Tremolo schematic with 100k RA pot

[printer2]

If I may ask, is there any good circuits to look at or should I just scale values of the tube ones?

[antonis]

If I may ask, what part of tremolo is that famous 100k RA pot..??

[Kevin Mitchell]

Does RA = C?
Also, "tube ones"?

[printer2]

I don't know it it is famous, it is the speed control. Reverse audio taper.

[Kevin Mitchell]

Oh I see! You're asking about replacing the 3MC (or 3MRA) pot in the classic Fender Tremolo circuit.
You'll lose a ton of range using a 100K. In my opinion you're better off finding the correct pot (I use CTS brand for my amps) or look at alternative tube trem designs.

You're definitely better off finding an optical based tremolo if you're looking for tube circuits - even Fenders take on it uses the same 3M pot to drive the lamp in the optocoupler. Subbing in your choice of LFO design would be super easy.

I've played with this a few years back. Though it's more of an amplitude modulation circuit according to the description - rather than a tremolo. I did one on breadboard years ago and recall it needing some improvements - I might have a video demo of it on youtube.
Vintage Vibe Submini Tube Vibrato

[Mark Hammer]

While it is difficult for us to perceive differences between, say, 0.3hz and 0.4hz modulation (i.e., once every 3.33 seconds and once every 2.5 seconds), it is much easier to hear the difference between 3hz and 4hz modulation.  That's just the way our hearing works.  So it is no surprise that potentiometers used for setting modulation rate "skip" through the high resistance values quickly, and devote more of their rotation arc to smaller resistances (high resistance yielding slower speeds and low/small resistance yielding faster speeds).  This allows for better "dialability".

Having said that, reverse audio is really only crucial if you absolutely NEED to have speed increase as you turn clockwise.  A normal audio/log pot can be used if you don't mind wiring it up "backwards", such that speed slows down as you turn clockwise, and increases as you turn towards 7:00.  It achieves the same level of dialability, with a pot you may have in your parts drawer.

For replacing a 3M C-taper pot with something more readily available, one could also use a 1Ma-taper pot, and use a toggle to stick a 2M2 fixed resistor in series with it, to yield a faster and slower range.

[printer2]

I guess I did not make it clear what I wanted to do. I have 100k RA pots, I want to make an amp for someone else and I just wanted to set it up like regular tremolo pots with the speed going up as you turn it up. It would not bother me to have the action reversed but would rather have it operate as 'normal' if I am building it for someone else. I just want to make the tremolo as an add on to the circuit, modulating the cathode of a gain stage, no high voltage needed, no room for another tube in the chassis. I just found a couple schematics with a 100k pot,





I was thinking of using a voltage doubler off the 6V supply or possibly set up a higher voltage supply as I may be adding SS reverb (with tank) also. Or I could go with a high voltage circuit and use a mosfet then modulate the cathode in the preamp as Fender has in the Vibro Champ. In that case I would expect that scaling the parts around the oscilator from 3M to 100k should get me in the same frequency range. But until I actually do something unverified I take my ideas with a gain of salt.

[pacealot]

Since you're starting with the pot and working your way backwards to the circuit, I feel that it's a good opportunity to give another plug to Transmogrifox's rEAgenerated Tremolo, the stock configuration of which uses a C100K:

https://www.diystompboxes.com/smfforum/index.php?topic=111925.0

I desired as wide a range on the speed knob as possible, so I modified my builds of it to use a dual C100K pot, but excellent (though somewhat less extreme) results can be achieved with the stock pot, along with some gentle massaging of the cap and associated resistor values — to taste...

[printer2]

Thank you. And yes, quite often I do things backwards.

[amptramp]

If you need a reverse rotation pot, there's always this solution and scrap printers usually have at least one gear train:

[antonis]

I always thought that pot rotation is determined by its outer lugs wiring.. 

[printer2]

I always thought that pot rotation is determined by its outer lugs wiring.. 

It all depends on if you have the lugs pointing up or down.

[antonis]

It all depends on if you have the lugs pointing up or down.

Is it so..?? 

[printer2]

Of course. I think it has to do with electron spin or something.

[antonis]

Of course. I think it has to do with electron spin or something.

Fair enough..

Maybe some down-under fellows could enlighten us about their pot orientation..

[printer2]

It reverses in the southern continents.

[amptramp]

Of course. I think it has to do with electron spin or something.

Fair enough..

Maybe some down-under fellows could enlighten us about their pot orientation..

My pots identify as female.

[stallik]

I'm just wondering what kind of pot some of our members are currently on

[pacealot]

Clearly, for some it reverses audio.

[amptramp]

Make the stompbox steampunk style and use the two gears to take a log pot and turn it into a reverse log pot.  You can put the gears on the outside of the chassis that way.