Morley Pik-A-Wah

[RickL]

I finally got around to building the Morley SAW Pik-A-Wah. Schematic is available here: http://www.morleypedals.com/downloads2.html

It's one of the one's that use a metal pick attached to the box to trigger the effect and I've always been impressed by how well they trigger.

It consists of two essentially separate parts: a filter controlled by a variable resistance (in this case an LDR), and a trigger that swells the brightness of an LED, with the swell time controlled by a pot. It simulates an envelope controlled filter and since the pick controls the envelope by grounding the circuit each time you pick a string it triggers perfectly every time.

The filter is a pretty basic one op-amp circuit and pretty much any resistance controlled filter should work with the trigger.

The interesting part is the trigger. The swell time of the LED ranges from almost instant to about 1 second. Since it is entirely separate from the filter circuit it could easily be used to control any number of other effects. Use it to control an amplifier and you have a "Slow Gear" that triggers perfectly every time. Use it in a distortion and the gain will swell up (or down depending on what the resistor controls) each time you pick a note. Replace the speed control of a chorus or phaser and it sounds like an envelope controlled rate control (similar to the envelope control in an EH Poly Phase).

I experimented a bit with LDR/LED combinations and everything worked to a greater or lesser extent. I was most pleased with a low current LED and low on-resistance LDR and with a VTL 5C1 and a CLM8500.

I expect to eventually add a switch to allow control of the filter with a pot and an LFO controlled LED in addition to the trigger circuit.

[clintrubber]

I realize this is an old thread, but started by user Rick who's still active, so why not post some more here 

Nice to find this thread - I've stumbled upon these Morley pedal-less units.

Saw some inside pics and couldn't help wondering about the somewhat messy component-placements on the PCBs,
combined with unused areas.

I'm aware of the copperside-up approach of those old Morley units,
but the PCBs inside these pedal-less units looks a bit like re-purposed PCBs, initially meant for something else.

OK, but it looks like you started from just the schematic, right ?

[clintrubber]

I experimented a bit with LDR/LED combinations and everything worked to a greater or lesser extent. I was most pleased with a low current LED and low on-resistance LDR and with a VTL 5C1 and a CLM8500.

Thanks for sharing that info, good to hear the VTL 5C1 is suited here.

I expect to eventually add a switch to allow control of the filter with a pot and an LFO controlled LED in addition to the trigger circuit.

Curious if you have the circuit still in use, or that about 10 years later the the novelty wore off 
Any further mods to the circuit?

[clintrubber]

BTW, there's a second Morley box, also without pedal, also with metal pick: the SAB.
Looks like there are errors in that schematic though, or some NPN BJTs used deliberately upside down. 

[RickL]

I never did get much further with this, but I haven't forgot about it. I made the Sync-Attack version as well and it works every bit as well as the Pic-A-Wah does. I put each of them into little fuzzy metal jewellery boxes that I picked up 20 years ago or so. I keep meaning to box up just the trigger part as an add-on to an already built phaser or chorus to control the rate.

The circuits of the small boxes are simple enough that I just made them on perf. If I dig around enough I can probably find the layouts that I used, but don't count on it for at least a couple of weeks. I'm off to Ontario next week to teach inspectors how to check scales.

I have one of the bigger pedal versions that uses the same concept as well but reproducing it on perf-board is a little more complicated than I want to get at this point.

[iainpunk]

BTW, there's a second Morley box, also without pedal, also with metal pick: the SAB.
Looks like there are errors in that schematic though, or some NPN BJTs used deliberately upside down. 

They might have done that with bjt's. They still work, but only at about ⅓ of the Hfe. Its a great trick to tame a fuzz pedal (especially with silicon fuzzes).

[clintrubber]

BTW, there's a second Morley box, also without pedal, also with metal pick: the SAB.
Looks like there are errors in that schematic though, or some NPN BJTs used deliberately upside down. 

They might have done that with bjt's. They still work, but only at about ⅓ of the Hfe. Its a great trick to tame a fuzz pedal (especially with silicon fuzzes).

Hi,

Indeed, vertically flipped BJTs would still work. I wouldn't be my first assumption, based on the resemblance between the schematics of the trigger circuits for the wah & attack boxes, but who knows...

I'll be able to verify the correctness of the SAB-schematic soon, have one upcoming.

[clintrubber]

I never did get much further with this, but I haven't forgot about it. I made the Sync-Attack version as well and it works every bit as well as the Pic-A-Wah does. I put each of them into little fuzzy metal jewellery boxes that I picked up 20 years ago or so. I keep meaning to box up just the trigger part as an add-on to an already built phaser or chorus to control the rate.

The circuits of the small boxes are simple enough that I just made them on perf. If I dig around enough I can probably find the layouts that I used, but don't count on it for at least a couple of weeks. I'm off to Ontario next week to teach inspectors how to check scales.

I have one of the bigger pedal versions that uses the same concept as well but reproducing it on perf-board is a little more complicated than I want to get at this point.

Hi,

Thanks for posting. These circuits indeed simple enough to make on perf. I happened to run into one for sale, and it works fine and I see creative uses for it that aren't easily duplicated with the usual other means (Slow Gear etc).

That simple 3 BJT circuit indeed a nice little circuit to use for other FX!

Thanks for the offer, but no hurry to dig up the layouts.
Just curious if you followed the SAB-schematic (6-23-81) exactly, including the two upside down A06 NPNs or that you 'corrected*' this for the SAB - so alike as these are drawn in the SAW schematic (5-12-81).

*: which might be justified or actually not ;-)  But it might in the end have no big impact on the functioning of the circuit.

Bye

[clintrubber]

FWIW, the Sync-Attack arrived.

Those upside-down BJTs both appear to be 2N5087's,

... so PNP's,

... so The Universe is in sync again   

Regards