Audiolab 8000A PS caps upgrade

oscroft

Member
2019-09-07 1:29 pm
I've just replaced the power supply caps in my Audiolab 8000A, and I thought people might be interested in my experience.

I'd had the amp in storage for a few years, and when I got it out to set up again I found the RCA sockets had started to break as the plastic bodies crumbled - a common problem. So replacing those was my first job - I got a new set from an eBay seller for £57 (which is not cheap).

The old caps are Elna 10,000uF 50v, and looking around what was available I settled on Mundorf Mlytic 15,000uF 63v (£50 for the pair, again not cheap). One of the nice things about the Mundorfs is that they're the same size as the old Elnas - I know that's trivial, but I think it looks nice when components look as if they fit.

Today was the day I did the job, and even with a pair of modest Tannoy Mercury MX1s (and an active sub run from the pre-amp out), the difference is... not small! Without even giving it a few minutes to warm up, it's enormously improved.

Imaging is stable and a lot more precise - instruments and voices used to wander depending on the notes, and guitars seemed like they were six-feet wide. The sound stage now has a bit of depth too - it was flat 2D before.

The biggest improvement is in louder passages, which is probably not surprising. Previously a loud passage would turn mushy (if you know what I mean) and detail and imaging would smear. But now, it's smooth, powerful and far more precise.

After all that, I decided to measure the old caps to see how they rated. I had to series them up to get within the range of my meter, and they measured at only around 4,100uF apiece. It's hardly surprising the difference the new ones have made, and it's definitely money well spent.

Anyway, next job is to replace the rest of the electrolytics in the amp - probably with Elna Cerafines. My recommendation for anyone considering replacing the power supply caps in an old amp is... just do it.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Sounds like you have done a good job there :up:

Rotting plastic (sockets and the like) can occur if the part in question has come into contact with various switch cleaners and contact cleaners, particularly those that were popular back in the 80's and 90's such as from Servisol and Electrolube.
 

oscroft

Member
2019-09-07 1:29 pm
Sounds like you have done a good job there :up:

Rotting plastic (sockets and the like) can occur if the part in question has come into contact with various switch cleaners and contact cleaners, particularly those that were popular back in the 80's and 90's such as from Servisol and Electrolube.


Ah, that's interesting, thanks. I've never cleaned it other than dusting it myself, but I did get it second hand so it's anybody's guess what the original owner might have done.
 

oscroft

Member
2019-09-07 1:29 pm
Desolder and resolder all. Minimal solder!
Replace the rectifier-bridge per shottkys.
Remove the eyelets of the "output-screws".

Fine pres, but horrible power-amps;-)-;
Thanks for the suggestions. Not sure what the eyelets of the "output-screws" are?

(And yes, the Audiolab power amp sound does seem to be a bit of love it or hate it thing :))
 
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These things;-)
 

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Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
Anyway, next job is to replace the rest of the electrolytics in the amp - probably with Elna Cerafines. My recommendation for anyone considering replacing the power supply caps in an old amp is... just do it.

See about Nichicon Muse BP non polar caps also if there are any signal coupling electrolytic positions to replace.
 
I've just replaced the power supply caps in my Audiolab 8000A, and I thought people might be interested in my experience.

I'd had the amp in storage for a few years, and when I got it out to set up again I found the RCA sockets had started to break as the plastic bodies crumbled - a common problem. So replacing those was my first job - I got a new set from an eBay seller for £57 (which is not cheap).

The old caps are Elna 10,000uF 50v, and looking around what was available I settled on Mundorf Mlytic 15,000uF 63v (£50 for the pair, again not cheap). One of the nice things about the Mundorfs is that they're the same size as the old Elnas - I know that's trivial, but I think it looks nice when components look as if they fit.

Today was the day I did the job, and even with a pair of modest Tannoy Mercury MX1s (and an active sub run from the pre-amp out), the difference is... not small! Without even giving it a few minutes to warm up, it's enormously improved.

Imaging is stable and a lot more precise - instruments and voices used to wander depending on the notes, and guitars seemed like they were six-feet wide. The sound stage now has a bit of depth too - it was flat 2D before.

The biggest improvement is in louder passages, which is probably not surprising. Previously a loud passage would turn mushy (if you know what I mean) and detail and imaging would smear. But now, it's smooth, powerful and far more precise.

After all that, I decided to measure the old caps to see how they rated. I had to series them up to get within the range of my meter, and they measured at only around 4,100uF apiece. It's hardly surprising the difference the new ones have made, and it's definitely money well spent.

Anyway, next job is to replace the rest of the electrolytics in the amp - probably with Elna Cerafines. My recommendation for anyone considering replacing the power supply caps in an old amp is... just do it.
You ain't heard nothin yet.
The Mundorf caps generally need quite some time to break in. Give them some 100 hours of playing time and listen THEN.
 

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
Will do, thanks.

There are input and output signal coupling electrolytics in all the preamp sections as I now see in the service manual. Candidates.

There is a TL072 DC servo in the power amp. One section for each channel. 18nV spec. Noisy by today's standards. Could be replaced with an OPA2134 of 8nV spec. Its generally a better chip in all aspects. JFET input type also, thus compatible.
 

oscroft

Member
2019-09-07 1:29 pm
There are input and output signal coupling electrolytics in all the preamp sections as I now see in the service manual. Candidates.

There is a TL072 DC servo in the power amp. One section for each channel. 18nV spec. Noisy by today's standards. Could be replaced with an OPA2134 of 8nV spec. Its generally a better chip in all aspects. JFET input type also, thus compatible.
Thanks for that. It looks like there are coupling caps in the phono (MM and MC) stages too, though I'm not touching those for now. I will do at least the MM stage at some time, so I'll bear it in mind for then as well.

Is the OPA2134 pin compatible with the TL072?

Great forum, I appreciate all the help folks :)
 

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
Is the OPA2134 pin compatible with the TL072?

Of course it is. Standard format twin op-amp types. Install an 8 pin socket also to can swap the chips for preference. Not to rework the board again for that. Its called DIP8 socket.

By the way, always measure for low DC offset on the loudspeaker outputs and mains insulation to the chassis after every time you did something in there. Either for passive or active parts reworks in the PSU or in the audio circuits, don't forget to confirm the basic safety of the amp, for you and the loudspeakers.
 

oscroft

Member
2019-09-07 1:29 pm
Of course it is. Standard format twin op-amp types. Install an 8 pin socket also to can swap the chips for preference. Not to rework the board again for that. Its called DIP8 socket.

By the way, always measure for low DC offset on the loudspeaker outputs and mains insulation to the chassis after every time you did something in there. Either for passive or active parts reworks in the PSU or in the audio circuits, don't forget to confirm the basic safety of the amp, for you and the loudspeakers.
Great, thanks.