Modding a Roland Rhythm 33 (TR-33)

gmeredith · November 06, 2008, 04:41:25 AM

Hey all,

I just scored a TR33 from a recycle shop for $15 hehe! It's an old boom-chick preset drum rhythm box from 1972. It's actually a great project subject because its sounds are of the CR78 style drum sounds, the forerunner to the TR808.

Inside, the circuit boards are all discrete transistors and components, and is a delight to poke around in (WARNING this is a mains powered device!!!!) if you are careful.

So far, I've been able to isolate most of the individual sounds and output them with separate out jacks. The Kick drum, Low and Hi Congas all have their own volume, pitch and decay trimpots. I'm going to mount these controls on the outside.

I've also found an output point that gives the Kick drum a much sharper, punchier sound (tapping off a pre-filter point). It sounds much more like the classic TR808 sound now, and if you turn up the decay trimmer on it you get that real big boom boom boom techno 808 kick, hehe !!

At the moment I'm trying to shape the snare sound - it's made up of 2 sounds - the "pfffttt" type noise, and also a wood block type sound for the snare "ring", which end up getting mixed together at one point in the circuit. I've got outs for both oscillators and mix them together externally. I've also added a pot/capacitor control for the "pfffttt" part of the snare that can dial in or out bottom end to fatten or thin it out.

I'd also like to look at manually triggering all the sounds, maybe even via MIDI. But that's later.

I'll upload some photos as I get these things sorted out, as well as some diagrams of all the points of interest, in case anyone else comes across one of these beasties!!

Cheers, Graham

nochtanseenspecht · November 06, 2008, 09:53:16 AM

wooh that is fantastic find ! you must be happy
maybe you could use one of these to trigger http://highlyliquid.com/kits/decoder.html
or find some points inside that change the rhythm
congratulations !

gmeredith · November 07, 2008, 12:24:51 AM

I was thinking about one of the MIDI kits from Highly Liquid but i didn't know about that one. That might do the trick.

Cheers, Graham

gmeredith · November 10, 2008, 11:00:58 PM

Well, I've just managed to find a service manual for it from a synth repair tech guy. This shoud answer all of my remaining questions regarding modding this thing

This guy has lots of service manuals and schematics, in pdf format for only $15;

http://www.muzikelektronix.com/MEsmListing.txt

I've pretty much mamaged to do everything I wanted to do to this machine.

I've got separate outputs for:

Kick, snare, hihats, low conga, high conga, rimshot/cowbell/claves. These last 3 share an output because the same oscillator produces all 3 of those sounds.

Controls for sounds :

Kick - pitch, decay, punch (sharp attack control)
Snare - ring, hiss, bottom end
Low conga - pitch, decay
High conga - pitch, decay
Mix output - volume, tone

Once I've got all the pots and sockets mounted nicely and I've played with it for a while, I'm going to look at adding MIDI, or at least triggering the sounds manually. I already have found some trigger points that fire some sounds when you touch them with a probe, from what I understand the early roland machines use a negative voltage pulse to trigger the oscillators, so this should be fairly simple.

I've printed out a nice control panel template to mount all my controls on the front panel, check it out below. I'll take photos of my finished work, inside and out, very soon!!

cheers, graham

Signal:Noise · November 12, 2008, 07:26:19 PM

Cheers for that link Graham, he's got a service manual I was after

gmeredith · November 13, 2008, 11:48:45 PM

OK, here's some pics of my prototype!

The fascia design was drawn up in a photo program and then printed out onto paper, then laminated. Easy!

The MIDI section is not installed yet so the front panel MIDI controls are vacant in that part.

The wooden sides are made of rare Tasmanian Huon Pine, I've yet to fine sand them and varnish them.

Cheers, Graham

gmeredith · November 13, 2008, 11:49:24 PM

and some more:

nochtanseenspecht · November 14, 2008, 08:33:10 PM

mp3! mp3!

gmeredith · November 16, 2008, 09:51:49 PM

I'll get some samples very soon - especially of that new fat kick drum hehe!

Cheers, graham

gmeredith · November 17, 2008, 01:56:33 AM

OK, here are a few mp3's of the some of the modded sounds, at the bottom of this thread here:

http://www.vintagesynth.com/forum/viewtopic.php?f=5&t=42957

I'd post them here but this site won't upload the mp3's

Cheers, Graham

nochtanseenspecht · November 17, 2008, 07:46:49 PM

very nice job, Graham !
i love that kick

DenDer · November 28, 2008, 09:38:59 AM

Nice work Graham that's absolutly stunning. Maybe starting to look for one if i can find one.

gmeredith · November 30, 2008, 10:53:17 PM

If you do, you'll find it easy to work on, since you were doing your DR55. It sounds similar to it, but the boards are nice and big and spread out.

Cheers, Graham

djsynchro · December 14, 2008, 03:01:40 AM

Niiiice does it still play the preset rhythms?

gmeredith · December 14, 2008, 10:04:19 PM

Yes, all the original functionality is still completely intact. When I do get the MIDI IN board for it, I will be able to run the preset rhythms and add extra drum hits via a MIDI sequencer, if I wanted to do that (although I think I'll end up just sequencing the whole rhythm and just use the machine as a sound module - easier than bothering to sync it to a sequencer).

Cheers, graham