No tremolo on VooDoo Labs Tremolo

[GussyLoveridge]

Hey Folks -

Having trouble figuring this out. I can't find a schemo online.

Here's what I do know:

The pedal passes signal both on and off.
The Intensity and Volume pots both seem to work.
Slope and Speed don't seem to do anything.
If I come down the ribbon cable from the Speed pot with my circuit tester I get some almost clicking that changes with the rotation of that pot - giving me the speed of the tremolo...
I'm kind of lost further than this.

Thanks in advance,

Gus
Cape Breton, Canada

 

[Khron]

Sounds like the LFO isn't working (properly)..?

Photos (well-lit and well-focused) might help.

[Edit] A bit of google-fu later:

https://www.reddit.com/r/diypedals/comments/3d3qyr/does_anyone_by_chance_have_a_schematic_for_an_old/

 

[GussyLoveridge]

VTL5C3 has been replaced - is that the LFO in this case?

 

[Khron]

Not as such, the vactrol is the control element, actually. LFO  = Low Frequency Oscillator (just to clear things up).

 

[GussyLoveridge]

Right, okay.

So what component/components make up the LFO then?

 

[Khron]

Now THAT is the million dollar question now, isn't it? Schematics for this particular unit seem to be unavailable, and since i'm no mind-reader, i have no idea what circuitry's in there

But for what it's worth...

http://experimentalistsanonymous.com/diy/Schematics/OOP%20Japanese%20Electronics%20Book/stereo-box.gif
http://www.tremolo.pl/Efekty/Tremolo/Tremolo.gif

 

[GussyLoveridge]

Thanks Khron - I really appreciate your help and patience.

 

[Khron]

No sweat I'm just sorry i can't give you any more specific advice - not really easy (or actually, possible) without a schematic to look at...

 

[midwayfair]

If you want to repair this and you can't locate a schematic, you're going to have to work out at least the basics of the effect's schematic.

Take a picture of the guts and post it.

Pull out your multimeter. measure the voltages on all active devices and post them. Make sure you label the pins correctly.

Make an audio probe (it's just a cable and a capacitor). Trace the audio signal from the input jack, through the switch, to whatever the first device in line. In every Voodoo Labs pedal I'm aware of, that will be one of the op amps. Continue tracing it through the circuit in a way that makes the most sense until you lose it. So probe the input and output pins of each op amp stage. You won't have signal on all of the stages.

Now set your multimeter to continuity. Locate the parts connected to the LED side of the vactrol and back trace it to the op amp that it's connected to. Make sure that you have an oscillating voltage on that op amp.

Other things to check:
1. Make sure your Vacrol isn't upside down, or backwards.
2. You can temporarily replace the LED side of the vactrol with an LED so you can see what's happening. Once you get the LED blinking, you can reconnect the vactrol.

Even without seeing the guts of this pedal, I almost guarantee you that the circuit consists of the following:

1. Non-Inverting op amp stage
2. Inverting op amp stage DC coupled to the previous stage with the Vactrol forming a gain control just in front of it as a series resistor.
3. Dual Op Amp LFO with a triangle output, where the first stage is the LFO itself and the second op amp buffering the LFO output from the depth control.

Which means one of the op amps will have a bunch of moving voltages, and the other won't. The dry path will be super simple.

 

[Whoops]

Hi Gus,
is this kind of situations where a schematic is not available online you should proceed like this in this order:

1) Always contact manufacturer first asking help for the repair and asking to buy a schematic from them. Normally they are helpful and sometimes they even provide you the schematics for free, specially when you are dealing with smaller companies like Voodoo Labs (bigger companies would be something like Roland or Yamaha)
Most common Faults in pedals are normally well know by the manufacturer by this point, so they are the ones that can easily point you in the right direction.
Have you tried contacting Voodoo Labs?
if not you should do it now

2) After step 2, you should post in a pedal oriented forum/community, the biggest ones are diystompboxes and freestompboxes forums, there's repair help and also people can help you trace the schematic from the circuit board

3) When you post a Repair Help in a forum without a schematic you should always post pictures of the PCB and guts of the pedal. If people dont see a schematic and there's no photos of the components it will be hard to help you and chime in, No one knows all the circuits and components by memory.
You should take pictures high res pics  of the PCB components Top view, and also from the pcb traces side, then in photoshop or similar software, merge the 2 together with some level of transparency (solder side photo will need to be inverted). This way not only can people see the circuit but also is really much easier to trace the schematic.
check this examples:

Hope this helps and that you will be able to fix the pedal soon,
I learned this tips and procedures by fixing a lot of pedals and equipment with the help of fellow forum members.

All the best




http://jbwid.com/guitar/ob2b1.jpg

 

[Whoops]

Just to add that when a Pedal manufacturer refuses to sell a schematic or provide any help, I will immediately trace the circuit myself and post it online.
Most of guitar pedals can and should be fixed and not binned or replaced straight away for a new one if there's a problem, It's my opinion that manufacturers should provide schematics for repair. And even more in the cases were they don't repair or service that item any more.