Zener clipping diodes

[panterica]

I ran across a typical TS-type schematic years ago made by Jack Orman that used 3.3V and (I think) 5.6V zener diodes for clipping. It's supposed to sound like tube distortion because of the asymmetrical clipping at different points of the sound wave (at 3.3V and 5.6V). I was new to the whole electronics thing, and I couldn't get it to sound right. Instead of bothering to debug it, I just gave up. Now I just can't help but wonder if any one else has tried this.

*Also, this is a little off-topic, but I was wondering if the 1N4001 and 1N4003 type diodes are good as any others for distortion. I believe I've only seen them used for rectification.

[anchovie]

I doubt that would have sounded very good if you were using a 9v supply. A typical op-amp in a TS won't be a rail-to-rail type, so with the bias in the centre of the power rails you have a voltage swing of somewhere between 3 and 4 volts either way before the signal gets clipped by the chip itself, so a 5.6v zener isn't going to touch it at all resulting in one half of the signal hitting the rails, possibly the other too. Op-amp clipping doesn't sound too great unless the circuit has been designed to use it specifically (e.g. SansAmp). If you want asymmetrical clipping, try two silicon diodes one way and one the other, or one silicon and one LED.

[aziltz]

I doubt that would have sounded very good if you were using a 9v supply. A typical op-amp in a TS won't be a rail-to-rail type, so with the bias in the centre of the power rails you have a voltage swing of somewhere between 3 and 4 volts either way before the signal gets clipped by the chip itself, so a 5.6v zener isn't going to touch it at all resulting in one half of the signal hitting the rails, possibly the other too. Op-amp clipping doesn't sound too great unless the circuit has been designed to use it specifically (e.g. SansAmp). If you want asymmetrical clipping, try two silicon diodes one way and one the other, or one silicon and one LED.

you wouldn't know what kind of design makes for "good" op-amp clipping would you?  I'm trying to figure out why my tech21 double drive sounds so good.

[GibsonGM]

Well, the MXR Distortion + is a classic example of opamp clipping, take a look at that....I find it harsh, personally, but that's just a matter of taste.

[biggy boy]

Heres some info on the distortion+ and some other distortion schematics are explained.

http://users.chariot.net.au/~gmarts/ampovdrv.htm


Glen

[earthtonesaudio]

*Also, this is a little off-topic, but I was wondering if the 1N4001 and 1N4003 type diodes are good as any others for distortion. I believe I've only seen them used for rectification.

Just as good as any Si diode, but very slightly different.  They have more capacity than signal/switching diodes, so they are sometimes described as warmer/darker/softer.

[anchovie]

I doubt that would have sounded very good if you were using a 9v supply. A typical op-amp in a TS won't be a rail-to-rail type, so with the bias in the centre of the power rails you have a voltage swing of somewhere between 3 and 4 volts either way before the signal gets clipped by the chip itself, so a 5.6v zener isn't going to touch it at all resulting in one half of the signal hitting the rails, possibly the other too. Op-amp clipping doesn't sound too great unless the circuit has been designed to use it specifically (e.g. SansAmp). If you want asymmetrical clipping, try two silicon diodes one way and one the other, or one silicon and one LED.

you wouldn't know what kind of design makes for "good" op-amp clipping would you?  I'm trying to figure out why my tech21 double drive sounds so good.

The clipping section uses a TLC2262 which is a rail-to-rail MOSFET op-amp. TLC2272 can be used too. In the double-drive schematic that I've seen, one side is clipped with two 1N914 in series and the other hits the op-amp rail. There isn't anything complex going on with filtering at all, just a passive tone control after that.

Well, the MXR Distortion + is a classic example of opamp clipping, take a look at that....I find it harsh, personally, but that's just a matter of taste.

I'd say that's actually an op-amp driving a clipper, as there's a pair of back-to-back diodes to ground after the output of the chip. The SansAmp doesn't use any diodes at all, just the op-amp rails.

[aziltz]

you wouldn't know what kind of design makes for "good" op-amp clipping would you?  I'm trying to figure out why my tech21 double drive sounds so good.

