The Sphere 920 is a vintage graphic equalizer that seems to be pretty rare. I've only ever seen one of these, and it was brought in by an outside engineer that I was assisting for. The 920 is made up of all analog components, and I'm not sure if they always come as a stereo pair, but the one that he brought in was indeed stereo. It was in a rack mountable, single space casing, but I'm not sure if this would be the norm or not.
It isn't difficult to use the Sphere 920 at all, as it's a pretty simple graphic equalizer. It's got 11 bands in total, including a high pass filter. It also has a few other control settings, but we didn't use any of them. I doubt that any inexperienced users will be coming across and using this anytime soon, so I'll say that pretty much anyone using this should be able to use it easily right from the start. I doubt you'd ever be able to find a manual for the 920.
The sound of the Sphere 920 is nothing less than fantastic. It's got a super clean sound and is versatile enough to be used across the board on just about anything. I'm generally a bigger fan of parametric EQs, but when an EQ sounds this good I don't really care what form it comes in. Plus, there's definitely a good amount of control between the bands anyway. This is definitely up there with the best sounding graphic EQ's that I've ever heard before.
Not too many people out there will get the chance to use a Sphere 920, as they are definitely rare and hard to find. If you do find one it will most likely be in a professional studio or in professional engineer's hands. The engineer that brought this into the studio had a whole ton of different gear with the 920 amongst it all. While I wouldn't recommend trying to find one of these as you probably won't be able to, if you do ever come across one I'd definitely recommend taking advantage of your time together!