After trying it out on a breadboard, it is time to finalize my version of MXR Distortion Plus. (I dubbed it MyXR Distortion ++ … lame, I know ?).
I’ll do the final schematic and bill of material, then do the soldering layout for a protoboard. I’ll plan out the enclosure, and finalize the enclosure. I’ll finally assemble it and do test and demo.
I tried out several things when I did the effect on a breadboard. I finally settled for a TL072 version (I have quite a few of these op-amps lying around) and I decided to add a toggle switch to toggle between two clipping options: “standard” silicon diode pair and a red LED pair. See the breadboarding post for all options I tried out.
Here’s the full schematic:
The difference from the one used in breadboarding is U1 – I used TL072. In the breadboarding video I tried it out along with LM741, sounded pretty similar. Since I changed the op-amp I added C7 (47p) to make the output response near identical. I tried out several values and decided to go with that value.
I also added R8 which is often added to reduce thump when switching the pedal on and off. I used 2.2 Meg resistor and I increased resistance of R2 to 2.2 Meg to keep the input impedance roughly the same. Neither should affect sound at all.
The biggest difference is addition of a toggle switch to support 2 different clipping modes – one with “standard” silicon diodes and one with red LEDs:
In one position, silicon diodes are connected to GND and LEDs are disconnected and essentially taken out of the circuit. In the other position LEDs are connected to GND and silicon diodes are out of the circuit.
Other than that, there are 2 more parts to complete the schematic fully.
That part above is for the unused op-amp from TL072. As I mentioned I have a drawer full of them, so TL072 it is for most builds ?. I could’ve used it for something more useful, and I might in future for a different build. But for now – wiring it up to minimize impact of it. Also, I added C9 – decoupling capacitor which is customary used for decoupling power supply for integrated circuits.
The last remaining part is wiring up stomp switch and power:
The above is just a standard way of wiring up 3PDT switch for the pedal I use. There are other options, but this one is simplest and as effective.
One thing to note, I’ve put 1K* for R10, that depends on the LED used and how bright I want it to be. In the final build I used 4.7K, I tried out couple of options and decided that’s the right level for me. The purpose of it is to limit current, but brightness depends on the current, so it also controls brightness. Higher the value, less bright the LED is. I’m just saying – if you’re using high brightness LED, 1K might be too low value and you might not be even able to look at the LED straight since it will be too bright.
Bill of Material
Here’s the final list of components I used:
|SBB170 solder-in breadboard by Proto Advantage (fits into the enclosure … nearly)
|Jumpers and wires
|24 AWG solid core wire and 28 AWG stranded wire (24 AWG might be slightly easier to use)
Anything thicker might be hard to stick into the protoboard.
|Lumberg 1614 09
|DC Power Socket. I usually use Cliff FC681473, but could not fit it into the small box
(Alternative: Switchcraft 12B, 11, 111X)
|In – mono Jack (I don’t use battery so mono. But I used stereo, it’s fine, I just ran out of mono jacks)
|Out mono Jack (I used stereo, it’s fine, I just ran out of mono jacks)
|Distortion pot: 500K anti-log pot (solder lugs, metal shaft and bushing)
Alternative pot: Bourns PTV111-1415A-C3103 for example (but I’m not sure it would fit into the small enclosure)
|Volume pot: 100K log pot (solder lugs, metal shaft and bushing)
Alternative pot: Alpha RV16AF-10-15K-A100K-3LA for example
|This depends on what pots you use. I used 6mm straight shaft knobs with screw. If using Alphas you might need knobs that fit 6.35mm straight shaft for example, or if using split shaft – you’d need push on split shaft knobs.
|Taiwan Alpha 3PDT latching foot switch
|Mini Toggle Switch On-On
|Just a random miniature toggle switch – on-on SPST I had around
|Metal film PET cap
|Metal film PET cap
|Metal film PET cap
|Electrolytic cap 25V
|Ceramic C0G (NP0)
|Electrolytic cap 25V
|Small signal diode
|5mm Red Diode for clipping (try out what works best for you)
|Low current red LED
|1% 250mW metal film
|R4, R6, R7, R9
|LED current limiting (and brightness determining) resistor
|8 pin DIL socket so I don’t solder IC directly to the board
There couple of things to note here. I used a two pin power socket, which is fine since I didn’t use battery and I don’t need switched pin. I had to use a socket that is smaller than my usual Cliff socket. This also means, the socket had to be installed prior to soldering because it fits differently from the Cliff one.
I used 16mm pots for this, they are barely fitting the enclosure, hence some decisions had to be made during the assembly to be able to fit everything in. So far I’ve done single pot pedals in this small enclosure, two pots are a stretch, and I should’ve gone for a bigger enclosure (1590B for example). In the end, I managed it … but it was not a pleasant experience to be frank.
Board Layout Plan
As usual, I prepared one possible layout with DIY Layout Creator:
This was a struggle to fit in. If you look at the bill of material, there is a lot of components, by far the most complex pedal I covered so far. (And by all means, it’s not a very complex pedal as they go).
I had to solder indicator LED and accompanying resistor directly to the foot switch, I had no room on the protoboard (actually, I could’ve fit it to the board, I had trouble finding where to fit it inside the enclosure, so it was easier to solder it directly to the switch).
I did usual enclosure planning in Inkscape:
Very tight, barely fitting, my toggle switch is slightly slimmer so I managed to fit it all in the end. But it was very tight. Likewise it required me being a bit more careful than usual since there was no much room for error.
Here’s the original SVG I used for this:
I did standard stuff with drilling the enclosure first using the above template. Before doing anything else I made sure all components fit, would’ve been pointless if I could not fit them all.
If you look at the first photo from the gallery, 1590B is way bigger (relatively speaking) compared to the two 1590A enclosures. I regretted not going for a bigger enclosure by the end of the build.
For this build I decided to go with using universal primer in spray can, then I used some acrylic paint as top coat, then I used some acrylic paint markers for the design and finished it off with several coats of varnish in spray can. Here’s the process and the final result:
Aaahh, Picasso would be jealous.
I’ll prepare a very crude video as an assembly log with all the steps I took at some stage (I hope).
The final assembly was a bit tricky due to space constraints. Nothing that I haven’t really covered before but just with an added complexity of that toggle switch. That may have been a touch too much. But somehow I managed:
I hate all the wires. They are making everything take a lot of time assembling. Also, very hard to fit everything in.
I had to trim some of the board with a Dremel tool to be able to fit everything in. I’ll invest some time to maybe come up with a PCB I could use for small builds.
Here’s how the finished pedal looks like:
Finally, here’s how it sounds:
I like the pedal. Nice sound, not a huge level of control, but it is simple and works just fine. Some noise can be heard, and funnily enough, when I turned off the lights – noise was almost completely gone!!!! (check it out around 6:30 mark – just so you know – switching off lights does not help in all situations! ?)