sandawa
Active Member
i have a vintage Yamaha B4 power amp (Japanese model), which i thought for years was the same as the Yamaha M4 (international model). i realized, however, that the B4 is a bit different in electronics and amp design after i saw an M4 manual at the Yamaha website: http://www.yamaha.co.jp/manual/english/index.php. axel of The Vintage Knob also identified differences inside these two amps a few months ago.
the case of the B4 and the M4 seems to be an example of Yamaha cutting corners, producing almost identical models (at least the B changed to M) but could have sacrificed on some aspects to reduce production cost and probably to sell more units in the international market. i just hope the revision did not sacrifice quality. the B4 photos are posted below and M4 owners could check their units if the differences as stated on photo captions are accurate. photos and details of the M4 could be viewed at http://www.thevintageknob.org/
this B4 is rated 120wpc class AB, and 30wpc class A. tests done by a Japanese website showed it could reach 36wpc class A with insignificant distortion. the left front side of B4 has the power button, speaker on/off switch, and class A to AB operation. for M4, the buttons are for power, speaker A and speaker B. the right side for B4 is an impedance adjustment slider - plus or minus one ohm - probably to smoothen out response from the speakers. for the M4, this was converted into a power output meter
the back panels of the two models are almost the same except B4 can accommodate only one pair of speakers while M4 has two pairs with spring connectors
significant changes were made inside, however: B4 has two transformers and four 15,000uF power caps while M4 has only one transformer and two 15,000uF power caps (as per manual)
B4 also uses different FETs, specifically four 2SC2461 and four 2SA1051. the M4, as per The Vintage Knob's data has four 2SC1850 and four 2SA889.
top view of B4
the case of the B4 and the M4 seems to be an example of Yamaha cutting corners, producing almost identical models (at least the B changed to M) but could have sacrificed on some aspects to reduce production cost and probably to sell more units in the international market. i just hope the revision did not sacrifice quality. the B4 photos are posted below and M4 owners could check their units if the differences as stated on photo captions are accurate. photos and details of the M4 could be viewed at http://www.thevintageknob.org/
this B4 is rated 120wpc class AB, and 30wpc class A. tests done by a Japanese website showed it could reach 36wpc class A with insignificant distortion. the left front side of B4 has the power button, speaker on/off switch, and class A to AB operation. for M4, the buttons are for power, speaker A and speaker B. the right side for B4 is an impedance adjustment slider - plus or minus one ohm - probably to smoothen out response from the speakers. for the M4, this was converted into a power output meter
the back panels of the two models are almost the same except B4 can accommodate only one pair of speakers while M4 has two pairs with spring connectors
significant changes were made inside, however: B4 has two transformers and four 15,000uF power caps while M4 has only one transformer and two 15,000uF power caps (as per manual)
B4 also uses different FETs, specifically four 2SC2461 and four 2SA1051. the M4, as per The Vintage Knob's data has four 2SC1850 and four 2SA889.
top view of B4
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