Replace R1 in the power supply with 200 ohms?

by katarakt on Sun Jan 25, 2009 7:13 am

I currently read http://www.ladyada.net/make/x0xb0x/mods.html "Picking the right transistors " and i wanted to pick the right ones on Q10, Q9 and Q8 but now i read that R1 should be changed to 200 ohms? Is this really necessary? ...does it affect some other things if i do that or can i leave the original R1 in there?
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Re: Replace R1 in the power supply with 200 ohms?

by phono on Sun Jan 25, 2009 7:14 am

you can leave that standard, since afaik its unconfirmed that it actually makes any difference
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Re: Replace R1 in the power supply with 200 ohms?

by guest on Sun Jan 25, 2009 7:24 am

the r1 mod was supposed to emulate the filter warble
of the 303 under high resonance conditions
but since the powersupply is so different
it doesnt really do a good job of it
and can make it sound worse

ive been thinking about ways of doing that mod better
and an lm317 would probably do the trick
but its more complicated to do
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Re: Replace R1 in the power supply with 200 ohms?

by katarakt on Sun Jan 25, 2009 7:57 am

Ok thx :)
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Re: Replace R1 in the power supply with 200 ohms?

by guest on Sun Jan 25, 2009 8:25 am

in case anyone is interested
i just measured the powersupply in my 303
and the output voltage is 15.7v
so in theory
you could remove r1
and replace it with an lm317 trimmed to 15.7v
and then use a 47uF capacitor at its output
connected via a 100ohm resistor to c8
and replace c8 with 47uF
that should be a pretty good emulation of the 303 powersupply
the to92 lm317 package is probably fine for this application
it would also help for people who have >500ma wallwarts

in case someone wants to use a switcher
the switching frequency on the 303 powersupply is 130khz
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Re: Replace R1 in the power supply with 200 ohms?

by rarara on Thu Mar 14, 2013 10:11 am

talk about resurrecting an old thread.... :roll:

anyone tested this lm317 theory from guest and care to comment on its effectiveness??
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Re: Replace R1 in the power supply with 200 ohms?

by Altitude on Thu Mar 14, 2013 8:59 pm

Interesting theory but I think you really need to go all the way and make the switching supply to make a full judgement. Brian Castro uses the Sumida transformers (the same parts as the original) in his BCb0x to replicate the 303 PSU exactly and I dont think you will get there with the LM317 which is just an adjustable voltage regulator, too modern, too stiff
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Re: Replace R1 in the power supply with 200 ohms?

by rarara on Fri Mar 15, 2013 2:01 am

is there any kind of documentation relating to what would need to be done?
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Re: Replace R1 in the power supply with 200 ohms?

by antto on Fri Mar 15, 2013 4:29 am

this could be interesting, scroll down to see what Robin Whittle says about the exact TB-303 power supply
http://analogue-heaven.1065350.n5.nabbl ... 06880.html
just sayin' .. don't expect the power supply to change the sound.. :wink:
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Re: Replace R1 in the power supply with 200 ohms?

by rarara on Fri Mar 15, 2013 6:54 am

hmmm, thats the problem with reading these things - nothing is conclusive. there will be plenty folk who will tell you with certainty it is a factor, and just as many who say the opposite.....

what about another 'myth' which i'm sure i read here some time within the past few months (can't find the thread tho) - someone posted that their x0x sounded different (the implication being better) when fed from the CV output of another machine rather than the internal sequncer??
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Re: Replace R1 in the power supply with 200 ohms?

by Altitude on Fri Mar 15, 2013 6:58 am

rarara wrote:hmmm, thats the problem with reading these things - nothing is conclusive. there will be plenty folk who will tell you with certainty it is a factor, and just as many who say the opposite.....

what about another 'myth' which i'm sure i read here some time within the past few months (can't find the thread tho) - someone posted that their x0x sounded different (the implication being better) when fed from the CV output of another machine rather than the internal sequncer??


no myth. i ran that test. driving the cv and gate from a 303 vs playing the same pattern had different results. using the 303 to sequence the x0x made them sound identical
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Re: Replace R1 in the power supply with 200 ohms?

by antto on Fri Mar 15, 2013 7:27 am

ugh
i want proof
recordings or technical explanation or something
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Re: Replace R1 in the power supply with 200 ohms?

by aminoacid on Fri Mar 15, 2013 7:35 am

Interesting. What os did you use and how did you connect the 303 to the xox?

I do read sometimes that people cant hear differencies when for ex using different caps or transistors. When my self have been socketing almost every transistors, alot of caps and some resistors, and finding alot that makes the sound. I feel that people either listens through Their computer speakers or they are old and half def.

I would like to mod my psu just to see if it does some to the sound aswell.

Is brian really using the original psu circuit? Cant find this info...
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Re: Replace R1 in the power supply with 200 ohms?

by Altitude on Fri Mar 15, 2013 8:34 am

my personal x0x is modded where i can switch between cv in and out. i should have made some recordings but i was really just testing everything on the tb and the client was in a rush to get it back. for me it was definitive though, tonally the x0x and tb303 are super close (id say indistinguishable) the difference is elsewhere. my personal theory is the sequencer, psu, and d to a behavior


ive built 30 boxes total and i can tell you that this or that capacitor isn't going to make a difference


Brian was showing off a box of the sumida parts on gearslutz
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Re: Replace R1 in the power supply with 200 ohms?

by antto on Fri Mar 15, 2013 8:38 am

he claims he does, he even has ordered the missing "sumida" transformer to be remanufactured for him
technology trasplant also have it (they sell it and they also use it in the TT-303)
but when i asked Brian what exactly does the powersupply change soundwise, he didn't give any convincing proof
plus, what would you do if you have purchased 1000 sumida transformers and it turns out the whole powersupply doesn't seem to make any audiable difference? would you admit it? or would you keep the myth alive?

i can be totally wrong here, Brian is still welcome to give me some proof, i requested audio recordings or anything
that's my own opinion, and you can see that RW states the same thing in the AH thread i linked to above
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