Faking a 25kRA pot for Vibro Champ AA764

[stingray_65]

Making a list, checkin it twice!

Getting all the parts in one box for this build.

Alas a 25k reverse log pot is not to be found! (reasonably) (for the intensity control)

So could I use a 50k lin and put a 50k resistor across the wiper and the outside lug and get something reasonably close?

Like this? or am I doing it wrong??

[sluckey]

AES has a CTS 50K RA pot. That's what I'd use. That pot will have 1547 ohms shunting it anyway when you wire it up.

[Willabe]

Ray, sluckey bet me to it. I looked around at a few web sites before I found it.           Man that rascals fast.        


         Brad      


Hey, hold the phone, Dougs got em, CTS 50kRA.      

Mojo has 3 of them @ 50kRA, CTS, CGE, and a MOJO that looks like an Alpha.    

[jjasilli]

You want the fixed resistor across the Outside lugs of the pot, to change it's value.   However, your diagram will do something to the trem circuit, and you might like it.

[stingray_65]

Doug is ALWAYS the first place I check!

It just seemed 50kRA is big, maybe not.

My mind starts clickin when I come to obstacles, LOL doesn't mean the trains going the right direction tho!

You want the fixed resistor across the Outside lugs of the pot, to change it's value.   However, your diagram will do something to the trem circuit, and you might like it.

OUTSIDE LUGS! DOH!

but will that simulate an Anti-Log?

I knew it works like that to simulate an Audio pot, so I guess I figured it had to be different for Anti-Log

OK LOL so will a 50kRA work in the Vibro Champ or is this another case of me making it out to be more than it is??

[sluckey]

That pot will have 1547 ohms shunting it anyway when you wire it up.

[jjasilli]

Here's more info:  http://www.geofex.com/article_folders/potsecrets/potscret.htm

Note the percentages of the fixed resistor to the pot value, to get various specific results, when wiring a fixed resistor to the wiper lug. 

Probably it's simplest just to try the 50K RA pot and see what happens.  If the universe implodes     then jumper a 47K resistor across the outer lugs. 

[stingray_65]

fromhttp://www.geofex.com/article_folders/potsecrets/potscret.htm "The secret life of pots"

"In a bit of good fortune, if you hook up the tapering resistor from the CW or hot side of the pot to the wiper, the pot emulates a reverse log pot, just as well as it did a log pot when hooked to the CCW side."

I was right! who'd a thunk it!

Thanks for the info JJ!

I can go on collecting parts!

Ray

Steve,

That pot will have 1547 ohms shunting it anyway when you wire it up.

What am I missing here?

You mentioned this twice and I'm sure I'm not getting it.

Because of the way it is wired in the circuit??

***EDIT***

wait for it...

AH! the 1500 Rk and the 47R half of the NFB voltage divider!!!

SOOOOOooooo...... a 50k RA pot we would only see a max value of 1500.6 and a 25k RA would see a max value of 1456.9

Again, much ado about nuthin 

Curse you Steve Luckey for making me think!

And do math!

[DummyLoad]

What am I missing here?

You mentioned this twice and I'm sure I'm not getting it.

it means...

calculate the parallel equivalent of 25K and 1547 - what's the result?

now calculate the parallel equivalent of 50K and 1547 - what's the result?

bet the difference won't be enough to write home about...

--DL 

[Willabe]

fromhttp://www.geofex.com/article_folders/potsecrets/potscret.htm "The secret life of pots"

"In a bit of good fortune, if you hook up the tapering resistor from the CW or hot side of the pot to the wiper, the pot emulates a reverse log pot, just as well as it did a log pot when hooked to the CCW side."

I was right! who'd a thunk it!

You did.       

Thanks Ray and JJ, that's a nice bit of info to know.


               Brad