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 Forum index » How-tos » Manuals, Instructions, and Documents
TB-303 Transistors
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BrassTeacher



Joined: Aug 24, 2010
Posts: 26
Location: Kennesaw, GA

PostPosted: Mon Sep 20, 2010 6:36 pm    Post subject: TB-303 Transistors Reply with quote  Mark this post and the followings unread

I know that this is a subject that has probably been discussed ad-nauseam, but I think my question may have a different wrinkle on the subject.

First, the reason I'm after this info is that I recently helped a former student build a x0xb0x, and I fell in love with the sound of the filter! I have quite a few vintage 2SC1583 and 2SC2291 transistors lying about, and I would like to clone the filter for a planned modular I'm working on.

For the middle of the ladder, the x0xb0x kit, and almost every other reference I've seen calls for 2SC536F NPN transistors. However, I'm looking at a fairly complete TB-303 service manual dated Feb 19, 1982, which is the source of the TB-303 Main Board schematic often seen on the web. This copy I have though has the previous page as well, with the not often seen Switch Board/Digital Board schematic. At the bottom of this page is a note: All NPN transistors on the main board are 2SC945 (P), All PNP transistors on the main board are 2SA733 (P). Oddly enough, the parts layout diagram in the same edition of the manual makes no mention of the 2SC945P, but shows that 2SC536F is used. To add to the confusion, the very next page of the SAME manual contains the parts list. No mention is made of either the 2SC945 or the 2SC536! scratch In fact, the parts list makes no mention of a small-signal NPN at all!

If anyone has a real TB-303 and doesn't mind looking under the hood (or bonnet!), I'd like to know which NPN transistors are mounted. I have a few '945 and '536 transistors, but not enough of either to finish the ladder. I'm also tempted to not worry about either one, and lay the board out to use 2N3904 instead. I'm not sure if the sonic difference would be audible or not. If anyone has any experience with the sonic difference, if any, between the three transistors mentioned so far I'd appreciate the input.

I say "mentioned so far", because I ran into yet another source that claims the BC182 is the SAME transistor as the 2SC536F, the only difference being the European vs. Japanese part number. Can anyone verify this? It seems that BC182 is still available, and cheaply.

Attached is a closeup pic of the service manual notation I mentioned...

Thanks!



EDIT (10/15/2010): After digging around for data since I posted this question, it appears the answer to 2SC536F vs. 2SC945P is both. 536 in the earlier builds, 945 in the later builds. Since there has been much talk of the effect of different semiconductors on the sound of audio/synthesizer circuits, especially the TB-303 and clones I've decided to do my normal thing to find the answers: Build a circuit in such a way that various parts being evaluated can easily be changed.

I've ordered a x0xb0x motherboard and processor and begun building it out. I'm not sure I'll even build the sequencer section or not, as the main thing I'd like to get out of it is a fun little monosynth (with a cool sounding filter!) and a midi-to-CV converter. A pic is attached of the first stage of the build, with only the diodes installed, and a machined-pin socket installed in EVERY semiconductor location:


TB-303 manual closeup .jpg
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TB-303 manual closeup .jpg



P6250001.jpg
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303 clone board w/sockets. Believe it or not, every socket on the board is salvaged from other dead equipment, or bulk purchased from surplus dealers.
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P6250001.jpg



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PrimateSynthesis



Joined: May 02, 2008
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PostPosted: Mon Mar 21, 2011 4:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's awesome. Overkill, but awesome, none the less. I would be curious if you found anything interesting.

Although, as someone who has two TB-303's, and played with numerous others, they all sound a bit different.
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Luka



Joined: Jun 29, 2007
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PostPosted: Mon Mar 21, 2011 11:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you havent already you need to review the information on the xoxbox forum. Lots of people have built their xoxbox with 945s. I cant hear any difference from those builds. Brain (bcbox) and some other forum members have done a lot of comparison work.

I always thought the tb303 sounded thicker throated in comparison to the xoxbox - I wonder if it just has to do with the age of the components / machines. I tried all sorts of mods on the ones i built and never got the 303 sound that all my reference 303's had. 98 percent there.

Some poeple say it is all caps, some say transistors, some say power supply.

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3phase



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PostPosted: Wed Nov 30, 2011 11:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

i think its an interesting question.
I changed my xox to 945 and it made it sound less glassy in the highs...

on the real 303 i imideatly suspected the one i got during my test run as one without 945..and voila..it is...

I am in a bit of a dilema now.. i have to mod it a bit anyway to suit my needs.
But i dont really like to swap the transistors.. just.. when iv to give it at testrun maybe i learn to like the 536 in the original 303..

In the original 303 the difference in sound that made me suspicious was a bit dryer more plastic sound it had to it, I wasnt used to..
Not like the xoxbox... that is having that too but with a nasty touch in the high filter peeks.. ..that nastyness is gone in a 536 real03 .. and that was the main issue that made me switch the transistors in my xox... So maybe not necessary to change a 536 303 into a 945 one..
I most definitely hope so.

However an intersting question because the sound differences between the two original 303 types are not really documented anywhere yet.

The interesting thing about the xox projekt was that i learned a lot more about the inner workings of a 303 than just looking at the schematics..

When i initially build it it hasnt sounded to me like a 303 at all... was doing the nice filter and accent dance too.. and sounded similar.. maybe better than a simulation plug in.. But not really satisfying for a long time 303 user that more or less grew up with the machine..

By now i did 2 more vintage rebuild projekts.. a mutron phaser and an old highend valve preamap..

and in all the projects the same circuit and same component types did´nt got the sound of the original..

and always the originals was a lot creamier..

So by now i dont see that as a specific xox box problem.. its just that same chematics and similar components are not the same!
Its not only because of the semiconductors used there..
The build quality of the capaciators and so on..

So the impact of the transistors is probably one factor too..but one of many..and maybe not the most significant..

the actual board layout and power supply of the 303 seem to do more on the special 303 squelch and scream than transistor choices..

however.. when we can optimize things by transistor choice..it would be good to learn about that..

I lately replaced 536 in a 808 with 945 ..partly..in the cymbal and hi hat section.. it actually made the sounds smoother

so by now i assume that the 536 has a sharper sound..

But thats for just an educated opinion. would need some more input on the topic to verify this.

Maybe this thread is a good place for the question. We will see whether over time additional info comes in..

Sofar i am not convinced enough to do experiments on a real 303 in that direction.
Its definitely not like in the 808 with the overly sharp hi hats i performed the change that clearly stted a difference, but there it was a clear better - worse thing, hurts,,,dont hurts... So out of question.. a 808 is better of with 945´s at least in the cymbal hi/hat department...
But nothing hurts with a 536 equipped 303 sound.
So the question better or worse or just differnet cant be really answered for me yet..
I am used to a 945 version. thats for sure.. but that dont says that i cant like the 536 version. have to see how our relation develops.
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