MOSFET Boost/Overdrive (And AArdvarks!)

[McSpunckle]

UPDATE


I deleted the old stuff. This is better, which is why it's here instead.

And Aardvarks!.jpg (122.88 KiB) Viewed 3377 times

This is the final version. I'm not gonna change it any more. It's basically a MOSFET Electra Distortion. (which itself is just a booster with clipping diodes).

The toggle switch has 3 positions. In the middle, the pedal mostly functions as a booster (but you'll get some distortion with the gain control up). The right position (if wired so it looks just like the layout) would send all of the signal to the clippers, while the left is a "bass" mode that leaves some lower frequencies untouched.

The parts going to ground are shown going to the back of the pots. Don't solder to the back of the pots unless you have a fairly powerful (40 watts+) soldering iron with a big tip, and be sure to prep right-- sand the pot where you're gonna solder, and use a bit of liquid flux. The reason is that the wiper in the typical pots used in pedals is made of plastic and will melt very easily.

For bypass switching, I recomend taking a look at GGGs wiring page. Choose what you want.

I left the traces larger than I normally would, because some may be hard to see. If you have any questions, yeahh.


Mods:
The clipping diodes (Q2 and D2) could be replaced with basically anything. For something easier to wire, replace the BS170 with a 1N914 (or similar). It won't sound just the same, though. If you can't find BAT42s, any schottky would work, basically. BAT42s are usually pretty cheap at Mouser.

Some MOSFET boosts use higher value bias resistors. The Super Hard-On uses 10M, which are only really available in carbon film. The And AArdvarks! has pretty low input impedance, so using such high values doesn't help. You can raise them if you want to, but you probably won't get much extra out of it, since the bias voltage is always going to be 1/2 the output voltage + drain voltage. If you want a hi-fi sorta boost, I recommend trying out Jack Orman's MOSFET booster instead.

And Aardvarks!.jpg (122.88 KiB) Viewed 3377 times

[nbabmf]

One of the nice things about a MOSFET booster like that is the ever so slight coloration... sparkle!

It never occurred to me to add clipping diodes. How does it sound?

[McSpunckle]

It's really natural. The boost is, well, a MOSFET boost. Really clean. I originally used a BJT, but the MOSFET had more headroom (or, just clipped more softly when it did). Before clipping, the difference wasn't all that huge.

The clipping diodes are great. It's very natural, really. Nice and open, not too bright. If you use Schottky or Germanium diodes, the output is a lot lower, but it'll fuzz up more.

When you really push the gain, it really fattens up.

-edit-

Using MOSFETS as the clipping diodes makes it a bit more natural sounding, but with the gain all the way up, it can make a weird glitchy noise that stops once the signal gets low enough. I'm guessing MOSFET overdrives usually don't have as much gain as this.

[nbabmf]

You can raise the clipping threshold by putting another diode in series with each of the MOSFETs. I've had good luck with germanium.

[McSpunckle]

This is a fun circuit to breadboard. So many changes!

The weird noise stopped. I realized I had a 100K feedback resistor in instead of 1M. I think the extra gain helped. A higher clipping threshold would sound cool, though. I tried LEDs but it was just too much.

Now it's super loud.

Adding a "mods" section to the first post.

[raginreggie]

Definitely gonna try this one as soon as possible

[fuzzmax]

What would be the proper wiring to add a bypass switch to this device??

thanx

[McSpunckle]

http://www.generalguitargadgets.com/tec ... ng-options

Any of those options. You really don't need input ground for this.

[fuzzmax]

Sorry for my Noobiness but the out is going to the spst switch, so is the bypass switch linked with the spst one?

[McSpunckle]

Could be. The SPST switch and the circuit output are connected.

You'll probably want to go from there to a volume control, then to the bypass switch.

When I get some time, I'll add volume, gain, and tone controls to the layout, and add the bypass switch.

[McSpunckle]

Bump for new/better circuit.

[stanimal]

Nice work !!! I look forward to building it!!

[McSpunckle]

Thanks. : D

BTW, if anyone builds one of the original, simpler ones, replace that 1N914 with an LED. If it gets enough voltage to conduct (my bass puts out over 1V when struck hard), it'll conduct and mess things up.

[magiclawnchair]

[sevenSHARPnine]

I'll take 3!