Nakamichi PA-5 upgrades

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#81
Hey! Hi Angelo!
Yup, that's where I set it. Right where the manual suggests. I did misunderstand you, sorry.

You will find it drifts around with supply voltage and ambient temperature. So the actual value isn't critical within limits.

Hopefull yeverything is good with you. Things here continue just fine ...

-Chris
 
#82
UncleAng said:
Hi Chris,

I think you misunderstood me; I'm not cranking up the bias by 2.5X; it's set at 40 mV. Actually, Chris, that's where you should have set it at since you're the last person who serviced it back in July of this year.

-Angelo
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https://www.firstwatt.com/pdf/art_leave_classa.pdf
 
#83
Hi nicoch58,
Hey cool! Earth shattering ... but wait! What amp are we talking about? Oh right, not one of those amps at all.

I also pointed out that speaker distortion is probably a great deal higher than the PA-7 for starters. Oh yeah! That's the amp we are talking about! You really have to think before trying to make a point.

-Chris
 
#84
anatech said:
I also pointed out that speaker distortion is probably a great deal higher than the PA-7 for starters. Oh yeah! That's the amp we are talking about! You really have to think before trying to make a point.

-Chris
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this is a non sense to me please explain your point , tnx
more bias to pa-7 lovered the thd that's for sure ,
I quote Nelson :"distortion is inversely proportional to the bias current."
with 55° at heasink ZERO problem a win win !
spk thd is another problem
 
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#85
The distortion produced by the PA-7 is pretty low already. I have seen, on the bench with my equipment, the reduction in distortion when higher bias is used. It is not worth the increased temperatures compared to the sonic differences.

Now, on the bench I am using Klipsch THX 6000 speakers (just the left and right). These are extremely flat (measured by two different individuals with two systems and mics) and very efficient. They are not cheap speakers and reveal everything. That's why I have them. The differences in bias levels are not discernible to humans. I proved my point to a client who believed as you do. He admitted there was no difference in sound quality.

Now one thing you must realise is that people without technical training or experience, no access to test equipment will read these posts and perhaps act on them. Assuming they don't blow their gear up through a mistake running the bias current up, they may well cook their amplifiers due to misguided advice. Just what kind of service do you think you are providing them here?

You want to do this to your equipment - have at it! But, do not advocate a practice when you are not familiar with the amp firstly, or have direct and extensive experience yourself. I admit I disagree with Nelson on this point, but I do for solid technical reasons. One thing you must take into consideration that 10 years is not a long time for equipment life. I have taken care of various models from inception until now and will do so in the future. My clients do expect good equipment to run 30 years - and it can. A Krell will not, period. Nor will any other amplifier that run very warm, never mind hot. So by running equipment at higher temperatures it costs clients at least hundreds of dollars (never mind electricity costs) for no improvement in actual, heard sound quality.
I serviced these amplifiers from new under warranty. Failure rate in Canada under warranty was low. I only ever repaired one PA-7 II under warranty. That's because a copper staple from the box fell inside and Nakamichi warrantied it anyway. I'm in the Toronto area, so many sold here. That was apparently the only failure in Canada. Later I had many more repairs on these, most due to upgrade attempts, but I am now seeing a failure mode that is easily solved but requires a part change. So why on earth would you take a good sounding amplifier and reduce the reliability for no good reason? Remember, I service them continually and can talk from a position of actual knowledge both listening and from measurements.

-Chris
 
#86
anatech said:
The distortion produced by the PA-7 is pretty low already. I have seen, on the bench with my equipment, the reduction in distortion when higher bias is used. It is not worth the increased temperatures compared to the sonic differences.

Now, on the bench I am using Klipsch THX 6000 speakers (just the left and right). These are extremely flat (measured by two different individuals with two systems and mics) and very efficient. They are not cheap speakers and reveal everything. That's why I have them. The differences in bias levels are not discernible to humans. I proved my point to a client who believed as you do. He admitted there was no difference in sound quality.

Now one thing you must realise is that people without technical training or experience, no access to test equipment will read these posts and perhaps act on them. Assuming they don't blow their gear up through a mistake running the bias current up, they may well cook their amplifiers due to misguided advice. Just what kind of service do you think you are providing them here?

You want to do this to your equipment - have at it! But, do not advocate a practice when you are not familiar with the amp firstly, or have direct and extensive experience yourself. I admit I disagree with Nelson on this point, but I do for solid technical reasons. One thing you must take into consideration that 10 years is not a long time for equipment life. I have taken care of various models from inception until now and will do so in the future. My clients do expect good equipment to run 30 years - and it can. A Krell will not, period. Nor will any other amplifier that run very warm, never mind hot. So by running equipment at higher temperatures it costs clients at least hundreds of dollars (never mind electricity costs) for no improvement in actual, heard sound quality.
I serviced these amplifiers from new under warranty. Failure rate in Canada under warranty was low. I only ever repaired one PA-7 II under warranty. That's because a copper staple from the box fell inside and Nakamichi warrantied it anyway. I'm in the Toronto area, so many sold here. That was apparently the only failure in Canada. Later I had many more repairs on these, most due to upgrade attempts, but I am now seeing a failure mode that is easily solved but requires a part change. So why on earth would you take a good sounding amplifier and reduce the reliability for no good reason? Remember, I service them continually and can talk from a position of actual knowledge both listening and from measurements.

-Chris
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OK but I write 55° is a safety working point ,I know we must take care of over temp inside ....
"It is not worth the increased temperatures compared to the sonic differences." is only a personal point I can ear difference in resistor type that load my mc.....we are diy's here play and test is a must
if differences in bias levels are not discernible for the OP thats fine 😉
 
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#87
We are DIYs, however we must advise people responsibly at all times.

