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DIY blend pot...

Discussion in 'Pickups & Electronics [BG]' started by RobbieK, Jul 10, 2014.


  1. The other day I had to make an A/C blend pot so I thought I'd takes some pics for y'all. There's a heap of discussion around here about the pros and cons of different blend pots, and really I don't want to dig all that up for this thread. There's also been a bit of interest in modding pots as well.

    If you need isolated tone controls and don't want the (minor) volume reduction associated with summing resistors, or if you have a warwick with a broken blend and you don't want to spend a fortune on a genuine MEC one from Europe. Perhaps you just need a reverse-log pot to mend a certain pedal and can't find a particular value. (Famously, the treble control of the old 2-band MM pre is a 1M reverse-log pot.)

    Because 16mm dual gang Alpha pots have two wafers facing each other, you can easily remove the lower wafer without harming the pot and install a wafer from a single gang log (A) taper pot and because it's been flipped upside-down, that lower gang becomes an anti-log (C) taper.

    Start with a single gang and a dual gang pot of the same log taper. Typically for a blend this will be 200K, 220K (for warwich replacement), or 250K. It's best to buy both from the same supplier if possible. Not all 16mm Alpha pots have the same dimensions.

    [​IMG]

    Put the shaft of the single gang pot in a vice and cut right through at the top of the threads.

    [​IMG]

    Next, lever up the tabs on the casing with a small screwdriver.

    [​IMG]

    Remove the casing and disassemble the pot.

    [​IMG]

    Discard all but the resistive wafer. Then lever up the tabs on the bottom of the dual gang pot, remove the lower wafer and replace with the donor wafer from the single gang pot.

    [​IMG]

    Carefully close the tabs with needle-nosed pliers. Squeeze the opposite pairs like this first to centre the wafer.

    [​IMG]

    Then like this to close the tabs down.

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    Check with a multimeter.

    [​IMG]

    With the pot at mid-rotation you should get around 15% of the pot's value between the wiper and the left lug, and 85% between the wiper and the right lug on the top gang. The lower (anti-log) gang will also read 15% and 85%, but of course on opposite sides.

    Job done. Two Alpha pots like this cost 5-6 bucks and this process takes only two minutes.

    One drawback of using (non-guitar) pots from an electronics supplier is that they'll usually only have around 6mm of thread. For installation on a pickguard or metal control plate snap off the anti-rotation lug and use a shakeproof washer. Easy.

    If you need to install this (or any pot with a short threaded bushing for that matter) through timber, don't be tempted to snap off the lug and skip the shakeproof washer to have enough threads poking through to get the nut on. It will almost certainly loosen and spin.

    Put the pot in the hole from the rear, push it and twist a few times. The lug will score an arc in the timber. With the pot orientated correctly, mark the lug's position and remove the pot. Measure the lug and use masking tape on your drill so you don't go right through the timber.

    [​IMG]
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    Install the pot with its flat washer.

    [​IMG]

    This pot will never loosen and spin. This technique is also very important for rotary switches.

    The other drawback of using a pot like this for blend is that it won't have a centre click. No problem for this bass as it has clearly visible centre marks on the knobs.

    [​IMG]

    On some of my basses I simply line up all the grub screws to the centre position. On another bass I gig with a lot, I've painted a thin white line on the knob for high visibility on stage.
     
    JustForSport and ex-tension like this.
  2. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    i like it! besides, the center click almost seems superfluous, since as far as i can tell your philosophy on this stuff is to not really have a "both pickups full up" setting anyway, but to instead have some loading between them for isolation even at the cost of a bit of level.

    so the original was what, two pot wafers going the same way at the same time?
     
  3. These days antilog pots are pretty easy to find on ebay, but years ago, if you were into pedals, old amps, mixers, they were impossible to find. This is a way I found of making one.

    Now you know how to make one for just a few bucks, I'd encourage you to try one, but put a (DP) switch across that summing resistance. You may be surprised that there is no volume loss, and if you are feeding an onboard pre, no treble loss either. Also try a switch on the earth to hear the difference in response. These work unearthed as well, just like MN pots.

    Anyway, as I mentioned, there's more than enough info about blend pots in other threads, I really just wanted to show a simple pot mod.

    Yes. A common, garden variety dual gang log pot. As long as it's an Alpha 16mm pot, you are actually getting a log wafer on top and an anti-log wafer on the bottom turned upside down to work clockwise. When the log wafer from the single gang donor pot is put in there it is now upside-down so becomes the anti-log gang of your new A/C pot.

    When I used this idea just for antilog pots back in the day, I didn't really care what value the dual gang pot was because I was only interested in that switched out lower gang.

    Alpha pots are cheap and easy to mod. I've even glued them back to back for triple and quad gang operation...

    Here's the pot in my Pbass Stingray pickup bass. It is for series to parallel blend. The extra gang gradually adds 5dB of attenuation as you wind back towards the series setting. This counteracts the volume jump you would normally get going to series.

    [​IMG]
     

    Attached Files:

    ex-tension, walterw and JustForSport like this.

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