Volume Control Sensitivity

[JammyDodger]

Hey All,

I'm wondering if there is a way to make the volume control less sensitive? I am completing my TrainWreck Express and let's say volume is at 0 (on a scale of 1-10) by the time I'm at 1-2 the amp is deafeningly loud and I don't get much gain beyond.

Is there a way to linearize this response. The volume pot is a 1Meg. Would a larger (or smaller) value work or a different taper.

I've noticed this trait on many amps, for example my Fender Twin is clean to 3-4 then not much more beyond that except crunch. For my taste, I would like to be able to go 1/2 way up with a clean sound, then a smooth transition to total crunch by 10.

Any suggestions?


Cheers, Mike

[txbluesboy]

I have the same feeling. It seems like the sweet spot on my Express is just about where the volume control goes from no sound to just barely turned on, and it's pretty loud there.

[skyboltone]

You could try putting a tail on the volume pot. At the end that goes to ground, try a 470K 1/2W resistor between the pot and ground. That's probably way too big but try it and go down from there untill you like what you hear.

Dan H

[gearhead]

Gotta ask the question, are you using an Audio/Log volume pot? If not, switch to that.

[LOUDthud]

There are two types of "Audio" pots in common use. There may have been a distinction at one time between an Audio and a Log pot but today, the terms are interchangable. The difference is the amount of attenuation when the pot is in the middle of it's rotation.

A linear pot has 6dB of attenuation at center.

One type of audio pot has 10dB and the other has 20dB. Carefull set the pot to midrange and measure the resistance from the wiper to the ground terminal. If it's 1/3rd to end to end resistance, it's a 10dB type. If it's 1/10th, it's a 20dB type.

If you can find any pots that have more than 20dB of attenuation at mid rotation, let me know, I'll buy them!

[LeftyStrat]

Same problem here. You can some custom tapering with a linear pot and an extra resistor, but it does have some downsides:

http://www.geofex.com/Article_Folders/p ... tscret.htm

I've even thought about using some of those hifi type rotary selectors, and selecting resistors to mimic the best curve.

Dan's idea seems interesting, find out where more on the volume pot doesn't do anything and replace that with a fixed resistor and then use a smaller volume pot for more control over the usable part of the range.

[Tube_S_Cream]

...anyone thought about using a cascaded stereo pot?
Connect wiper from the first stage with the hot end of the 2nd. stage. Both "cold" ends of the tapers are connected to ground. Use wiper out from the 2nd. "stage" as output.
Even a linear stereo pot will now deliver a logarithmic curve with approx 12db in the middle instead of 6dB.
A 10dB stereo log pot will now work as a 20dB Type and so on.
This curve may be too extreme for other audio applications, but it is a good way to tame a gain monster like the TW.
Remind that the preamp is loaded with half the impedance a normal pot has. In case of the TW Express (1Meg A) the first stage will be loaded with 500K when the pot is cranked to maximum. To avoid that , you can use a 2x2Meg A Stereo pot, but that's really not necessary.

Greetz

Tube_S_Cream

[Tdale]

You could try putting a tail on the volume pot. At the end that goes to ground, try a 470K 1/2W resistor between the pot and ground. That's probably way too big but try it and go down from there untill you like what you hear.

Dan H

I'm not sure if I get that.. If you put a resistor from the grounded end of the pot, won't that give you resistance to ground, even when the pot is turned alle the way down, giving you even more gain at lower levels?

[oldhousescott]

Yes, it will. Put it on top of the pot. Maybe try 470k resistor into 500k pot, or 680k into a 250k pot.

[skyboltone]

You could try putting a tail on the volume pot. At the end that goes to ground, try a 470K 1/2W resistor between the pot and ground. That's probably way too big but try it and go down from there untill you like what you hear.

Dan H

I'm not sure if I get that.. If you put a resistor from the grounded end of the pot, won't that give you resistance to ground, even when the pot is turned alle the way down, giving you even more gain at lower levels?

I could very well be wrong Tommy. I frequently wire pots backwards. PRR once mentioned taking a pot apart, turning it all the way clockwise and then putting the lug that the wiper touches towards "more". More in most cases is the less "groundy end.

Having said all that, don't think it would work because the volume tap wouldn't change resistance anyway. It's still going to be from 1 meg at full soft towards nothing at full roar. Adding a tail doesn't change that. A two meg audio pot would though I think.

Dan

[skyboltone]

Yes, it will. Put it on top of the pot. Maybe try 470k resistor into 500k pot, or 680k into a 250k pot.

Thanks old housescott. But can we get to full roar? I definitely hear more feedback and harmonics the further clockwise I get with the two hole liverpool. At about 2 o'clock notes go almost immediatly into harmonics. Wouldn't want to loose that.

[JammyDodger]

OK - So I've attached a quick picture of what we have. I've tried the Resistor on the tail of the pot to ground, made things worse.

I'm wondering if the bright switch caps might be passing the signal sooner. How 'bout if there were are resistor before the caps?

Any suggestions?

[Tdale]

It got worse? That's what I thought would happen.

Without the resistor, the pot can ground completely when the volume is turned down. If you put a resistor between the grounded lug and ground, means that the resistance between pot and ground will never be less than 470K, making it impossible to turn the volume completely off.

It would make more sense to put a resistor from the input side of the pot, to ground...

Tommy

[RedRock]

Try a 1 meg resistor from the middle lug of the pot to ground.
This will decrease the pot's resistance to ground (compared
to stock) as the pot is turned up. The greater the resistor
value, the less effect it will have; the smaller the value of
the resistor, the more effect it will have.

[RedRock]

Sorry for the double post.
You could also try a 500k pot instead of the 1 meg.
The general rule is: the lower the value of the pot, the more
signal it will bleed to ground.