SOLVED Mofeta too much bass

[Telepathy club]

I’ve recently built a mofeta preamp. I’ve done the C8 mod John from eae suggested. Replacing the LPF C8 from 680pf to 270pf. But my build has either way too much low end or an attenuated high end. Everything works. The eq sweeps a decent amount for all bands but doesn’t overcome the massive low end signal. The 2n5457 are biased to 4.5v. The eq works. I’m just getting something like +10 - 12db for everything below 400hz. I am using a tle2072 instead of ye ol tl072 but that’s should just drop in and have lower noise. If I record the signal I can add +10db with an eq to everything above 1k and I can see I have highs in the signal up to about 7.5-8khz. So I think I just have wayyyyy too much low end even with the control at 0. Turning up the bass knob I just get even more bass. Any suggestions as where to start probing? Its almost as if I need to tilt the entire eq at 1khz +6db above 1khz and -6db for everything below 1khz.

 

[Zanshin]

Assuming there are no real issues in your build... with that tone stack - bass and treble at minimum and middle at max is as flat as it can get. Have you tried starting there? You talk about your treble and bass settings but not your middle, they are all very interactive with each other.

 

[Telepathy club]

Accidentally had C21 as .1 not 1nf. Swapped and solved.

 

[Zanshin]

Awesome

 

[comradehoser]

What does the suggested c8 sub do, and where is that discussion?

 

[Telepathy club]

There’s a Reddit thread of the mofeta where John the designer of the circuit mentions c8 is wrong in the build doc compared to his circuit. And it should be 270pf not 680pf. He mentions it as a way to make lower gain tones not as muddy. He designed it so I trust him. He also mentions a couple power decoupling caps on the ICS to lower noise.

What does the suggested c8 sub do, and where is that discussion?