my sound lab doesnt work :(

[neo644]

well, i've finished my sound lab and it doesnt really work..
i've checked the wiring already and it seems okey, plus i labeled all the cables so its very strait forward.
the main problem is that osc-1 and osc-2 don't work. but for example if i put osc-2 in ramp mode it apears to be working.
but then i have another issue with the main output pot because i have to turn it all the way to the right to hear anything, and its still very low.
i'm using stereo conectores, should i short cut the left and right channels?

i have added the fine tuners, the osc-1 mod by osc-2 and the led indicators. also the 1v/oct scalling, which i havent really adjusted yet, but i dont think this is causing any problems.

another thing that happens is that the LFO led indicator apears to function correctly, but if i connect it to the VCA, it wont follow the led's status. for example, i tested it with the noise source (since the oscilators dont work). the vca pot works correctly. now when i turn the lfo switch on, the vca will jump from one volume to another but very hard, and not sincronized with the led, which is fading in and out smoothly

also the square waveform in the LFO doesnt seem to work, at least by looking at the led indicator, it only produces triangle and the 2 ramps
/\/\/\/\
/|/|/|/|
|\|\|\|\

i have used some different components:
- TL074, TL092, LM13600
- 2M, 3M resistors = 1M's in series
- 500 ohm = 2 * 1K in parallel
- 620k = 470K + 150K
- 2uF tantalum = 2.2uF tantalum
- 1uF, 2uF ceramic = 1uF, 2uF polyester (the ones that go in the front panel and the osc-1 mod)

i used 1% resistores where indicated and also in some other places which it said to use 5%. but this shouldn't be a problem.

another detail is that i didn't connect X1, X2, X3 (the gate and cv inputs) since i'm testing it in a prototype casing and i wasnt going to use them anyway. could this be causing any problems? i think not because if theres nothing plugged in its an open conection anyway.


well, i dont really know what to do now. its sad; i was expecting it to work right away hehehe
thanks!

[Pehr]

[neo644]

yes i read that somewhere. i tried the switch in "rect" and then changed the other one (the one with the 3 positions) to every possible state and it worked as if the square/angular switch just wasnt there. it always did one of those waveforms

[Pehr]

Hmm, could be a bad switch. I've had to replace a few since I "fried" them with the soldering iron.

[neo644]

yes that happened to me too but the last time i checked this switch was working well. i'll have to recheck it.

i'll have to recheck everything though, because it still doesnt work

[neo644]

after alot of debugging i have found some little stupid mistakes, like a broken track which i had already seen and marked to be repaired in the soldering process, but i forgot.. stupid me.

apparently whats happening here is a problem with the oscilators. the vca and ar gen and filter work okey. the mixer alos works. the general output doesnt work, since i have to max out the pot to hear anything, but i'll try changing the pot, maybe its that?

but the thing with the oscilators is that osc-2 seems to work though the pwm pot doesnt do much, and some times it looks like it is connected to the LFO even though the switch is "off".

and if listen only to osc-1 all i get is an annoying beeeeeeeeeeep which doesnt respond to the freq pot or the LFO / AR gen switches.

i have also changed the IC but that didnt do anything. i'll try remove the 1V/oct mod to see what happens.

what could the problem be with the oscillators now oscillating?

[neo644]

yay!
i've removed the 1v/oct mod and the oscillators now work! i suspect i might have burned out the transistor since i had some trouble soldering the trim pot, maybe it was that, i dunno. but since i'm not going to build a controller right away i dont really need that mod now. i'll add it later on.

now there only seems to be 2 problems: the main output is still doing whatever he wants.. today i'll tray changes the 1uF cap to see if thats the issue. and on second hand the LFO doesnt produce the square wave, but i'll get to that soon.

if anybody has any ideas i'll really apreciate it

[Pehr]

[neo644]

i'll try to change the switch again then to see what happens.

i'm using a 100K pot, and i'm plugging it into my PC. but the thing is that it will only work when its maxed out. else i dont hear anything at all, not even a "very low signal". its just dead if i dont max the pot. i think it may be the pot thats broken.

[neo644]

nope, it wasnt the pot. i even tried removing the led indicator, and changing the LM13600 but nothing happened.

i'm very lost here. i think i'll just start all over again, i bet its some very simple and stupid mistake and i can't seem to find it with all this mess.

[Pehr]

What values do you use on R23 and C22?

[neo644]

R23 = 1K 5%
C22 = 1uF multi-film (or something like that. i couldnt find plain "ceramic" capacitors of this value. i've also tried with 1uF polyester)

i'm using stereo jacks, could this cause any problems?
i'm also using my PC as an amp, plugging the sound lab to line in, though this can't be an issue, or else how did everybody record their samples?

[Wild Zebra]

I think I can speak for alot of DIYer's when I say we've all have bugs to work out. I suggest you just step away from it for a day or two. Don't give up and start over yet. How do you have it set up. I now when I first took mine to a friends, who's been a synth geek for years. He didn't realize the VCA "initial". So if the AR what patched to the VCA and the VCA's initial was turned up you couldn't hear the AR. Just straight tone, get what I'm saying, simple mistake. I would of thought something was wrong with the circuit, nope something was wrong with my friend.
Do you not have an amp? Do you have a friend with an amp? Is the line in on your soundcard turned down? Is the master and the VCA turned up. I don't know, I'm just asking, it may not even be technical.
I've done stompboxes were I forgot to put the tranny in the socket. I may not be helping much. All I'm saying is take a break, then dive back in.

[neo644]

it's okey, i apreciate your help.

i'm aware of the VCA, to be able to hear anything, i have to turn it all the way up, the same with the mixer pots and general output. else i dont here anything.
i've tried line in and mic inputs of my soundcard. and i have turned their volumes up but still nothing. i can hear a very distant osc-1
and a very irritating beeeeeeep all the time, but i think thats because i have volumes to high.

but anyway i'll do that, i'll take a break for a couple of days. cause i'm going to have an osciloscope for the weekend so lets see if i can figure out whats wrong before restarting all over

[neo644]

scopes are nice
OSC-1, LFO, VCA, VCF, AR Gen works perfect! i even had fun playing around with the AR and seeing it in the scope. i got my hands on very cool digital tektronix which kicks ass

anyways, the problem with OSC-2 is with the square wave. the ramp works okey. i've followed ray's indiations on checking the PWM circuit. aparently the PWM pot isnt working, so i'll be changing that tomorrow.

on the other hand, when i look at the signal in point Z, which goes to the main output pot, the signal is very dirty. i'm only mixing in osc-1, noise and osc-2 are both silent. if i look at the raw output of osc-1 i see a nice clean ramp waveform, but in point Z its kinda "dirty". is this because of the filter and all the other processes the signal goes through?
anyways, it reaches the output pot okey, but then i only see it at the wiper of the pot when it is turned up all the way. i have the led indicators ground connected to this pot's ground, i'm going to try removing that, maybe it causing some trouble. i've already changed this pot for a known working one, so that can't be it.

also, the signal found at point Z is very low, maybe 1V when i have the VCA maxed out. is this okey?

thanks to anyone who reads this hehe

[Pehr]

Have you tried to set the filter to low pass with maximum cutoff frequency and minimum resonance? Also turn the osc freq to lower frequences, I would set it to ~ 440 Hz, since I know I've got a "dirty saw" when I turn the frequency too high