Do I remember?-: The preamps suck on the positive power supply and pull it down about 1 volt, compared to the negative power supply. The offset is, do I remember right? not adjustable and always wrong. In general, the output stage is quite unstable. Take a look at the output R-C element. The resistors could already have worked visibly.-)
Not 100 hours yet, but probably well over half that time, and the sound has definitely improved further - hard to describe, but everything just seems to be tighter, more detailed and more precise. I haven't made any more changes to the 8000A yet, because I wanted to get used to the effect of the PS cap replacement first.
I have all the caps I need for replacing the rest throughout the 8000A, but I'll put that off for a little longer as I've just added an 8000SX to use for passive biamping and replaced my speakers with a pair of vintage Mission 780s, and I'll listen to it like that for a bit first.
Final destination is to fix up my old 3-way electronic crossover and arrive at a fully-active crossover system (like I used to have years ago). I've got a kit-built powered sub for the low end.
Anyway, thanks again to everyone for their helpful thoughts.
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Hi folks, as someone has just asked me about this, I thought I'd update things in case anyone is interested.
I did the full electrolytic re-cap on the 8000A, and I replaced the op-amp as suggested. I used mostly Elna Cerafines, with a few Elna Silmic where I couldn't get Cerafines in the right values. The only thing I haven't done yet is upgrade the few signal path caps to Nichicon Muse. I have the Muse caps to do it, but I haven't had time yet - and I'm also thinking of maybe using film caps instead (which apparently is what Redhill do).
I've also done the same full recap on my 8000SX power amp, using Mlytics for the PS caps and Elna for the rest, and I replaced the op-amps. I also discovered some almost burnt resistors on the power rails - it seems it's a known overheating design fault, and it was far worse on the 8000SX than on the 8000A. The 8000A just has some board discolouration, and I'll replace them next time I'm in there. The tracks were a bit damaged in the 8000SX too, but I managed to patch them up and replaced the resistors with higher power ones.
Anyway, the result is that both amps sound a whole lot better now - lower noise floor, cleaner transients, better detail and imaging. So, thanks again for the advice.
I just have one more Audiolab amp to recap now, an 8000P, when I find room on the bench for it.
As an aside, I haven't fixed up my crossover yet, because when I looked at it closely I realised it really wasn't well constructed - the PCB's are low quality single sided ones, for one thing. And it's an old design. So I've decided to build a new Linkwitz–Riley crossover instead - I have PCBs from Rod Elliott, and I can build it inside the old case and using the old power supply.
I did the full electrolytic re-cap on the 8000A, and I replaced the op-amp as suggested. I used mostly Elna Cerafines, with a few Elna Silmic where I couldn't get Cerafines in the right values. The only thing I haven't done yet is upgrade the few signal path caps to Nichicon Muse. I have the Muse caps to do it, but I haven't had time yet - and I'm also thinking of maybe using film caps instead (which apparently is what Redhill do).
I've also done the same full recap on my 8000SX power amp, using Mlytics for the PS caps and Elna for the rest, and I replaced the op-amps. I also discovered some almost burnt resistors on the power rails - it seems it's a known overheating design fault, and it was far worse on the 8000SX than on the 8000A. The 8000A just has some board discolouration, and I'll replace them next time I'm in there. The tracks were a bit damaged in the 8000SX too, but I managed to patch them up and replaced the resistors with higher power ones.
Anyway, the result is that both amps sound a whole lot better now - lower noise floor, cleaner transients, better detail and imaging. So, thanks again for the advice.
I just have one more Audiolab amp to recap now, an 8000P, when I find room on the bench for it.
As an aside, I haven't fixed up my crossover yet, because when I looked at it closely I realised it really wasn't well constructed - the PCB's are low quality single sided ones, for one thing. And it's an old design. So I've decided to build a new Linkwitz–Riley crossover instead - I have PCBs from Rod Elliott, and I can build it inside the old case and using the old power supply.
Its nice for the DC servo job but you can easily measure its higher noise contribution vs other lower noise JFET input chips. About 6dB higher grass level on FFT with emphasized 1/F for servo work in a 10dB gain line preamp. When applied in higher than average gain circuits this can be more of a problem.
Thought I'd let you fine folks know I've done a bit more with the 8000A now. I replaced the signal path electrolytics with Nichicon Muse, and that made a significant improvement - in terms of clarity, detail, tonal separation and imaging. I listened like that for a while, but still wondering what film caps might sound like.
There's a handful of 4.7uF signal path caps in the pre-amp and phono stage, so I got some Wima film caps to replace those. And that was another step up - more of the same improvements again.
There was still a 47uF cap in the main signal path, and a 10uF one in the tone circuit, but they're a bit harder to do as film caps in those values can be quite chunky. Anyway, I've just, finally, got some film caps for those, and I've managed to fit them in. I had to stick the 47uF ones to the board and connect them up with wires. And there's another significant jump in sound quality. It's very satisfying to discover that these old amps are capable of so much more than in their factory spec, just by using better components.
I also replaced the underrated and overheating resistors a little while ago, with higher power rated ones. And I've also stood them off the board to get a bit of air round them. As I'd feared, the tracks were shot due to the heat, but I got them connected up fine.
I still haven't built my crossover, as I've decided I need a scope first to properly test it and debug if necessary. Or, to be more honest, the crossover is a nice excuse to get a scope 🙂
There's a handful of 4.7uF signal path caps in the pre-amp and phono stage, so I got some Wima film caps to replace those. And that was another step up - more of the same improvements again.
There was still a 47uF cap in the main signal path, and a 10uF one in the tone circuit, but they're a bit harder to do as film caps in those values can be quite chunky. Anyway, I've just, finally, got some film caps for those, and I've managed to fit them in. I had to stick the 47uF ones to the board and connect them up with wires. And there's another significant jump in sound quality. It's very satisfying to discover that these old amps are capable of so much more than in their factory spec, just by using better components.
I also replaced the underrated and overheating resistors a little while ago, with higher power rated ones. And I've also stood them off the board to get a bit of air round them. As I'd feared, the tracks were shot due to the heat, but I got them connected up fine.
I still haven't built my crossover, as I've decided I need a scope first to properly test it and debug if necessary. Or, to be more honest, the crossover is a nice excuse to get a scope 🙂
The golden age of Hi-Fi was then not now. Large and small teams of electronics experts were competing to outdo each other's achievements. Using the research resources of large industries they were working for. The schematics of classic Hi-Fi are a goldmine of application wisdom.
But those machines in majority were targeting middle class mass consumer budgets so the components and production methods were at an industrial level. Most of expense went towards metalwork and many facilities. The first thing to compromise was chassis glory after the golden 70s through the 80s until Hi-Fi died as a consumer market in the late 90s. Some personal care unleashes their true potential if inclined.
What we now call Hi-End is the boutique version of the once mainstream Hi-Fi accessible experience. Top tier Hi-Fi was quite into a best industrially possible concept already though but without being labeled Hi-End back in the day.
Yes, I agree all the way there. Middle market equipment was inevitably compromised by cost considerations, but I think audio engineering was indeed at its finest. As you say, a golden age.