Yamaha m-4 effektforsterker

Klenodium og meget unik yamaha effekt forsterker selges .

spiller som den skal med null støy . utrolig musikalsk og en høy følsomhet .

8 Ohm power : 2x 120W (8 Ohm, 20Hz...30Khz, 0,005% THD)

4 Ohm power : 2x 170W (4 Ohm, 20Hz...30Khz, 0,005% THD)

IMD : less than 0,002% (half rated power)

Frequency response : 10...100Khz (8 Ohm, 50W, 0,02% THD)

Bandwidth : DC...100Khz (-0,7 / +0,5dB)

Damping factor : 200 (8 Ohm, 1Khz)

100 (4 Ohm, 1Khz)

S/N ratio :

Stereo separation : 118dB (IHF-A)

90dB (1Khz)

70dB (20Khz)

Input : 1V / 25kOhm (for 120W / 8 Ohm output, 470pF)

PC : 900W max.

Dimensions : 43,5 x 14,5 x 37,4cm

Weight : 18,5kg.

List price : 250,000¥ (1979)

Features : gold-plated RCA inputs

gold-plated speaker outputs

2,5mm pure copper bussing

phase-corrected polystyrene caps

ground termination

AC+DC inputs

A little beast-seller of sorts the M-4 !

Perhaps more than the M-2, the M-4 circuit is placed within a truly excellent design - stark, bold but not loud.

Splendid Yamaha looks and an excellent amp, too, even if the basics of this design were first attempted at by Hitachi with the HMA-3790 and HMA-4590.

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, two transformers instead of one, 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 !

Thanks to Roger Bownds, here are some excerpts from the M-4's owner's manual :

"The voltage amplifying stage employs a cascode-connected differential two-stage circuit throughout.

The use of a Dual FET input and a new cascode bootstrap circuit in the first stage and a cascode-connection, current-mirror and push-pull output in the pre-driver stage ensures a high degree of stability, low distortion and improved high-frequency characteristics.

In the driver and the power amplifier, a three-stage emitter follower is paralleled with pure complementary OCL SEPP circuitry using high-fT transistors. This accounts for wide bandwidth, high output and low distortion.

Two extremely large 15,000µF capacitors, two separate constant-voltage power supplies for the voltage amplifying stage, and the use of a pure copper plate earth line for ultra-low impedance guarantee greatly reduced intermodulation distortion, improved separation and absolutely stable operation.

Except for the chemical capacitors in the power supply section, mylar and styrol capacitors are employed throughout ; layout of parts, wiring, earth line as well as many other aspects have been given due consideration."

I believe the transistors for the M-4 to be four pairs of 2SC1850 and 2SA889 ; those of the original B-4 are 2SA1050B and 2SC2460B.

Like the M-2 / B-5, the M-4 / B-4 are, specs-wise, also quite different.

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