Help please: StringRinger half-working

[mph]

Hello

I've finished the build of the string ringer V1.2 project today.
The volume, blend, timbre and drive pots are working, but on the 4 pos. oct/ring switch I can't hear a change and it pops loudy when switching between two positions.
The other pots and 4 pos. don't seem to change something. And strangely, the  LFO/Unlock LED is always on (it lights a bit brighter when the DPDT switch is engaged.

The only difference between my wiring and the one in the pdf file is the LFO Depth jack socket. As I hadn't a stereo double switched socket, I used a stereo closed on one pin only ( a Lumberg like this: http://www.banzaimusic.com/Lumberg-jack-closed-Stereo.html). I have inverted the ring and sleeve connections to switch them properly.

Of course I have checked the solder joints, the IC's and trannys orientation...

Any idea of what's wrong?
http://img204.imageshack.us/img204/4850/imga0199.jpg
http://img215.imageshack.us/img215/4544/imga0200.jpg

Thanks a lot!

[Taylor]

Do you hear an octave up sound at all? If so, this tells us that the ring modulator and audio sections are working, but the LFO and VCO sections are not. We can't debug from afar, but this will at least give you some idea where to look.

On big projects like this, my first order of business for debugging is to go through and carefully reflow all solder joints. Just because a joint looks good doesn't mean it is.

The right rotary switch is not for ring/oct, it selects the VCO waveform, and it won't do much if the VCO isn't oscillating. Build an audio probe if you haven't yet and poke through the circuit. Check the traces going to the VCO wave switch and see if any of them are there. If you have one, but not the others, the problem is in the filtering circuitry between the TL074 and the switch. If you have none, the TL074 is not oscillating.

[mph]

Thanks a lot Taylor!

yes I hear the octave sound, this part of circuit seems to work properly.

I have built an audio probe then checked some joints to track VCO signal. On the right rotary switch I have a signal which seems to be a square wave on points A4, A3, A2.  But I have nothing on point A1.

I can't find why the associated LED is always on. What is involved in the switching of this led?

Do you have more suggestions?
Could it be a dead resistor somewhere?

[mph]

Hi

well, I've found the problem:
I have not paid attention to this LFO Depth jack, it has a different ground from the other jacks. I have it wired correctly but the jack socket was not isolated so it was also connected to the main ground via the metal enclosure.
So simple...

After changing the jack socket with an isolated one, everything is fully working!
That's a great effect and a great project, thanks to everyone who has worked on this!

[Taylor]

I used these jacks for mine:

Http://www.smallbearelec.com/Detail.bok?no=771

plastic, so they don't need isolation, and they have a switch for all 3 contacts. They're the same type Lovetone used. Bit late for you, but maybe somebody else will see this in a search and find it helpful.

Glad you got it working, it's a very fun project.

[mph]

Taylor, you're right, I used the same jacks (from Banzai)... I call them isolated because that's plastic housing but I may name it in the wrong sense.

i just have another question:
the pedal is working properly audio-wise... but the yellow "LFO/Unlock" LED is not flashing completely. I mean I can see there's just a little variation in the light. On the other hand the green  "Oct/Ring" Led is flashing in the good way (a real "on" and "off" behaviour).
Can I adjust something to make this Led flashing on and off properly?
Does the 1K trimmer has an effect on this Led?

many thanks for your help.

[Taylor]

Experiment with different values for the resistor next to the yellow LED, R40. You could put in a trimpot to adjust it if you have one and don't want to swap out a bunch  of different resistors.

The 1k trimpot controls the hidden LED, the one pointed at the LDR, so adjusting this will only affect how that LED works. I must admit that I don't really get the point of the hidden LED; it seems to act as a tremolo when in ring mod mode.

[mph]

Hi

I have tried a 10K trimpot but when I reduce too much it makes D16 completely "off", and in the other way ( no resistance) it just does nothing but making D17 really "weak".

The problem seem to be around the amplitude of voltage modulation applied to D17. I am quite a noob so I don't know if I explain correctly this problem, but for me the amplitude is too limited to completely flash this LED "off".
Of course this problem is only present when the LED flashes in sync with the LFO.

Could it be a problem with IC3?

thanks again.

[Taylor]

I can't really think what the problem would be here. Is the LFO's effect on sound also weak? Have you tried changing the LFO depth?

[mph]

thanks  Taylor

yes, the LFO works properly, it has a good amount of depth (in FM or Freq. modes). Do you suggest to tweak the PWM trimmer? I thought it was to adjust the wave shape to the power adaptator I use with; and I have adjusted it to obtain a nice sine sweep.
I have tried to follow the pulse that is coming to the LED but I don't understand why it is not modulating D17 like D16. I have used my DMM in resistivity mode (the LED checking mode) and I have this pulse coming out pins A4 and A2 of the rotary switch...
Also I forgot to mention I used red LEDs for all the 3 external LEDs (if it matters).

For me it seems D17 is modulated by a tiny sine wave, instead of D16 which seems to be modulated by a good deep pulse wave... but as I am really a noob I cannot explain more precisely.

[Taylor]

The red LEDs could make a difference because of the different current limit resistors, but since you said you tweaked that and it didn't matter, we can scratch that.

The PWM trim shouldn't make any difference to the LFO, it effects the shape of the VCO, not the LFO.

D16 is modulated by the square wave LFO signal, D17 is modulated by the triangle, so it's right for them to be different.

[mph]

Ok so that's right like that.
I will try to find a yellow LED, if not I will let the red one in place.

Many thanks for your help!

[mph]

I have changed D17 for a yellow LED and D16 for a green one... there is a very small difference in the flashing (I don't think it's useful to have D17 in yellow compared to the red one).
And I am not sure, it seems that the max LFO rate is slower than with the red LEDs.
Is it possible?