Active Volume Pedal

[tubelectron]

Hello All,

This subject may have been already answered, but I found nothing suited in the forum...

I want to build a simple foot-volume-control active pedal (for example in a GCB-95 enclosure).
With or without slight or adjustable boost, maybe.
I was thinking about a 2N5457 in a buffer mode (hi Z in/lo Z out) with the pot at the end (a 50K, for example).
(Of course, I can do it with tubes, but it is a bit "heavy" and merely questionable in use easyness, so forget it !!!)

Some of you have surely work on that subject, or have any other experience in building a volume-control pedal (with or without signal boost function, tone-control, etc)...

Thanks for your genious ideas, suggestions, advices and maybe schematics.

Best regards & A+!

tubelectron.

[Mark Hammer]

Just stick any booster circuit you like in the wah shell and wire up the output level pot as the foot-controlled volume.  If the circuit has adjustable gain, then you can dial in anythng from unity gain up to boost/overdrive.

The constraining factor is that the output volume control for whatever circuit you use be something that will fit the available space in the wah shell and which the pinion part of the gear mechanism will fit over.

[tubelectron]

Thanks Mark,

While you were writing your answer to my post, I was drawing the schematic of what I am thinking about, and it is similar to your description. Here it is :



The "gain compensation" pot is intended to compensate the loss due to the buffer, so it is an internal adjustable pot. But it may be external and labelled "volume boost".

Any comments ? Any detected mistake ?

A+!

[maxj]

I think this looks a  decent one. I'm gonna try it.

[Mark Hammer]

Take a look at Tom Henry's article here on page 3:  http://hammer.ampage.org/files/Device1-8.PDF
You don't have to use the exact same circuit, but the battle plan is identical.

[merlinb]

Any comments ?

If you used an opamp buffer then you wouldn't need the gain compensation. You could also use a dual-opamp and so get an output buffer for free (after the vol po), which would improve noise rejection.

[tubelectron]

Hi & Thanks for your suggestions +++,

Here's what I opted for, finally : a single FET very low power consumption circuit, where the battery would die by ageing... Because I do not use this device often ! I dropped it in an used Dunlop wah, and it's done. It's not the best, but it's enough FWIW.



A+!

[Gus]

You could use this
http://www.diystompboxes.com/smfforum/index.php?topic=763.0

Make the 5K pot two 10Ks in parallel
Don't use the 47uf at the pot
use a 100K volume control at the end instead of the 100K pull down
Add a 1K series input resistor before or after the .1uf
Add a 10Meg input pull down resistor
use a 2n5088, MPSA18 etc.

Fixed gain of about x2 (10k/5K) with a volume control at the end

[maxj]

Or you can use Tilman's FET preamp, and replace 51K with a pot as a volume control.

http://www.till.com/articles/GuitarPreamp/

[tubelectron]

Thank you all for these informations ++++

A+!

[YouAre]

What about a Mosfet Boost? They're unity at "0" on the gain pot. Tack a volume control after that and you'll get what you want. You can replace the gain pot with a switch if you want a set amount of boost. I figure the mosfet boost would be work really well because of it's full range voicing, and that it's unity at 0 gain. So you don't have to do math to figure out where unity is when you build a bjt transistor booster.