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FIRST WATT

F1 POWER AMPLIFIER

SERVICE MANUAL

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Summary of Contents for F1

Page 1: ...FIRST WATT F1 POWER AMPLIFIER SERVICE MANUAL ...

Page 2: ...eing a current source the F1 operates differently with a loudspeaker A regular audio amplifier supplies an arbitrary output voltage and the speaker draws current according to its complex characteristic As such the current through the loudspeaker is not exactly proportional to the voltage in either amplitude or time A current source amplifier delivers a precise current to the voice coil of the loud...

Page 3: ... your system to get the best performance It does not often work well with ordinary passive crossover networks the components and their locations tend to be reversed It won t break but probably won t sound good If you have an electronic crossover you re in better shape at least until I can finish a white paper describing passive crossovers for use with a current source If being a current source amp...

Page 4: ...don t expect the amplifier to operate properly if you attach either output to ground The fuse is a 3AG slow blow type 4 amps for 120 VAC and 2 amps for 240 VAC No substitutions Contact First Watt if you have any questions The power supplies of each channel are isolated from each other electrically except for a thermistor on each which connects the circuit ground to the chassis and earth ground In ...

Page 5: ...s the outputs where the loudspeaker is connected The DC bias current from the bottom constant current source is divided between the two Mosfets and is taken up at the output by two other constant current sources so that the loudspeaker only needs to see the AC current variation not the DC If you are familiar with the Zen series of amplifiers published in AudioXpress then you will see more than a p...

Page 6: ...Here is the schematic of one channel of the real amplifier ...

Page 7: ... at audio frequencies The gain of the amplifier is determined by the transconductance of the Mosfets themselves plus the parallel Source resistors for a current gain of approximately 0 6 amps per input volt This figure gives 14 dB of gain into 8 ohms The speakers operate across the Drains of the gain and current source Mosfets This is at an absolute potential of 13 8 V DC but the differential volt...

Page 8: ...This is the printed circuit board layout for the left and right channels Note that they are mirror images right and left ...

Page 9: ...Here is the schematic for the power supply for both channels ...

Page 10: ... standoff mounts It also is connected directly to the rear of the chassis by the ground case tabs of the XLR input connectors Each of the two analog grounds is isolated from chassis Earth through the thermistors TH1 and TH2 which ordinarily operate at 5 ohms or so in the amplifier but which rapidly reduce their resistance so that the fuse will blow before the thermistor fails in the event that the...

Page 11: ...Here is the PC Board Layout for the power supply board Note the placement of thermistors for AC voltage on the left hand edge 120V 120V and 240V All four mounting posts go to chassis ground ...

Page 12: ... 1 75 amps Frequency response 3 dB 3 Hz 100 KHz Noise 30 uV unweighted 20 20 KHz 8 ohms Power consumption 200 watts 100 watts channel Fuse 3AG slow blow type 4 Amp for 120VAC 2Amp for 240 VAC Warranty Parts and labor for 3 years not covering shipping or consequential damages This amplifier is a specialty product There is no representation that the amplifier will make you happy Zen amplifier is a t...

Page 13: ...Typical performance curves ...

Page 14: ...More Curves ...

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