Hi Gugliemo
I had a IVSJ about 15 years ago and remembered it to be the same as IV-S for playback- that is from a distant memory. One very rare and interesting machine I had about 3 years ago was this Sony 770 4 channel portable deck. It was set up for 7 1/2 and 15 ips and had balanced mike inputs. It was as much money as a Nagra at the time and Sony only sold about 20 of them. It came with mimeographed operating manual as they never came up with a colour manual. It is a fine sounding machine, although nowhere near as rugged as a Nagra or Stellavox. They are much more common in 2 track format.
I've used Stellavox(sp-7 and sp-8), Nagra IV-S and T-Audio, Lyrec PTR-1, Sony 770 for location recording and playback. The Lyrec and Stellavox are my favourites for sonics. The Nagra IV-S is a fine recorder and not so great for playback. Charlie and I did put Stellavox electronics into a Nagra IV- this turned out to be a sonic disaster- likely due to the heads not being entirely happy with the 'vox electronics. The Lyrec is both a great recorder and playback device, but two drawbacks are lack of mic preamps and mechanical noise levels. The reliability is not wonderful from my experience with 4 of these over the last 10 years.
Regarding the ABR- it is totally Rube Goldberg like in operation. Totally lame for playback, due to almost non-existent tape tension. The QGB(Nagra) is the reel deal- great engineering and build quality. The ABR is only useful for location recording IMO.
Rich Brown
Portland, Oregon