Voltage controlled resistors for tube amp applications?

[LeftyStrat]

Most of the digital pots available leave a lot to be desired, ie poor resolution and only low voltage/power handling.

I've played around with LDR/LED's and a microprocessor, first in a feedback loop to build a table to get a linear response volts to resistance.

But all the LDRs I have come across are rated at 1/4 watt.

My goal is a microprocessor controlled resistor that could be used in tube amps. Two of them in series to mimic a pot.

It just seems like such a win to go to microprocessor controlled pots. I can program any taper I want, and even be able to change the value of the pot on the fly.

Any suggestions for other technologies to explore?

[chief mushroom cloud]

well...most of those log taper alpha pots are only rated at 1/4W

[MCK]

I am very interested in where you're going with this as well. I looked at motorized pots to use in a build but sadly I could not find the values I was hoping to find. Going completely digital for the pots would be amazing for the reasons you outline but finding the right voltage and current rating will be a challenge if I'm not wrong.

[JazzGuitarGimp]

I can program any taper I want, and even be able to change the value of the pot on the fly.

Show off....

[katopan]

If you could shield that micro from getting digital noise into every stage of your amp, that would actually be very cool.

Would've thought 1/4W LDRs would be plenty for where this sort of thing would end up. DIY MIDI controlled amp anyone?

[LeftyStrat]

My thoughts are a microprocessor amp that can switch between a Dumble low plate classic and a Dumble high plate skyliner.

[DonMoose]

There are threads here and on Music-Electronics-Forum (used to be Ampage) with a workable circuit.

Search for PhotPot.

If Mesa can do it with the TriAxis, you can do it, too.

Hope this helps!

[LeftyStrat]

There are threads here and on Music-Electronics-Forum (used to be Ampage) with a workable circuit.

Search for PhotPot.

If Mesa can do it with the TriAxis, you can do it, too.

Hope this helps!

I'm searching but not finding anything. Any other pointers?

[MCK]

I think I found a link. http://music-electronics-forum.com/t30551/

There is another thread linked inside the above one.

[LeftyStrat]

I think I found a link. http://music-electronics-forum.com/t30551/

There is another thread linked inside the above one.

Thanks!

[MCK]

My pleasure. Seems like a lot of like minded folk has walked the same path so I hope we can find some tangible outcomes.

[dorrisant]

Even if this was just for testing purposes this is so cool. Just think of being able to dial in, within seconds, the type of taper or the value of pot for any specific location.

Watching this one!

Tony

[DonMoose]

There's another one: http://music-electronics-forum.com/t1015/

My bad - photOpot, not photpot.

The circuit I came up with is scaled with fixed resistors, but you could do any taper (Sunn Beta series 'Sigma' tapers, anyone?). Making the value programmable could be done with sets of resistors and a good analog mux.

The noise from the micros should be very small - modern ones like the Atmel ATMegas use so little current that switching noise is minimal - and you won't be manipulating these values very often.

Oh - the dual-element (4-terminal) LDRs are all but impossible to get - you're going to need to build your own - and a matching fixture to select matching pairs of LDRs and maybe pairs of LEDs.

Hope this helps!

[Aurora]

You might find someanswers here .

http://www.diyaudio.com/forums/analog-l ... reamp.html

http://www.diyaudio.com/forums/analog-l ... ntrol.html

[LeftyStrat]

Thanks for all the info. I didn't realize that LDRs change over time.

I may try and order some samples and see how many I can fry.