Power amp intermittent fault

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: Joe., lisa, luketeaford, Kent

Post Reply
User avatar
MAXTHEDOG
Wiggling with Experience
Posts: 388
Joined: Sat Dec 17, 2016 8:15 am
Location: All over di place, maan.

Power amp intermittent fault

Post by MAXTHEDOG » Sat Feb 08, 2020 3:24 am

Hi All,
I’m looking for some guidance. One of my Audiolab 8000P power amps has an intermittent fault; on powering up it operates normally i.e. sound comes out of the speakers, but after about 3/4 minutes it shuts down and the sound disappears. I can leave it for around 2/3 minutes and it’s ok again. I’ve had a look inside and there are what I assume are speaker protection relays one of which has had an ‘incident’ judging by the slightly melted plastic cover. It operates( makes and breaks) as per the other though. On the other channel there is a 2k2 2W resistor with one end blackening up. I’ve had my meter on the coil terminals of the ‘incident’ relay and it started out at 60vdc and gradually fell of until about 16vdc then the relays dropped out. All this was without audio so I’m assuming that is the point that the audio would’ve stopped. One thing I can’t understand is the relay coils are rated at 24vdc, yet that seem to be subjected to 60vdc. I would’ve expected them to have failed ages ago as I bought these two 8000P’s in the mid 90’s.

On the ‘net the only schematic I’ve seen is only for the audio with no sign of the circuitry with the relays or PSU.

I’ve got access to another 8000P which is working perfectly so will be opening that up and comparing. I’ve access to a ‘scope and a signal generator and multimeters. Any help, advice on making headway with this would be greatly appreciated.
Regards,
MtD.
Lovely parrot, the Norwegian Blue....its pining for the fjords.

Current setup : https://www.modulargrid.net/e/racks/view/529118
My avatar is my old tricolour Border Collie. Long gone now.....

ashleym
Veteran Wiggler
Posts: 592
Joined: Thu Oct 22, 2009 3:34 pm

Re: Power amp intermittent fault

Post by ashleym » Sat Feb 08, 2020 3:50 pm

This could be your chance to get rid of them and get some better sounding amps.

Your working ones will tell you what to expect on the relays. I’d test using a load on the speaker outputs (you’ll know this but an 8ohm power resistor).

User avatar
MAXTHEDOG
Wiggling with Experience
Posts: 388
Joined: Sat Dec 17, 2016 8:15 am
Location: All over di place, maan.

Re: Power amp intermittent fault

Post by MAXTHEDOG » Sun Feb 09, 2020 8:48 am

Hi Ashleym,
:hihi:
I did think of it as an opportunity to get me some active monitors, but I’m used to how they sound, plus I’m using them with a pair of Acoustic Energy AE2’s on their dedicated stands. The whole shebang is a throwback to when it was my hifi system. The thought of advertising them as a whole, I wouldn’t wanna split them up and be left with speakers, stands (32kg each), or amps that all take up space and can’t be used on their own fills me with dread.....
I like the challenge of getting the thing working again. I’ve ordered a couple of relays, and some 2k2 2W resistors and will replace them and see if it recovers. I’ve also contacted Audiolab but had no reply, same for the place I bought them. Yes, they’re still going.

Having said all the above, and thought about the whole situation and what you suggested, I think I’ll get some active monitors.
I’ve listened to some Focal Alpha 50’s, the room is small i.e. 8 ft squarish so I’m guessing that I’ll not need massive cabinets but going from 200W per side bi-amped to 50W per side with small actives might be a bit of a shock. But at least I’ll be able to compare them side by side till I get rid of them.
Cheers,
MtD.
Lovely parrot, the Norwegian Blue....its pining for the fjords.

Current setup : https://www.modulargrid.net/e/racks/view/529118
My avatar is my old tricolour Border Collie. Long gone now.....

ashleym
Veteran Wiggler
Posts: 592
Joined: Thu Oct 22, 2009 3:34 pm

Re: Power amp intermittent fault

Post by ashleym » Sun Feb 09, 2020 11:25 am

:slapfight:

I had AE1's. I think we were all sold down the river of "near electrostatic" sound. I liked them at the time, thats why I bought them but once I had some speakers with a bit more get up and go at home I realised that it is music for pleasure at home. The Linn Kans I was comparing them with bottomed out too much (Epos 14s after and currently original Linn Isobariks, this is over 30 plus years- I try to get things right and hang on to them).

I dont blame you using you old hifi for monitoring, there is terrible snobbery about hifi for monitoring. You will have to spend some proper money to better what you've got. As for going from 200W to 50W, dont forget the absolute dB difference between the 2 isn't great. Although i think of "real" watts in a proper amplifier rather than plate amp watts probably with some budget SMPS, as superior.... There are losses through passive crossovers and the AE1/2 have a meaty one because of all the ringing metal drivers and this will get rid of most of the theoretical dB differences.

Could I suggest you try the Neumann 120s as they could work if you are used to AE2's? Plus the small ATCs are great and could work off your amps- although they would be happier with better amps. I am being a little rude but i really didn't like the Audiolabs when i was "in the game"

User avatar
MAXTHEDOG
Wiggling with Experience
Posts: 388
Joined: Sat Dec 17, 2016 8:15 am
Location: All over di place, maan.

Re: Power amp intermittent fault

Post by MAXTHEDOG » Sun Feb 09, 2020 12:49 pm

Hi,
Thanks for your input. It’s been helpful and interesting to get another perspective.
Don’t worry about ‘being rude’ it’s a very subjective issue.

I realise I’ve some serious moolah to drop to get something appreciably better and my 60 year old ears might not appreciate it.😁

Plan is (for this week 🤔):
See if I can get two working 8000P’s, audition some monitors ( the Neumann weren’t on my radar) but can audition them along with Focals, Adam, KRK, Genelec, and Mackie, if I get them both working, on the market it’ll go. That can go towards the budget (£1k) which may double it to £2k. If not, the change’ll have to wait as I don’t want it all hanging around the place.
Thanks again,
MtD.
Lovely parrot, the Norwegian Blue....its pining for the fjords.

Current setup : https://www.modulargrid.net/e/racks/view/529118
My avatar is my old tricolour Border Collie. Long gone now.....

ashleym
Veteran Wiggler
Posts: 592
Joined: Thu Oct 22, 2009 3:34 pm

Re: Power amp intermittent fault

Post by ashleym » Sun Feb 09, 2020 5:12 pm

Thanks for understanding my tongue is in my cheek.

If you haven’t had the covers off your speakers for a while, I would have a look at the foam surrounds. They have a tendency to go. I think the AE2s weren’t made for too long and only had the bass drivers made by Mordaunt Short (same basket as Naim IBLs and possibly one of the versions of the MS10 but I’m probably wrong there).

I will be really interested to see what you think of some of the newer 5” bass driver active types. There aren’t many that match up to a hand crafted, plaster filled cabineted, custom drivered speaker designed by a very talented person.

Post Reply

Return to “Music Tech DIY”