Diode lift switch (Electra)

[dennism]

Can someone point me toward a veroboard diagram of an Electra distortion with a diode lift switch, so it can either have the diode clipping or just act as a booster of sorts?    Thanks for any assistance you can give.   I just can't get my head around how to do it or what I need for a switch (SPDT? DPDT?)

[smallbearelec]

Here is a breadboard version of an improved Electra:

http://diy.smallbearelec.com/HowTos/BreadboardUrsaMinor/BreadboardUrsaMinor.htm

The "break" to take out the diode pair can be on either side of C3, and a SPST or SPDT switch will be fine. Build it on the breadboard first and try some of the many possible tweaks that work with it. A full build on PCB is here:

http://diy.smallbearelec.com/Projects/UrsaMinor/UrsaMinor.htm

[Mark Hammer]

Another approach is to provide a variable clipping control, by inserting a pot between ground and the ground end of the diode pair.  As the resistance is increased, the clipping will be reduced.  I can't speak to what sort of resistance would virtually eliminate ALL clipping, but 10k ought to be enough to reduce it substantially.

Some posted Electra schematics show a diode pair of a germanium and silicon to produce asymmetrical clipping.  Personally, I see no particular advantage to trying to achieve that here.  A silicon diode pair will yield more output, decent clipping, and a better shot at dialing in a clean or lightly coloured tone.

[dennism]

Thanks to Steve and Mark for replies.   I actually started out with a potentiometer to pan between clean and clipped, but the changes were extremely subtle (and much more toward the heavily clipped side of things, not much cleanup).   I was using a 20k linear pot wired as a variable resistor.   Perhaps 20k isn't enough resistance?    Anyhow, since that wasn't working really well, I thought I'd just go for an all or nothing switch.    This gives me enough info to experiment with both approaches, so thanks!

[Mark Hammer]

Where was the 20k pot situated in the circuit?

[dennism]

Lug 2 connected to the 100nf output cap.   Lug 1 connected to the end of the diode pair.   Other end of the diode pair to ground.

[dennism]

And lug 3 of volume also attached to lug 2 of 20k pot.

[dennism]

I just tried it with a 50k pot for the variable resistor.   It's less subtle, but still not much clean.   I think my main problem is that I was expecting too much clean from the Electra circuit and it's just not going to get that clean especially with the NPN russian germanium that I used for the transistor.    It sounds amazing actually, I was just hoping for the versatility of a clean boost and a great overdrive from the same box.   Probably too much to wish for with the Electra circuit.

[Mark Hammer]

Sounds to me like the stock circuit is cranking the germanium transistor to its limits, and the diodes are simply topping up the resulting distortion.  Have you tried lifting the diodes, and if so, does it clean up at all?

Have you considered increasing the emitter resistance to reduce gain?

[dennism]

I did do the diode lift and it's also subtle, but audible through a clean amp at stage volume.    Not what I went into the build looking for, so although I won't use the diode switch much, it's still an amazing sounding germanium overdrive that will get significant use in the dirty mode.   Lots of control with guitar volume and tone knobs.   Lot of bang for your buck for a circuit with about 7 or 8 parts.   I'm going to have to get my breadboard out of hibernation and do some experimenting with the Electra.

[Mark Hammer]

Though they have since moved well beyond it, many of the first offerings from Lovepedal were essentially variations on the Electra.  Didn't hurt them one little bit.