Q8 transistor - possibly many alternatives

[antto]

hi guys
i believe you can use many other transistors for Q8 instead of the 733P, as they appear equaly good (soundwise) or maybe even slightly better
i just tested all kinds of transistors i had around here, and like.. 30% of them worked (square wave sounds good, no need to twist legs or place backwards..)
some of them i can't clearly read the labels, if anyone's interested i can try to list their names

[Brassteacher]

hi guys
i believe you can use many other transistors for Q8 instead of the 733P, as they appear equaly good (soundwise) or maybe even slightly better
i just tested all kinds of transistors i had around here, and like.. 30% of them worked (square wave sounds good, no need to twist legs or place backwards..)
some of them i can't clearly read the labels, if anyone's interested i can try to list their names

Was one of them 2SA1015? I've been meaning to try it, it is the complement to 2SC1815

[antto]

so far i've found these to either sound equally as the 733P or maybe slightly better (but definately not worse)
A1267GR
A033 (label not really clear, can't be sure)
608 FOM (or maybe it's 508 F0M)
A833 S RZ (could be A933, btw the front side is gray on this one)
A984 KE18
A15610 U (this one has a funny shape, it's not tall, but wide and the legs are spaced perfectly to go in holes on the PCB without bending them)
some of these are from broken PC-mouse, others are from my old broken VCR (Sony) which also has many Sanyo parts

btw, if anyone has a list of other possible alternatives to the 733P - go ahead, i can try anything
i'm not sure if these parts will also work (technically) in the filter or the other sections of the synth where 733 are meant to be
but something tells me that if they're good enough for Q8 - maybe they are good enough for the filter too? is this correct?

i can try to put more sockets around the filter or in specific places
btw, the other transistor which is responsible for the waveforms was some K30A it's a FET right? i'd like to also try stuff in that spot (me wants a more 303-ish sounding square)

[antto]

found another one
A1703 S OM (this one has a similar funny shape as the other i mentioned above)

i also socketed Q28 and tryied some stuff
3 parts worked, but they all changed the tunning of the VCO dramatically (and tweaking TM5 can't fix that)

[Brassteacher]

btw, if anyone has a list of other possible alternatives to the 733P - go ahead, i can try anything
i'm not sure if these parts will also work (technically) in the filter or the other sections of the synth where 733 are meant to be
but something tells me that if they're good enough for Q8 - maybe they are good enough for the filter too? is this correct?

i can try to put more sockets around the filter or in specific places
btw, the other transistor which is responsible for the waveforms was some K30A it's a FET right? i'd like to also try stuff in that spot (me wants a more 303-ish sounding square)

Try these for Q8: 2SA933, 2SA1015, or 2SA1115. 2SA1115 comes in a very small package, and usually only the numbers "115" appear, mainly because that's all that will fit in one row!

As far as the JFET goes, I'm sure you already know about J201. Also, 2SK118 is a good substitute. The 2SK118 also comes in the tiny package, and usually only displays "K18" across the top.

[antto]

i think the A833 i mentioned in the first post is actually A933 (kinda hard to distinguish) it's front side is gray, and is a smal package as you say

i tryied to measure the hFE with my cheap multimeter
my original A733P gives 270
the other transistors give values between 219-242 so i won't mention them
the lowest hFE i can find is:
A15610 - 182
A984 KE1B - 162

the highest hFE value i can find is:
A984 F1H - 275
A1267GR - 295
A1267GR - 300

even with all these different values - they sound the same (thus i haven't made a more scientific test yet)

Brassteacher: thanks, i'll see if i can find these in the shop and i'll get them next time i go there

[Brassteacher]

i think the A833 i mentioned in the first post is actually A933 (kinda hard to distinguish) it's front side is gray, and is a smal package as you say

Yeah, I've seen 933's in both packages. I have both lying around someplace, especially the bigger ones, and all are vintage.

even with all these different values - they sound the same (thus i haven't made a more scientific test yet)

That reminds me, I have REALLY got to get back on that project! I've been busy working on other synths and rebuilding the garage shop.

Brassteacher: thanks, i'll see if i can find these in the shop and i'll get them next time i go there

If you have trouble finding any of them, yell, and I'll send you some decent spares that have been salvaged from vintage gear...

