Some ways to reduce the output of a pedal?

[midwayfair]

This is specific to the whisker biscuit, but I'd like to be able to transfer the knowledge to other pedals, like silicon fuzz faces (which are also sometimes too much output for my tastes).

This seems like something I should be able to figure out on my own, but I'm a little short on ideas.

I've been working on Whisker Biscuits after getting a handful of boards from CultureJam recently. The last one I ended up swapping out the 100K volume control for a 20K and it was more usable. Any smaller on the volume pot and it sounded weird. It's still a very loud pedal (I can use it up to about 10:00 on the dial instead of just 8:00). Going smaller on the volume pot wasn't helping. I've had the same problem reducing the volume pot in other circuits. Sometimes it sounds fine, but other times it makes things fizzy until the volume's where it "wants" to be.  Since one of the versions I want to build would have a mids boost, I really need to find a way to lower the volume otherwise.

So I'm wondering if maybe there's an minimal-parts way to reduce the volume at the end of a circuit without drastically changing the overall frequency response. Is that even possible? And does anyone have any tips?

Here's what I came up with:
1) Sagging the power source, as long as I can do some re-biasing. Can this be done without harming the upper frequencies?
2) Maybe an extra resistor from lug 3 of the volume to ground, like a second hardwired volume pot? Does this work? Or should it just be a resistor in series with the output?
3) I know that there's probably a way to reduce the input cap and then follow it with a low-pass filter, but that has some major issues in a fuzz circuit (where it wants to see your full guitar signal to distort properly), and I really wouldn't know how to calculate it.

[culturejam]

Adjusting the Volume pot is a good way to scale back the output volume.

But, you also need to take into account that the Volume pot and the output cap form a high-pass filter. So you must adjust the output cap to scale with the change in the value of the Volume pot, in order to get the same frequency response.

I'll repost the equation from the recent thread here on filter response calculations:



First punch in the original values so you can see what the cutoff frequency is for the high pass. Then adjust the value of the resistance to your preferred pot value. And then adjust the cap value to match the original.

Here's a nice online calculator:
http://sim.okawa-denshi.jp/en/CRhikeisan.htm

[midwayfair]

Thanks, that was a big help. However, it turns out I need to put the output cap all the way up to 4.7uF for a 20K pot and 10uF for a 10K pot. Won't that just mean that much more signal output?

[culturejam]

It should be quieter because there is more signal being dumped to ground, but at the same cutoff frequency.

Try it and see.

[stecykmi]

personally, I think method 2 is the best because is doesn't mess with the rest of the circuit since it keeps the output resistance the same. If you swap the 100k pot with a 50k pot, and add a 47k in series before the pot (lug 3), you should get about half the max output (with the output dimed with a 50k pot, it's equivalent to a 100k pot at half rotation, ignoring the taper of the pot).

unfortunately, you're somewhat limited by the value of pots you can find, ie a 75k pot (+ 25k resistor) might work better in a lot of cases, but good luck finding one. you can try faking it by putting a resistor in parallel with a pot, though. A 300k resistor in parallel with a 100k pot is 75k. i've never tried this myself, but it should work.

[Scruffie]

Why change the pot? A pot with a lug to ground, one to signal and the middle out is working like a divider right? So just put a resistor in series and to ground before it like a fixed pot to cut the volume.

[midwayfair]

Why change the pot? A pot with a lug to ground, one to signal and the middle out is working like a divider right? So just put a resistor in series and to ground before it like a fixed pot to cut the volume.

Yup, this is what I had wanted #2 to say, but I worded it poorly.

CJ's calculator is still necessary, though. Adding a divider network will still change the series resistance.

I have a feeling that the ultimate answer is going to be some combination of series resistance, output cap value change, and perhaps reduced pot value as a last resort.

[culturejam]

CJ's calculator is still necessary, though. Adding a divider network will still change the series resistance.

Yes, and changed resistance = changed cutoff frequency of the HP filter.

As a third option:

You could first change the pot value to get the volume you want, and then adjust the tone control values to compensate for the change in frequency response. It's more complicated, but you'll probably learn something in doing it.