Hello from power amp recycler in Luxembourg

[Tom4s]

Enough lurking, and time to send my greetings from the Green Heart of Europe.

I have lived here since 1991, when I emigrated from Sweden. I brought with me a Spectro Acoustics 500 Watt amp that I bought 1979 in the US. It overheated once too many times, and there are some seriously expensive TO-3 trannies to replace in that amp, so it has been in the cellar for the past ten years or so. I replaced it with an Adcom GFA-585, which eventually also broke down. My speakers are Infinity Quantum 3, a 4-way design from the late seventies, re-edged woofers, and replaced both pairs of midrange elements.

One channel on the Adcom is still fine, but the other one has about 45V DC on the output. It suffered from leaky caps and I think the electrolyte has permanently damaged some other components on one of the driver boards. I contacted Adcom in the US, and got great help along with a PDF of the service manual. I re-capped both of the driver boards, and washed them with isopropyl. Still no good. The bias servo chip had had electrolyte on it, so I wanted to replace that too. However, it was a "adcom" branded chip. My contact in the US gave me the "real" manufacturer's name and designation, but it was a difficult part to source in Europe. The only place I could find it was in the US, from JameCo who wanted to charge me $35 shipping for a $2 part... Eventually, I returned to the chip manufacturer's web site and noticed a link to request product samples. Well, it was of course meant for businesses, but I anyway filled it out as honestly as I could (ie, it was going to be used for repair), and two days later I received a letter with my free samples!

Still, it didn't help fixing the DC problem. I gave up on it, and contemplated on how I could offload the amp on eBay; either as a defect unit, or I could slaughter it and sell parts separately. It has a huge encapsulated toroidal transformer and there are 4x18000uF 100V ADCOM caps in there.

Recently, I stumbled across a thread about Class D amps in another forum (http://www.soundonsound.com/), and came to find this place, along with 41Hz, NewClassD, ColdAmp, etc... Great, now I know what to do with my Adcom chassis! I'll keep the power supply, and find a suitable pair of amp modules to rebuild it with. My speakers are 4 Ohm and notoriously inefficient (I recall it being 87 or 88 dB at 1W, 1m), and difficult to drive due to a dual voice-coil design in the woofer.

If it turns out well, or not so well... then I might recycle the old Spectro Acoustics too!

I have loads of stuff going on tho, being in a rock band, occassionally doing sound duties for the local amateur theatre groups, and being treasurer in my commune's parents-of-students association... So, I will go slowly with this project. My first tasks are to strip down the Adcom chassis, and investigate further the various amp modules on offer.

Well, hmm.. enough rambling for this time... See you soon in the Class D forum!

[Cal Weldon]

Hello Tomas and welcome to the forums.

[gni]

There are some great threads doing exactly what you are doing. .
search and find. . . great tips. Good Luck!

PS - I'm doing similar things with a Yamaha M-45 and possibly Coldamp.

[Tom4s]

Hi Chris!

Thanks for the tip. My Adcom has 80V power rails though, so in order to keep that my choices are severly restricted. The only module I've found so far is the 700W UCD from Hypex... But, I will check out the recycling threads and see if anyone knows about other higher voltage modules.

Cheers,
Tomas

[gni]

Looks like the Aussie Amplifier NX400NL is shown on the website
as handling more than +/- 80 VDC. . . For me it is down to one
of these two options: Coldamp or Aussie.