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previous: David Manson Actually I'm just messing around wi... -- 10/13/1999 9:36 PM View Thread

Re: Smoothing out the diodes.. rounding the edges,,,

10/20/1999 11:47 AM
Dai Hirokawa
Re: Smoothing out the diodes.. rounding the edges,,,
Does anyone use resistance on one side only? This (small value--a 470 ohm--pot in series w/one diode) is something that I've done in my TScreamer copy thinking that it would make the signal more asymmetric(my assymetric fixation rearing it's ugly head, ha ha). I didn't want to add R on both since the lower Vf side seemed to determine the amount of compression, and I wanted the amount of compression to be maintained. The effect of the resistance here is subtle but I hear it.  
Also, has anyone tried a Selenium rectifier as a clipper? I finally got ahold of one and tried it on one side, w/a small signal Si on the other side. The output and distortion dropped, the sound lost a lot of top end, and the signal seemed more tube like. Basically it wouldn't distort as w/the ordinary Si diodes, even when diming the drive and tone pots. It would just stay clean but get louder when turning up the output level pot(I thought something was wrong becase it wouldn't distort as I expercted, but realized after switching to a lower volume bypass signal that it was doing something). In my efforts to get more distortion out of it, I kept upping the resistance in series w/it (presently a 47k pot), and I finally got some distortion in the high end. I also know that these diodes emit poisonous gas when going bad but hopefully this is light enough duty for them that this won't happen. Also, I've read that these leak when aging and need to be reformed by slowly applying reverse voltage(something I will try later), so maybe I'm not hearing what the Selenium rect. sounds like in an optimal, healthy state. These seem to have a lot of potential as clippers--too bad they aren't made anymore(I have read however that they are easy to manufacture, though I have no idea if modern engineering can solve the poison gas emission problem--which seems to me to be a big prob. w/these).  
Also, re: "capacitive compliance":  
Isn't the 51pF just a normal thing to prevent oscillation(small value cap like 30pF-50pf or so placed in an opamp's fdbk. loop)? Maybe you could call the part in the TS circuit w/the .22uF caps as having cap.compliance, but the 51pF? Ah, hell, maybe I'm just nitpicking...  
Dai Hirokawa  

Gus Ta caps,,, -- 10/20/1999 2:24 PM