Clipping options

[teknoman2]

I am trying to make work a 3way clipping option with an spdt on-off-on,
so I realise that if I want to have 3 different sounds I must omit the LED clipping option, so I have 2 options with cliping and one without clipping
but with a small boost of volume.
Does anyone know a different way to have 3 clipping options using an spdt on-ff-on?

[RobA]

I am trying to make work a 3way clipping option with an spdt on-off-on,
so I realise that if I want to have 3 different sounds I must omit the LED clipping option, so I have 2 options with cliping and one without clipping
but with a small boost of volume.
Does anyone know a different way to have 3 clipping options using an spdt on-ff-on?

Check out the way the LaVache does it http://www.madbeanpedals.com/projects/LaVache/docs/LaVache.pdf

I did a design that uses the same type of clipping but using LED's instead of the Schottky diodes. The key is to get the clipping level of the off position diodes slightly higher than the two options.

[croquet hoop]

I think madbean's Uproar offers a similar arrangement, in which there is always a set of diodes (LEDs) connected (in the "off" position).

As said in the other thread, if you want three truly independent clipping modes, you'll likely need a dpdt on-on-on.

[midwayfair]

Check out the way the LaVache does it http://www.madbeanpedals.com/projects/LaVache/docs/LaVache.pdf

The lavache is functionally identical to what the OP posted. The method the op posted is actually slightly preferable in one way: The limiting resistors can account for the reduction of the Fv by the LEDs in parallel with the other clipping options when the switch is on in either position.

OP: D4 has a higher forward voltage than the red LEDs, and therefore will not offer much of a change (that is, it won't have a higher Fv when you're in that switch position). You need to start with the highest forward voltage in the "always on" part, and allow the "on" positions to reduce the Fv further. In fact, you could omit D4 and it would sound almost identical. You also need to make sure that a blue LED will even clip the signal being produce. Their Fv can be over 3V, and many transistors and chips will being to clip at that point on their own, leaving nothing left over for the blue LED.

Also, you might consider just using single 1N914s on the symmetrical side instead of four germanium diodes. It's the same Fv.

[croquet hoop]

Also, you might consider just using single 1N914s on the symmetrical side instead of four germanium diodes. It's the same Fv.

Isn't this precisely the kind of situation where it's possible to hear a difference between silicon and germanium clippers of similar fv? (as you explained in a recent thread about 1n34A diodes — clippers are connected to ground with no extra cap post clipping)

[RobA]

...
The lavache is functionally identical to what the OP posted. The method the op posted is actually slightly preferable in one way: The limiting resistors can account for the reduction of the Fv by the LEDs in parallel with the other clipping options when the switch is on in either position.
...

The important point about looking at the way the LaVache does it is the relative clipping voltages and how this shapes the clipping. Yes the topology of the two is similar, but the results won't be the same without rigging the forward voltages to work.

[midwayfair]

Also, you might consider just using single 1N914s on the symmetrical side instead of four germanium diodes. It's the same Fv.

Isn't this precisely the kind of situation where it's possible to hear a difference between silicon and germanium clippers of similar fv? (as you explained in a recent thread about 1n34A diodes — clippers are connected to ground with no extra cap post clipping)

Yes. I was just making sure the op realized that the Fv was the same. Without seeing the rest of the circuit, we can't know what else is going on here. In any case, you could also just adjust the limiting resistor instead of using two diodes. Then you could use one resistor for silicon diodes or a different sized resistor for germanium and save space on the board and cost on the final build. Basically, there's no overall benefit in using four germanium diodes instead of just two in the circuit shown.

[croquet hoop]

Another fine explanation on diodes, thanks Jon (the clipping section shown in the first post if from the uproar, and the original Suhr Riot uses this arrangement with four ge diodes)

[culturejam]

Does anyone know a different way to have 3 clipping options using an spdt on-ff-on?

Yes. You can have LEDs, silicon, and germanium (or whatever else you want) with a center-off SPDT or DPDT switch.

The trick is to leave the LEDs in the circuit all the time, and let the switch toggle between off (LEDs), option X, and option Y. As long as the option X/Y diodes have a lower FVD than the LEDs, they will turn on before the LEDs and clip (and the LEDs will not). So you can have three choices.

But if you do it that way, you lose the option of "no diodes".....unless you want to have the diode selector switch itself connected to the main circuit via a second master diode on/off switch (SPST). 

[teknoman2]

So to summ up,
my best way is to put the higher Fv on the always on part of the circuit (off possition on the switch) and put two lower Fv clipping options on
the other two options of the switch.
Do you think that if I put on D4 another 1n914 the total Fv will be lower comparing to the two red Leds or do you think should I increase the value of R16 ?

[midwayfair]

For reference, here are estimated forward voltages of reasonably common parts:
Blue or White LED: 3.2V
Green or Yellow LED: 1.8-2.2V
Red LED: 1.7V
Typical silicon: 0.55-0.7V
Typical germanium: 0.25-0.38V
Typical Schottky: 0.2-3.5V

Diode datasheets are difficult to suss out this information, but diodes are mostly cheap, so just buy a wide swath and measure them with your multimeter.

Special stuff:
3.3v Zener: Fv is 3.3V in one direction and 0.7V in the other
BS170 or 2N7000 MOSFET: 1.2V+ softclipping (never hard clips) or 0.7V silicon body diode. Do a forum search for more information about using these

A resistor in series with the diodes reduces current and therefore raises the Fv. You can test the difference by putting the resistor in series with the diode and measuring the Fv again.

[teknoman2]

I will try everyrhing you suggest,
thanx again for all the infos.