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Tone pot not working - correct cap?

Posted by Brian Tubb on November 21, 2013 at 8:12am in Building Secrets, Tips, Advice, Discussion

Greetings everyone.  First build, first post but having a blast.  Building a 4 string with piezo with tone and volume.  My test gets good sound and volume works.  However no change in tone.  Also, if I touch the tone pot (bare -with no knob) i hear a grounding hum through the amp.  This doesn't happen with the volume pot.  Pots are new 500k from CB Gitty, but I used a cap from a pot I bought a long time ago from Guitar Center with a volume pot for my Strat (cap is new - unused).  The cap has on it (as far as I can read with magnifying glass!):

ic

MSR 022k

250H

I have no knowledge of electroncs, but know how to solder and followed the diagram for hooking these up.  The cap goes to the middle post to ground (top of pot) like it shows.  Could this cap be bad or am I missing something?  Thanks to all.

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Replies

  • Brian Tubb November 22, 2013 at 8:32am

    Thanks all.  I think I've made up my mind to just bypass this..  More trouble than it's worth.  The amps I'll play through have plenty of tone control already.  I'm going to just have one knob for bling!

    • David McQueen > Brian Tubb November 22, 2013 at 9:20pm
      Or... Have 2 piezos each with volume control... One at the neck and one at the bridge?
      • Brian Tubb > David McQueen November 23, 2013 at 5:48am
        Now that's a good idea! That way, I'd have tone "blending" with volume pot for each. And... Pots are already there. Only question is... Would I wire each piezo to its own volume pot and then each pot to my one output jack? I may be off to radio shack today to get another piezo.
        • David McQueen > Brian Tubb November 23, 2013 at 6:05am
          Yes. Even nicer if your pots will go to the off position. Wire in parallel, each with own pot, back to the jack.
  • Dan Sleep November 22, 2013 at 8:26am

    Due to the way that piezos and capacitors work, it is unlikely that you will see any tone change by using a capacitor without a preamp.

    If you really want to be able to adjust the tone, you should go with a magnetic pickup instead of the piezo.

  • darryl kernaghan November 22, 2013 at 8:15am

    brian,my experiances with p/discs suggest that unaide with a pre-amp of some type,tone controls are just a waste of time and 1 more potential problem,if you really feel the need for a tone circuit,you may get some responce by putting in another disc ,parrallel with the 1st which i,ve been led to believe can make the discs more responsive to tone

  • Brian Tubb November 22, 2013 at 7:58am

    Well now after reading the link in David McQueen's reply, I'm more confused than before.  The diagram in that link shows the tone pot (for one humbucker, one tone & one volume) hooked up different that what I've seen for a piezo, 1 tone & one volume.  From what I gather in the article, it may be easier to just eliminate the tone and go with just a volume.  Problem is I already have holes and pot installed for a tone... I could just bypass and have a dummy knob for show!!  As for the capacitor, is there a test with a multimerter to confirm if its good or not?  I hate to order just one cap.  So is the "MSR 022k" on the cap saying its the suggested one for 500k pots.  Again, all this electronic jargon is new to me..  although pretty interesting.  FYI: I got my wiring diagram straight from the "Homemade Music Factory" book advertised on the Gitty site.  Another point:  I really don't think I fried the cap as I left the 'legs' full length (long) and didn't hold the soldering iron on long enough for the heat to travel that far.

    • David McQueen > Brian Tubb November 22, 2013 at 8:28am
      I went and took a look at the diagram. It is pretty standard for a volume/tone set up. When I am soldering in the real world, I just bring the ground for the tone pot back to the volume pot and connect it there at the ground. Then it runs from there, everything negative runs back to the negative on the jack.

      The things the diagram do not show are:

      1. The treble pypas capacitor
      2. The 100 K resistor coming off the positive lead (from the white centre section) of the piezo.

      Normally tone controls do not work well on a piezo. I gave the link because this fellow appears to have made it work. I have not tried it yet. There was another post from a lady who did with dual piezos to a violin and she was happy. She was using 500K pots.
  • The Phrygian Kid November 21, 2013 at 8:01pm
    Do you know you need to put a heat sink on a capacitor before you solder or you can very easily fry it? :)
  • David McQueen November 21, 2013 at 8:47am
    Do not pass go. Do not collect $200.

    Do go here for passive piezo tone control.

    http://www.cigarboxnation.com/forum/topics/passive-tone-control-for...
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