Build Your Own Clone Message Board

I need a B500k pot for a build that I am doing. I have a B1M in my parts bin. If I place a 1m resistor across lugs 1 and 3 I get a 500k reading on my DMM.
My question, is that an acceptable cure for my issue? I read, in another forum that by doing that, it would change the B taper of that pot to a C taper.
Is that true as well?

Thanks, in advance.

-=SteveO

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“To know, and not to do, is not to know”

Is its purpose to provide a variable resistance (2-terminal device) or to "select a voltage in this range" (a 3-terminal device)? How good a solution that would be depends somewhat on what it's for.

If the former, a 1 M B-taper might work just fine by itself, though yielding possibly useless (or, hmmm, "dangerous") results for half of the rotation of the pot. ("Dangerous" = for example providing more gain than desired in an op amp if the variable R is in the feedback loop.)

Got a schematic for the part of the circuit where it's used?

Yep, really depends upon whether the pot is being used as a variable resistor (two circuit connections, middle and one side or the other) or as a voltage divider (all three lugs connected to the circuit). The pot value makes a much larger difference for the former. Check the schematic, if available, or look at the PCB traces to see how they are connected, if it's a PC-mount pot.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

It is a voltage dividers (all 3 terminals are used). See attached schematic. The board is a "Tone-TwEQ" from GuitarPCB and is a 3 band EQ with a volume control. The B500k pot is used to control the high frequencies. So I guess I'd better get one of these on order if I want it to function properly.

Thanks gents for the education!

-=SteveO

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“To know, and not to do, is not to know”

To answer your question about "making" a 500K pot with a 1M pot and 1M fixed resistor: Yep, that will work, but it will change the pot sweep to an extent. I still think it would work well enough for your needs, 'cuz it still starts at 0 and ends at 500K and the sweep change isn't extreme. It will just increase the resistance a bit more quickly at the start of the sweep and a bit more slowly at the end. I have an EXCEL spreadsheet set up to calculate the "effective resistance" of a pot + fixed resistor combo, so I plugged in your values. The chart below shows the effective resistance plotted in dark blue vs. the theoretical straight line sweep of a linear pot (fuchsia line). Sure looks usable to me:

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Thanks Bob for the 'above and beyond' answer and accompanying graph! Visuals always make it easier for me to understand!

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“To know, and not to do, is not to know”

If it were me *and* I were in a hurry I might be tempted to just put the 1 M pot in there and see how it goes. In this circumstance I would also consider changing R5 and R6 to 3.3 k or 3.9 k, and be prepared to change C3 by a factor of two if I don't like what the other changes lead to.

Thank you for the heads up! I was on BYOC's web site an hour or so ago and noticed that they had most of the Crown Jewel modules back in stock. So I place an order for a couple modules that I've been wanting and included several B500k pots with them.

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“To know, and not to do, is not to know”