FAT Freebass / MAM MB33 Problems + Midi channel settings

[spk]

crusty paul u have the PM!

[DOXXOD]

Hello chaps and chapesses, i'm a forum newbie here. Just got hold of a FAT Freebass off a colleage, and after replacing a few doddgy pots am ready to do some bending. Already had a poke around with my wet finger tips n found some ineresting points, one that seems to by pass the decay n turn the tones almost SIDchip style. Will be posting some details as soon as i have some pots n switches hooked up. Any one got any pointers of what area to start looking for the FM mod or the VCO/VCF input switch mods?

Any help would be much appreciated, i dont want to blow this little beast!

Thanks in advance for any replys

Matt.

[Circuitbenders]

bugger, sorry people, ii completely forgot about this, everything has been a bit hectic over the past couple of weeks.

I've just shipped off the only MB33 i had already modded so i can't put up any photos but i'll dig out my notes asap and see what i can do.

From memory, the switch that cuts the VCO from the input when you plug a jack into the VCF input is the middle switching connector on the VCF input jack. If you cut the switching lever off you can connect a switch across the gap to turn the VCO on and off. I usually use a DPDT switch wired so that when its in the ON position the connection is made across the gap but when its OFF the switching lever side is connected to ground.

[Circuitbenders]

Already had a poke around with my wet finger tips n found some ineresting points,

Not something i would advise on a Freebass. You may have one of the versions that isn't prone to dying or you may just be very lucky, but thats asking for it.

[bliprock]

  yeha thanks circuit benders for the only place i can find my mb33 dipswitch settings. i copied it and went straight to my mb33 and found that it seems upside down. No drama cane farmer though... just read it upside down........i wonder if they put the dip switch in upside down?? or is it just different on the mb33 mk2..anyways keep up the good work and thanks again....

[superset]

Hello all… this is my first post but hopefully not my last.

Like most of you I have a non-functional FB383.  I bought it off of ebay for $10 and figured I’d be able at least, to utilize the filter section and maybe wire up the oscillators for external control.

I’ve documented my work so far which includes  three mods your all familiar with… the Resonance Boost mod, the filter input switch mod, and a Filter trigger mod which triggers the filter section allowing it to be used with external signals.

But what I think will be most helpful to all is a detailed circuit diagram which outlines signal flow through all components of the FB383 and MB33.  I’ve also detailed ground, the supply rail, the 5VDC lines and jumpers throughout.  Take note that the resistors with one black line are zero ohm resistors and are used liberally as jumpers.  You’ll also see overlays on most of the ICs so you can quickly identify the multiplexers, op amps, D/A converters, etc.

What I’m working on now is a schematic of the oscillator section for you all to look at, f with, and bend to your delight.  So far I’m having luck using pin 10 of the TLC2741N quad op amp as a CV input but the circuit begins to oscillate out of control… which some of  you may like, but a bit more stability would be useful in revamping these machines.  I’ll post more as I have something functional.

Anyway… you can find all the pics and documentation to the mods on the Flickr Collection here:

http://www.flickr.com/photos/97633426@N00/collections/72157606341720299/

and the high res circuit diagram is here:

http://www.supersetsounds.com/images/FB383/freebass_signal_flow_final.jpg