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Recreating the original TB 303 CPU? Is it really that hard?
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Recreating the original TB 303 CPU? Is it really that hard?

by illCarl on Fri Dec 03, 2010 8:29 am

Hi everyone

ok, here's an electronics-noob asking a question, so please be nice :D

I was just wondering why there is no CPU replacement available for TB 303's. The synth-part of my 303 seems to be fine, however the CPU is gone.. It's quite hard (acutally.. Impossible) to find an original CPU, so I don't quite understand why there is no replacement available. The x0xb0x has a more complex CPU then the 303, so I would guess "it can't be that hard" (must hate this sentence) :) I think there was this guy doing the ULTRA 303 mod (which included a CPU replacement and a display), but looks like he's not doing that anymore. I would prefer to not change anything on my 303 anyways, so a display is a no-go :)

If for whatever reason a CPU can not be recreated, would it be possible to use the x0xb0x sequencer to trigger the 303 via midi? I wouldn't mind adding a midi port to my 303.. but I don't really want to change anything else on it :)

I'm quite desperate to be honest.. I've been looking for a 303 for years, finally found out by coincidence that a guy who works here with me had one in a drawer.. he's actually not even asking big money for it.. but then we figured out the CPU is gone. ARGH!


many thanks for your answers! :)
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by phono on Fri Dec 03, 2010 11:46 am

there are simply none available, theres no easy way to recreate it either. Theres a very long thread on the analog heaven mailing list about this subject.

Put simply its not going to happen anytime soon. However drop fiercefish a private message here, he was recently selling one and may still have it.
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by Luap on Fri Dec 03, 2010 1:03 pm

Hey illCarl, It was you I was talking to about this over on the Props forums, right? Has the CPU been confirmed as broke then?

But yes, unless you can track one down (which would be hard, and largely down to luck), then it doesn't look good. One other quite drastic option though... BCbox is looking to make 303/X0xb0x crossbreed PCB's. So it's basically a 303 with a x0xb0x CPU. Or, a x0xb0x in a 303 case, if you like.
It would be a lot of work, as the entire thing would need stripping down and rebuilding, but quite doable. And you would of course be re-using all the key components from your original 303.

Ripe909 has already done it, but I don't believe he's selling PCB's..

A big job, but its a possible option to consider if that CPU is definitely toast.
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by mazatta on Fri Dec 03, 2010 1:19 pm

Is it still possible to trigger (from an external source) a 303 or x0x without a functional CPU?
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by phono on Fri Dec 03, 2010 1:42 pm

mazatta wrote:Is it still possible to trigger (from an external source) a 303 or x0x without a functional CPU?


if you modify it for cv/gate inputs then yes
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by xlarge on Fri Dec 03, 2010 6:20 pm

http://www.beepworld.de/members52/accenter ?
midi303, a retrofit. I don't know the inner works of it.
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by Altitude on Fri Dec 03, 2010 10:27 pm

xlarge wrote:http://www.beepworld.de/members52/accenter ?
midi303, a retrofit. I don't know the inner works of it.



That's just a midi backpack that patches into the circuit, has nothing really to do with the CPU
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by darffader on Sat Dec 04, 2010 6:03 am

textile's cpu upgrade + antto's n0nx0x and some code hacking will be perfect

in fact, once that is possible, i'll sell my 303 cpu's and mod my 303's with n0nx0x and 16 extra leds.

it's a matter of time
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by xlarge on Sat Dec 04, 2010 6:38 am

Altitude wrote:
xlarge wrote:http://www.beepworld.de/members52/accenter ?
midi303, a retrofit. I don't know the inner works of it.



That's just a midi backpack that patches into the circuit, has nothing really to do with the CPU


Yeah, that was the point as the OP also asked about midifying his 303 bypassing the possibly borked cpu.
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by phono on Sat Dec 04, 2010 6:43 am

darffader wrote:textile's cpu upgrade + antto's n0nx0x and some code hacking will be perfect

in fact, once that is possible, i'll sell my 303 cpu's and mod my 303's with n0nx0x and 16 extra leds.

it's a matter of time


this is probably the most viable cpu replacement option for a 303, please catalog it when you do since it'll be interesting to see how you impliment the rotary switches.
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by illCarl on Sat Dec 04, 2010 4:17 pm

Hi All

First of all.. Wow! Thanks for all the posts / tips :)

@phono
Thanks for the tip.. I have already sent a PM to fiercefish, hopeffully he see's it soon :) I'll also check out the analog heaven mailing list, thx for the tip again.

