Modding Bespeco "Weeper" Wah

[smoguzbenjamin]

Hey everyone!

I was looking around at all the info on modding wah-wah pedals, and I have a cheap-ass bespeco weeper pedal. Now I was wondering, is there a way to make this sound better, increase the range of the sweep or something?

I look at the PCB. No inductor. just 3 or so transistors, a bunch of caps and loadsa resistors. I tried making a schematic from the PCB but I got frustrated in the end.

Does anyone know either where I can find the Bespeco weeper schematic, or does anyone have any mods I could try?

cheers

[Marcos - Munky]

I have a schematic here, but the schematic shows only one transistor.

[smoguzbenjamin]

I had a look in my pedal, there's only one transistor. But I can't find the weeper scematic on your site...?

It does have general wah-modding info, but that only applies to wahs with an inductor. Now either I'm blind, or my pedal just simply doesn't have an inductor.

I guess I'll take my 5K pot and connect it to random points on the pcb for fun   See what it does.

[brett]

Hi. If your wah doesn't have an inductor, it might implement the notch or bandpass filter via a "T" filter.  If it does, you'll probably find that the pot goes to ground on one side and to the junction of a couple of capacitors on the other side.  Fooling with these caps will change the width/depth/position of the notch.  But it might not be a T filter either, in which case it is very interesting and you should draw up a schematic and get it posted on the web!!!  No matter what the design, I'm sure somebody could help you with mods once we see a schematic.

[Marcos - Munky]

I uploaded it in Geocities. I pick this schematic at Hemmo's site some time ago, but he don't have the schematic uploaded now. Here is the address:
www.geocities.com/munkydiy/besbeco.gif

[Tim Escobedo]

If yours is the same as the old Hemmo schem, there are a couple mods you can try.

Try putting a small cap (< .001uF) in parallel with the 220k input resistor. This could add a little more breakup and quack.

Change the 68k resistor-to-ground with a 100k trimpot and dial in the resonance. Beware! At low resitances, it'll probably howl in oscillation.

Twin T filters usually specify matched component values in the "T" networks. I find that purposefully un-matching these components, particularly the caps, not only changes the sweep range, but can also sound a bit nicer.

[smoguzbenjamin]

Munky - geocities gives me a "We're sorry, but this page is currently unavailable for viewing" error.

Uhm. I tried making a schematic (three times), but I always end up with a mess, and I get confused. I've only just started out with electronics, and I always wonder about how people get a complete circuit on so small a PCB.  :oops: I branch everything off in different directions and about halfway through I'm either confused if I haven't allready had that branch, or I think "nah 4 resistors in series can't be right" or whathaveyou.  :roll: I'll try my best this evening though, and if I manage I'll try and get it posted online.

Now yesterday I paralelled the cap right before the output (I think it's 22uF but it's hard to read) to a 5k pot wired as a variable resistor (lug 3 to ground). I sortof found that I could fiddle around with the treble/mids (although the amount of which I could fiddle with was rather limited). I did it, without having the foggiest of what I was doing, so could someone take the leisure of explaining to a total newbie what I did?

cheers,
Ben

[smoguzbenjamin]

This used to be a double post. Now it isn't.

Why does that happen?

BTW the cap I paralleled with my 5K pot reads 22j. Help! :oops:

[Marcos - Munky]

Copy the URL and paste in another browser window.

[smoguzbenjamin]

Yeah, that's it!

It kinda resembles what I had on paper, but my schem was messed up with me copying things down twice etc.  

Just one question:
On the schematic it shows the sweep pot with the output from the the 560ohm resistor connected to lugs 1 and 2, with lug 3 going to ground. But when looking at my pedal, I see a yellow whire going from the PCB (labelled pot. lat.) to lug 2 of my pot, and lug 3 going to ground! Now is it me not being able to read the schematic right, or should lug 1 and 2 of the pot have been connected?

Right, now lets see how everyone can help me mod this...
paste this link into another browser window!
//www.geocities.com/munkydiy/besbeco.gif


Suggestions?

[smoguzbenjamin]

Ok, I bought some parts today:

1 100K linear pot. (I thought it would be cool to have a pot sticking out so I could fiddle with it as much as I wanted, without having to remove the back)

1 toggle switch (on-on).
A bunch of wires.



Now I'm wondering, Tim said to replace the 68 k resistor, but I was connecting it in parralel to the resistor (just wrapping wires around the lugs), because I have to use a soldering iron at school, I don't have one at home. I thought I noticed a difference, but I couldn't place my finger on it. It certainly wasn't astounding, and it also howled at me as I rotated the sweep pot. Anyway, I'm thinking: "two resistors in paralel is less resistance, right?" But I'm not sure. Somewhere vaguely I remember being told that 2 resistors in parralel are less resistant. Someone help me out!  :oops: