Rocket Distortion Contortions

[cheezit]

That odd behavior brought on by the guitar's volume control sounds suspiciously to me like a wiring or solder bridge problem.

I built a circuit for a friend once that had some amazing problems that could be altered by messing with the guitar's volume control.  After a lot of troubleshooting, I discovered a trace that hadn't been completed removed during the PCB fabrication problem.  It was allowing some inappropriate positive feedback plus some DC shift at the input jack (the feedback was before the initial coupling capacitor).

So...

1) Check for bridges again...  and again... and again...
2) Check wiring again...
3) Plug a standard cable into the input (to turn the effect on), but do NOT plug in your guitar.  Use your voltmeter to see if there is a DC voltage between the tip and sleeve on the input jack.  There shouldn't be...  If there is, this is indicative of some sort of wiring problem -- typically a bridge of some sort on the circuit board.

Perhaps OT, but I bought an Ibanez analog delay a long time ago that would vary the delay when I moved my guitar.  It was almost cool, I could turn around and the echo would wobble like crazy, as if I were wiggling the rate knob.  It was too unpredictable though---when I wanted it to wobble it wouldn't do it!  Finally took it back, and the GC guy thought I was insane.

[Brushthrower]

Before I rewire this pedal one more time does anyone want to give me their opinion on the accuracy of the wiring of  3pdt on this layout?:

http://www.generalguitargadgets.com/diagrams/rocket_lo.gif

It is a bit different from the one suggested here:

http://www.diystompboxes.com/smfforum/index.php?topic=970.0

I'm a little confused as to the variations.

Thanks!

[tungngruv]

Why not just try this to get the fuzz working, then get the led after the pedals up and running.

[PerroGrande]

Yes -- the wiring link you posted *IS* correct.  It *is* a little different because it grounds the board's input when it is not in use.  Otherwise, it looks good.

However, the previous poster's point is really good...  Simplify for the purpose of testing.

I actually take it a step further.  I test the board with no switching involved at all.  I use alligator clips to connect the output of my guitar to the input of the board.  Likewise, the output from the board goes to the amp... No switching, etc...  Same for the battery/power supply.  Simplify!

[Eric H]

  Instead of reading all the way back through...
  Are those tantalum capacitors ? [polarized?].
  It would seem the AC portions of the signal path could put both + and - voltage across the staging caps at least.
 

Pete has a point here. Tantalum caps are a form of electrolytic, and are by nature polarized. There may be non-polarized tantalums, but I've not seen them.

-Eric

[Brushthrower]

However, the previous poster's point is really good...  Simplify for the purpose of testing.

Good idea. I don't really need the LED (it's a fuzz: if you don't know it's on then there's something wrong!) but I wasn't sure if it was integral to the design. Now that I have a better understanding of how the 3pdt works I feel a little more confident about straying from the layout.

I'll also remove those caps and pop in some ceramics.

Thanks for the input, guys.

[petemoore]

  Sometimes you can tell if they're passin' DC while in the circuit.
  Measure the DC on one side, then on the other side of the cap in question...then figure if they're the same 'is the cap or something else' the reason for that.
  Like if you have an output cap and DC on the outside of it, figure it might be a leaky cap.
 

[Brushthrower]

OK, I have a nice fuzzy sound now and good gain. However I'm still picking up radio interference and sounding a bit like Nigel Tufnel at an airforce base with a cordless amp. I was hoping for something a little Spinaltapesque. 

It seems like the LED affects this somewhat. If I was to eliminate the LED altogether should I just leave the lug it's attached to open or should it be wired to something else?

[tungngruv]

Check this thread out:

http://www.diystompboxes.com/smfforum/index.php?topic=59016.0

Basically you can put a small cap on the input that will prevent this. Do a search here for rf interference.

[aron]

Is it in a metal box now?

[Brushthrower]

Thanks Tony, this is going over my head a bit. I'm a little confused by the 3pdt layout for this pedal. Which exactly if the input lead? Do I simply solder it between the end of the input wire and the pcb? 

[aron]

All they are saying is to take a 47pf cap and wire it from the input of the circuit to ground.

It's in the FAQ - search for radio station:

http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ

[tungngruv]

Like this: ( a modified drawing on Aron's FAQ )



Try this , I'll also ask a friend of mine as I think you can add a resister along with this if it doesn't get rid of the noise. Did you get the LED back on yet?

[Brushthrower]

Hey, thanks a lot for that. Yes the LED is back on and now it's mounted in it's enclosure the rf problem is resolved (obvious, really  ).

The fuzz still seems a bit weak, and I've been playing around with different transistors but it doesn't appear to be a gain problem. I think I'm going to set this one aside for a bit and work on something fresh in the hopes of having a better perspective on it when I return. I might take some readings tomorrow though and I'll post those here.

Thanks everyone for all their help and patience with my endless and probably obvious questions. You've all been a great help. Really despite the frustrations I know I have learned way more with the difficulties I've encountered with this project than I could have it everything gone smoothly. I've become quite addicted with the smell of hot solder and this definitely will not be my last project - in fact I've started an new one already.