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Friday, 3 February 2017

Harman Kardon PM660

Hamstall called by. I've got this 'arman Kardon, can you give it the once-over?



Yeah, why not.

It a nice early 80's integrated amplifier. Spec recons on about 80 watts per channel into 8 Ohms. No spec is given for power into 4 ohms. It's a completely discrete design. Not an op-amp in sight.



Nicely laid out...











A good-sized transformer and rectifiers... and plenty of smoothing caps.










10,000 uF , and there's 4 of 'em....













... and that "Sony" on//off switch .... (it all looks a bit Sony to be honest)











Super phono pre-amp, MC and MM....












... fitting with a smattering of ELNA "for audio" capacitors, so you know where your money went....











... and four position, front panel adjustable, capacitance loading for your odd-ball cartridge....


















Underneath reveals, well, not a lot really. 4 pairs of Toshiba 2SB775/2SD845 output transistors. Cleverly mounted through holes in the PCB, straight onto those gargantuan heatsinks....































Speaker wiring takes a bit of a long route home....











... and through some rather flimsy looking speaker select switches. I don't think I'd want to be switching speakers whilst playing....

























Two tape loops, two phono inputs (with short circuit plugs if you're not using one to keep the noise out), an aux and a tuner input....









So ... set the bias up (a blissfully easy procedure, thanks to a great service manual), a clean up of the pots and switches, all the caps look in great condition, and testing the ESR of a good few proves this to be the case.

The tuner indicator lamp is open-circuit...

Diminutive little lamp, so we'll replace it with a warm-white wide-angle LED...










The holder had to be drilled out slightly to enable the slightly fatter legs of the LED to pass through, and a 10K currently limiting resistor is fitted, to run the LED at a low ~1mA.









Not a bad colour match....

It plays effortlessly. I've no idea on it's output power as it easily over-ranges my audio wattmeter at 50 watts, with no sign of distress.

The phono stage is a delight. Nice and quiet.

Tone controls have a lot more range than is probably required...

There... another repair done...

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