I know there are none available, and I know that these things are not produced since the 80's. I just find it kinda weird that no one has tryed to emulate the old cpu.. Whoever can do it COULD make loads of money if he really wants to.. Just think of all the 303's with broken CPU's around the world. At least I'd be willing to pay quite some money for such a replacement CPU :) Or maybe someone tryed but doesnt want to share.. I don't know.


@Luap
Yes that was me on the Props forum.. You're kinda everywhere right? :)
The guy who analysed the 303 basically said that "he's pretty sure it's the CPU.. Since it seems t b doing something different every time".. Well.. sounds like CPU to me too, but then again I'll probbly ask someone else to check it again.. A x0xb0x in a 303.. That would be an option.. but since I suck at electronics it's probably nothing I'd try.. But who knows, maybe someone is willing to do that for me :D


phono wrote:
darffader wrote:textile's cpu upgrade + antto's n0nx0x and some code hacking will be perfect

in fact, once that is possible, i'll sell my 303 cpu's and mod my 303's with n0nx0x and 16 extra leds.

it's a matter of time


this is probably the most viable cpu replacement option for a 303, please catalog it when you do since it'll be interesting to see how you impliment the rotary switches.



That sounds pretty cool.. I just read a good part of the n0xn0x thread (viewtopic.php?f=13&t=16065) Great stuff!. What exactly is "textile's cpu upgrade"? Also, I thought these are all x0xb0x upgrades / mods..? Would this really fit in a tb?

Finally.. Please hit me up if you hear about a CPU in some drawer or a valid CPU re-build makes it's way to the interwebs :) If I have to wait, then I will wait I guess :)
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by antto on Sun Dec 05, 2010 3:01 am

n0nx0x is the firmware i'm developing, it's all about providing the basic functionality of a real TB-303 sequencer (pitch mode, time mode, you know..) and adding modern features on top of that (complex pattern manipulation..)
unfortunately, the original x0xb0x CPU is pretty small and this firmware exceeded the size it can store.. and i haven't yet started to put the good stuff in the firmware O_o
so the only way for this to work is a new, BIGGER cpu
that's what textile is doing, a bigger CPU mod (upgrade) for the x0xb0x
once i get my hands on this.. i continue developement of n0nx0x :wink:
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by illCarl on Sun Dec 05, 2010 3:55 am

antto wrote:n0nx0x is the firmware i'm developing, it's all about providing the basic functionality of a real TB-303 sequencer (pitch mode, time mode, you know..) and adding modern features on top of that (complex pattern manipulation..)
unfortunately, the original x0xb0x CPU is pretty small and this firmware exceeded the size it can store.. and i haven't yet started to put the good stuff in the firmware O_o
so the only way for this to work is a new, BIGGER cpu
that's what textile is doing, a bigger CPU mod (upgrade) for the x0xb0x
once i get my hands on this.. i continue developement of n0nx0x :wink:


Ahh! Got it now :) OK.. Good luck with the project then!! Just in case you're bored... I'm happy to send you my 303 to get your mod built into the 303 :D If it fits.. :D
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by antto on Sun Dec 05, 2010 5:17 am

:shock: uhm..
i don't have a "mod" .. i'm just writing code and flashing it onto the x0xb0x CPU via USB
if you don't need the 303 (you gonna throw it away) sure, send it to me ;P~
textile is doing the actual CPU mod, it's a small PCB containing the new (bigger) CPU chip which has to be connected to the x0xb0x (thus the original x0xb0x CPU removed)
as for the firmware.. there are some issues..
TB-303 has 24 buttons, and 2 switches
x0xb0x has 23 buttons, 2 switches and 1 tempo encoder (with a button)
and there is a huge difference in the number of LEDs they have

so the n0nx0x code would have to be modified in order to work on a 303
EDIT: also, n0nx0x can't do some things the same way as on a 303 because of the number of buttons and how they are placed on the panel, so some changes/compromises had to be made
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)
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Re: Recreating the original TB 303 CPU? Is it really that hard?

by westfw on Sun Dec 05, 2010 6:22 am

So let me see if I understand this...

The original 303 CPU is some sort of ROM-based NEC microcontroller for which neither the documentation nor the orignal code is availible. Duplicating it exactly is essentially impossible.

What MIGHT be possible is to program a modern microcontroller with similar-acting code, and put it on a sort of module that would plug in to the spot where the original CPU plugged in (I can't tell whether this was socketed.) However, most of the people doing this sort of mod are aiming it at the more modern cpu socket already in the x0xb0x units instead, and the code is also aimed at the x0xb0x button/etc layout...
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