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Old 7th September 2005, 03:21 PM   #21
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I often see a transistor besides VAS transistor (Q107 here). What is the purpose of this transistor. It seems like limiter, but does it contributes something to (good) sounding?

Also, some members are thinking about clipping behavior. What is this "clipping behavior", does it also contributes to good sounding? Does Q107 have to do with "clipping behavior"?

oops.... one more.

Why is the VBE multiplier sits not at the VAS line? The lower VAS CCS drives 1k resistor, not VBE multiplier.
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Old 7th September 2005, 04:14 PM   #22
oPossum is offline oPossum  United States
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Quote:
Originally posted by ocaukrell
Personally i would love to see the entire service manual (I know someone with a pa7).
Any chance of getting a scan of the whole thing ?.
Complete service manual is here
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Old 7th September 2005, 07:37 PM   #23
K-amps is offline K-amps  United States
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Quote:
Originally posted by amplifierguru
Hi Bra,

Are all these parts available in your country? Why would you choose such a dinosaur to copy when it can easily be seen off by inspired Class AB design, a handful of BC546/556 and some everyday output MOSFETs.

It's Kitsch value??

Cheers,
Greg
Greg,

I have owned these amps, they do sound VERY good. I am not the one to fall for hype, but they were very nice. Handsome brutes too.
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Old 7th September 2005, 08:02 PM   #24
lgreen is offline lgreen  United States
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Default hi

Hi Bra, good to see you again, did you make the krell ksa-50 clone or are you making it?
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Old 7th September 2005, 09:03 PM   #25
anatech is offline anatech  Canada
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Hi Greg,
These do have a special sound, they stuck out in my mind even though I've serviced most major brands and most of the "classics". I've taken some home too. They look really good. Even my wife likes them.

They don't run too hot. For the design they only use as much current as needed. They sound beter than a Carver Lightstar (had one for years), but the Lighstar is soooo cool!

I have heard many different amps I like, but nothing extremely efficient seems to sound good. I would suggest you take the time at some point in your life to listen to one of these. I think you may be surprised over what you see in the schematic.

Oh, no "Kitsch value" at all. Most people don't know what a Nakamichi is over here.

Cheers,
-Chris
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Old 7th September 2005, 09:17 PM   #26
bscally is offline bscally  United States
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Default Gloriously un-subtle design

What a gloriously un-subtle design.

The output stage scares the he-be-gebees out of me.

Those device must be matched at least on three parameters.

IMO that is no way to design a good producable amp.

Also as was pointed out the Miller VAS compensation is er... well plain bad.

I would sugest that any update/clone includes (at a minimum) the following improvements..

1) Better HF limiting - may be an inclusion of a double pole filter that could be easily worked around for those who wantthe orthentic sound
2) Deal with the miller caps on the Sziklai pairs
3) Deal with the loading requirements on the Sziklai drive transistor
4) Deal with the lack of base stoppers on the Sziklai paris
5) PSU noise injection into the input ground due to LTP cascode and bias current reference points

Attached is a PDF of the scans, I thaught it migh be a bit easier to handle.


Brian
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Old 7th September 2005, 09:28 PM   #27
anatech is offline anatech  Canada
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Hi oPossum,
Thank you very kindly for the files. There are a few manuals I was really unhappy to give up. I now have one of them (sort of).

-Chris
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Old 7th September 2005, 10:39 PM   #28
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Here is a photo of a Threshold S-300 powr amp......
Attached Images
File Type: jpg 1108922190 copy.jpg (74.0 KB, 1088 views)
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Old 7th September 2005, 11:01 PM   #29
anatech is offline anatech  Canada
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Hi Mark,
In all fairness, the build quality with Nakamichi is higher than some Threshold I've seen. Sorry, but it's true as I serviced both.

There are no reliability problems with the PA series Nak amps. The type II design addressed the over active protection circuits, there was a mod for the original ones available at no charge for a while. I installed many.

As far as what Nelson was and wasn't happy with, I'd rather hear it from him in response. Happy with Nakamichi and happy with these amps are two different things entirely. Actually, I'd love to hear what suggestions he may have. His designs have advanced beyond this series, he's moved on. Hindsight is valuable.

I do not hold the Nak amps up as being the best, but they sound very good. I think in that light they are well worth consideration as a project for those who know what these amps are all about. You could do a whole lot worse.

-Chris
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Old 7th September 2005, 11:54 PM   #30
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Quote:
In all fairness, the build quality with Nakamichi is higher than some Threshold I've seen. Sorry, but it's true as I serviced both.
When I think of STASIS I try NOT to think of the NAKS however
I agree with you in regards to build quality on some of the very older Thresholds. Compares to parts quality used in later Thresholds or to todays parts what you got back then was state of the art for that time and place, you would find similar parts used in Audio Research products of the same era for instance..... but what you ALSO see and get is the difference between a hand built product and an assembly line product. Basically the way a Masaratti is built versus a a Chevy. The prices of used Threshold Amps vs. Nak amps of the same time periods also reflect this very well.... Thresholds always have higher values, sometimes by a wide margin. Although Nelson says that he feels that NAK lived up to the Stasis circuit its still in my vision a *** product through and through. I've also serviced many of those amps but not to do upgrades to the MK-1's but to replace blown outputs and rectifiers and other associated parts, there were not many MK-1's around when I was doing these repairs. I'd have rather sat and repaired Thresholds all day long but they don't have the break down incidents of the NAKS. What I had to repair was I admit pretty common stuff but non the less were problems. I guess if you want the REAL thing you would WANT TO clone one of the originals that Nelson designed not one that some Japaneese engineer thought might pass(no pun intended!) for it.

Mark
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