Diode-Compression Opamp - nooooooooize!

[Phorhas]

I bread boarded the Joe's Diode-Compression Opamp (2N5087/2N5089). it sound really nice by itself and in a Dist. plus type thing I tried, but it's noisy as hell. it has alot of noise and high pitch squeel. I tried the advanced version as well, and it too, as well as the tone maybe, is VERY noisy and squeely.

I tried a hi cut cap to ground on the input and out put and a hi cut cap in the feedback loop... nothing...

help... plz?

[Phorhas]

A little update. I got rid of the nasty oscillations with an inverting stage, but this crkt is still very noisy. Am I doing some thing wrong?

[Joe Davisson]

Sometimes you need a filter cap on breadboards, even if the power supply is well-filtered. I run into this a lot.

Other then that, make sure the output is near 4.5v, adjusting the 6.8k resistor if it's off. It also might need a more stable bias, use 10k/10k voltage divider, filtered by a 10uF or so cap, then the 1M going to the input. I think the input resistance is less than a real opamp.

The basic version is probably best for most purposes, the only advantage to the more complicated one is to drive a bigger load.

[Phorhas]

I use a chip to do the voltage dividing, and it's really precusr and stable. by board is filter aside of the existing power supply filtering.

I succeded in quiting the beast down now I'm very happy with the nosie floor. thing is, it's has alot of bass at high gains (500k pot /.1uf->2k4) and with a pair of Si doides it doesn't clip as hard as say, a tube screamer.

Any thoughts?

[WGTP]

When I had mine partially working, I used GE diodes for a lower clipping threshold.  I'm also wondering if a Darling transistor for Q3 might help raise the output level.  

[petemoore]

Here's what I found...
 output [lower
 Noise Floor [lower
 Sound [different, opinion is it's a good improvement [only a/b'd Vs. LM741] I'd venture to say that the compression amp works handily in the DS-1 Cologne.
 Looking for bigger boosted outputs?...look elsewhere...
 Looking for great sounding/otherwise performing OA...there 'ya go !
 Pretty large difference I notice, really for once likin' the DS Sound, it still boosts, not as much.