Cambridge Audio A500 Amplifier problems!

[Mark Hennessy]

Actually, Mark, it states 47k for R267 on the circuit diagram. Must admit I haven't checked to see what value is fitted.

No, definitely 47 ohms

[Old Sparky]

Actually, Mark, it states 47k for R267 on the circuit diagram. Must admit I haven't checked to see what value is fitted.

No, definitely 47 ohms

My apologies, Mark - I could have sworn it said 47k- ('should have gone to specsavers!!)

[AlanBeckett]

Mark,

On the Circuit Posted above R267 is 47R as far as I can tell.

Alan

   

[Mark Hennessy]

Mark,

On the Circuit Posted above R267 is 47R as far as I can tell.

Alan

OK, now I'm really confused! Is "Old Sparky" also called Mark? If not, you're telling me what I already said in post #12

Any progress with it yet, Sparky?

All the best,

Mark

[AlanBeckett]

I think I typed while the other Posts were appearing.

Alan

[Joe]

I wonder if the brand-name 'Cambridge' was an attempt to get some kudos from associations with Pye?

- Joe

[Old Sparky]

To avoid any confusion, in post #12 I was apologizing to Mark Hennessy for misreading the circuit diagram. My name is Mike. Haven't progressed any further with the A500 yet. The next step is to check those o/p transistors. AFAIK Cambridge Audio is so called because they are(were?)based Cambridge, not due to any association with PYE.

[Mark Hennessy]

No worries Mike - it sounds like Alan had an old copy of the thread open on his browser, so didn't see my reply...

Cambridge Audio date back to the late '60s. I'm not aware of any connections to the big companies - they were always a small-ish concern focusing solely on hi-fi. One of the great British cottage industries. There were lots of those, as you can imagine - none of them attempted to hang on to the coat tails of the names we'd consider as "greats". Indeed, it was often the other way around - the big companies like Rank would swallow up the great names like Bush and Arena to get a foothold. Back then, hi-fi was a big scene, and not as easy to break as you might imagine. Especially if you wanted to make loudspeakers; no large company could get close to producing a Spendor BC1 or a Quad ESL.

They were acquired by Audio Partnership in the mid-1990s. This is a company that is owned by Julian Richer (51%, according to Wikipedia) - that's Julian Richer of Richer Sounds fame - and that's why you can only buy Cambridge Audio in Richer Sounds. Funnily enough, if you ask their sales staff for advice, the answer is always Cambridge Audio! The products are designed in the UK and manufactured cheaply in China - build quality is a bit marginal on the stuff I've seen, although I haven't looked at the latest products.

For a while, Douglas Self worked with them (no idea if he still does), and he produced some great designs which were very well-reviewed. I don't think the A500 was one of them...

Interestingly - or perhaps not - there was a company called A&R Cambridge which was formed in the mid-'70s and did much the same sort of thing as Cambridge Audio. As you can imagine, this caused some confusion! For that reason, A&R Cambridge are now known as Arcam (I think that happened sometime in the 1980s). Arcam are still their own company as far as I know, and apparently do a fair bit of manufacturing in the UK. They make pretty good stuff - I have 2 of their CD players and an old amp, and recommend them. The design and build quality is streets ahead of the Cambridge Audio stuff I've seen.

Here endeth the lesson

Good luck - here's hoping those transistors are OK...

Mark

[Old Sparky]

Mark,

On the Circuit Posted above R267 is 47R as far as I can tell.

Alan

In the A500 I am (carefully)checking, there is no connection to the 'Chassis Ground' side of C210/R267, and never has been. I have added an earth wire to this point.
The speaker common negatives are returned to the '0V' line, whilst the mains transformer center tap is connected to the 'Gnd' side of R267/C210. No other components check faulty or look stressed/damaged, so maybe only the transformer was faulty after all

[Old Sparky]

For some reason my reply to Alan Beckett's post #13 doesn't appear!. In the A500 which I'm (carefully)checking, there is no connection to the 'Chassis Ground' side of R267/C210, nor ever has been.
The speaker common negatives are connected to the '0V' line, whilst the mains transformer's secondary winding is connected to the 'Gnd' side of R267/C210. In other words there is no connection between the center tap and the '0V' line. Maybe this caused the transformer to fail? I have now added a ground wire, and will fit a replacement transformer after further tests. None of the components test faulty, or appear stressed or burnt, though!