Harmonic Energizer fizzy distortion

[Ben79]

Hi guys,

Following on from the gain pot woes in the thread below which I finally managed to resolve today I now have another problem with my HE build.

It's some kind of distortion which sits right up in the high frequencies.  Perhaps it's unavoidable but the noise is unpleasant and reminds me of that digital sounding background hiss you hear when you play through an LM386 amp (Ruby, Smokey etc.).

Anyone encountered this before or have an idea what could be causing it?  Perhaps it's just a limitation of the circuit?

I've modded the gain section so I have a 250k gain pot instead of the stock 50k and a pair of switchable clipping 1n4001s.  With plenty of gain and the diodes in circuit, the nasty sound gets lost but I think that's just it being swamped by the diode distortion.  The bad distortion is there at any gain setting.

Any ideas gratefully received.

[Ben79]

Well I've played with this a bit.

The distortion sounds like digital clipping.

It does vary somewhat with the gain and how much bass is being let through.

On someone's kind advice I poked about with a 1m resistor to ground but to no avail.

If anyone can offer any ideas I'd be super grateful.

[Mark Hammer]

Well, maybe a 250k gain pot is simply too large a value at max gain, and you're running out of headroom...at least in the non-clipping setting.

[Ben79]

The clipping is there with the pot at near minimum so unless the pot is goosed I don't think that's it but I'll temporarily clip a 68k resistor in parallel with the pot just to make sure.