Japanese solid state amps
- Thread starter RobJ
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Robert
Tapehead
STK modules were a good idea in some respects. They aren't amplifiers on a chip like we see today, just the output stage. Sometimes referred to as Darlington packs.
Keeping the components thermally tied with very short connecting traces is a fine idea if well executed.
I have an Akai power amp which uses them and it works very well if you aren't expecting to drive 2 ohm loads.
They need care over heatsinking and coupling to the heatsink.
Keeping the components thermally tied with very short connecting traces is a fine idea if well executed.
I have an Akai power amp which uses them and it works very well if you aren't expecting to drive 2 ohm loads.
They need care over heatsinking and coupling to the heatsink.
notevenclose
pfm Member
Yamaha CA800 and CA1000 were probably as good (integrateds) as they ever made. Subsequent models like the A1 had some interesting ideas, but never quite scaled the same heights sonically or aesthetically. My view is that the best sounding Japanese integrateds were late 70s Sansuis, sadly this is hardly a unique opinion nowadays and second-hand prices for the likes of AUx17/x19 series are through the roof. Some of the Lux amps of the time were prettier, but the Sansuis sounded better.
The Class A option on Yamahas of the time reflected the enduring popularity of high efficiency speakers, invariably with paper bass drivers and simple crossovers, in the Japanese home market. In the UK, we'd discovered the alleged merits of 'higher tech' cone materials like Bextrene (quack), and crossovers you need to wire direct to the National Grid to squeeze a signal through.
I remember hearing virtually zero difference with Class A operation on my CA1000 with the typical UK speakers of the day until I hooked it up to a pair of Lowther Mini Acoustas, when the difference became very apparent.
The Class A option on Yamahas of the time reflected the enduring popularity of high efficiency speakers, invariably with paper bass drivers and simple crossovers, in the Japanese home market. In the UK, we'd discovered the alleged merits of 'higher tech' cone materials like Bextrene (quack), and crossovers you need to wire direct to the National Grid to squeeze a signal through.
I remember hearing virtually zero difference with Class A operation on my CA1000 with the typical UK speakers of the day until I hooked it up to a pair of Lowther Mini Acoustas, when the difference became very apparent.
Arkless Electronics
Trade: Amp design and repairs.
I disagree. All the ones I've seen are thick film modules with all the electronics in the module. I can't recall ever seeing one with just the output devices in the module, although I don't doubt they exist. They can be just as good as a discrete circuit as they are pretty much the same circuitry but integrated into a sealed module. The problem is if they go wrong....
laverda
pfm Member
Picked these YAMAHAs up for £120 the pair the tuner (CT610) is unmarked and just needs a wipe down with some spirit to bring the facia back to life. I think in its 40 year life its been in a smokers house for a while.
The amp (CA600) was sold for parts 'not working' but on the bench all was found to be working?? The bias on both amp boards needed a small tweak to bring back to spec ...and the power on lamp/bulb which was blown, which I replaced with an LED. Which is why I think the seller thought it wasn't working but not really sure.
Sound wise, the tuner is quite good and the integrated amp is a surprise, very nice.
The amp (CA600) was sold for parts 'not working' but on the bench all was found to be working?? The bias on both amp boards needed a small tweak to bring back to spec ...and the power on lamp/bulb which was blown, which I replaced with an LED. Which is why I think the seller thought it wasn't working but not really sure.
Sound wise, the tuner is quite good and the integrated amp is a surprise, very nice.
Robert
Tapehead
There are different variants. Some contain the output stage, some include drivers, some (sold a little later) include the whole power amplifier shebang in one package. The Akai I have contains 2 STK packages per channel, 1 containing the front end and pre drivers, the other the output stages. This is a 1980 design. Interesting to compare with the Pioneer receivers from the 70s which used a discrete amp board with the divers and output on the STK.
But yes, if you blow them you are pretty much at the mercy of finding decent used replacements as current 'new' versions are cheap fake replicas.
