MAM MB33 WITH ACID FM MODS & EXTERNAL VCF CV INPUT- £165

For those of you who don't have a ridiculous amount of spare cash kicking around for a real TB303 (and we're willing to bet thats most of you) the FAT Freebass (otherwise known as the MAM MB33) is a very close substitute. If you want more info on the basic machine then we recommend searching the net for Freebass or MB33, suffice to say that the Freebass came out at the top of the Stay Up Forever records '303 clone test' conducted by DAVE the Drummer and Chris Liberator. Outside of Hardfloor, nobody knows acid better. The only drawbacks to the standard machine being that '303' is all it really does and the filter kind of loses it with the resonance full up and the cutoff over 3/4.

BUT WAIT! as ever the nice people at circuitbenders swoop down to rescue you from the tedium of dull acid lines with our bin buggering Acid FM mods!

Yes indeed ladies and gentlemen, our mods add 4 switches, 2 knobs and a jack input round the back to allow a whole extra smorgasbord of sonic mayhem. A veritable 3 course breakfast of orgasmic analogue delight! Something along those lines anyway :) 

The mods consist of:

VCO On/Off Switch: One of the most annoying problems with the standard Freebass is the way that the VCO is cut from the mix when a jack is plugged into the VCF input. This makes it impossible to stick it in a rack without spending half your time reaching round the back trying to find the VCF in socket. We have solved this problem by preventing the VCO being automatically cut when a jack is inserted, and instead adding a VCO on/off switch to remove it manually if you chose to. This means you can now permanently wire the VCF input into a patchbay.

VCO Drive: In our experience onboard distortions tend to be rubbish and you'd do a much better job driving an acid line through an analogue mixer so this isn't really a super distortion but rather just drives the VCO into the filter to add a little more bite and dirt to the acid sound.

Resonance Boost Switch: Another annoying issue with these machines is that the resonance never reaches full self oscillation (but then neither did the TB303) and also drops off considerably when the cutoff is over 3/4 of the way up. We've solved this problem by adding the resonance boost switch. With this switch activated the filter starts to squeal with the resonance about halfway up and then just screams at any higher settings.

VCF FM Controls: These consist of three controls and a jack input. Essentially VCF FM allows you to modulate the filter cutoff at audio freqencies to create all kinds of clanging cross modulation and bizarre alien splatters & sweeps. This effect works best with the resonance cranked up into self oscillation which is where the resonance boost mod comes into play. The FM controls allow you to select one of four sources for the FM signal. The first is the normal VCF input socket round the back. This means you can run a sound through the filter section, but also use that sound to modulate the filter cutoff at audio frequencies at the same time. The second source is a new FM input jack on the back of the rack. Using this source allows you to run a sound through the filter from the VCF input, and at the same time modulate the filter cutoff with an entirely independent sound source at the FM in jack. The main VCO signal can be added to the mix at any time. The remaining two sources are the sawtooth and sqaure wave signal from the main oscillator. These can be selected as sources completely independently of the setting on the VCO wave knob

The last the controls in the FM section are the VCF FM on/off switch, which, in line with common convention turns the VCF FM effect on and off, and the FM amount knob. This final knob controls how much the source signal modulates the filter cutoff.

External VCF CV input/: One of the major annoyances of these machines is the lack of MIDI filter control. While we can't add full MIDI control this is a 1/4 inch roundjack the back of the machine that will accept an external CV to control the filter cutoff. The voltage control sweeps the filter cutoff over 0-5 Volts, and possibly a little bit more if your midi-cv convertor can supply it.

There is no manual but seeing as tts about as hard to operate as a pencil you don't really need one, a page of instructions for the mods will be supplied.

For demo mp3's of this machine click on the buttons below. The first demo mainly features the VCO drive and Resonance Boost, the second and third are some filter FM action from internal and external sources. The final demo is of two percussion loops sent through the filter section.

We're working on a new contact system, in the meantime if you are interested in any machine on this page, click the button on the left and fill in the form on the page that opens.