With the Band FOMO we have an analogue 303 clone (Future Retro Revolution) at the heart of the band, creating the Acid House flavour.

When using a 303 you soon come to understand that it's an instrument and the playing with the relationship between filter cutoff, env elope amount, accent and accent delay is the source of the magic associated with the machine.

Also you come to understand that without some kind of distortion or overdrive the sound is not the one that captures you on the dancefloor - the acid shriek, that comes from hitting a device that will fold in some of resonance to where we can hear it as the 303 on it's own soon ascends into bird like warbling rather than full throated acid.

Where do you start? Obviously with the Proco Rat - beloved distortion pedal of Hardfloor the acknowledged kings of 303, famously using 2 of them an Hardfloor Aceperience.

Match made in acid heaven

This was where we started, but I felt there was an issue with the sound. Now there are Rats and Rats and we're using a 2000's era Proco rat, which, if you're a rat afficiando, has the wrong op-amp in it and all that stuff. But I felt like the problem was more systematic than that - where was the bass? The Revolution has a really nice overdrive switch - it's just on off but gives a great thick sounding overdrive effect but the acid shriek was missing - to warm!

And so began the quest for the ultimate acid disto pedal.

Gathering information

Where else to start but Analgue Heaven? Check the thread: http://analogue-heaven.1065350.n5.nabble.com/303-distortion-pedal-td149790.html

I got a lot of great responses -

modded Boss DS1 - i replaced the clipping diodes w red LEDs and the fet with a J201. Much creamier, rounder and thicker distortion. Instant hardfloor on a 303! Travis

Boss HM-2! David

I recommend trying a re-amp box to get a little more out of the line level 303 to guitar level pedal. Now I have 2 of these L2A's and they are really nice: https://www.diyrecordingequipment.com/products/l2a These boxes have brought so much joy as any pedal can work its specific wonders on my synths. My distortion pedal changes its character dramatically with this thing. Kenny

modded Boss DS1 - i replaced the clipping diodes w red LEDs and the fet with a J201. Much creamier, rounder and thicker distortion. Instant hardfloor on a 303! Em

dod death metal and a dod grunge in series. has gain. lorne

HM-2 got a lot of shouts! One of my favorite responses came from Andy @ Cytomic -

The Rat's drive is a combination of slew rate limiting from the initial op-amp, and then hard clipping for a pair of diodes. If you want the same tone but to lower the high pass (to keep the bass) you could wire in another capacitor in parallel to C5:


If you put this cap on a switch then you can switch it in circuit when you want to lower the cutoff. A 47u capacitor (of the same type as is currently used in the Rat) in parallel to C5 will lower the cutoff from 1.5kHz down to around 70Hz. The other parallel capacitor path with C6 is at 60Hz, so that should be fine for lots more bass and exactly the same gain. A 47u cap is a pretty big value for cap, so they cost a few dollars each, but you only need one!

I would also recommend checking out an Ibanez Tube Screamer TS-9 DX. The TS-808 / TS-9 cut the bass way too much so aren't so useful for synths, but the TS-9 DX has a mode switch which lowers the high pass filter and swaps in different diodes, which makes it really versatile since some songs a thinner mid sound works well with low gain, but most of the time you want to distort and gain up the bottom end as well. The TS series always mix in the dry signal so you get parallel distortion of the form:

output = input + shaper (gain * highpass (input))

with low gain and low highpass you get a very parallel gentle drive sound, but when you gain it up with the TS-9 modes and then lower the output you get a pretty wet sound.

If you're ok with loading plugins and want to have a listen to what the TS-9 DX sounds like then you can grab the beta of The Scream: https://cytomic.com/scream and then grab this preset pack: https://cytomic.com/files/scream-beta-presets-2.zip , it has all the TS-9 DX modes in there so you can have a play.



Dude! I ok with literally anything you say! I love the internet!

Em though pointed out this page: http://www.acidvoice.com/tb_303_best_distortion_pedal.htm - candy!

Looking through the highest voted on that page my eye was caught by the Fultone OCD - I already had an OCD pedal that I'd got for guitar so that is our current - has plenty of bottom end and on the right setting also has the scream.

The only problem is that as it's an overdrive it also has a fuzzy warmth where the rat had a kind of precision that gave the sound great definition.

So the next step is to try out a build of the MXR Distortion + - highest rated on the acid voice page and used by Iron Maiden. I was tempted by the Turbo Rat which uses red LEDs for the diode distortion stage - so I will try red LED's in a Distortion + clone and report back with some audio!

Later notes

After trying the Distortion + I came back to the Proco Rat and settled on the Turbo rat. I'm still playing about with the best op-amp chip there (it is one of the few distortions where changing the opamp actually changes the sound).

The biggest single change came from lowering the signal to guitar pedal levels using one of these: https://www.diyrecordingequipment.com/products/l2a - the quality of the sound in the mix is much clearer. It was especially apparent with the echo (using a Korg SDD-3000). I now need to go back and re-evaluate all the pedals with the lower output as I believe this will make a sizeable difference.