Q8, Q9, Q10 IN TB303

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Mussi81
 
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Q8, Q9, Q10 IN TB303

Post by Mussi81 »

Hi people

i now have a self sourced x0xb0x kit ready and waiting to be built. but before i start i want to get my sorry tb303 back up to standard.
i plan on having my 303 professionally serviced and calibrated.

but before i do this, one thing i want to do is replace the transistors in q8, 9 and 10 with high beta.

does it matter what order the transistors go in? i.e lowest beta transistor in q8 and the highest in q10?

or does it not really make any difference at all

thanks in advance

Luap
 
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Re: Q8, Q9, Q10 IN TB303

Post by Luap »

My understanding was that this tweak was largely recommended for x0xb0xes due to the substitute transistors that are often used. IE, when using 733P's instead of the 733AP's that TB-303's use (P's are still readily available, AP's are rare and more expensive). The gain structure is different, hence why you can compensate by putting the higher beta ones in those positions.
But your 303 will already have 733AP's anyway, so there should be less need to optimise them?
See the transistor section of the mods section here: http://www.ladyada.net/make/x0xb0x/mods.html

As for getting the 303 serviced. Given that it is nigh on the same inside as a x0xb0x (bar power supply and sequencer sections) I expect what you learn in building the x0xb0x will help you a lot in being able to service the 303 yourself? I guess it depends what might be amiss with it though..

Mussi81
 
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Re: Q8, Q9, Q10 IN TB303

Post by Mussi81 »

Hi luap
thanks for the reply

My reason for wanting to do this is that my 303 has never really had "acidy resonance" when the cut off and resonance are fully open.

Yes my 303 does have 733ap already but I just though that maybe they were lower gain ones.

Could there be another issue perhaps?

Mussi81
 
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Re: Q8, Q9, Q10 IN TB303

Post by Mussi81 »

I suppose that I could service the 303 myself. I just want to make sure it's all done correctly

Once I've built my x0x I would probably have more confidence in doing it myself

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phono
 
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Re: Q8, Q9, Q10 IN TB303

Post by phono »

Mussi81 wrote:Hi luap
thanks for the reply

My reason for wanting to do this is that my 303 has never really had "acidy resonance" when the cut off and resonance are fully open.

Yes my 303 does have 733ap already but I just though that maybe they were lower gain ones.

Could there be another issue perhaps?
Some 303's just don't sound as acid as others, but it may be a simple task of calibrating, especially the vcf setting, check out my blog , you can find the 303 service notes there. I would strongly recommend running through that procedure first before pulling any parts.

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antto
 
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Re: Q8, Q9, Q10 IN TB303

Post by antto »

Mussi81 wrote:Hi luap
thanks for the reply

My reason for wanting to do this is that my 303 has never really had "acidy resonance" when the cut off and resonance are fully open.

Yes my 303 does have 733ap already but I just though that maybe they were lower gain ones.

Could there be another issue perhaps?
any audio samples demonstrating this? i'd like to hear it.. (dry samples if possible)

Mussi81
 
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Re: Q8, Q9, Q10 IN TB303

Post by Mussi81 »

Thanks for the replys guys

I think a good starting point would be to calibrate it first and see how it sounds afterwards.

Since I have played around with the pots it has improved the sound slightly but it's only been done to my ears and not a meter or a scope.

I'll put some audio on my soundclound over the weekend

Mussi81
 
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Re: Q8, Q9, Q10 IN TB303

Post by Mussi81 »

hi

i have added a sample to my soundcloud.

http://soundcloud.com/musselwhite/dry-303-loop

please take a moment and listen to it and tell me what you think

thanks

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isak
 
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Re: Q8, Q9, Q10 IN TB303

Post by isak »

i dont know if this sound clip is with the 733AP's or the 733A's but its sound very good to me man.

Luap
 
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Re: Q8, Q9, Q10 IN TB303

Post by Luap »

isak wrote:i dont know if this sound clip is with the 733AP's or the 733A's but its sound very good to me man.
733A's :?: It's his 303 which as he said earlier in this thread, has the original 733AP's in it ;)

Anyway, the clip sounded ok to me. Needs some tuning though I think? Unless it was an oddly programmed riff. It was hard to tell.

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antto
 
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Re: Q8, Q9, Q10 IN TB303

Post by antto »

thanks for the sample
well, i'd like just some tiny bit more resonance there (this is easy, i did it on my x0x, with a 10K pot in place of the 10K resistor at R97)
other than that it looks pretty normal, square is good

the only thing else i noticed is the VCA "attack" (we got a discussion in the other forum about it) shape looks like on most of the x0xb0xes = not very smooth
a hint to the electronic geeks, maybe find the answer to "why the x0x VCA clicks"
btw, the attack here is ~32samples long (at 44100Hz) while my x0x is somewhere around 23-26 IIRC

but overall your 303 is in perfect shape.. maybe you really want some tiny bit more reso..

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rv0
 
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Re: Q8, Q9, Q10 IN TB303

Post by rv0 »

Soundclip sounds perfect to me.

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phono
 
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Re: Q8, Q9, Q10 IN TB303

Post by phono »

darffader wrote:Soundclip sounds perfect to me.
slightly dull on the open filter, may just be vcf center freq set wrong

Mussi81
 
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Re: Q8, Q9, Q10 IN TB303

Post by Mussi81 »

Thanks for listening

So basically if I calibrate it things should be ok?

I thought adding the high gain transistors would give it that extra resonance. But maybe in try a pot in r97 instead.

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antto
 
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Re: Q8, Q9, Q10 IN TB303

Post by antto »

by "calibrate" - what do you mean? centering the cutoff knob to 500Hz like the manual says?
your 303 is okay, i can't see anything wrong with it soundwise

as for R97 maybe first try to mesure the actual resistance
in my x0x it was 9.97K, and after replacing it with this pot now, the usual value i tend to use is between 9.0 and 9.5K, but it gives me freedom to tweak it however i want (since i'm doing some experiments..) the pot is connected from outside the box (soldered some long wires in the place of R97)

in your case a 10K trimpot might be better, so you can directly solder it inside

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