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Refreshing of Audiolab Pre-Amp
Refreshing of Audiolab Pre-Amp
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Old 2nd February 2021, 11:14 PM   #1
Zenza is offline Zenza  United Kingdom
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Default Refreshing of Audiolab Pre-Amp

Apologies for the long winded post and I hope I posted this in the right section of the forum.
So this Audiolab 8000C has been my pre-amp for what must be +10 years now and is paired with a 8000P power amp, the latter being in mint condition and rather well looked after.
The pre on the other hand I got totally screwed when buying it, other than the age the thing was caked in heavy cigarette smoke and whilst it doesn't smell any more on the outside, the inside still smells and is coated in a thick layer of tar.
At that point I pretty much gave up and just ended up using it as is for god knows how long.

It's always had some issues i.e. scratchy pots with poor channel matching, faulty relay, susceptible to mains pops and a scratchy eq on/off button.

Now instead of buying something else and selling this (it's pretty worthless in it's current state no?) I thought it would be nice to get it back up to spec as it's not a bad pre but just needs some TLC.

Plan of action so far is as follows;

Replace all Electrolytic capacitors > Ordered ELNA Silmic II's and Nichicon LKG for the PSU mainly cos the solder tabs just make it easier and they're easily available at Mouser.

Replace Volume and Balance pots > Still Need to source

Replace Relay > Still Need To Source

Now I am not an expert and would love peoples suggestions/input on here, am I missing something etc.
The pre-amp obviously gets hot, those transistors with the heatsinks are very close to the caps etc.
Is it worth while replacing some of the polyester and polystyrene capacitors in the future too?

I am having difficulty sourcing suitable pots (Noble dual log 30k) and if anything will use a 50k pot albeit I still have difficulty sourcing something of that particular size and that is of quality.
Almost thought of using a ALPS RK-27 and just using jumper wires instead of mounting it to the PCB although size is probs an issue.

Switches.. One day haha One thing at a time at the moment.
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Old 2nd February 2021, 11:57 PM   #2
Zenza is offline Zenza  United Kingdom
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Ops forgot to add some pics..

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Refreshing of Audiolab Pre-Amp-img_0490-jpg

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Old 3rd February 2021, 12:09 AM   #3
rayma is online now rayma  United States
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"Is it worth while replacing some of the polyester and polystyrene capacitors in the future too?"

Definitely not, they don't degrade.
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Old 3rd February 2021, 12:27 AM   #4
Zenza is offline Zenza  United Kingdom
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Quote:
Originally Posted by rayma View Post
"Is it worth while replacing some of the polyester and polystyrene capacitors in the future too?"

Definitely not, they don't degrade.
Thanks those were my initial thoughts over the years from what I read and have been told but recently read some conflicting views so wasn't sure any more.

I did attach some pictures of the insides for any one else if they were interested but they aren't showing yet, most likely as I'm a new member and it needs approving.

Re the electrolytic caps I ordered, I just went for standard like for like values.
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Old 4th February 2021, 04:56 PM   #5
Mark Tillotson is offline Mark Tillotson
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Polystyrene are fine unless there are solvents in the air (not ideal in industrial environments!), but polyester in the signal path isn't the absolute best. Polypropylene replacements would be better - though it may not matter to you, its not a huge effect (and you probably can't find size matches anyway).

As all the resistors are carbon film, its probably not worth worrying about upgrading polyester caps really... Elderly electrolytics are a definite issue, and much more practical to replace too.


Cleaning the PCB of smoke residues with a suitable solvent is probably a good idea before working on it, stinky tar is unpleasant


[ don't use any solvents that attack polystyrene, note - it seems even alcohol and IPA can attack it(!) ]

Last edited by Mark Tillotson; 4th February 2021 at 05:00 PM.
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Old 4th February 2021, 05:44 PM   #6
Zenza is offline Zenza  United Kingdom
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Quote:
Originally Posted by Mark Tillotson View Post
Polystyrene are fine unless there are solvents in the air (not ideal in industrial environments!), but polyester in the signal path isn't the absolute best. Polypropylene replacements would be better - though it may not matter to you, its not a huge effect (and you probably can't find size matches anyway).

As all the resistors are carbon film, its probably not worth worrying about upgrading polyester caps really... Elderly electrolytics are a definite issue, and much more practical to replace too.


Cleaning the PCB of smoke residues with a suitable solvent is probably a good idea before working on it, stinky tar is unpleasant


[ don't use any solvents that attack polystyrene, note - it seems even alcohol and IPA can attack it(!) ]
Thanks for the input Mark.

I did initially start to clean it with IPA when I got it then gave up as it's easier with all the electrolytic caps removed out of the way and then just never got round to doing the job properly until now.

Also thanks for your input on the caps. I'm pretty sure those little silver caps are Polystyrene. There seems to be one (22pf) per L&R channel for each output section i.e. pre-out and headphone out.

I spent most of last night scratching my head trying to figure out how to best do the volume pot. The ALPS RK163 looks like an almost drop in replacement size wise but at the same time I'd also like something better.
The rest of the pre-amp seems well designed and of high quality but then you stick cheap pots and switches
The issue is if I were to use anything else even if not mounted to the PCB board and using some leads, size/mounting will be an issue.
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Old 4th February 2021, 06:18 PM   #7
Zenza is offline Zenza  United Kingdom
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Also meant to add once I do the main things on there I'd like to modify the MM stage slightly.

At current I use a Cambridge Audio 640P which I removed the input loading caps from with a Audio Technica AT-150MLx cartridge.
The turntable interconnects generally provide enough capacitance (around 100-120pf) so there aren't any issues with oscillation (that I am aware of)

The Audiolab states in the specs it has 85pf as standard (bare in mind I think this changed on later models to 100pf?) and it also this early model gives provisions for adding more capacitance at the rear of the pre using plugin RCA's with some capacitors.
Any whom I'd like to basically bring the capacitive load to pretty much nothing albeit the schematics are so grainy I have no idea.
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Old 4th February 2021, 10:25 PM   #8
ejp is offline ejp  Australia
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I found this unit very susceptible to the quality of the rather numerous electrolytic coupling capacitors. Had to change them all for better ones after the customer complained.

It's one of the best sounding preamps I've ever heard.
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Old 4th February 2021, 10:55 PM   #9
Zenza is offline Zenza  United Kingdom
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Quote:
Originally Posted by ejp View Post
I found this unit very susceptible to the quality of the rather numerous electrolytic coupling capacitors. Had to change them all for better ones after the customer complained.

It's one of the best sounding preamps I've ever heard.
What did you end up using?
I find the sound of this pre pretty neutral and don't find it adds much which is nice. Certainly never hard or fatiguing.
It's funny how trends go, at least in the UK a lot of people hated these components which I never understood. Whilst I'm no expert the designs always looked very elegant whilst not being over engineered or complex.

It would of been great if they made it modular with the modules on cards, actually gave it some decent ventilation, used decent pots and have the tape outs buffered but hey. The looks I don't mind, people instantly think it's some cheap and nasty thing
Later ones I think used those black ALPS pots but early ones like mine have those horrible potentiometers which is a pain.

On a offside rant so many active pre-amps now days lack basic controls, I mean I want a balance control at minimum.
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Old 5th February 2021, 05:25 AM   #10
ejp is offline ejp  Australia
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Sorry, cannot remember, but they were several bucks each. 100uF NP if I remember rightly.
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