Volume Pot Issues - all bunched up!

[tommycataus]

Hey guys, I hope you're all basking in the joys of DIY pedal building!

I must say that I am, although I have run into a really simple problem. I build a Catalinbread Heliotrope - Harmonic Pixelator from the Guitar FX layouts website:

http://tagboardeffects.blogspot.com.au/2012/04/catalinbread-heliotrope.html

For some reason there is no volume until the pot is turned to about 9 o'clock, then it goes loud very quickly. There are some issues with the build such as noise, but it's not exactly the kind of pedal you expect Eric Johnson to whip out! I just wonder whether these are having an effect on the volume although it seems unlikely.

The original states to use a 100K linear pot. I've used linear and logarithmic of various values ranging from 1K to 1M, all with similar results.

The closest I've had to a desirable result was the 1K linear pot, but as soon as I connected ground to lug 1 there was no output at all. I'm considering just removing the volume pot altogether, but it is a build requested by a friend so I'd rather not. Any ideas chaps? Hopefully I'm overlooking the obvious.

Thanks so much!

[GibsonGM]

Well, there's no schematic to see where the pot connections go, but you SHOULD be ok with the linear pot. The troubles come more often with the A taper pots, in my experience, due to the rapid increase in resistance....yours SOUNDS like a REVERSE A taper, by the way....(?). 

I suspect you have something wired wrong, Tom.   No way should you just get no output with one lug tied to ground, if it's wired up correctly.   Review the wiring to the pot, all 3 of them...

[nocentelli]

On the original heliotrope traced schematic, the volume pot was wired in an unusual way, with output from the board sent to lug 2 and the output of the pit taken from lug 3. I suspect IvIark has changed it back to the usual arrangement.

Check the pull down resistor connected to pin 2/output is actually a 1M. I used a 100k log pot in my build and the travel is smooth. I actually didn't bother with the 1M pull down as it seems unnecessary when a volume pot is used. In general,  a log pot for volume seems to give a more intuitive travel/taper with most dirt pedals. Obviously, all pedals circuits have different output levels, but for something standard like a fuzzface, BMP or tubescreamer, if a log pot gradually reaches unity around 1/2 o'clock and goes up smoothly from there, a linear of the same value seems to abruptly reach unity at midday.

[zombiwoof]

Well, there's no schematic to see where the pot connections go, but you SHOULD be ok with the linear pot. The troubles come more often with the A taper pots, in my experience, due to the rapid increase in resistance....yours SOUNDS like a REVERSE A taper, by the way....(?).  

I suspect you have something wired wrong, Tom.   No way should you just get no output with one lug tied to ground, if it's wired up correctly.   Review the wiring to the pot, all 3 of them...

Sounds to me that he could try reversing the leads on the pot (if it is some sort of audio taper pot), so it spreads out the taper at higher settings, but it will work backwards (rotate counter-clockwise to turn up).  If that works, you can then just buy a regular audio pot if your pot is a reverse audio, or buy a reverse audio pot if the current pot is regular audio, of the same value, to replace the current pot.  The experiment won't cost anything, and you can see if you like the different taper, and you can wire the replacement pot normally, so it increases volume when turned clockwise.  Of course you could just use a linear taper pot, but I'd try reversing the leads first, to see if that works for you.

Al