M-4
(1980 - 1983)

A little best-seller of sorts the M-4 !
Perhaps more than the M-2, the M-4 sports an excellent design - stark, bold but not loud. Splendid Yamaha looks and an excellent amp, too.

The japanese version of the M-4, named B-4 (to keep the "B" prefix inaugurated with the B-1 in 1975), is fairly different: two more PS caps, 2 transformers instead of 1, LED meters replaced by an "output impedance" slider (as seen in a few other contemporary Yam' units) and, mostly, the possibility to switch the B-4 in Class A operation! You may see the B-4 on this great online resource.

I believe the transistors for the M-4 to be 4 pairs of 2SC1850 and 2SA889 ; transistors used in the original B-4 are'nt the same as that of the M-4.

Thanks to Tim, the "more" button below will show the insides of the worldwide version.
Thanks to Hernan, B-4 owner, a comparison of the two versions can be seen here.