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Hafler 500 rebuild
A brief history of a recent rebuild project: To begin I picked up a well used Hafler DH-500 off an auction site.
It was in bad shape and looked like it had seen some heavy band or DJ use. One large cap had been replaced and an output mosfet had been replaced with a generic. Still, it powered up and sounded ok.
Next I added an old set of Musical Concepts PA-3B boards. But I found that I couldn’t bias it properly because of the generic mosfet. Matched sets of Hitachi mosfets don’t exist anymore, so I shipped it to Musical Concepts and it updated with matched Exicon mosfets and a pair of new PA-3E boards. I had them swap over my Blackgate caps from the old boards…can’t lose those.
Once back home, I went ahead and removed the DC relay and replaced the caps with new 39,000uf 100V versions and rewired everything in a dual mono arrangement. That’s 156,000uf of storage, heh. Yes it’s only a single transformer and not true dual mono but it’s close enough for me. I replaced the diode bridges with IXYS 600V versions. Voltages are now exact at 92.3V per channel.
Finally, I added some pebble black paint to the cover and a NOS faceplate. Final result is a new looking amp and rock solid 255 watt+ per channel. The mods give it a 3D clarity with pinpoint imaging at all volumes, bass is taut and correct with lifelike dynamics. I’ve used Musical Concepts mods since the late ‘80s and the results are always very worthwhile.
A brief history of a recent rebuild project: To begin I picked up a well used Hafler DH-500 off an auction site.
An externally hosted image should be here but it was not working when we last tested it.
It was in bad shape and looked like it had seen some heavy band or DJ use. One large cap had been replaced and an output mosfet had been replaced with a generic. Still, it powered up and sounded ok.
An externally hosted image should be here but it was not working when we last tested it.
Next I added an old set of Musical Concepts PA-3B boards. But I found that I couldn’t bias it properly because of the generic mosfet. Matched sets of Hitachi mosfets don’t exist anymore, so I shipped it to Musical Concepts and it updated with matched Exicon mosfets and a pair of new PA-3E boards. I had them swap over my Blackgate caps from the old boards…can’t lose those.
Once back home, I went ahead and removed the DC relay and replaced the caps with new 39,000uf 100V versions and rewired everything in a dual mono arrangement. That’s 156,000uf of storage, heh. Yes it’s only a single transformer and not true dual mono but it’s close enough for me. I replaced the diode bridges with IXYS 600V versions. Voltages are now exact at 92.3V per channel.
An externally hosted image should be here but it was not working when we last tested it.
Finally, I added some pebble black paint to the cover and a NOS faceplate. Final result is a new looking amp and rock solid 255 watt+ per channel. The mods give it a 3D clarity with pinpoint imaging at all volumes, bass is taut and correct with lifelike dynamics. I’ve used Musical Concepts mods since the late ‘80s and the results are always very worthwhile.
An externally hosted image should be here but it was not working when we last tested it.
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This was my sound system in 1979. My turntable is on slides behind the large panel on the right. A few years later I bought a Kenwood KD-600, SME arm and Shure V15 Type-IV-Cartridge.
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And I thought I was the only one who sees gold in those old dance hall amps.
I'll have to give that "multiple diode bridge" a try.
Likely to sound a lot better than your class D integrated with dual triode valve input stage
(Philishave 908)
Hello Arius,
Excellent design and works!
A good design always looks beautiful and makes people feel comfortable.
John
Very beautiful construction.
Respect for the laborious task of the perforated plate
All for better air flow and heat sinking
John
Hello Andrew,
Thanks a lot for your kind answer.
It sounds to me that triple stage (pre-driver, driver and output) is the better design for bi-polar power amp, isn't it?
John