The Mighty NEC A-10II Integrated

That sounds like a great plan - I can't think of anything to add. I'll get the bug to work on mine someday, but I don't want to be without it for too long. :D
 
It seems to me that piece of gear that's most important to me and gets the most use should get the most attention :).
 
Help! HElp! How do you do!!! Help please with schematic and service manuals on amplifier NEC A-10 much need.
 
Hifirob2 said:
As much as I've wanted to "roll" opamps to find out what improvements can be had (if any), I've never attempted it. After reading & following this informative thread:

http://www.audiokarma.org/forums/showthread.php?t=403386

I'm not too sure I want to experiment just yet on my (now) favorite integrated.

If I knew it could safely be done (no oscillation issues, proper voltage requirements), then I would probably go with a nice OPA2134 or similar opamp. The ones used in the A-10II were fine for back in the day, but much better ones are available now. I'm curious to see what differences in sound can be obtained - since these two opamps seem (to me) to be the weakest links in this amp.

If you were to hook a good CD player up directly to the main in jacks, and switch the operation mode to "separated", I believe you'll bypass the preamp opamp (by the volume pot), and then be able to hear any improvements in direct mode. If you can hear an improvement, then I'd wager that that opamp is the weak link, and an upgrade may help. Just my guess from tracing out the circuits to my untrained eye.

AK member jhoyt swapped out the opamp in the phono section of an MCS 3285 (another NEC creation) that he had for a while. The phono preamp circuitry is somewhat similar, and he was able to hear quite an improvement. I believe he used a LME49860 in that position.
Click to expand...

Hey Rob, amp is out of storage and going into daily use, any progress on locating new/better op-amps yet?
 
scott1019 said:
Hey Rob, amp is out of storage and going into daily use, any progress on locating new/better op-amps yet?
Click to expand...

Hey Scott - I wish I could tell you yes, but I've kind of put that project on the back burner. I used to get emails from Texas Instruments (or whoever acquired Burr Brown), and wanted to send away for free samples of different op amps to swap in the amp and see if there was any sound improvement - but I never got around to it, and I think you now need a commercial email address to ask for samples.

I'll do it someday after I've done it successfully on other pieces first - I don't want to mess up my A-10II.

I also need to dig into my A-11 and see what's what with the phono preamp in it. Too many projects - too little time. :yes:
 
Have you gotten as far as digging into exactly where the op-amps are and if they are soldered onto the board... accessible etc.?
 
I know where the two opamps are, but I haven't gotten any further than that. One is soldered to the phono preamp board - kind of under that metal shield, and the other is soldered onto the board just to the left of the main volume pot - under a wiring harness that's a little tricky to get to. For that one, you'll need to solder in an adapter board, and most likely extend that wiring harness by a few inches to fit over the new opamp.

Maybe when I replace the volume pot on my other A-10II, I'll dig into the opamps then.
 
sdtintin said:
NEC a11 bidding on eBay right now. Any difference between this and the a10?
Click to expand...

The A-10 and the A-11 are similar, with the A-10 being 60 wpc and the A-11 being 70 wpc. Though, the A-11 has no moving coil phono preamp.

Differences between the A-10 and the A-10II are much more drastic, as the A-10II was an improvement on the A-10. The A-10II seems to be a simpler design, with a much less complicated preamp and phono preamp - resulting in shorter signal paths. Also, the A-10II uses all audio grade caps - even the large filtering caps are audio grade. The A-10II uses heavy bracing and has a thick metal bottom plate for isolation - even special alloy feet. The A-10 and A-11 doesn't.

Sound differences? That is very subjective, but I prefer the sound of the A-10II over the A-11.
 
Hifirob2 said:
The A-10 and the A-11 are similar, with the A-10 being 60 wpc and the A-11 being 70 wpc. Though, the A-11 has no moving coil phono preamp.

Differences between the A-10 and the A-10II are much more drastic, as the A-10II was an improvement on the A-10. The A-10II seems to be a simpler design, with a much less complicated preamp and phono preamp - resulting in shorter signal paths. Also, the A-10II uses all audio grade caps - even the large filtering caps are audio grade. The A-10II uses heavy bracing and has a thick metal bottom plate for isolation - even special alloy feet. The A-10 and A-11 doesn't.

Sound differences? That is very subjective, but I prefer the sound of the A-10II over the A-11.
Click to expand...

Thank you for the detailed impressions and thoughts. Yeah, I pulled the feet off my A-10 II once and they must weigh about a pound a piece!
 
Hifirob2 said:
I know where the two opamps are, but I haven't gotten any further than that. One is soldered to the phono preamp board - kind of under that metal shield, and the other is soldered onto the board just to the left of the main volume pot - under a wiring harness that's a little tricky to get to. For that one, you'll need to solder in an adapter board, and most likely extend that wiring harness by a few inches to fit over the new opamp.

Maybe when I replace the volume pot on my other A-10II, I'll dig into the opamps then.
Click to expand...

Please keep me posted Rob, I'd love to do this! I know the improvements first hand that can be made from op-amp replacement. I'm sure they used the best they could at the time, but technology has sure improved since then.
 
pashka said:
All about NEC -A10 ( I , II , III X)
Some information from the Japanese sites.
Use a translator.
http://homepage2.nifty.com/2001odakun0801/subdtestA10.html
http://blogs.yahoo.co.jp/namechan9999/21914.html

I'm looking for a schematic of NEC A-10II , if someone has, please give a look. :)
I want recap this monster .
Thanks
Click to expand...

This was on one of those links. It is a particularly good photo archive of the different variants of the A10: http://www.geocities.jp/freak_audio/A-10HISTORY.htm
 
Thanks Hifirob2 .
////////////////'//////////////////



Restoration of NEC A-10Ⅱ :
http://www.page.sannet.ne.jp/kokada/newpage30.html (Use google translate )
3 pages .


https://translate.google.com/transl...//www.page.sannet.ne.jp/kokada/newpage30.html
https://translate.google.com/transl...//www.page.sannet.ne.jp/kokada/newpage31.html
SANY025911.jpg

SANY02731.jpg
SANY02751.jpg
 
Thanks for those links. I've stumbled upon them before, and read about the relays and the power switch light. Mine is out also, and when I measured the 46 volts, I scratched my head and said, "that's strange, but whatever - I can live with it being out." LOL It would be nice to get it working again, though.

I wanted to replace the thermal grease on all the outputs just for routine maintenance, but to get to them, you have to remove about three dozen screws - including the transformers. That seemed excessive, but mine does run VERY hot, so I run two cooling fans over the vents above the heatsink.
 
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