Re: Diode question

Posted by induction on Oct 26, 2015; 1:42pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Diode-question-tp25483p25502.html

The two interesting characteristics for clipping diodes are Vf (at what voltage does it start to conduct) and the knee (how sharp is the transition between conducting and not conducting). There are some disagreements about how important the knee is in hard clippers, some say only Vf matters and the rest is the power of suggestion. With soft clippers, like in the circuit you're looking at, the knee is going to be even less important. Even silicon will give you soft clipping in the feedback loop, so the softer knee isn't going to make much difference.

If you just want to see what will happen, try it out. That's what breadboards are for. Here's what I predict: Output volume will drop enough that you'll need a makeup gain stage. There may or may not be an increase in compression, but it will be hard to tell in an A/B test because the volume will be so different that Fletcher-Munson will start to be a major factor.

The only designs I remember seeing with Ge feedback clippers have been asymmetric: 1 Ge and 1 Si, anti-parallel. I suspect that this gives nearly the same perceived volume as pure Si, but I haven't tried it. I won't guess what the tonal difference is, but I wouldn't be surprised if it wasn't especially noticeable. If you want to explore more, try 1 led and 1 Ge. This will make the asymmetry more pronounced.

If you really want to use your Ge's in a feedback clipper, try putting two or more in series. That will kick the Vf up to a more useful level. It will also use up your Ge diodes faster, while giving a result that is probably not especially different from using single Si's.

It's a good topic for breadboard exploration. Let us know what you find.