troubleshoot VCO: no SAW, only SQUARE

[kokoon]

haha thanks so much man, you've really helped me. i'm so happy this is working now... i'm already at phones amp/mixer and i hope to finish the thing today

[kokoon]

finished! everything works like a charm

thanks again for all the help, phantom "guest"!

[cheesy]

I too seem to be only getting square, no saw (assuming square is when the switch is in the lower position, and square is on the upper pin of the switch). It's very strange and flaky, but then again I'm using headphones and everyone seems to say headphones suck. I'd rather not try the stray-wire-on-desk method

First, when I plug in the power and don't apply any voltage to R89 sometimes I get a nice clean signal on the square pin, but sometimes it's a verrrry low frequency. Also sometimes it jumps between a few frequencies. When I apply approx 2.6VDC (two AA batteries) to R89 it definitely changes the frequency. Also when I change either of the trim pots or tuning pot the frequency changes, which is a good sign, but it's still very finicky and will randomly change frequency sometimes.

Second, when I try to probe the saw pin on the switch I just get a loud click like it's a DC voltage, then sometimes a very faint signal (which isn't affected by the pots), but the weird thing is when I go back to try to probe the square pin it usually doesn't work at all until I turn the x0x off then back on!

This can't be right, any suggestions? Should I just move on to VCF? I'm sure I've soldered in all the components correctly, the only thing I can think of is that there's some bad connections or fried components.

Thanks! I'm looking forward to getting this thing working hopefully by the end of spring break (after I get back from Cabo San Lucas, of course )

[cheesy]

I decided to measure R89 while listening to the square. When I'm getting the very low freq signal it's about 0.3VDC, medium is 2.5VDC, and high is 4.8VDC, so it appears the actual square oscillator is working (and I'm assuming R89 is fluctuating because nothing is controlling it...or it that bad too?)

Still, it doesn't explain the lack of saw...

[elmacaco]

Not to contradict the instructions, but I'd skip the headphones thing since it's easy to short the test point to something next to it, and mess up something that may be working as it should. also applying the voltages can be difficult and another opportunity for a damaging short.

It is possible to fix things with the whole unit completed, it might be better to just move on and deal with it later.

But I'm no engineer, so listen at your own risk!

[kokoon]

i'd also recommend you to move on... i mean... i DID get a clean signal on both sqr AND saw in the end before moving on... but it also did involve the "stray-wire-on-desk method". but i think everything actually worked okay from the start (i've re-socketed a transistor in the VCO later and it's still working - so it wasn't that either)

i've also experienced the behavior you're describing - the saw always had DC bias (a loud pop) - and sometimes after that i couldn't get sqr either (until reboot/recharge of some cap?)

i'd say spend like 5 more hours and you can have the entire thing finished. and test it properly then.

[cheesy]

Alright well I've completed the VCF section and it appears they both work when listened through the VCF, but still not through the switch...I guess it's my headphones or something.

[Krippe]

I had exaclty the same problem. The waves where hard to hear when probing at the switch in the VCO but when probing at the VCF everything worked like a charm.

[strangedave]

I seem to be having a similar problem. I'm only up to the VCO, and the square seems to be working more or less OK (I can't get my sound card scope to work that well, but headphone probing sounds more or less like a saw and freq varies with pot), but from probing the square at R105 I get nothing, no DC bias at all and no sound.

Up until this point, everything seemed fine. Power supply is more or less as expected (my multimeter seems lacking significant digits, so I only tuned to 5.33v not 5.333v, but surely that is not a crisis). I'm putting a bit more than 3 v, maybe 3.5V or more, across r 90 due to a flaky power source, but again, should that be that big a problem?

Any suggestions? Should I just go ahead and build the rest of it for now?

[phono]

I seem to be having a similar problem. I'm only up to the VCO, and the square seems to be working more or less OK (I can't get my sound card scope to work that well, but headphone probing sounds more or less like a saw and freq varies with pot), but from probing the square at R105 I get nothing, no DC bias at all and no sound.

