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

10/13/1999 2:38 PM

Jimi2000

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

quote:
" the resistor only knocks down high order harmonics and
doesnt really round out the signal"

Knocking down the high order harmonics *is* rounding out the waveform, but that doesn't mean the sound rounds out as well.

I took the article to mean that the addition of the resistor would allow control of the harmonics in proportion to the original signal, but it doesn't add any even-order artifacts to the clipped signal which would make a more tube-like sound. The bounding resistor is just a volume control for the clipped harmonics the diodes are adding.

J2K

10/13/1999 4:04 PM
Jehan	so far the only way to really round out the blocky signal is to use an fet booster afterwards (from what i read) the only other 2 are using a resistor in series or a cap in parallel with the diodes Try biasing the diodes on with a current source - it causes the clipping section to operate in a manner akin to an amp running in Class A/AB mode. It definitely fattens the sound up if that is what you are looking for. Jehan

10/13/1999 4:04 PM

Jehan

so far the only way to really round
out the blocky signal is to use an fet booster
afterwards (from what i read) the only other
2 are using a resistor in series or a cap in
parallel with the diodes

Try biasing the diodes on with a current source - it causes the clipping section to operate in a manner akin to an amp running in Class A/AB mode. It definitely fattens the sound up if that is what you are looking for.

Jehan

10/13/1999 9:36 PM
David Manson	Actually I'm just messing around with different devices -- seeing which would round out the diodes signal the most on the scope.. 2 transistors in series in the fuzzface seem to be pretty rounded.. (with the right voltages) - i wonder if an led/ transistor series combo would do something...

10/20/1999 11:47 AM
Dai Hirokawa	Hi, 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

10/20/1999 11:47 AM

Dai Hirokawa

Hi,
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

10/20/1999 2:24 PM
Gus	Ta caps,,, Dai was it you that was looking into the Ta caps used in screamers?? I THINK I am hearing different Ta's making a change in the sound. I have not measured the values and parameters yet. It could be as simple as cap value but I am not sure as of yet.

10/21/1999 7:49 AM
Dai Hirokawa	Hey Gus, Yes, that was indeed I. I did eventually find two types that look like two older versions of the .22uF tants in my Turbo TS. I did some A/B testing w/other caps using a sw. to go back and forth between dif. sets of .22uF caps in a TS copy I made, and I did find that the older ones sounded very slightly better than the newer older ones, but that was only after listening very very hard. I also found some .22uF mylars ("robbed" from a late 70s solid-state amplifier) which sounded good (in terms of helping the overall sound become less harsh and making the tone control more effective in taming high end). What I really disliked were newer manufactured Tants, which had too much high freq. response(and consequent harshness). W/the new ones, I also tried using a higher value, but it didn't seem to help w/reducing harshness(one thing that I haven't tried yet was adding an inductor in series--might work to reduce harshness). >>I THINK I am hearing different Ta's making a change in the sound. The thing that seems most obvious to me (when comparing caps) is the high end(some tants add sort of a sharp, grating harshness--any harshness you might encounter doesn't seem to be solely due to the tants,just ). Is this what you're hearing? If I may, I would suggest that you trust your ears, Gus. (I'm assuming you have some years of experience w/"this stuff", and by now have a certain sense of what you like or dislike--sort of an "aural logic"). If something sounds better, go for it! If you've come up w/a great sound, it's still worth something even if you can't explain everything that is going on technically(you can do that part later as you get more info). Also, in my experience w/the TS circuit, the Trs used for the input and output buffers matter also(I took a hint from a Mike Fuller--of Fulltone fame--interview and tried a NPN Ge for the input, and that sounded better to my ear). The coupling caps, filter caps, and diodes also made a difference. It seemed to me that the more I chose parts that sounded less harsh, the cleaner the distortion got. If I were to take a guess as to why this was so, I would say that maybe all of the finicky-ass parts selection that I was doing resulted in less intermodulation distortion. Or maybe not, I don't really know for sure. Oops, guess I'm rambling again, Dai Hirokawa

10/21/1999 7:49 AM

Dai Hirokawa

Hey Gus,
Yes, that was indeed I. I did eventually find two types that look like two older versions of the .22uF tants in my Turbo TS. I did some A/B testing w/other caps using a sw. to go back and forth between dif. sets of .22uF caps in a TS copy I made, and I did find that the older ones sounded very slightly better than the newer older ones, but that was only after listening very very hard. I also found some .22uF mylars ("robbed" from a late 70s solid-state amplifier) which sounded good (in terms of helping the overall sound become less harsh and making the tone control more effective in taming high end). What I really disliked were newer manufactured Tants, which had too much high freq. response(and consequent harshness). W/the new ones, I also tried using a higher value, but it didn't seem to help w/reducing harshness(one thing that I haven't tried yet was adding an inductor in series--might work to reduce harshness).

>>I THINK I am hearing different Ta's making a change in the sound.

The thing that seems most obvious to me (when comparing caps) is the high end(some tants add sort of a sharp, grating harshness--any harshness you might encounter doesn't seem to be solely due to the tants,just ). Is this what you're hearing? If I may, I would suggest that you trust your ears, Gus. (I'm assuming you have some years of experience w/"this stuff", and by now have a certain sense of what you like or dislike--sort of an "aural logic"). If something sounds better, go for it! If you've come up w/a great sound, it's still worth something even if you can't explain everything that is going on technically(you can do that part later as you get more info).

Also, in my experience w/the TS circuit, the Trs used for the input and output buffers matter also(I took a hint from a Mike Fuller--of Fulltone fame--interview and tried a NPN Ge for the input, and that sounded better to my ear). The coupling caps, filter caps, and diodes also made a difference. It seemed to me that the more I chose parts that sounded less harsh, the cleaner the distortion got. If I were to take a guess as to why this was so, I would say that maybe all of the finicky-ass parts selection that I was doing resulted in less intermodulation distortion. Or maybe not, I don't really know for sure.

Oops, guess I'm rambling again,

Dai Hirokawa

10/21/1999 11:19 PM
David Manson	Tubes and transistors as diodes.. Has anyone tried using tubes or transistors as diodes already to see what it sounds like... I saw this idea in o'connors book and was interested.. any real changes in the overall sound? maybe rounder/softer than a regular diode?

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