Microsynth troubleshoot! (Filter Question)

[j.frad]

ok so R105 is now 11k, the filter does seem to sweep a little, the attack delay works or not depending on my "trigger" setting, IC3 doesn't really heat anymore with the squelch set properly,

but IC13 is still heating, the sound I'm getting is massively distorted, I don't get a clean octave sound, just distortion and is sounds like the filter is overdriven too, I had a similar sound with my nurse quacky, I get oscillation if I turn the square pot too high, maybe because my power wires are a little too close to the cd4013, which I could try changing...
the trigger is acting really wierd...

It's getting better though, but the voice pots (octave/sub/guitar/square) all get me similar sounds and it seems I get sound whatever combination I dial on those pots, shouln't I have no sound with all pots low?


I'll be away for a week or so, but any suggestion until I can get back to setting up the right power supply and replacing the cd4013 is really welcome!!!

[RaceDriver205]

If you run into trouble, race driver, make sure you tell us ok

Sure thing, but my work on the synth will likely not resume again until after next monday, whence my studying will be over, and begun my holidays are.

[StephenGiles]

I had 2 original microsynths and they both ran hot, but this didn't affect the sound in any way. I made one on veroboard - what else!! powered by2 PP9 batteries and it worked fine. Frankly, I would be inclined to do the same, less chance of blowing your CA3094s.

By the way, it's bloody hot in England at the moment, we have something like 30C and high humidity which is likely to continue for the rest of this week.

[j.frad]

the weather is a little cooler here in france, is great and sunny.
yup, I've got exams here too!

last checks before I stop for a while,
-(BAD) The test amp I was using is a piece of crap so I plugged it into speakers, I can get an ok clean sound, the square wave, the octave up, no sub octave, so the cd4013 could be fried (I had a short circuit at the very beginning)
-(GOOD/BAD) that short probably burned the start freq pot that I replaced, now the filter sort of works, not very well though, unless I'm expecting the wrong sound, other thing, it only gives a good amount of sound whenn turned fully on/off depending on the wiring, else the output is very weak
-the octave up is not really an octave but I get sound, dirtier than my green ringer
-(GOOD) the resonance pot has an effect,
-(BAD) the rate doesn't seem to do anything
-(GOOD!) I had the attack pot miswired, now I get from no attack delay to swelling attack

And I'm off to check for other fried pots...

EDIT: ok no more dead pots. question: the power supply in the files is said to be -10/+9, someone said it had to be -10/+8, would it be really wrong to use -9/+9?

one more question: my short circuit was on board 3 under IC6, between V- and pin2  of the IC, is there anything that could be fried? I'm still getting the square wave signal so C6 should be fine, maybe it's just the pot that fried that saved everything...

[j.frad]

News from the battle field!
My cd4013 wasn't dead, I had the fet (bf245a) the wrong way, it's not the opposite from what is showed on the layout and I get octave down.
It seems the four types of sound interact with each other, maybe through the point where they all mix together, I can't get only octave up or only square wave, eiter the guitar pot needs to be up, or the sub octave, but thats ok for me...

I replaced the gain pot with a 10k, the clean sound only comes if distorted, like IC1 is misbiased (maybe it is because of the -9/+9 supply that I haven't changed yet).

I think the "voice" pots should be log...

I replaced the squelch with a trim pot since it needs very carefull setting and I don't ever want to have to set it again, here's how I did:
-set all 4 "voice" pots all the way up, "attack" as short as possible so that the noise is not gated,"trigger" full on too so the filter is way open (at least I thinks so),
-then if you adjust the squelch, on the negative voltage side I hear lots of noise and oscillation coming from the octaves and distortions, on the positive side it is gated.
-The trick is to find the point a which the noise is just barely gated, the, increase the attack delay time and it should be working... then you can do slight adjustments on the trim to make it soung the way you like, but it is an extremely sensitive pot...

Having realised the trigger pot controlled the filter (stupid me to just realise now) I played with it and realised the filter changed it's behavior. It's not great yet though. the resonance works, the rate works alright depending on the trigger setting, if the trigger it full on, setting the rate to zero results in no sound, I didn't expect the sweep to be so slow, maybe thats why i didn't notice it a first, it's like 5 seconds long, is that normal?
Problems remain with the start and stop pots: I get sound out of the unit only if the start freq pot is set a maximun (or minimum, most of my pots seem wired the wrong way) and the stop freq pot seems useless... I replaced IC 13 (damn ca3094s are expensive here! 9 euros! thanks there's smallbear! next time I do something like thins I'll make sure I order an extra chip just in case...) because it was heating but that didn't seem to be the problem. Maybe I'll try changind IC 9 too. Any idea of why I'm having this problem?

The gating at the end of the notes is a little abrupt and sustain is short, if I probe right after IC1, it sounds misbiased, the notes gate pretty quickly, no sustain. So 2 issues: misbiased sounding at IC1, any suggestions? and abrupt gating of the attack decay portion, would matching the 2n5088 help or is it useless?

Well that was pretty long, hope I was clear...
It's an almost workin unit! yeah!

[j.frad]

ok here's my question: the remaining malfunctionning area of the unit it the filter sweep, that's the start stop pots, IC9A (4558) IC13A (CA3094) and zener diodes, then to the sweep rate pot.
Assuming the ca3094 and rc4558 are fine , Q3 is oriented the right way and voltage at point 7 is behaving correctly, could a lower threshold voltage of the zeners (5.1v instead of 6.8v) produce what I'm experiencing: stop frequency pot useless and start pot allows the unit to put out sound only if set to an extreme position?

Does anyone know what subbing those zeners cause? because I had to do it. thanks!

[RaceDriver205]

I think having a 1.7v change in value has a good chance of causing circuit problems. I think you'd best change that. If its impossible to get the 6.8v zener, you can increase the effective voltage by adding three normal 1n1418 diodes in series with the 5.1v zener.

[j.frad]

thanks, I'll have a chance to do a trip at the electronics shop today, I'll try to get the right ones or else do as you advise...