Reverb Build Question

[canman]

Hi guys,

I'll be building the Deluxe Rub a Dub reverb in the near future and I have a couple questions before I get started.  Luckily, they're basic.

I'll be using this layout:



If I want to bring the trimmer out as an external volume control, is a 10k linear pot the best to use?  Or would a different taper work better?

And my other question...I'll be hooking up the BTDR-3H brick to a daughterboard and just sending wires out from that little daughterboard to the main board/pots.  I just want to be sure here, but the brick will be getting power from the pin 1 connection off the main board, right?  About 4.5v, I believe?

Thanks!

[samhay]

Schematic is here, and very helpful for questions of this nature:
http://1776effects.com/wp-content/uploads/2014/11/Rub-a-Dub-Deluxe-BOM.pdf

The volume trimmer will adjust the volume from nearly unity to about a gain of 2. I don't see how this would be a terribly useful control to bring out of the box, but if you do, I suspect either a log or linear pot will work reasonably well.

The brick takes its power supply from the 5V regulator - labelled BTDR 1 in the layout you posted.

[canman]

Perfect, that's all I needed to know, thank you!  Would changing the value of the volume trimmer (or external pot) to 20k allow me to increase the volume?

[samhay]

yes - more resistance from the trimmer = more gain = more volume until you run out of headroom. This is in series with a 10k resistor, so you will never get to 0 gain / volume.

If you want to get a significant boost from it, and also have it go to 0 volume, you could remove the 10k resistor immediately left of the trimmer and connect an e.g. 100k pot with lug 1 to pin 7 of the op-amp and lug 2 + 3 (tied together) to pin 6 (or vice versa) - i.e. in parallel with the 100p cap.

[canman]

Awesome, that's a sweet idea!  I may just have to give it a try...thanks man!