Ring Stinger problems

[Taylor]

I built a Ring Stinger and am trying to get it to work. Here are the symptoms:

-Sound only comes out when bypassed
-on/bypass and LFO lock/unlock LEDs turn on and off as they should
-ring/octave LED is always on. When I stomp on the switch, the LED becomes a little brighter
-LDR LED is lit up, but not flashing as I assume it should be with the LFO
-Substitutions: I subbed a diode array IC for the diodes. I also swapped C5 (should be 3.3n) for something close... forget what.

I triple-checked that all ICs are in right. I don't really know what voltages I should be reading, but all ICs are showing some voltages at their pins.

Any thoughts on what's happening or what to look for to narrow down the problem?

[soggybag]

Time to break out the audio probe! Make an audio probe and start from the input and follow the signal until it goes wrong. This will help locate the problem.

[Taylor]

Here's the schematic:

http://homepage.ntlworld.com/paul.nelson666/StringRingerv12r.pdf

So, audio is fine until it hits R3. Supposed to be a 2200k, I used 2.21m which I'm pretty sure should be fine. I pulled out the one in there and put in a new one. Same problem. Right after coming out of R3, there's no sound. Any idea what to look at that could be causing this?

[oskar]

That's like an insane amount of components...   

So, audio is fine until it hits R3. Supposed to be a 2200k, I used 2.21m which I'm pretty sure should be fine. I pulled out the one in there and put in a new one. Same problem. Right after coming out of R3, there's no sound. Any idea what to look at that could be causing this?

One side of R3 is a Vref. which should be silent. Does the signal reach the OP-amp?

[Taylor]

Ok, fooled around with it for quite some time, and I now have sound, including ring modulation, coming out of the output. The problem now is that I only have 1 carrier frequency. Turning the frequency knob has no effect. The LFO is also not working - the LED/LDR pair is lit up, but not flashing, and turning the depth and rate knobs, as well as the LDR trimmer, does nothing.

Probing around the circuit where I thing the VCO should be audible, I hear a tone. This is the tone that is modulating the input, but as I said, it doesn't change frequency or wave shape, and I'm not really sure if this is even the tone that's supposed to be there, or just some stray oscillation.

Any thoughts?

[Nitefly182]

Here's the schematic:

http://homepage.ntlworld.com/paul.nelson666/StringRingerv12r.pdf

So, audio is fine until it hits R3. Supposed to be a 2200k, I used 2.21m which I'm pretty sure should be fine. I pulled out the one in there and put in a new one. Same problem. Right after coming out of R3, there's no sound. Any idea what to look at that could be causing this?

Looks like you subbed a resistor with a value an order of magnitude larger than it should be. Did you really sub a 2.2 meg resistor for a 2.2k one?

[Taylor]

No... Reread that. 2200k = 2.2M, no?

[Taylor]

One other thing I subbed is an electrolytic cap for C20, which should be a non-polarized type. I read that you can do this, and I put it in both ways, but the problem's still there. Could this have anything to do with the VCO problem? Is there a reason that an electro won't work here?

[Nitefly182]

No... Reread that. 2200k = 2.2M, no?

Ok Im just confused because no one else really mentions resistor values in the meg range as multiples of a 1k value. You mean you put in a resistor with a value of 2200x1000 ohms? That would be 2.2 megs. Its just weird that the schem lists the value that way.

[oskar]

One other thing I subbed is an electrolytic cap for C20, which should be a non-polarized type. I read that you can do this, and I put it in both ways, but the problem's still there. Could this have anything to do with the VCO problem? Is there a reason that an electro won't work here?

But audio come through allright, doesn't it? An electro should do for C20, they are polar and should see either the same DC level on both side or more in favor of the + side. Check this with a DVM across the cap.

Turning the frequency knob has no effect. The LFO is also not working - the LED/LDR pair is lit up, but not flashing, and turning the depth and rate knobs, as well as the LDR trimmer, does nothing.

I'ld start by checking up on the Vref's. Check all DC voltages/ref's going to the VCO and LFO. Vref2, V+1... etc.

[Taylor]

OK, but what should those voltages be?

[oskar]

Are you familiar with the concept of a voltage divider? That's how the reference voltages are produced.
V+1 slightly more than V+. Vref1 is V+/2. Vref2 is (V+1)/2. Voltages denend on power source.

[Taylor]

Thanks for the help so far.

Poked around reading voltages, but couldn't make any sense of what I was getting, so I went around reflowing solder joints and it works!

Well, almost. The LFO waveshapes all seem right, but the VCO isn't putting out the right shapes. They are all pulse-ish waves. I can't get the square square or the sine sine-y. The LDR LED is lit, but not flashing, and I'm guessing that it's there to smooth out the waveform. I am adjusting the PWM trim, but no luck. The LDR trim doesn't seem to do anything.

Any ideas what could be malfunctioning?