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-   -   To improve the sound of Nakamichi PA-5 ? (http://www.diyaudio.com/forums/solid-state/163741-improve-sound-nakamichi-pa-5-a.html)

c3conv 24th March 2010 03:01 AM

To improve the sound of Nakamichi PA-5 ?
 
I read from audioreview.com a certain Mike had this to share in his review. "When I first took the PA-5 home I thought it airy and very nice..until I played Judy Collins and other high-pitched singers. They sounded truly bad,like early solid-state recievers. I put the amp on the test bench and found that it easily met all its specs. So what was wrong? Well,when I put square waves into the amp (a way of testing the transient and phase behavior of an amplifier)they did not come out the way they went in...this is never a good thing. Upon analysis I found that the feed-back loop was not configured to properly address the low midrange/upper bass. Attempting to find out what was up I called Nakamichi. Everyone I spoke to refused to talk to me about it...until I got to one brave tech who told me he knew what I was talking about but would be fired if he said anything!
Well,it turned out the solution was to examine a REAL Stasis amp and incorporate the componant feedback values into the PA-5. What a difference! The amp was warmer with better dynamics and the voices were now coherent. It seems that Nakamichi set the feedback values to make the amp look good on paper at the sacrifice of its real world
performance! At any rate the total cost of parts was $5.00
so I would not hesitate to buy this amp on the used market.
Now to the sound...The PA-5 has a warm softly detailed quality,never bright, and is very gentle on the ears. It produces a COHERENT soundstage.
" You can find this here:Nakamichi PA-5 Videos and Related Media
My question is does this make sense? Can anyone share their thoughts on this? Does anybody know the feedback value of the Stasis amp? Does all the Stasis amps have the same feedback value? I have a PA 5-A and wouldn't mind spending $5 investment for such great improvement. It will also help others have the PA-5 or help others maybe get one and do the cheap upgrade.
Your help will be greatly APPRECIATED!!!

JamesBrennan4 24th March 2010 06:30 PM

Can you be more specific as to which components were changed?

c3conv 24th March 2010 07:29 PM

Sorry I am not a tech guy and I am wondering if what he said makes sense. Does it makes sense to you? thanks for the reply.

JamesBrennan4 24th March 2010 11:46 PM

Just took a look at the schematics for the PA-5, PA-7 and several Stasis amplifiers.
The PA-5 and PA-7 have a 10uF (C102) in the feedback loop, giving a low frequency roll off at ~ 50Hz.
The Stasis amplifiers have a 470uF capacitor, giving a low frequency roll off at ~ 2Hz.
Even so, I have never noticed my PA-7 being deficient in bass response.

c3conv 25th March 2010 02:42 AM

Thanks again for the reply. Based on what he said...
"Well,it turned out the solution was to examine a REAL Stasis amp and incorporate the componant feedback values into the PA-5. What a difference! The amp was warmer with better dynamics and the voices were now coherent. It seems that Nakamichi set the feedback values to make the amp look good on paper at the sacrifice of its real world performance! At any rate the total cost of parts was $5.00 so I would not hesitate to buy this amp on the used market. Now to the sound...The PA-5 has a warm softly detailed quality,never bright, and is very gentle on the ears. It produces a COHERENT soundstage."
...is it possible that what he was driving at could be to change the 10uF (C102) in the feedback loop of the PA-5 that was giving 50Hz to whatever was needed (can be the same value of 470uF capacitor) to reach 2Hz then things will improve?

JamesBrennan4 25th March 2010 03:32 AM

Yes.

If you try it, let us know the results.

c3conv 25th March 2010 02:29 PM

Thank you for the help. I have to find time as well as ask somebody to help me do this. Will get back to you as soon as I get to try it.

analog_sa 25th March 2010 05:44 PM

Quote:

Originally Posted by JamesBrennan4 (Post 2130399)
The PA-5 and PA-7 have a 10uF (C102) in the feedback loop, giving a low frequency roll off at ~ 50Hz.
The Stasis amplifiers have a 470uF capacitor, giving a low frequency roll off at ~ 2Hz.



A little knowledge can be dangerous. Do you actually believe the Nak engineers are that stupid?

analog_sa 25th March 2010 06:07 PM

The PA-5 circuit appears virtually identical to the Threshold circuits. After staring at it for a while the only topological difference i can spot is the VAS which is a cascode in the Threshold amps. No idea if this alone can bring such a substantial difference in sound but with some imagination i can see it being transplanted dead-bug style on the Nak board - it's just a single transistor and biasing. Then there is the slightly different compensation, the protection relay and obviously all the different parts. Nothing looks in any way inferior than the Threshold amps. I suspect ** in the audioreview quote.

Nelson Pass 26th March 2010 07:34 PM

My experience is that bias values are the most likely issue.
Nak's circuits seem to be intelligently done as a rule, but
the circuit does depend on a healthy output stage bias -
something that doesn't reflect in the curves.

If you can adjust the bias so that the long term heat sink
figures are 50 deg C (cover on, 2 hours later, etc.) then you
may experience an improvement.

:cool:


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