Modding a Roland Rhythm 33 (TR-33)

[Circuitbenders]

which is why i used an old AVO analogue ohmmeter i've had kicking around for years 

[Circuitbenders]

Well, i just hooked together 10 x 150mH inductors in series and its almost there. It sounds like it could do with about 2 or 3 more to take the pitch down a little so its more like the original sound i've heard on youtube demos of the TR55, but its certainly usable.

I guess the original inductor must be meant to be something like 1.8 - 2H. 

[gmeredith]

Will changing any of the other component values in the network change the pitch instead eg. resistors or caps??

Cheers, graham

PS you've got to do a MIDI fitout to program your own crazy rhythms from a sequencer on this thing - I'm going to do it to my TR33 when I get through all my other projects 

[Circuitbenders]

I just tried exactly that about 10 minutes after my last post. In the TR33 service manual theres a section on adjusting the sounds and it mentions adding smaller caps in parallel with the coil if the sound isn't tuned quite right, i.e. adding extra capacitance to the LC circuit.

On the TR55 theres actually a couple of empty holes in parallel with the coil to add extra caps. I just added a bit more capacitance and now its sounding pretty much spot on.

The next problem is that fact that both the hi and low conga/bongo LC circuits are constantly oscillating very quietly so theres a kind of low humming noise floor, kind of like a mains hum. TR77's are also a nightmare for this and despite all my efforts i never managed to iron it out on one of those, so i'm pretty much certain that this is impossible to eliminate, unless anyone has any ideas? The hum is definitely coming from the inductor circuit on each sound as i can change the pitch with the same adding capacitance technique.

If i can't sort out the noise floor, i'm not sure theres any point to installing midi, but its next on the list.

[gmeredith]

In section 11-3-3-2 of the TR33 service manual, it mentions adjusting the "semi-fixed resistor VR305" to adjust the decay time - I'm thinking maybe the decay time on your congas are too long, such that they never completely shut down - or their output adjust volume is too high. Maybe that will relate somehow to your 55?? In section 11-3-3-6 there is a specs chart for all of the drum sounds, including peak output voltages, decay times etc. Methinks an oscilliscope might be needed to see what's going on with your congas.

Also, take a look at my individual output mod I did for the 33 - there are output points on the board for some of the instruments, and for the ones where there isn't, just poke arounnd the transistor solder points with a small set of computer speakers and some multimeter probes/clips attached to the speaker input plug. if nothing else, it may help you to process troublesome voices individually (like a noise gate pedal on the conga out etc)

Cheers, Graham

[rqckmounted]

Hello TR 33 owners

Glade to know this post is still alive...

I would like to simply mod the TR 33 with Din sync, I have tried to locate where and what to solder using the tr77 mod thinking it will be the same thing but havent found anything yet.!!

http://www.burnkit2600.com/tr-77/

If someone could point me into a dirrection with the TR 33  how to do the same thing ( will be very appreciated )


I need to sync it up with my  Akai mpc  and Doepfer Mcv 24 that give me the ability to have differents/ any PPQN I want.

Best regards,