Volume Pot Taper Question

[Custom 100]

Putting the finishing touches on an xpress clone using the Kelly90 schemo. Having trouble with the volume pot being more of an "on-off" switch. Have tried a PEC log taper, both 500K and 1Meg, a PEC 1 meg lin taper with the resistor on it to fake a log taper and another generic 1 Meg log taper. They all react pretty much the same. Is this how volume pots act in this circuit? Seems very similar to some early 70's Marshalls if had. Very touchy. Is there a quick fix that I missed? Any help would be great. I should mention that the amp sounds really great and everything functions as it should. Have the gain "hiss" but no squeals or weird noises.

Thanks for the help

[Robert]

The volume control in the Kelly 90 clone should not behave in that manner. You have substituted several different high quality pots, i.e. they all couldn't have been bad. Therefore, I would consider a source other than the volume pot for the unusual behavior. You might consider a poor solder joint/loose connection on a wire coming from the volume pot or other component in close proximity in the circuit. You can always try the chop stick method to localize it. Keep trying and you will get it corrected.

[Bombay]

A volume pot can act like this when it has a bright cap across it. Do you have a bright cap on it?

[Custom 100]

I tried it both ways, with the brite switch/caps and without. Didn't seem to make a difference. I'll check the schemo again. Seems like it should be something simple as everything else seems to work correctly.

Thanks for the replies

[Mark]

Dear Custom100

In my experience using a variety of average brand pots (Alpha, CTS etc.)

I found that in both case the amp should stay "clean" till you hit the 9 to 10 o'clock position on the volume control. As far as pot brands go I though the CTS worked quite well.

Mind you, Komet uses Clarostat, and a lot of people like the PEC brand pots.

[Legin]

Custom, did you ever get your volume pot sorted out, I am experiencing the same symptoms of the pot going from off to loud in a short space of turn.
Nigel

[Custom 100]

It still does not have a gradual taper like some other amps I have. Pretty much loud and louder. I can set the volume pot to the loudest setting that I need and then control the overall volume from the guitar. Not sure if this is how a real wreck responds or not. I'm happy with the sound and may keep tweaking the volume pot response but I've kinda gotten used to it. Sorry I don't have the magic answer. If you come up with anything I'd love to hear about it.

Happy building

[908ssp]

I know this isn't what you were after. But for me I use my Richter attenuator for volume control and use the volume pot for gain. It generally runs about 12:00 or a bit higher.

[Legin]

Thanks for the answers guys, you might find of interest Paul Rubys reply in my "Finished Express but have buzz" thread where he describes adjusting the "fixed" MV on the amp.
Nigel

[PaisleyTube]

Hi

There are several tapers regarding LOG pots; I've seen 10% and 35% ones. Most modern 1M log pots are 10%.
I suggest trying another (10% log) pot 1st.

Hope this helps,

Chris