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So I bought an old Morley PWA... I don't get it at all.

Discussion in 'Effects [BG]' started by kohntarkosz, Dec 10, 2013.

  1. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    Hello all.

    I live very near a pawn brokers. For months it had a Morley way of some sort in the window for £35. I eventually tested it out and bought it at the weekend.

    Firstly, the thing is a state. All the Morley badging is missing. It is rusty in places.

    Secondly, I don't think it works correctly. The thing sounds nothing like any other wah I've tried. If anything it is more like the filter section of an analogue synth. I cannot get that much treble out of it, and it appears to act more like a low-pass filter than a band-pass filter. I've been fiddling around with it to try and get more treble out of it.

    In a fit of madness I bend the LDR up so that it faced vertically. I then turned on the 'flashlight' app on my phone and shone it at the LDR with the pedal switched on. Suddenly it has a lot of treble on tap! However my phone's flash is apparently a 4watt white LED, whereas the stock LED is a faint red unit. I've tried swapping it with another red LED, and I've lowered the value of the resistor before the LED, but it still doesn't sound as treble. I guess the next solution is to purchase an ultra-bright white LED...

    Do Morleys all sound this way? Muffled and bassy with limited treble on tap? Has somebody been in and tampered with mine? I can provide gut shots if people like...
  2. Crater


    Oct 12, 2011
    I'm not familiar with all the different models of Morley wahs, (and I've never owned one) but it's likely your intuition is correct. Some Morley wahs don't use the "standard" (as used in Crybabies and Vox wahs) inductor-capacitor resonant circuit, they use a twin-t filter circuit. I DON'T KNOW if the Morley Power Wah is one of these. Other morley wahs (like the 'Bad Horsie') do use an inductor.

    Secondly, the early Morleys used an incandescent bulb for the light element, and it was a rather odd bulb too, spec'd to work at 28 volts or something. Some genius was probably thinking he'd make the pedal more reliable by replacing the bulb with a (much dimmer) LED.

    The good news in all this is that Morley posts schematics of their pedals right on their website, so you (or a competent tech) can figure out and repair the problem. Try a brighter LED for starters, I think sealed LDR units use a yellow LED.
  3. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I bet that is exactly what happened. It was designed for a bright white lightbulb, so you'll need to fix whatever the "genius" did to it to install that LED.
  4. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    Some of the solder points are a bit questionable looking. Inside there was a dim red LED. No inductor by the looks of it, and just a single op-amp. The majority of the circuit board is mapped out for more components, but remain unpopulated. Some dude in the Morley factory ticked off the wee box for 'PWA' on the circuit. :p

    Looks like one version had a back-to-back diode clipping circuit in it. I guess they made one with distortion!

    I will try and get a bright LED at the weekend.
  5. Sponsored by:

  6. icecycle66


    Feb 4, 2009
    The sound you describe isn't normal at all.
    I have a handful of Morley wahs from different eras and they all go from muffled, to honky, to treble scream.

    Post a good gut shot of the circuit board. I'll compare it to some of mine.
  7. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    Thanks for offering to take a look. Will try to get a nice photo in the next couple of days.

    Mine looks like this though;


    A dim red LED. The resistor R9 varies the brightness. Stock it is 4.7 kohms, and I've stuck a 2.2 kohm resistor in parallel with it. I know the LDR can be made to work much harder though!
  8. Crater


    Oct 12, 2011
    I may have spoke too soon...the fact that the printed circuit board is marked with the + symbol tells me that the LED is probably original.

    Here's the schematic:

    It does confirm my suspicion that the PWA is a twin-T filter wah. Any company that would post their products schematics online is awesome. :) The correct LED and LDR are spec'd on the schematic too.

    And yes, there is a version with distortion, and also a switchable wah/volume pedal version.
  9. kohntarkosz

    kohntarkosz Banned

    Oct 29, 2013
    Edinburgh - Scotland
    It seems weird then that mine doesn't work right. As I mentioned before, if I shine my phone's white LED flashlight at the LDR I can hear the envelope open much further than the weak red LED can. I've done the phone trick whilst the pedal passes signal, and apart from a bit of hiss overall it sounds a lot better than just with the red LED alone. I guess if you use a lot of distortion you don't want an especially trebly wah with too-strong a Q, just to keep feedback down. :meh:
  10. icecycle66


    Feb 4, 2009
    Sorry for not following up, did you ever figure this out?

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