Sound quality discrepancy in Nakamichi Stasis receivers - diyAudio
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Old 22nd February 2015, 11:31 PM   #1
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Default Sound quality discrepancy in Nakamichi Stasis receivers

I've had an SR-2A for a long time and always liked it a lot. I have a home studio with ProAc Studio 100 monitors that I've powered with a McIntosh MC2015 for a while. I decided to check out how the SR-2A sounded and it really opened up the sound for me. A lot more detail in the vocals, reverbs, and representation of space, etc. Figuring that one Nak Stasis receiver should have the same basic sound as another, I got a TA-3A on Craigslist so that I could get more power as well as power amp direct ins. It does sound more powerful, as expected, but the vocals sound quite recessed in comparison as well as some weird, very subtle distortion. The SR-2A sounds a lot more open and detailed, although less punch in the low mids.

Any ideas if this is just a function of the different models, perhaps from design differences and manufacturing techniques, or if it would be worth investigating getting the TA-3 to sound more like the SR-2A.

TIA
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Old 23rd February 2015, 01:36 AM   #2
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more physical info/facts ?
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Old 23rd February 2015, 02:39 AM   #3
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Originally Posted by Zen Mod View Post
more physical info/facts ?
What would be helpful? I don't have any measurements, just that when I hook up the SR-2A, it sounds as I would expect and then, same cables, same speakers, same source (Metric Halo ULN-8 as conversion), the vocals recede into the background and there is a very tiny twinge of distortion.

I am thinking it would be interesting to test the i/o with SpectraFoo, but I've never tested the output of an amplifier before, so I'd want to make sure I don't toast the input of the ULN-8. SpectraFoo has the ability to measure transfer function, so that might be helpful. I can get a load resistor, so I just need to figure out how to safely pad the signal down.
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Old 23rd February 2015, 03:09 AM   #4
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have a link to sch/service manuals ?
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Old 23rd February 2015, 03:26 AM   #5
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Originally Posted by Zen Mod View Post
have a link to sch/service manuals ?
Not at this time, but I'll see what I can dig up!

Thanks!
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Old 23rd February 2015, 06:39 PM   #6
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Hifiengine has the schematics you are looking for.

I took a quick look at the amplifier section of both and they are virtually identical, save for the fact the SR-2A has a +/-37VDC compared to the TA-3A's +/-53VDC rails. I was surprised to see that the TA-4A model used 2SK389 jfets as the LTP input, nice. All of the lower models used bipolars in their LTP. You might want to look at things in the signal path that can degrade over 20+ years of usage, i.e. protection relay contacts, A/B speaker switch contacts, etc. If it were mine, I'd look to install a new protection relay and figure out how to clean/deoxit the switches while I was at it. You might also want to look at other things like electrolytics to see if any are bulging or leaking.
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Old 23rd February 2015, 07:00 PM   #7
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Thanks so much. I just found those schematics as well. My guess is maybe the electrolytics did degrade. Although it's weird that the older receiver wouldn't have that problem. Maybe they used better parts.
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Old 23rd February 2015, 08:32 PM   #8
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Quote:
Originally Posted by Chamberman View Post
Hifiengine has the schematics you are looking for.

I took a quick look at the amplifier section of both and they are virtually identical, save for the fact the SR-2A has a +/-37VDC compared to the TA-3A's +/-53VDC rails. I was surprised to see that the TA-4A model used 2SK389 jfets as the LTP input, nice. All of the lower models used bipolars in their LTP. You might want to look at things in the signal path that can degrade over 20+ years of usage, i.e. protection relay contacts, A/B speaker switch contacts, etc. If it were mine, I'd look to install a new protection relay and figure out how to clean/deoxit the switches while I was at it. You might also want to look at other things like electrolytics to see if any are bulging or leaking.
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Old 24th February 2015, 07:28 AM   #9
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An update, if you are interested.

Well, being pressed for time and not possessed of the experience or test equipment, I dropped it off with a local tech with decades of experienced who has done great work with my Mac gear. He's going to scope it out and see how it's performing against original spec. He's quite familiar with Nak equipment, so I'm in good, if not bargain basement hands. What I'm hearing doesn't sound like dirty contacts, but it could easily be tired caps. I would think that if it were dirty contacts, or something else fixable with deoxit, it wouldn't be so focused in the midrange and it probably wouldn't be both channels. I'm really hoping that the amp isn't just operating according to spec and that it has a naturally scooped tone according to its design, but that's quite possible. In the meantime, the SR-2A is holding down the fort quite nicely.


He said that he could completely rebuild it, including a complete recap for $300. It's tempting, but I don't know if I have the cash for that at this time. Or if it would be more worth putting the money and time into something else, maybe even getting a Hypex kit. I can do simple recapping myself, having done quite a few Fender amps, etc., so I could deal with a lot of that.

I'll know later this week what the story is.

Thanks for chiming in, everyone.
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Old 24th February 2015, 07:48 AM   #10
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do recapping by your self

if you need some help , post necessary info here (sch , photos)
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