Robert
Tapehead
Bargain for both units. Nice find.
Picked these YAMAHAs up for £120 the pair the tuner (CT610) is unmarked and just needs a wipe down with some spirit to bring the facia back to life. I think in its 40 year life its been in a smokers house for a while.
The amp (CA600) was sold for parts 'not working' but on the bench all was found to be working?? The bias on both amp boards needed a small tweak to bring back to spec ...and the power on lamp/bulb which was blown, which I replaced with an LED. Which is why I think the seller thought it wasn't working but not really sure.
Sound wise, the tuner is quite good and the integrated amp is a surprise, very nice.
ToTo Man
the band not the dog
I owned a CA-1000 and had no idea about that, I assumed it was instantaneous. Maybe that's why I could hear jot all difference between the Class A and Class AB modes! Not that I'm complaining, as AB still sounded excellent to my ears.
Arkless Electronics
Trade: Amp design and repairs.
It is. It may well sound better after some time but it goes into class A instantaneously upon pressing the switch.
My main amp here is a class A jobby of my own design and that does sound at its best after an hour.
James
Lord of the Erg\o/s
Can you posit an explanation for this phenomenon, other than your ears getting used to the sound. I run a pair of low-speed fans under my Pioneer M-22 in the interest of keeping it coolish and last longer, but I'm not sure if I'm not letting it reach full class-A goodness if the heatsinks are still comfortably touchable.
Arkless Electronics
Trade: Amp design and repairs.
Two examples are hardly a phenomenon so I wouldn't be thinking that this is typical behaviour by any means. It sounds good from cold and is certainly not any night and day difference but from the upper mid upwards it does seem to get even more open and sweet, noticeable after about 20 mins, and as good as it gets after about an hour. I'd leave the fans personally and I am planning on fitting fans to mine at some point, which should also allow even more power in class A.
I don't know of any real explanation for this no but the characteristics of the output devices (3 pairs of mosfets here)will change somewhat with temperature, as will those of bipolar transistors. There is no reason to assume the change will be in a beneficial direction though! To clutch at straws, it could have something to do with the expansion of the die due to the heat reaching a point where it is in equilibrium but we're in real cloud cuckoo land here!
laverda
pfm Member
Tis a strange thing....Class A and why these amps sound better after a period of 'warm up' is a strange thing. As stated they sound good from power on but after a while the sound changes especially the top end. (to my ears anyway) Sweeter, more refined. Iv'e read many times (on other forums who specialise in this) Heat is your friend in Class A which needs to be balanced via bias current and the temperature at which the heat sinking used will saturate or no longer dissipate the heat generated by the output devices. In other words the hotter the better.
The 'equilibrium' is where the heat sink can radiate the heat (before saturation) at a given bias you dial in to get there. Its a bit of a balancing act or thats how I see it. It took me three days to get one amp to a steady state of equilibrium.
But this doesn't answer the question of why they sound better after a warm up...I have a feeling it has something to do with the current passing across the output device junction/s. After power on the bias current starts to rise and keeps on rising until the sinks hit their setup temperature and no more bias current can be passed.
Be interesting to hear others interpretations.
The 'equilibrium' is where the heat sink can radiate the heat (before saturation) at a given bias you dial in to get there. Its a bit of a balancing act or thats how I see it. It took me three days to get one amp to a steady state of equilibrium.
But this doesn't answer the question of why they sound better after a warm up...I have a feeling it has something to do with the current passing across the output device junction/s. After power on the bias current starts to rise and keeps on rising until the sinks hit their setup temperature and no more bias current can be passed.
Be interesting to hear others interpretations.
ToTo Man
the band not the dog
All my vintage Class A/B amps sound better an hour after being switched on too, 'sweeter' is the word I guess describes it best. I don't notice this phenomenon so much on newer amps though. Maybe ageing parts need more time to stabilise and/or sound their best at a more specific operating temperature.
Arkless Electronics
Trade: Amp design and repairs.
