thought i'd chime in and set the record straight..
the 535-7 performs quite well on +-15v. a bit less headroom, a tiny bit more distortion, (as expected!), but not a square wave generator by any means.
the pads are still on the pcb for voltage converters to bring the the power up to +- 24v. this is a simple modification, and if anyone is interested i can provide part numbers. (the addition of the converters will void the api vpr certification!).
i would like to point out that the 535 is NOT unity gain stable! flickinger has the need for speed! this is a big factor in the sound of the desks.. the amp runs at about 12db of gain.. and then is padded back down.. completely "wrong" from a design standpoint.. but the consoles do sound amazing!.. (and if you open up the channel you can get tape hiss simulation for protools!)..
the sound of the flickinger console is anything but "natural". thats why i like them.. they sound hyped, especially on the low end. big and thick like a 1073 but with an extended bottom. less focused in the low mids.. and a rounder, very smooth top.. less sizzle than a 1073.. i had a bcm 10 in my studio for a while and it was similar enough to the flickinger that i sold it and bought a melbourne and couple of 49's.. couldn't justify the $ tied up in it for such a similar sound. the melbourne sounds sooo different.. bright and tight.. i like it for different things..
there were several different eq's...but the first sweep "4button" was designed by j.weit, and the second.. "6 button" by bill isenberg.. both sound fantastic.. very musical.. 3 band, hipass, shelving on the hi and low bands.. the 4 button is non reciprocal.. and has about 12 db cut/boost.. the 6 button is reciprocal.. has a bit more cut/boost and individual in/out for each range..
Flickinger did a lot of experimentation with FET switching of audio on the later consoles. From the bits and pieces of this I've seen, these implementations were a bit too cutting edge. The Sly console, the Sound Pit console and the monitor controller from the Paragon console all used this approach, and it's not clear that it was a good one. There may be other opinions, but it's hard to beat a signal path devoid of anything but copper wire, precious metal relay contacts, transformers and class-A amplifiers (no fet switches, no VCA's e.g.).
it is not clear it was a bad one... no switch crackles! my console is still going strong.. built in 1970.. i haven't had any of the problems of the earlier flicks (or any other consoles from the era) with the pushbutton style matrix.. imagine 720 dirty, broken switches.. also i think it is foolish to question the sound of the fet consoles...ike and tina (nutbush!), sly, pfunk, ray stevens, johnny cash, glaser brothers (waylon!), sound pit (bohannon!)... and mine is still making hits today.... ha! maybe distortion from the FETs is the secret to the sound?!
i have done many tests with opamp/transformer combinations, and i can say the the transformers play a huge role in the flickinger tone. we've also tried a variety of different op amps in place of the 535-7.. and the magic is in the combo of the amp and the trannies.. (and tantalum caps)..go figure..
two more things..
one... is that i've found that quite often the flickinger schematics differ from the actual circuit.. i think that they were never corrected..maybe it was out of laziness, or just the fact that they were hurrying to get done.. and besides ..the schematics weren't intended to be distributed to the clients!
two.. i don't believe that any of the flick consoles caught on fire! i know that marty feldman of paragon studios had one of the first m56 machines go up..(before mincom put the pancake fans in).. and he had a flickinger.. maybe the stories are getting crossed..
remember that more often than not.. a byproduct of the designers original intention is the the thing that people like about gear! (sorry guys!).. there are so many factors that go into designing gear (price point, availability of components, deadlines!).. the final "sound"...the thing producers and engineers will latch onto... is completely impossible to predict from a design standpoint..what a designer may consider "wrong" is actually the factor that makes the gear sound good! look at neve! he wouldn't design a 1272 again! that is why its important to get the gear into the studio and use it everyday.. try it out.. put it up against other gear..very revealing!
crayotone... i will consider a di on future runs of the 736.. i just liked the aesthetic without a di.. contact me off forum and we can talk about doing a side by side comparison of originals and the 500 series 736.. ray stevens console was sold by blevins years ago, and has been parted out! you are welcome to come to the keyclub and record!
Geoff738 if you'd like to try out some gear.. please lemme know.. we have demo units out there!