Stig Carlsson, Sonab's founder, handed the R4000 project to Clas-Göran Wanning, Sonab's Chief of Product Design, in 1969.
The goal was to offer superior sound in a compact and attractive enclosure and extensive reliability that would allow Sonab to offer a 5-year warranty. Two years later, the R4000 was put into production.
Even if Sonab mainly rings a bell for its ortho-acoustic OA loudspeakers, design-wise, of course, the R4000 is to be remembered (and is remembered) as a staple of early 1970s design.
Perhaps only the R7000 is even more... cryptic. But nevertheless inviting by the very mystery its layout evokes.
More lush and fashionable would be the Lecson AC1 or Lecson Orpheus. The black colour might have been replaced judiciously with something more open such as an off white or gunmetal anodization à la TA-N86B...
The chassis is made of a two-piece diecast aluminium, the top, front and 1/4 of the bottom being one piece, the other being the remaining 3/4 of the bottom.
According to Sonab's literature, a car could run over the R4000 without damaging it :)
The R4000 shares the same basic chassis with the P4000 integrated amplifier (with minor differences in the way the front is cut out to let the controls through) and is, circuit-wise, a smaller R7000.
There seems to be at least three other versions but I don't know of the circuit differences between them : R4000-2, R4000 /1S, R4000-3 - they all look almsot exactly alike from the outside...
Sadly, none of my catalogs say anything about circuit design so, until I find something a bit more meaty, specifications is alI I can publish.
However, the presence of a Sonab version of the british Cambridge P50 in the swedish 1971 general catalog makes me think the Sonab separates might have been partly built by Cambridge... (?)
Thanks to Björn Dimming, here is a bit more :
"Under the lid in every Sonab receiver there was (is) an envelope with the circuitry !
There is a minor difference in the front layout on the revisions of the receivers : around the tuning presets, there is round individual holes on the revision 2 model, and on the revision 3 model there is a common rectangular shaped hole."
All about Stig Carlsson and the Sonab adventure at carlssonplanet.com - all but the hifi separates...