Bargains on ebay? (Part 2)

[walpurgis]

Thanks Paul.

This one does indeed sport the 'Super A' title. I recall a few Japanese amplifiers from about then having a similar type of claim. I also own a rather small Technics amp that purports to offer something of the kind. It does sound far better than its looks would suggest. I understand the idea behind biasing into 'A' at lower outputs. I (may be wrong but) believe Yamaha were the first to offer this with the CA-800 and CA-1000 (nice units) integrated amps.

[PaulStewart]

The Yamaha system was different as I recall, with SuperA the transistors never switch off, you will probably find it runs a bit hotter than you might expect, certainly the first range did.

[walpurgis]

Actually, now you say that. I seem to recall (it was a long time ago) that with the Yamaha integrateds, it was low output pure Class A only if switched on, but at very reduced output. I've not tried one. I'd like to, but prices are now just silly.


(I wonder if Luxman ever did something similar. My favourite Jap make)

[istari_knight]

I presume you've seen this Geoff ? http://www.hifi-pictures.net/amplifi...%20AX-A441.htm

I have the service manual if you're interested.

[PaulStewart]

Not surevof the phono stage on yours Geoff, may me MM only AX-9 and 7 had MC too, but yours is from the digital source age. JVCs phonostages were always pretty good though, but I'd like to hear that with a goid phono stage. The best AX system I had at home, purely for the task of showing it to HiFi journos you understand, was MC1 cart in a QL8 into the AX-9 and then into Zero 5s with the ribbon tweeter. Awesome sound, fantastically dynamic and detailed.

[walpurgis]

I presume you've seen this Geoff ? http://www.hifi-pictures.net/amplifi...%20AX-A441.htm

I have the service manual if you're interested.

Thanks James (do you ever use Jim?)

I showed that site on my original postings. But there's bugger all much else I can find out there. No matter. I'll give it a try out tomorrow and post my opinion (which is usually an honest and intelligent one) tomorrow.

[istari_knight]

Ha yes, family tend to call me Jim ! Drop me your email address if you haven't already got the service manual.

JVC marketing depts take on "Super-A": Super-A works with an Active Bias Circuit IC strapped across the input of the power stage. This "ABC" controls the amount of bias following the output level's variation. By feeding them sinusoidally-varying reverse bias during their half-cycles of non-conductivity, output transistors never switch off. No switching distortion as in normal Class B, no useless heat production as in Class A.

In layman terms: It monitors the sum Vbe of all output devices, plus the voltage drop that occurs on the emitter resistance. This voltage gets compared to a fixed threshold, and when the total voltage gets beyond this threshold, plus a little something, a transistor fitted into the Vbe multiplier arrangement acts to gently increase the multiplication coefficient.

I believe it was originally termed "sliding bias" by a Japanese company [may have been JVC!] but they all had their own variant, Denon had "optical class A", Technics had "New class A", Pioneer had "non-switching" etc etc FWIW Technics later "MOS Class AA" had more than a little in common with Quads "current dumping"

[walpurgis]

Not sure of the phono stage on yours Geoff, may me MM only

It has a phono input and MM & MC are separately switchable. I have yet to plug this item in and see what happens. Judging by the superb condition and appearance, all will be good. I shall check it all over tomorrow and report back. I'm optimistic. This will l be a back-up, spare, or extra amplifier in any case, but hopefully rather good.

[Macca]

Could be a lot of speaker for £60 http://www.ebay.co.uk/itm/2517724524...%3AMEBIDX%3AIT

Okay, so they have waffly cabinets, cheap vinyl wrap veneer, spitty tweeters & crap-o-la crossovers..... Hang on why am I posting these on here ?! Oh yeah, they have potential

Sold for £75 quid - someone got a bargain. I recall a Hi-Fi world speaker test (from many years ago now) in which they were deemed to be head and shoulders above the other contenders. A bit of tweaking, as you say, and they will be a serious speaker system.

[istari_knight]

http://www.ebay.co.uk/itm/Very-rare-...item418dc6d0ac