Ibanez WH-10 wah - Tweakable!

[Mark Hammer]

Forum member MovinInSloMo recently expressed his appreciation of the Ibanez WH-10 wah.  After listening to a couple video demos, and looking at the schematic of the pedal, this presents a nice opportunity for wah enthusiasts to tinker.

The WH-10 uses a circuit that appears distantly related to the Systech Harmonic Energizer.  Except, where the SHE is intended as a fixed resonant boost, the WH-10 is a foot-controlled one.

But what's nice about both circuits is that, unlike most Cry-baby type wahs, centre-frequency is varied by a single variable resistance, rather than a voltage divider. The range of sweep is also moved via a single resistance.  Moreover, there is no requirement for any exotic or expensive inductor.  The WH-10 lends itself quite easily to being built with off-the-shelf parts.

So...ideas.

First, the unit has a "Range" switch, that converts it from Guitar to Bass range.  All the switch does is bridge one of two 15k resistors in series, such that the total resistance to Vref is either 30k or 15k.  That could easily be replaced with a 12k resistor in series with a 20k pot, to move the range around from a bit higher than stock, to a bit lower than the stock bass range.  If you like things simple, I suppose it could always be a 3-way toggle to pick a range in between "guitar" and "bass" (7-string/baritone guitar?).

The foot treadle varies a 50k resistance.  One could easily plunk an LDR in parallel with that resistance, and vary the LDR with an LFO pushing an LED, or with an envelope follower driving the same LED.  Or if you wanted to get fancy, an LFO could work the range setting, and an envelope follower work the specific frequency.  Or you could work the foot treadle yourself, but have an envelope follower move you to a progressively higher range as you pick harder.  The possibilities, as they say, are endless.

[Kipper4]

I might have to bread board the filter to check the response and see how I like it. Thanks Mark.
I guess the 50k variable resistance varies the Q of the filter? Just wondering.
It looks like a fair candidate for a envelope detector I've been working with too. Hmmmm.
Edit any suggestions for subs for the bjt and jfet welcome.

[Mark Hammer]

No idea what it does to the Q but it varies the centre-frequency of a bandpass filter.

If any of you more EE-types could identify what component or components can alter the Q, that'd be sweet.

[mac]

Rich, you can use any of the usual transistors but note that 1815 pinout is b-c-e

Mark, I'd  tweak the 220p/1k pair, or the resistors going to bias, or r17.
r18 looks like a freq limiter when r18 is zero.

mac

[Mark Hammer]

So I etched a board from a posted layout, and built one last night.  Tested it out tonight, and it works as advertised, providing a pleasant sweep.  Presently perfing the envelope-follower subcircuit, after having sifted through the parts bin for a suitable LDR.

The "Depth" control doesn't seem to do an awful lot; at least that I can hear.  It certainly works, but I'm only hearing a modest boost.

I did sub a 12k resistor for R21 and a 20k pot for R14 and S2.  That also works as I proposed, though I have to say that I don't think a person would be missing much by rigging up a 3-position toggle instead of the pot.  On the other hand, I have it sitting on a PCB on the benchtop, and not installed in a foot pedal.  I can see where the sweep range would be a darn sight easier to adjust with a pot than with the traditional method of moving the gear or pot shaft over a tooth or two.