55°C is not a reasonable operating temperature, it is too high - period. Failure rate doubles every 10 °C rise in temperature, that is a documented, known fact.

When you hear a difference in some component types, it is expectation bias. My equipment measures easily and reliably 30 dB + below -90 dB from -10 dBu. I'm measuring things below a human beings ability to even perceive. So forget hearing that stuff. This is backed up by listening tests. That is the cold, hard truth. Some folks may not be measuring the right things, or interpreting the results.

Now it is possible to easily hear component type differences where they are inappropriate for the circuit location, but that is easily measured as well. Again, proved over the years. Notice I said component type, not make / brand or model.
 
#89
From a May/2009 interview with NP in Stereophile regarding his amp patents.....

Today—which is your favorite? It changes, depending on what I'm doing at a particular time, what else is in the system, what I'm listening to, how I'm feeling. Each one is a different experience. Plus, there are different situations where one type of amp is better suited than another. Yeah, I get asked that question pretty often. You know, I can't answer it. [laughs] They're like children...it's like asking which is your favorite child. —Nelson Pass

NP states it well including 'how I'm feeling' which, subjectively affects one's listening pleasure more than your bias adjustment.
 
#92
Hi nicoch58,

Nelson's statement is true of his low feedback designs. Not so of more normal designs. You have just got to equate what he is talking about to what we are talking about.

BTW, I have met Nelson a few times, and he is an extremely nice fella. But he is also honest about his design directions and they are not absolute. He follows his current interest. He has also found a lucrative design direction - which he follows. At least he is realistic.

I use different amplifiers of totally different designs for fun. But I come back to a modified Marantz 300DC (power diamond buffer output design) as my favorite. Nelson's statement about different amplifiers is perfectly valid. I'd be fine with a Nak PA-7 or a few other designs to be honest.

Once you understand how amplifiers work and things that make a difference you will understand much better. You don't. I measure IMD, between that and THD in a spectrum you fully characterize an amplifier except at high power levels. Testing level is industry standard 1W into 8R, and I do use the industry Dale 8R, 250W, non-inductive, 1% dummy loads mounted on a large heat sink. At high levels PCB layout and your AC supply impedance come into play. The higher the amplifier transconductance (everything else being equal), the better the amplifier will behave.

So let's talk about the Nakamichi PA series. They are cleaned up over the classic Stassis as well. Better amplifiers, but then the original Stassis amps are much earlier in time.

-Chris
 
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#94
anatech said:
Hi nicoch58,

Nelson's statement is true of his low feedback designs. Not so of more normal designs. You have just got to equate what he is talking about to what we are talking about.

BTW, I have met Nelson a few times, and he is an extremely nice fella. But he is also honest about his design directions and they are not absolute. He follows his current interest. He has also found a lucrative design direction - which he follows. At least he is realistic.

I use different amplifiers of totally different designs for fun. But I come back to a modified Marantz 300DC (power diamond buffer output design) as my favorite. Nelson's statement about different amplifiers is perfectly valid. I'd be fine with a Nak PA-7 or a few other designs to be honest.

Once you understand how amplifiers work and things that make a difference you will understand much better. You don't. I measure IMD, between that and THD in a spectrum you fully characterize an amplifier except at high power levels. Testing level is industry standard 1W into 8R, and I do use the industry Dale 8R, 250W, non-inductive, 1% dummy loads mounted on a large heat sink. At high levels PCB layout and your AC supply impedance come into play. The higher the amplifier transconductance (everything else being equal), the better the amplifier will behave.

So let's talk about the Nakamichi PA series. They are cleaned up over the classic Stassis as well. Better amplifiers, but then the original Stassis amps are much earlier in time.

-Chris
Click to expand...
1668197725411.png
 
#95
I am well aware, but if you look at the two amplifiers they are physically different. The Threshold build quality was much lower, thermal efficiency was lower too. The outputs used in the Nak product have a flatter current - gain curve also. That and matching was better even though the 1R0 emitter resistors minimized that requirement.

There are actually many differences that may not look like it on the schematic. I know both products reasonably well. I liked the Threshold amps, but I would actually wouldn't mind owning a PA-7, not so with the Threshold.
 
#97
anatech said:
The Threshold build quality was much lower, thermal efficiency was lower too.
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I am surprised by that. The build quality on the Threshold S series (what I am familiar with) is pretty darn good. I will have to check out a Nakamichi at some point. They seem to be more popular just a bit smaller. Addressing your point before about Bias and sound quality, I run my Threshold S/500 amp at about 48 degrees. That seems to be good enough for me. Any hotter than that and I can run into an issue if the room gets warm for some reason.
 
#98
So this thread is about upgrades. I thought I would share my project. I have a Threshold Stasis amp. I have been playing around with a couple of things on it lately. Nelson pass made a new version of his front-end design. The front end is a simpler circuit with newer components. This could work for the Nakamichi amps. Look for the thread. 'New Stasis Front End' is the title. The Gerbers, schematic etc are all there.

I had adapted that front end to work with my S/500 which has stock 80v rails. It worked but the sound was a little off. The amp was prone to oscillation etc. I modified the amp even further by putting a lower voltage dual mono power supply in it with the DIYaudio Power supply boards and a couple of Antek 30vac transformers (39v rails) as well as the Diy audio softstart. That worked a lot better.The amp has never sounded this good. 🙂

So if you want to try to run the Nakamichi Stasis as a Class A amp with that new front end, that may be a worthy project. Zen Mod made his own stasis circuit board that is more compact.

I have been keeping my eye out for a good deal on a broken stasis amp to rebuild with the new stuff. If anyone has something laying around, let me know.
 
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