[antto]

i bought 10 x 2SA1015Y
hFE ranges between 212 and 220 (one or two had a little higher)
sounds the same

i also found 2x 2SA733P (the labels on them are different than the 733P's in my x0x)
one of them is hFE ~260
they both sound the same too

yet i still think i can't quite get the 303-ish square
i'm thinking i gotta change something around the transistor
could Roland had placed yet another capacitor in reverse in that part of the circuit, similar to C29?

now i'm waiting for J201 and probably SK118, i hope they order them so i can get em

meanwhile i can make audio comparisons with different transistors in Q8

EDIT:
9transistors.rar test with a single pattern, 2 pattern loops per transistor (i've cut the audio so it loops perfectly) the right channel is the same but i've faded each take to have a "visual" aid, and there is a .txt with the transistor names, 96KHz 16bit (rar is 7.5MB)

so far i can't hear any difference

[Sokkan]

I did some tests a couple of years ago regarding Q8-10 and the combination with a proper Q28:

http://forums.adafruit.com/viewtopic.php?f=13&t=6735

There are examples there with 4 different transistors at Q28 combined with high and low beta 733s at Q8-10. You might find the sound examples interesting, and maybe you will come to the same conclusion that I did.

[antto]

Sokkan: cool but the files there are missing

[antto]

meanwhile, since i have a breadboard now.. i replicated the x0x square waveshaper and rerouted the x0x sawtooth (from Q28) thru the breadboard and back to the waveform switch (i removed Q8 so the internal square is not audiable)
http://www.box.net/shared/26zoiu21p06763usbkqt

i used an adaptor for the 12V to R45 on my breadboard, also..
i didn't have a 22K resistor for R45, so i used a 100K pot and tweaked a bit.. PWM ;]

[juicepatrol]

i bought 10 x 2SA1015Y
hFE ranges between 212 and 220 (one or two had a little higher)
sounds the same

i also found 2x 2SA733P (the labels on them are different than the 733P's in my x0x)
one of them is hFE ~260
they both sound the same too

yet i still think i can't quite get the 303-ish square
i'm thinking i gotta change something around the transistor
could Roland had placed yet another capacitor in reverse in that part of the circuit, similar to C29?

now i'm waiting for J201 and probably SK118, i hope they order them so i can get em

meanwhile i can make audio comparisons with different transistors in Q8

EDIT:
9transistors.rar test with a single pattern, 2 pattern loops per transistor (i've cut the audio so it loops perfectly) the right channel is the same but i've faded each take to have a "visual" aid, and there is a .txt with the transistor names, 96KHz 16bit (rar is 7.5MB)

so far i can't hear any difference

I know this is a pretty old thread but some thing that I did to get my square sounding like the 303 is a combination of a 945 transistor at Q11, and a 733p/ap at Q8 both as high hfe as you got. Then most importantly do the pwm mod. I can't remember exactly which resistor in the vco it is but you just swap it with a pot. If you search the forum in xoxmods you should be able to find it. This will allow you to get very close to the 303 sound and more.

[antto]

hi
Q11 has nothing to do with the square wave
Q8, according to the results i got here, the hFE has no significant effect
the "pwm" mod - yes, certainly

[juicepatrol]

Q11 does not have anything to do with the square but it effects the way the filter sounds. It gives in my opinion a much warmer sound compared to the 536 which came with my xox. And I know there is lots of debate about beta gain making a difference. After socketing Q8 and going through about 50 733ps it does have an effect. It makes the square more rubbery and full in the middle frequencies which gives the resonance more to play with. And what I did with the pwm is borrowed my friends 303 and just tweaked my xox until it was to my liking.

[antto]

saying that "Q11 affects the way the filter sounds" is like saying "tweaking the cutoff knob affects the way the filter sounds"
Q11 is not part of the filter's audio path, it's part of the cutoff+envmod+accent parameter coupling
...at least as far as i know

you tested 50 transistors in Q8 and they didn't sound the same? that's interesting
i tested many transistors too, picked 9 of them with various hFE, and made a recording.. they sound the same to me
i also played with the square wave in a simulator, which confirmed that the hFE of Q8 didn't have a significant impact
the passive elements around Q8 (resistors and capacitors) have a much bigger impact on the waveshaper
maybe i wasn't looking in the right place, can you explain where is the difference exactly? "more rubbery and full" doesn't really say anything to me