Author Topic: Spackler Demeter Mid Boost Mod  (Read 873 times)

fair.child

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Spackler Demeter Mid Boost Mod
« on: August 26, 2023, 11:37:28 PM »
Quick question, I like how spackler sounds but hereís the caveats

1. It used B50k. I mean yes, I understand it needs to be linear to control the boost. My question here is how can I implement it with A500k linear pot? What values should I change on the PCB?

2. I want to use it in my strat and use 9V. You know, just like Demeter mid boost for James Tyler however I want to use it with push pull potentiometer and in this case I need to be able to use it with A500k since Iíll use humbucker to control the tone as well with the mid boost. I know itís mouthful but the idea here is when I pull the knob, the A500k will work as the control pot for the Spackler but when I push it, the knob will work just simple as tone control for strat.

It will use A500k DPDT potentiometer and I had figured out the wiring scheme so itís not problem.

To my knowledge, it sounds like simple to figure. Mainly, if I know how to make it work with A500k, instead of B50k then the problem will be solved. I tried to do the pull down resistor technique (a resistor in parallel between lug 3 and 1 to bring down the value) but the issue is with the taper pot. The curve wouldnít smoothen out the mid boost and will jump out at the end.

What could possibly be the solution to this problem?


mauman

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Re: Spackler Demeter Mid Boost Mod
« Reply #1 on: August 27, 2023, 08:31:19 AM »
<edit: I failed to notice you've already tried this until after I'd posted, sorry.  You're right about the taper.>

In this application, you can convert a 500k pot into a 50k pot by adding a 56.2k resistor across terminals 1 and 3, as you say.  56.2k and 500k in parallel yield ~ 50k.  The taper of this modified A-taper pot will be different than a 50kB pot, since most of the change will happen in the last 1/2 rotation, but if you can tolerate that, it should work.  In the Spackler schematic, this added resistor should go between the C5/C6 junction, and the negative side of C7.   
« Last Edit: August 27, 2023, 08:35:09 AM by mauman »

fair.child

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Re: Spackler Demeter Mid Boost Mod
« Reply #2 on: August 28, 2023, 11:01:32 AM »
Yeah, the taper is the main issue. When you put 56.2k across terminal 1 and 3, you'll feel the jump close to the end of the A500k. Unless, I got to ask Bourns or Alpha to make a custom pot then it'll be more doable but I need to order thousands of it and it's really not off the shelf solution. The key to solve this problem might be adjusting the value of R3, R5, R8 to compensate the taper pot curve

mauman

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Re: Spackler Demeter Mid Boost Mod
« Reply #3 on: August 28, 2023, 06:35:34 PM »
There may be a way here:  http://www.geofex.com/article_folders/potsecrets/potscret.htm
See the part about adding a resistor between pot terminals 3 & 2 of a linear (B) taper pot, to give it a more anti-log (C) taper.  If you do that to your log (A) taper pot, it should bring it a bit closer to a linear (B) taper ( log + antilog = linear.)