David is seen using the EMS Synthi Hi Fli. This was used primarily in "On The Run", although some sources indicates that the auto filter was used to emulate Leslie tones on "Any Colour You Like" also.

According to an article on Guitar Lobby titled "Ritchie Blackmore Guitars & Gear (2022 Update)," Ritchie Blackmore used the EMS Synthi Hi-Fli synthesizer during the 1970s.

Tom Rowlands, of Chemical Brothers fame, working in his studio. Just check out the complete list of this synthesizer nerd … an instant daydream … and also explains the original sounds on their records!

On Steve Hackett's official website, he lists the EMS Synthi Hi-Fli guitar synthesizer among his gear.

Used live, on Solid and on Crosscut Saw. By June 1978, it was being used to boost his Guild amp.

Ca. 1973 photo of McPhee on stage (pictured), via Easy on the Eye, "Tony McPhee & The Groundhogs" (April 2013)

https://easyontheeye2.wordpress.com/wp-content/uploads/2013/04/tony-ts-mcphee.jpg

Tony TS McPhee with The Groundhogs, photographed on stage at the Sheffield City Hall.

Solid back cover

Effects using:

A Synthi Hi-Fli, Audio Design Phaser, Vari-Pitch Revox

1974 footage of The Groundhogs performing "Light My Light" at The Marquee (visible; prominent at 2:46)

Beat, March 1976, "Tony McPhee: The Hogs Return" by Chris Simmons, pg. 25

Amps

In the amplification department, Tony is still undecided as to what he will use for the gigs. "I used to have a big Laney cabinet, and I'll probably end up using that. I have been in the studio with a Davoli amp (with a 15" speaker) which is great for straight things, but as soon as I put my Hi-Fli through it it just breaks up. Perhaps I'll end up driving the Davoli through the Laney cab, but I'll have to experiment more fully first. Actually, the real problem is not amplifying the guitar but my synthesizer.

Distort

"You need a system that won't distort the sound and still has enough poke behind it to carry. On certain gigs you will find that the set-up you have is perfect and on others you will hate it. Then, another problem is that I need a whole lot of top as I use my fingers instead of a pick. Recording is obviously a different bag; I use a pick in the studio to pick out definite notes clearly. It doesn't matter on stage but when you use your fingers some notes are a little down on others. Anyway, if one note's a bummer so what? The main thing is feel."

One might guess that with his penchant for sound experimentation, Tony supplements his guitar with various effect units, but surprisingly he sticks to his Hi-Fli and Echoplex only. He explained his feelings. "The Hi-Fli is a pretty underrated instrument — I've seen a lot for sale secondhand which means that people buy them and then get rid of them. The Echoplex I find very versatile, and that's what appeals to me particularly. What I really want is an amp to handle all the different sounds properly. Earlier on I was trying out a system using either an HH or JBL 2x15 cabinet, with Gauss speakers, and little Eagle tweeters for top. The amp was 100 watt HH. This was ideal for some things but once again it was quite difficult to get a straight sustain."

Beat Instrumental, June 1978, "Don't Mention the Gr**ndh*gs! says Tony 'T.S.' McPhee. Peter Douglas apologises" by Peter Douglas, pg. 18

In line with this begin-all-over-again approach Tony has ditched a lot of the equipment he accumulated with the old band through some remains. "I'm still using the EMS Hi-Fi, mainly because I use it as a power supply. Let me explain: when this band got together, I thought right — I still had the Laney cabinets and all that sort of stuff I used to use — you can't walk into a pub with that stuff. So I thought I'd look around for some smaller gear. I'd got a fifty watt Marshall, but I found that was too loud — I couldn't get it to scream without It deafening everybody. Anyway, I was round at a friend's house and he brought out this amplifier — it was an old Guild, circa 1960 I should think. He said it didn't seem to work, and I didn't have any tools with me at the time, so I couldn't look inside it.

He told me he'd had a bit of an accident with it — he'd plugged it in and smoke had poured out of the back. Apparently there was a fuse missing and they'd forgotten it was a 110 volt amplifier. It had never been changed from the American voltage. So I walked off with it, bought myself another transformer and a few resistors, stuck 'em all in, and it worked fine. It's the sort of amp where the inputs are marked 'organ' or 'accordian'!

"I took the speaker out, 'cause I blew it. Anyway, it was obviously quite low sensitivity, so I knew I'd have to have to put something in front of it to wind it up. Now for some time I'd been using a transmitter/receiver, and that boosts the signal up a bit, but with the receiver it was always awkward to know exactly where to stick it. So I stuck the receiver on the pole of the Hi-Fli and plugged it into the Hi-Fli using the power supply. And the Hi-Fli boosted the signal up a bit more so I can get a raw sound at quite a low volume. I just plug it in, turn it right up, and away it goes."

Paul Freestone, January 25, 2014 comment on Easy on the Eye, "Tony McPhee & The Groundhogs"

I think this was taken on 30th Nov 1973, during the band’s ‘Soldier’ tour. The effects unit behind TS is the EMS Hi-Fli, which he was using for the first time at these gigs. All details of line-ups, equipment, gigs, etc, are included in my book about Tony McPhee – ‘Eccentric Man: A Biography & Discography of Tony (TS) McPhee’.

Bernard Paganotti is confirmed to have used the EMS Synthi Hi-Fli in 1975, as evidenced by a Facebook post from Klaus Blasquiz, the singer of Magma at the time.

In the video Weidorje Live Chorus 1979 on Youtube, we can see the EMS next to Bernard.

Rodney Orpheus is confirmed to use the EMS Synthi Hi-Fli, as it is listed on The Cassandra Complex gear page, authored by Rodney himself.