1987 Dave Goodman'sMOSFET amplifier
distributed through Maplin Electronics UK (no longer available) |
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The aluminium case is now powder coated (Charcoal) Green RS main switch Brushed metal shown below
CIRCUIT DIAGRAM. DETAILS MUSIC MAKER PROJECTS VOL 1,1983 (DAVE GOODMANS MOSFET)
Lights flicker when this boy switches on!
Internally its all power supply. Two tiny amp boards mounted vertically in corners. This amp was based around a Maplin's kit which was in production up to about 2000. It uses a monstrous 625VA toroidal transformer and 4 coke can sized RS approx 15,000uF electrolytics in its power supply. It will continue to play low level music for about 2 minutes after switch off. The only 2 components that has failed in 18 years of daily use is its mains switch and the bridge.. Radio Spares still make the original switch and this was replaced June 2001. These amp board's are brilliant,(Dave Goodman design) very simple 7 transistors including 2 MOSFETS and 100W. THIS IS A MONSTER PARTY AMP. WE HAVE HAD LOTS OF GOOD TIMES TOGETHER MOSFETS will simply lower output (switch off) if they get too hot. This is an extremely good amplifier which has always done well when compared against serious HIFI gear. I feel its success comes down to its massive power supply and simple design. There are very few components and solder joints in this PCB. The solder tracks have also been built up with extra solder particularly around the output stage.
1987 version uses Hitachi K134 + J49 complimentary pairs.......Very long lasting...I change the heat transfer compound every 2-3 years. This amp still uses the original "thick can" Hitachi MOSFETS. These are still industry standard devices. Very beefy power supply 625VA + 60,000uF CASE "brushed aluminium" Dead simple 7 transistor boards, lots of silver wiring. This amp makes the house lights flicker at switch on. Amp features Zobel network which allows it to operate with a swinging impedance. It drives difficult speakers including electrostatics with great ease The MOSFETS are practically bomb proof. This amp has been used daily since Jan 1987 since it was originally designed as a guitar amp. I really like the end results, and it makes sense to me reducing the number of components. It is very easy to "work on and improve" The huge power supply here is way over what the design requires.
Here is one of the later production amps. (1999) Now sporting EXICON MOSFETS 1987 QUOTED SPECS Power output >75W into 4 ohms, >50W into 8 ohms Sensitivity 650mV for rated output, input impedance 47Kohms, Power supply 44-0-44V DC 2A Frequency response 20-20,000Hz virtually flat Harmonic Distortion < 0.005% Signal to noise 120dB 1997 Quoted Specs Power output = 100W into 8 ohms Sensitivity = 860mV for rated output, power supply 55-0-55V 2.5A 8 ohm or 5A 4 ohm Frequency response = 20- 40000Hz THD 0.01% THESE KITS ARE NO LONGER AVAILABLE IF YOU CAN ETCH YOUR OWN BOARD THEN USE THE INFORMATION IN THE LINK SHOWN BELOW CIRCUIT DIAGRAM. DETAILS MUSIC MAKER PROJECTS VOL 1,1983 (DAVE GOODMANS MOSFET) |
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