz - most distortion and drive pedals, tight, mid focussed
1.5kHz - thin trebly, think sexpistols vibes or toe-down wah sounds

2>
i recommend a fixed and a variable filter. not a 2nd order variable. also that needs a dual pot, which is harder to come by.

3>
no, probably not, but if the gain is really high, you might want to add one in anyways, maybe a weakened filter.

4>
gain. if both clippers have a gain of 10 and clip at the same threshold, clipper 2 puts in an 100x amplified signal into its clipper, instead of a 10x. also. make the first one as asymmetric as possible so that the other one doesn't make it symmetric again. and don't forget to take out the DC when going in to the second clipper, since the asymmetry needs to be carried over, if you don't, the second clipper takes out part of the asymmetry (or all of it if the gain is high enough)

[Vivek]

How does this sound

For first HPF
Fixed first order at 150 Hz

And another variable first order from 100 Hz to 2 kHz


Then after clipper1,

If low frequencies were already removed earlier and Clipper1 did not create new low frequencies, please help me understand if a HPF is needed after Clipper1

Do tube amps have HPF in between all stages ?

[iainpunk]

If low frequencies were already removed earlier and Clipper1 did not create new low frequencies, please help me understand if a HPF is needed after Clipper1

Do tube amps have HPF in between all stages ?

yes, but the cutoff frequency is often way under audible spectrum.

some have ''diminished'' filters, hpf with a resistor parallel to the capacitor like here in the Marshall JCM800, it gives a shelf filter effect of -3db/oct with a max attenuation of -6dB


but i think you should try to get results by experimenting, especially with this stuff.

cheers, Iain