hi antto, interesting stuff....
with TM5, if it only makes some patterns better do all the others sound the same or in any way worse?
TM3 - i think i previously turned this fully clockwise to get the resonance mod (x0xio) sounding better. is that sensible or will that make any difference to other parts of the overall sound?
envelope minimum decay R138 - is it possible to nail the sound by ear (spectrogram?), and would there be any worth in leaving R138 as a pot?
resonance adjustment R97 - think I may do this mod...
C13 socketed - anything specific in terms of type/beta works best, or just randomly swapping?
C11 - same question as above?
R36 - same..
Q9, Q10, Q11 socketed - again, just get a bunch of alternatives and swap at will? most threads have stated high beta of 8,9,10 and possibly low beta of 11 (seen mention of swap 526 to 945 - need to check what I have) are best. confusing
I still seem to be seeing a lot of conflicting info about other components though:
TM6 - been mentioned that going from 5.33 to 5.84v works well. anyone care to comment?
still leaves the following C19,C20,C21,C24,C25,C26,C27 - am i correct in thinking that foil caps for these are difficult to source
antto wrote:as i already did some tests about Q8 - it makes no difference, not just the hFE value but even the the transistor itself (i found 9 different types of PNP transistors from my old VCR which all worked and sounded the same)
TM4 and TM5 won't make your x0x more 303-ish since these are for tuning your VCO, however, if you slightly detune the "width" (TM5) you can make certain patterns sound a bit more interesting
i think probably in quite a number of acid tracks, the 303s that have been used were "off" more or less
TM3 is a more interesting adjustment, it shifts the frequency range of the filter (so it's equivalent to adding offset to the CUTOFF knob)
many people immediately say that "these two 303s/x0xes don't sound the same AT ALL" if only this setting isn't equal on both units, so it makes a huge difference altho it's a very simple thing
C29, as was discovered not long ago, on all TB-303s this capacitor is soldered "backwards"
it doesn't make a huge difference tho, i suggest you socket it...
now.. for making the x0x sound more like a 303, you need a reference, do you have a TB-303 there?
i have been doing this thing since i got my x0x, and while i don't have a TB-303, i have audio recordings from darffader's 303, which i use as reference
so i did some adjustments according to that
1) my envelope minimum decay time was slightly longer (this is the decay time on accented notes or when DECAY pot is at minimum)
this decay has an impact on the shape of the "wow" on accented notes
i desoldered R138 and used a pot to be able to temporary change it's value while looking on spectrogram to compare the decay time vs the reference, when i nailed it - i measured the resistance of the pot and used 2 resistors in series that gave the same value
2) resonance adjustment - i really recommend this to everyone
in my case i simply wired up a 10K pot in R97 because i need to be able to bring the feedback up to crazy levels for scientifical purposes
but for normal usage i would say you probably only wanna adjust the R97 value between 10K and 8K (below 8K it becomes really insane)
so maybe use a 2K trimpot with 8K resistor or something
i also socketed some other components
C13 - this acts as a LPF and creates the "wow" on accents
Q8 - square waveshaper transistor, tho it makes no difference what i put in there
C11 - square waveshaper this DOES have an effect, it is responsible for the PW characteristics of the square
R36 - square waveshaper this DOES have an effect, it can offset the PW of the square
Q28 - sawtooth buffer, i have placed a J201 tho it didn't change anything
IC11 - ehm, this doesn't have much to do with the sound
Q9, Q10, Q11 - these do some voodoo and are responsible for the VCF cutoff frequency and the parameter "coupling" between the cutoff/envmod/accent, haven't tested them much but basically the act as amplifiers for the signals i think.. Note: i haven't socketed Q11 actually