Up until this point, everything seemed fine. Power supply is more or less as expected (my multimeter seems lacking significant digits, so I only tuned to 5.33v not 5.333v, but surely that is not a crisis). I'm putting a bit more than 3 v, maybe 3.5V or more, across r 90 due to a flaky power source, but again, should that be that big a problem?

Any suggestions? Should I just go ahead and build the rest of it for now?

the 5.333 isnt a problem really (one of mine is tweaked up to 5,8 for extra squelch) as for the 3.5, should be fine also, it just affects the pitch of the note. As to if you should proceed, i guess double check everything (including your testing method) after taking a short break. You could probably continue (your choice) but its better to pass all the tests before so that you dont have loads of problems at the end and no clue whats causing what.

[lameboy]

okay i modded the wallwart (i went to 12 shops and found ZERO AC/AC wallwarts) - so i just pulled everything out of my AC/DC wallwart and connected the wires. now i can get a nice 4.5 - 13 VAC out of it (selectable)

however, plugging it into the x0xb0x didn't help one bit. everything is the same, all the voltages are the same... it looks like the whole thing could run off a 12VDC as well.

I understand you have reportedly fixed your VCO, but i am very confused by what you have posted here...

you have a selectable AC voltage wall wart? I am not sure i have ever heard of one of those... Only DC selectable ones.

You need to have a 9V AC supply...
if you read Limor's page on the supply you will note there is a voltage doubler circuit in there...

http://www.ladyada.net/wiki/x0x/powersupply

If you use a standard 12VDC supply your voltage will be under due to the rectifier diodes, and filtering... which will shift things off a bit for the 12V supply.. not by a lot but possibly enough to make an audible difference.

I recommend using a 9V AC wallwart as stated in the directions, it will remove any doubts to if there is anything wrong w/ your supply voltages..

[DjunaSaurus]

Also got the same problem as a few others in here had. Can't hear a saw (don't have an oscilloscope or something), only a loud click at the beginning. But if my connection with my 3V adapter is a bit bad, then I can hear a very low frequency. Strange.
Square wave sounds good though, also when I use the tuning pot it goes up and down like it should. But that damn saw isn't sounding right.

I've read some posts here about the voltage at some transistors and I've got different ones:
Q26:
pin1 -2.23V
pin2 -2.23
pin3 -1.68
pin4 -5.01
pin5 -2.18
-> should be different right?

Tuning pot:
turned left
1: 3.11
2: 3.11
3: -2.21

centered
1: 3.11
2: 0.16
3: -2.21

turned right
1: 3.11
2: -2.22
3: -2.22

-> is this correct? Shouldn't pin 1 be that 5.33V?

All the previous tests were fine though.. Makes me wonder whether I should go on with soldering, since I got 2 signals (even though one isn't that clear).

[SubStyler]

check the area around C11, C31, C32 (voltages across) Q24, Q25 and the solder joints at S1.
maybe one of your eletcrolytic capacitors is bad or soldered in a wrong direction?
if you try to get saw wave, IC23 is getting hot?

cheers,
SubStyler

[guest]

its very common to not hear the saw
id suggest continuing with the build
as there is probably nothing wrong
especially consdering that the sqaure
cannot exist with the saw

[DjunaSaurus]

check the area around C11, C31, C32 (voltages across) Q24, Q25 and the solder joints at S1.
maybe one of your eletcrolytic capacitors is bad or soldered in a wrong direction?
if you try to get saw wave, IC23 is getting hot?

cheers,
SubStyler

I triple checked and everything is soldered right. But I didn't solder C31 and C32 yet (the manual didn't say so), but that normally shouldn't have any effect on the saw right?

especially consdering that the sqaure
cannot exist with the saw

That's kind of a relief. I'll solder the remaining parts then. I'm going to make a soundcard scope too, just to be sure when I''ll begin with the VCF.

Thanks for the replies guys! Cheers.