The clipping section uses a TLC2262 which is a rail-to-rail MOSFET op-amp. TLC2272 can be used too. In the double-drive schematic that I've seen, one side is clipped with two 1N914 in series and the other hits the op-amp rail. There isn't anything complex going on with filtering at all, just a passive tone control after that.

Can you get a similar effect using a discrete op-amp made from Mosfets?  I was going to try to compare IC op-amp rail clipping to discrete op-amp rail clipping and hopefully improve upon the double drive.

[owenjames]

I can't believe none pointed this out, Zener diodes act the same as any other diode in the forward direction:

http://upload.wikimedia.org/wikipedia/commons/0/07/V-a_characteristic_Zener_diode.svg

so with parrallel back to back zeners, of any value, you will still have clipping at 0.65V. So it wont sound particularly different from any other diode. If you want to mimic assymetric, try putting two normal diodes in series with one in parallel back to back, or maybe use an LED one way and a normal diode the other way. an LED does have a different threshold voltage of about 2V

[slideman82]

*Also, this is a little off-topic, but I was wondering if the 1N4001 and 1N4003 type diodes are good as any others for distortion. I believe I've only seen them used for rectification.

Just as good as any Si diode, but very slightly different.  They have more capacity than signal/switching diodes, so they are sometimes described as warmer/darker/softer.

This is a great data! Better for a Muff... maybe...

[anchovie]

I can't believe none pointed this out, Zener diodes act the same as any other diode in the forward direction:

http://upload.wikimedia.org/wikipedia/commons/0/07/V-a_characteristic_Zener_diode.svg

so with parrallel back to back zeners, of any value, you will still have clipping at 0.65V. So it wont sound particularly different from any other diode. If you want to mimic assymetric, try putting two normal diodes in series with one in parallel back to back, or maybe use an LED one way and a normal diode the other way. an LED does have a different threshold voltage of about 2V

Ah yes, to clip at the zener voltages you'd have the diodes in series with the anodes joined (maybe there is a proper technical term for this - "reverse series", "antiseries"?).

[owenjames]

I can't believe none pointed this out, Zener diodes act the same as any other diode in the forward direction:

http://upload.wikimedia.org/wikipedia/commons/0/07/V-a_characteristic_Zener_diode.svg

so with parrallel back to back zeners, of any value, you will still have clipping at 0.65V. So it wont sound particularly different from any other diode. If you want to mimic assymetric, try putting two normal diodes in series with one in parallel back to back, or maybe use an LED one way and a normal diode the other way. an LED does have a different threshold voltage of about 2V

Ah yes, to clip at the zener voltages you'd have the diodes in series with the anodes joined (maybe there is a proper technical term for this - "reverse series", "antiseries"?).

Oh I see. Ah I see why you said it will go into opamp clipping beofre zener clipping now.

[mattpas]

The eternity uses Zener for clipping but i forget which ones.

[panterica]

*Also, this is a little off-topic, but I was wondering if the 1N4001 and 1N4003 type diodes are good as any others for distortion. I believe I've only seen them used for rectification.

Just as good as any Si diode, but very slightly different.  They have more capacity than signal/switching diodes, so they are sometimes described as warmer/darker/softer.

This is a great data! Better for a Muff... maybe...

My thoughts exactly. They should be perfect for the bass distortion I'm working on.

I can't believe none pointed this out, Zener diodes act the same as any other diode in the forward direction:

http://upload.wikimedia.org/wikipedia/commons/0/07/V-a_characteristic_Zener_diode.svg

so with parrallel back to back zeners, of any value, you will still have clipping at 0.65V. So it wont sound particularly different from any other diode. If you want to mimic assymetric, try putting two normal diodes in series with one in parallel back to back, or maybe use an LED one way and a normal diode the other way. an LED does have a different threshold voltage of about 2V

Ah yes, to clip at the zener voltages you'd have the diodes in series with the anodes joined (maybe there is a proper technical term for this - "reverse series", "antiseries"?).

So it is possible to clip at the zener voltage levels? I'm not sure what you're describing, though. Do you mean you should put them in series but back-to-back so that the anodes are together with cathodes facing away from eachother?

[anchovie]

So it is possible to clip at the zener voltage levels? I'm not sure what you're describing, though. Do you mean you should put them in series but back-to-back so that the anodes are together with cathodes facing away from each other?

Yes, that's right.