Morley M2 Volume Wah (M2WA) schematic

From the vendor

Morley M2 Volume Wah (M2WA) schematic

Apr 27, 2023 2 min read

There's not much information about this series from Morley. This company seems to have tried many different control schemes for the wah, from LDR to standard pots, to the nylon string and faders this one uses; this is probably the most interesting feature of the pedal.

Similarly for the circuit, Morley seems to be alternating between using bridged-T filters and classic crybaby circuits. This one belongs to the latter, as signaled by the inductor and two transistors, but I couldn't be sure until I had seen a schematic. Since there were none available for this model, I set to tracing it!

As suspected, the wah circuit is practically identical to the crybaby/vox wah, with a series potentiometer to the input as a way to adjust the volume and respectively increased gain on Q2 to give a bit more. The only other difference is a series resistor to the inductor, to raise the effective ESR of the inductor to match some requirement.

The buffer is good, just a simple TL071 op-amp with clean biasing, which begs the question of why they botched the volume control right at the last time. It would have been easy to have a 10k potentiometer and a larger output cap; instead, even if the input had been buffered, they used a 1M potentiometer, which just has too high output impedance whenever it's not at full. I guess it's in theory possible to replace the fader but it wouldn't be as easy as with a rotary potentiometer given how it's mounted.

There are other curious things of note: I can't think of a reason why the transistor LED switch would be better than just connecting it mechanically as usual. It's one step away from being a soft start circuit, but there's no capacitor on the transistor base to make it so.

Similarly, R4 could seem like a way to filter the power to the sensitive wah circuit, but there's no capacitor after it.

Finally, there was a trace connecting TN to ground on the output jack, meaning the output would have been shorted to ground with nothing plugged into it, but this has been cut in this unity. I don't know if this has been a factory modification or it happened later, but I agree with it. The wah wouldn't mind the short, and the op-amp probably neither even when at full volume, but it's still not ideal.