[sdiy] Tellun Neural Agonizer Question

[Scott Juskiw]

The distortion comes about due to clipping in the recovery amp. The  
resonator circuit on the recovery amp can cause certain frequencies to  
"go through the roof" and this causes the clipping that you hear. Some  
suggestions:

1. Turn down the drive so that the recovery amp won't clip. Not so  
good a solution when you want that overdriven sound, unfortunately.
2. Lower the high frequency gain (TP2) of the driver. Clipping seems  
to occur with high frequencies, even if it's a harmonic of a low  
frequency sawtooth.
3. Add a limiter/compressor to the recovery amp. It would have to be  
inserted before the recovery amps (pin 3 on U15 and U17). I haven't  
spent any time figuring out how to do that. Maybe I'll try something  
out with a MUUB board one of these days.

On 3-Feb-09, at 2:22 PM, Romeo Fahl wrote:

> I finally got mine working, and for the most part am very, very happy
> with it. It's got a very clean sound, lots of headroom, and does far
> more than any other spring reverb out there.
>
> One thing that I'm trying to figure out is how to tame its distortion.
> If the drive pot is turned up beyond a certain threshold, some really
> nasty clipping kicks in. I've determined that the distortion is not
> happening in the "Drive" circuitry, so I'm assuming that it's starting
> somewhere in the feedback loop. One thing that I want to try is to
> swap out the TL072 and OPA275s with BA4558s to see if that softens the
> distortion a bit. If that doesn't do it, I may try figuring out some
> sort of simple limiter circuit to kludge into the module.
>
> To those of you that have built a NA, did yours have a distortion
> problem, and if so, how did you fix it?
>
> Romeo