Help with a Vox guitar with built in effects.

[Jamforthelamb]

Hey Everyone.
I have a late 60's Vox Apollo that has a built e tuner, active tone boost, and dist. Everything on it works except the distortion. It switches on, but the effect is extremely light, and the pot doesn't have any effect. I tested the pot, and it seems to be working (1k value if that sounds right).  I'm going to TRY to test the wires next to see if everything has a good connection, but of course I'm wary of doing too much because I don't want to mess up this guitar. The circuit is a sandwich board that's accessed from a panel in the back of the guitar. Anyone have any tips for fixing it (besides don't fix it  )

Here's some photos.

[frankclarke]

Take photos of both sides of the fuzz PCB, and maybe someone will know what it is. It might be a simple fix. Nice!

[Jamforthelamb]

I tested the pot, and the switch. Both seem to working properly. I put it back together for now, but I will pull the back cover off and take some more photos soon. Here's what it's supposed to sound like:http://www.vintageguitars.org.uk/voxUltrasonic2.php
Mine only lightly distorts the signal (more so when playing hard), and it cuts the volume down when you turn the distortion on.

Thanks!
Kevin

[DWBH]

And I thought that Matt Bellamy was a pioneer...

[drewl]

That one should be easy...I fixed one that had the E-tuner, Bass/Treble boost, distortion, MRB effect, AND a wah all built into a 12string.
Anyway, each effect has it's own module.
The distortion is pretty much a fuzz face. One of the components is probably bad, coupling cap or most likely one of the transistors

[petemoore]

  Eye poppin' Axes !

[Jamforthelamb]

Drewl: Dude!!!!!!!! You have a Vox Ultrasonic 12 string! Those are super rare. I've been searching for a 6 string one for a while now. Lucky!

Back on topic. I figured it wouldn't be too hard. The biggest problem is that the board is a sandwich (circuit boards on the top and bottom, components in the middle). That's what makes me a little leary of going at it too much. Of course the wire is super thin as well.

[drewl]

If you look at the pc boards they connected by components or bus wire.
Just write down or sketch how they are connected....take your time and simply test or replace each component.
There aren't that many.
I have a wiring diagram and parts list, but not for the individual modules....if they went bad they were simply replaced.
Of course they haven't been available for about 40 years

[Mark Hammer]

Ooooh, ooooooh, I know, I know!!! (he says, waving his arm wildly so the teacher will notice).

It's a Vox guitar so it will be a Vox distortion from that era.  The distortion will in all likelihood be something of the Fuzz Face family (see Geofex article), meaning that a 1k pot is highly likely.  The 1k pot will most assuredly have an electrolytic cap from the wiper to ground, just as we see on all the Fuzz Face derivatives.  In this way the cap is connected to the emitter by varying resistances, with smaller resistance paths between the cap and emitter producing larger gains.

IF the cap is dried out or otherwise off spec, then the gain of the transistor can not be increased by having a more efficient AC path to ground.  If the gain of the transistor can notbe increased, then even a good pot will still not produce much output level or much distortion.

So....before you do another thing, change that cap.

Then, and ONLY then, you can come back here and tell me how right I was.....or not.

That's my best guess.

Incidentally, what a delicious-looking guitar.  Makes me miss my old Epi Windsor something awful.  Same thin-scale ES-125-style body with a floating bridge.  You're a lucky man.

[DougH]

That's really a cool looking guitar!

[nightingale]

very "warlocks"!
nice,
ry

[drewl]

No fair Mark, you're too advanced for the rest of the class.....
If you get a hold of some of the SS Thomas vox amp schematics, the effects in them will be very similiar to the effects in your guitar......same people made them.

[Jamforthelamb]

Thanks for the help guys!

Mark: We are in the midst of moving, plus I have a plethora of half done projects as always. I will make it a priority to open it back up once we move to prove how right you are 

God bless,
Kevin

[Jamforthelamb]

Ok, I found this...


Now, when this was still in the circuit, and I jumpered over it with a 10uf cap, I get full fuzz with no change from the pot.
I removed it, and tried pressing some different value electorlytic caps where it was, and nothing happened (effect was quiet).
Is this indeed an electrolytic cap like I think it is ? If so what value is it ? (100uf?).

Thanks!
Kevin

[drewl]

100uf at 12volts positive side up in your pic.

[~arph]

ducati ? 
Cool, I did not know there was an electronics company called ducati too. They specifically make caps.

http://www.ducatienergia.it

http://www.ducati.com

[Jamforthelamb]

Hey Everyone!
Sucess!!!! I replaced the first cap (that I put the picture of) and it didn't fix it. After some more looking I found an axial cap (10uf), replaced it, and now I have thick fuzz with working knob! You wouldn't even know it was a hollowbody if you didn't see it with the fuzz on.

Thanks for everyone's help (especially Mark).

God bless and Merry Christmas!
Kevin

[petemoore]

  Hello Vintage Fuzz !
  So good to see a Vintage item such as that restored, and having a happy owner who loves it !

[drewl]

Let me guess...black axial cap with red ends?
They go bad quite often on the Thomas Vox SS amps, the same guts of which are in your guitar.
All those caps have to be replaced when fixing those amps, they cause all kinds of problems.

[frankclarke]

Hello, I'm wondering if the treble/bass boost is this one: http://www.geofex.com/FX_images/apolobst.gif
Could you check the resistor values if you still have the guitar open, please?.
Glad you got it working, lucky you .