Yamaha A-1000 amplifier, how many versions?

spaghetti

Active Member
Hi, I am checking the Yamaha A-1000 amplifier and google returns two different models that come from the same years of the 80s (there's a third one from the early 90s named DSP A-1000, but that's clearly a different beast).

The first one, reported by thevintageknob website has all the controls in plain sight, and has internal differences as well compared to the one listed on hifiengine which has a front lid that hides almost all the rotatory controls, and a different top cover as well.

I tried to find some documentation about the differences without any success. And the only service manual available seem to be the one for the "hifiengine" model. Does anybody has any details on this matter?

Andrea
 
Hi Andrea - there are a few very clued up Yamaha tech's around on here - but perhaps they would see your post sooner if you had your post moved to the Yamaha sub-forum - just a thought. ;)
 
Moved to The Yamaha forum for better exposure.
Regards,
Jim
 
Hi, I am checking the Yamaha A-1000 amplifier

Yes, there are a few different names and models depending on market, it can be a bit confusing.
  • First there's what most people would refer to as the A-1000 here (introduced in 1983) which is the "real" Class-A amp with the 4 big filter caps in a square formation, and the flap on the front covering the tone controls. This came in silver and black, in various voltage models including 220-240V, 110V, and a multi-voltage version. A special version of this amp also existed for the Japanese market, which is essentially identical and called the A-950. It received some upgrades such as black-anodized heatsinks, and copper parts in the chassis, however the circuit and specifications are the same. The Japanese model replaces the "Auto Class-A" button with "Class-A turbo" but the function is the same. These amps are the larger siblings of the A-700 which also shares the same circuit design (and same MT-200 output devices).
  • There's also the Japanese market "A-1000" (1984) shown on TVK, which isn't the same as the above and loses the "real" Class-A operation in favour of was later referred to as HCA. This is not a true Class-A design even though Yamaha marketing tries to suggest it (the rare MX-10000 is the only exception from my understanding), however I'm sure they are still excellent sounding products. The same applies to the A-2000 and A-2000a, these amps are in the same family (although the internal layout is changed significantly on these two), and you'll notice on all of them the "Class-A" button is replaced with a "Richness" button which is unrelated and described on TVK. These amps all have prettier exteriors (wooden panels, polished knobs, etc).
  • The DSP-A1000 version is a home theatre amp and not related to any of the above.
  • Finally, it's worth noting that the German / European delivered versions of the 1983 models do have a different top cover/vent design (on both the A-700 and A-1000) compared to all other markets, utilising a plastic grille fitted into the metal cover, however the amp and functionality / performance is identical otherwise.
Hope that covers it!
In my opinion the original 1983 series is likely the best choice if you interested purely in sonic performance. They are easier to get too, with both the A-700 and A-1000 occasionally showing up for sale in Germany/France (sometimes also Italy) in 220-240V switchable versions.
 
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@zaibatsu thank you so much for the insight, you've been very helpful, I hope I can buy the A1000 that's currently flying in my radar, it's a true Class A specimen.
 
@avionic Help needed.
I have been working on Yamaha A 950 (A 1000 internationally). It has a strange problem. The amp won't come out of protection untill i put it on DBT. I have changed most of the electrolytic caps on power amp board. The caps were not reading well (680uf reads 500uf and 330uf reads 230uf). I changed these Alongwith small ones 10uf 100uf 47uf and 22uf. Cleaned the remanants of glue. Now the problem remains the same. When i increase its bias on class A on DBT, it again goes in protection at about 80mv. Is it related to class A switching trim pot adjustment? I am kinda stuck here. The equalizer 14 pcb (set of resistors) seems burnt. Definitely heat issues. Not to mention that Avionic rescued my ca 1000 ii during 2010. Will post some pics of amp soon.
 
@avionic Help needed.
I have been working on Yamaha A 950 (A 1000 internationally). It has a strange problem. The amp won't come out of protection untill i put it on DBT. I have changed most of the electrolytic caps on power amp board. The caps were not reading well (680uf reads 500uf and 330uf reads 230uf). I changed these Alongwith small ones 10uf 100uf 47uf and 22uf. Cleaned the remanants of glue. Now the problem remains the same. When i increase its bias on class A on DBT, it again goes in protection at about 80mv. Is it related to class A switching trim pot adjustment? I am kinda stuck here. The equalizer 14 pcb (set of resistors) seems burnt. Definitely heat issues. Not to mention that Avionic rescued my ca 1000 ii during 2010. Will post some pics of amp soon.
Check your output transistors.. Don't even try to T-shoot or adjust class A until you get class AB squared away.
 
Check your output transistors.. Don't even try to T-shoot or adjust class A until you get class AB squared away.
Thanks for the response. I have checked the output transistors. All OK. Amp is producing clear sound under DBT set up. Yet it is not coming out from protection on wall socket. I have played it for hours on DBT to see if there is any unusual distortion or pop up sound hut Couldn't find any. The lamp is not showing any shorts either. However, relay goes into protection upon pressing class A turbo switch (ideling current at 100mv plus). Relay gets disengaged by slightly decreasing the idling current (around 6mv class AB and 80mv class A). Amp plays music for hours under DBT at this point. Not to mention that biasing value remains still.
Any help would be highly appreciated.
 
It is normal for amp to go into protection while on DBT if you try to use Class-A mode. The current draw is very high thus the DBT acts the same as in a short condition. The amp also draws reasonably high current even in AB mode so you need a 100W light bulb (minimum) to support the AB draw. Keep in mind you cannot accurately set bias while on DBT, 5-6mV in Class-AB on DBT will increase to approximately 11mV under mains power.

However, it is obviously not normal for the amp to not come out of protection when directly on mains power.
Was the amp working correctly on mains power before you changed the caps? Or the problem existed prior to your work?

If the problem was previously existing, I would check the protection area transistors, occasionally the small NPNs (2SC2603) can get tired. You can replace with KSC2383 from mouser.
 
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