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Old November 22nd, 2012, 03:53 AM   #1 (permalink)
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Potentiometer question for the Gurus...

I'm building a simple byoc classic compressor (2knob version) with the vintage upgrade kit. I am also placing illuminated pot shafts and translucent knobs, as opposed to the typical LED. My question is; the kit calls for one A100K linear pot (level), and one B500K audio pot (sensitivity). The illuminating pots that I have are B100K linear and A500K audio. I know the first letter in both model numbers are different, but are these pots compatible with my build? Thanks in advance for y'all's expertise!

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Old November 22nd, 2012, 11:11 AM   #2 (permalink)
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I'm building a simple byoc classic compressor (2knob version) with the vintage upgrade kit. I am also placing illuminated pot shafts and translucent knobs, as opposed to the typical LED. My question is; the kit calls for one A100K linear pot (level), and one B500K audio pot (sensitivity). The illuminating pots that I have are B100K linear and A500K audio. I know the first letter in both model numbers are different, but are these pots compatible with my build? Thanks in advance for y'all's expertise!
I'm a little confused by your post. You refer to the 'A' and 'B' pots with two different tapers.

An "A" pot is an audio, or log taper pot.

A "B" pot is linear.

And, FWIW, a "C" is reverse linear taper.

I'm not sure what the build calls for, but as long as you use the same letter coded pot in the same position you'll be ok.

Aside - I did a FF build several months ago and used a clear shaft pot with an LED in it. Pretty neat!

-Kevin
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Old November 22nd, 2012, 05:06 PM   #3 (permalink)
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I'm also confused, because the build states it comes with 1- A100k linear (level) and 1- B500K audio (sensitivity). That is exactly how it refers to the pots that come pre packed in the kit. That's why I'm confused, because the transparent pots I bought are linear 100k and a 500k audio. They aren't listed with an "A" or "B" in the model number??? I did put the pedal together last night (minus the LED's) and everything worked until I turned the 500k audio all the way up and it gets staticky and the whole signal disappears, no sound at all (I'm thinking maybe I got a bad pot???).
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Old November 22nd, 2012, 08:39 PM   #4 (permalink)
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I looked at the schematic and the build instructions.

They definitely have the description in the text wrong with regards to the pots. An "A" pot is audio, not linear as they describe, and a "B" is linear. If they are Alpha pots, the value should be stamped on them, e.g. "A100K" or similar.

It makes more sense to me that the 100K should be an audio taper since it's the level. And the 'sustain' pot should be linear.

I'd suggest trying it with the pots that came with the kit - the 100K for level and the 500K for sustain, and see how it works. That's a starting point, and it's what it was designed for - and if it works properly, then you have something to build on. You can try the other pots you have once you know the pedal works.

If you're using the 500K for level, and the 100K for sustain, that's the opposite of the way the circuit's designed, and might cause an issue.

-Kevin
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Old November 23rd, 2012, 04:32 AM   #5 (permalink)
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In Europe the pot code is A for linear and B for log.In the US it is the opposite.
When I buy surplus and I am not sure if the pot is lin or log I turn the pot roughly half-way
and measure the resistance between the wiper and each end.If they are close the pot is linear.If not logarithmic. In your case Mule,you have to stay with the value as Kevin says.Of course you can mail byoc and ask them why the pots are marked this way.
It could be that they have a Norwegian selecting the parts. ;-)

Just kidding.Your Polish jokes are our Norwegian jokes
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Old November 23rd, 2012, 11:26 AM   #6 (permalink)
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I was going to mention the fact as Limbe mentions, that in Europe the A and B are reversed, but I didn't want to confuse the issue.

Norwegian jokes? That explains why my Saab laughs hysterically at a mention of Norway.

-Kevin
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Old November 23rd, 2012, 12:27 PM   #7 (permalink)
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Appreciate y'all! I've ordered a couple more pots also, and I will start experimenting. I will let you guys know how everything turns out.
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Old November 24th, 2012, 03:54 PM   #8 (permalink)
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[...]

And, FWIW, a "C" is reverse linear taper.

[...]
There is no such thing as reverse linear. I think you wanted to say reverse audio or reverse log.
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Old November 24th, 2012, 10:52 PM   #9 (permalink)
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Any ideas about the sustain being turned up to max and the signal disappears?
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Old November 25th, 2012, 10:36 AM   #10 (permalink)
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There is no such thing as reverse linear. I think you wanted to say reverse audio or reverse log.
Yes, thanks. I got scrambled between my brain and my fingers.
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Old November 25th, 2012, 05:01 PM   #11 (permalink)
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Any ideas about the sustain being turned up to max and the signal disappears?
Cheap pot? oops, meant to say faulty...
Seriously, I think that's just your pot acting up. Wire it reverse and you'll find the problem occurs at the other end of the sweep.
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Old November 25th, 2012, 05:03 PM   #12 (permalink)
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Yes, thanks. I got scrambled between my brain and my fingers.
Well, these things get confusing with all the A and B and C and them pesky Yurpeans and their bassackwards marking.
I think I read somewhere the whole EU vs US inverse marking is an Internet Myth. Mind you... I think I read it on the Internet.
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Old November 27th, 2012, 10:14 PM   #13 (permalink)
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Well I'll try these replacements and if they don't work, I'm going with the pots I know work. You guys sound like you know your stuff. Thanks a lot!
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Old December 2nd, 2012, 05:32 PM   #14 (permalink)
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The pots that were provided in the kit say A100K and B500K ??? The replacement pots I've got say A500K and B100K. Will these do the trick?
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