Used on "The Rapture" and "Galaxy Of Tears", as specified in this July 20, 2012 breakdown of a A Fine Pink Mist gear list printed in the October 1996 issue of Young Guitar.

"That was the distortion pedals, exactly the same ones I'm using now. There's a very old Schaller Wah-Wah, and a Big Muff distortion box. I've never used any special amplification, I think it is very important for a musician of quality to be able to play on whatever equipment is at hand. If you play with your ears any instrument will do." -Michael Karoli on the effects used on Tago Mago.

The Schaller Yoy-Yoy Bow-Wow is confirmed to be used by Dave Stewart, as it is visibly placed on the floor next to his Hammond L-122, as seen in the provided image proof.

"yoy yoy or bow wow #wahwah #schaller I'd to thank everyone in nyc for coming to the show last night, the organizers, everyone at trans-pecos, all the wonderful artists, my collaborators, everyone who ever drove a taxi, special thanks to my hotel deep soak bathtub and everyone who ever had a heart"

Besides this photo, McPhee's Schaller wah-wah is known from the following sources:

August 27, 1970 photograph by Charles Everest of The Groundhogs at the 1970 Isle of Wight festival

ZigZag, March 1971, "Tony McPhee... Groundhog" by John Tobler

What about records? You’ve never thought of bringing in Moogs and what have you?

No, I’m not really a weird noise freak. I think it’s much better and cleverer to get a strange sound out of an ordinary instrument, which is why I admired Hendrix so much. He could make Moog noises with a guitar, and though I don’t consciously try to copy him, I do sometimes get similar effects.

Yes, and the wah-wah pedal often accentuates the similarity...

Well, a lot of people don’t realise about wah-wahs....I mean, every little step you bring it down is a different tone, and you can get all sorts of noises from it. I’ve also got an octave splitter which sounds great through the Laney gear — it gives you an octave above and an octave below. Hendrix uses one on ‘Machine Gun’ — it gives a sort of modulated note, where you have the note and other frequencies with it which aren’t really related, so you end up with a weird sort of dischordant sound. And I’m just discovering exactly what you can get out of this device.

Beat, May 1971, "Groundhogs' 'Split'" by T.T., pg. 17

'A lot of the strange sounds you hear on Split were actually done in the studio,' he adds, 'but all I use on stage is me guitar, me amp, and a wah-wah.'

Melody Maker, June 5, 1971, pg. 34, Any Questions?

I use a Laney 100-Watt stack, plus an Arbiter Add-A-Sound octave splitter, which adds higher harmonies, producing a "violin" sound and also lower octaves, which used [sic] on "Cherry Red." I modified this unit and built in a pre-amp with high-pass filter which acts as a treble boost. I also use a Shcaller [sic] wah-wah pedal. On "Thank Christ" we had completely different equipment, so the sound is different on "Split", plus the fact that I also used a Fender Stratocaster for many of the numbers on "Split," notably parts 2 and 4, using a combination of wah-wah and tremolo arm to get "whizzing" effects. I use two other guitars, a Gibson SG which I've had for ten years, and recently I bought a Zemaitis, which I used on Top Of The Pops. This guitar was custom built for me by Tony Zemaitis and has an engraved metal front. It has one Fender and one Gibson pick-up but any could be fitted. Cost of similar guitar would be around £250 from Tony at 19 Laitwood Road, Balham, London SW12 (01-675 1342). On "Junk Man", the wind sound is transistor noise from the wah-wah pedal and the other effects were obtained using the Stratocaster with tremolo arm, wah-wah pedal and volume pedal simultaneously, and then playing the track through a speaker at one end of the studio picking it up with a mike at the other end, panning this against the original track in the mix at the same time varying the speed of the 8-track machine! All the other effects were obtained with pedals and channel panning. I played the organ which happened to be in the studio that day. I sang to a pre-recorded backing track on Top Of The Pops, but it would have been a lot easier to have done the whole thing live!

Sounds, March 18, 1972, "The Groundhogs: Tony McPhee At The Talk-In" by Jerry Gilbert

Since Thank Christ For The Bomb you've started to get into sounds and effects which you can obtain by using the studios and also by modifying your guitar and amplification.

Yeah definitely. Studios are weird things, you know you can get a sound on stage which suits you but you can't get it in a studio so you have to muck about with it quite a bit and in doing so you get a different sound. I use a wah-wah pedal which I'm using less of now – it got a bit tiresome after a while – then there's a new thing called an octave splitter and that just sort of gives you a rough octave above and below.

You can get sounds like a bass and sustained sounds with a weird quality and in effect it's like an electrical Rory Gallagher – you know this ability he's got of striking harmonics, well in actual fact that's what it does, so you can cheat quite well on those things. Also playing two notes at once it gives you the same effect as a ring modulator which is very trendy these days... notes which are the subtraction and addition of the two frequencies and this sort of thing which gives you a bubbly sort of sound. That's all I get along with really but I do feel now that I want more – not simply from gadgets because I don't use these as gadgets, I use them as separate instruments really.

The whole point is I knew I could imitate things like strings on the new album but I wanted the actual strings sound for some reason otherwise it makes it another freaky album which I didn't want to do. When the mellotron comes on stage we are going to have to re-think quite drastically – not that we do much thinking; we'll probably just slide along like we always do.

• July 8, 1972 photos from Carl Dunn of The Groundhogs performing at Concert 10, posted to Facebook by McPhee on September 12, 2011 (Photo 1, Photo 2) (visible)

Sounds, May 5, 1973, "Mac’s Home Cooking: The Groundhogs" by Jerry Gilbert

For having exploited the full range of guitar sounds via the various echo and wah-wah pedals and octave splitter, he turned to the electronic keyboard instruments just as a duck turns to water.

"I only want to use a synthesiser to synthesise — nothing more. I synthesised a drum kit and got an amazing brass sound. I want to use a brass sound on the new album, but brass musicians are a pain in the arse so this is ideal. You can never mistake a synthesiser for the real thing, though, because it has characteristics of its own".

Hogwash liner notes

Schaller Wah Wah Pedals

Facebook, Tony McPhee, September 13, 2011

Succinctly put,Col, I even had a Schaller Wah-wah nicked off the stage Newcastle City Hall. People were searched as they went out but they'd obviously stashed it somewhere.

Facebook, Tony McPhee, September 13, 2011

Tony McPhee Succinctly put,Col, I even had a Schaller Wah-wah nicked off the stage Newcastle City Hall. People were searched as they went out but they'd obviously stashed it somewhere.

Col Price Daunting when your out on tour. That message came through and i had Split pt2 on. Full on wah riff.

Tony McPhee That was the Schaller pedal, better than the Cry baby in my opinion, hard to find now. Actually I might try Ebay!!

Interview with Tony Bacon for The SG Guitar Book: 50 Years of Gibson's Stylish Solid Guitar (2015), excerpted in Guitar, "The oral history of the Gibson SG" by Tony Bacon (September 3, 2019)

“Also, I put a push-button switch mid-body that put a capacitor across the output, like a tone control – my version of a wah-wah pedal, before I got my first Schaller wah. I’d press it in solos and so on to imitate a wah pedal.

A Wau-wau Bow-wow used by Davis was donated to the Science Museum Group by his wife, Pam. It is now catalogued there with the object number 2007-117.