Hmm... no the bias doesn't rise at all in a well designed amp and in fact efforts are made to keep it stable! This is in fact much more important in class A/B amps but that's another story.
The cooler the better is the ideal as heat is the enemy of reliability and there is no part of electronics theory that suggests hotter is better. Some parameters of the output devices do change with heat (a bloody nuisance!) but this is pretty irrelevant as there will be transistors you could have chosen that which will give the same gain when cold as lower gain ones reach when at 55C...
The thermal mass of the large heatsinks required to dissipate the heat of a class A amp means that it takes some time to reach thermal equilibrium, ie it 's got as hot as it's going to get and will now remain at say 55C for as long as it is switched on. It is "illegal" for any part of a consumer device which can be touched to reach more than 60C BTW.... but I have measured the temp of some MF amps like A1 and MA50 as nearer to 70C!
Fans can make a huge difference and a fan cooled class A amp of 50WPC could manage with heatsinks more suitable for only 10WPC without fan cooling. This can enable them to be considerably smaller, cheaper and lighter in weight but there is public opposition to it as some won't tolerate even barely audible fan noise.... and it can be made barely audible IME.. as in you need to be in a silent room and within 2 foot of the amp to hear it at all!
Single ended amps, whether SS or valve, can only be class A, but have their own issues. In the case of push pull amps such as are the norm and are what we are discussing here, class A is indeed better in pretty much every way technically. No crossover distortion, no switching distortion, greater bandwidth, much lower large signal distortion, much lower intrinsic output impedance before negative feedback, no half wave rectified currents present in power rails and ground returns, to name just the main ones... The only negatives to class A are heat, price, weight and "non greenness".
martin clark
pinko bodger
+1, and amp should measure as good as it gets very quickly after turn-on.
That said - two heat-related effects I can think of, which might have a positive bearing on amplifier performance, esp for, shall we say, the willfull end of the design spectrum using weirdly-low feedback and/or having poor PSRR and the like:
1. ESR in big caps tends to drop a bit as they run warmer. Which will take a while from a cold start.
2. Hfe, current gain, increases in BJTs: which means - a hot amp might have a tad more effective feedback / have the output stage demand less from the drivers, once hot.
It would have to be a pretty odd amp for these to matter - but they are out there!
That said - two heat-related effects I can think of, which might have a positive bearing on amplifier performance, esp for, shall we say, the willfull end of the design spectrum using weirdly-low feedback and/or having poor PSRR and the like:
1. ESR in big caps tends to drop a bit as they run warmer. Which will take a while from a cold start.
2. Hfe, current gain, increases in BJTs: which means - a hot amp might have a tad more effective feedback / have the output stage demand less from the drivers, once hot.
It would have to be a pretty odd amp for these to matter - but they are out there!
Arkless Electronics
Trade: Amp design and repairs.
Yep. The ESR issue should be negligible though and I dealt with your 2nd point when i said that even though Hfe rises etc, higher gain transistors could have been specified in the first place...
The greatly improved performance of class A amps over A/B does mean that one can get away with no or low feedback with a class A amp of course.
Dowser
Learning to bodge again..
Maybe off-topic a bit, as this relates to single-ended 845 valve/hybrid DIY monoblocs I have, but they take 20 mins to get up to their 55 degree operating temperature, and sound much better for it. Due to the mosfets, valve, (low value high voltage caps) or what? They sound good from cold, but just hit a very sweet spot once hot.
James
Lord of the Erg\o/s
Thanks for your views. I have been using the much vaunted class A/B Dynavector HX-1.2mk2 over the last couple of days, just to keep its caps formed, before swapping the M-22 back in. Again, I'm reminded there is a very audible improvement in clarity, listenability and naturalness from the class A amp. I seem to recall that the M-22 has temperature sensors on the heatsinks and is designed to self-adjust as it warms up or cools down. Hopefully, those mechanisms are in good order as the way it sounds suggest.I keep my fans running at their lowest speeds, and they seem not to compromise the sonic goodness.