MKCv4 getting fuzzy/saturated

[Anonymous]

Hi there,

Just finished my MKC4 (note that i’ve built dozen of other pedals, amps, devices…) and I’m getting a bit of cranked/fuzz (would rather say an opamp saturation) as soon as I try to get more gain2/drive or enable bass boost.

With low level output guitar such as my strat on the first part of the audio sample, that’s almost unnoticeable (at least without bass boost on), with a lespaul (2nd part) it gets cranked and unusable with bass boost (and more generally this problem is very noticable on low frequencies notes).
Note that I get the same fuzz/crank issue with any of my tube amp or in my emulator rack device used for recording.

Interesting thing is that it gets worse without clipping (I have a ON/OFF/ON switch with 2 diodes sets and a null position waiting for a ON/ON switch delivery) so It may suggests it’s a opamp saturation due to too much feedback level?

Thank you for your help.

Audio recording: https://drive.google.com/file/d/1jHKIg4g_K9QYepXFxzyw6Pz90KmPdgu2/view?usp=drive_link

[Barry]

Recheck your resistor values by color code.

Bass boost does not technically boost bass. It only allows more bass frequency range through the circuit. If one of your resistor values is incorrect that affects the overall gain of the circuit then the extra bass frequency is likely just making it sound worse. Also do not test without clipping diodes in circuit.

With thousands sold, and many build posts over the last 13 years, I have never heard this particular issue. That leads me to one, or both of those.

 

[Anonymous]

Thanks barry, already checked twice as this would be the typical problem.
I did also check voltage value on both ICs and they are good.

So I’ve followed signal path:

Problem seems located on the opamp stage, postive IC1B is clean but negative input get a complete distorded sound (and so get amplified on IC1B pin 7 ouput and then sum up with the others feedforward network.

I’m really getting stuck on this 😐 thanks for your help

[Anonymous]

Note that the fuzzy output is present on the musikding demo video: https://www.youtube.com/watch?v=-nLkj5-wMM4

[Barry]

I suggest using the MKC within its intended range first. Our circuit offers mods that are being used in the demo you posted above. I see and hear that he is using the Ultra Gain Mod (potentiometer) half way between stock and the hotter Ultra Gain value throughout the entire video. He then cranks it even further at the end. I do hear unnatural tones because he is indeed using the ultra gain mod (an “always on” potentiometer) in tandem with turning up the Gain pot. That is why it is breaking up. The mods are intended for experimentation beyond the original circuit.

If that is not appealing, then I would limit those options to within your needs. The purpose of his video was likely to explore how far he can go with those mod options and that person probably found them pleasing to his ear.

The ultra gain mod he is using is done with a potentiometer on the lower right so his is always on. If he removed it, then it will not clip. He was certainly pushing his to extremes with both mod and gain pot.

So be sure of your gain resistor value, mod values, or keep it stock, if you do not want added clipping to any degree.

Also use the parallel potentiometer more in step with the Gain.

When modding you would have to find your happy values from within to work that are best for you.

 

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