Fixing Morley Power Wah noise

[kdawg]

I dug out my old Morley Power Wah, a 55 volt lamp-based LDR Wah. I like it (besides being HUGE), but two problems:

1. VERY very noisy (hissssss) when on, all throughout the wah range
2. Too much frequency sweep. Needs a narrower range for my use

The schematic is at http://www.morleypedals.com/pwotr.pdf. Could someone help me out? I want to get the noise floor down by at least half, and I'd like to add two pots: a bottom frequency and top cutoff frequency adjustment.

Does anyone know the resistance range of the LDR-1 here? (I haven't tried to measure it yet, but will soon)

Are the MPSA12 and MPSA06 generally noisy transistors? Some replacement suggestions?

Some inside notes:
* PS caps seem pretty old, getting crusty
* All carbon resistors
* Transformer looks kind of worn out, but is working fine.

Thanks
-kdawg

[Travis]

The old Morleys get a bad rap, but I like them too.  If it's an old chrome piece, I'd just go in and replace all of the electrolytic caps.  That will almost certainly take care of your noise problem.  Even with the internal transformer, these are generally quiet pedals.  You can add some extra PS filtering if you continue to have noise, but I've never needed to do that after a cap change.

As for the range of the sweep, you should probably just get in there and measure the LDR's.  Morley (and the old Tel-Ray) components changed from week to week.  The basic circuit remained the same, but they seemed to rely on as much cheaply bought surplus as possible.  They adjusted the circuit to fit the available parts.

Incidentally, if you do really like the sound, I'd change the 1uF polarized caps last.  If you can get rid of the hiss with only a PS recap, let it stand at that.

[Peter Snowberg]

I've got a power fuzz-wah so I know what you mean. You can adjust the range simply by moving the CdS cell and the shield around to get the mix you want. Beyond that you could add two pots... one in series with the CdS and another one across it. I don't know what values to try though.

To get rid of the hiss, first try replacing the resistors with metal-films and ceramic caps with films too. New electrolytics would be good too. If that doesn't do it, I think replacing the transistors is all you have left.

Good luck!

Take care,
-Peter

[kdawg]

Wow I love this place. Where else can you get answers in less than 5 minutes!

Thanks for the tips, I will try some new caps tomorrow (today?). I'm thinking of maybe using 1 pot now for freq, since I can manual adjust the start or stop freq with the light screw adjustment.

If I wanted to do an overall gain adjustment though (this thing has crazy gain!), would I change the voltage divider resistors on Q1 or on Q2? I'm not used to having 55 volts around the transistors. Maybe I need to divide by 5 in my head