Okay so thanx for nothing guys 
no it's okay.
I never found any servicemanual, schematic or adjustment procedure, so I had to reverse engineer the whole shabang and calculate decent standing currents myself.
Note the schematic and adjustments are somewhat different for the other models PA5, PA7 and PA7mkII, so please use this only with PA5EII and maybe the non-european version PA5 mkII.
So I will here share my findings in case someone else will need to adjust his/hers Namaichi PA5EII.
This procedure gives approximately 10mA through drivers Q114+Q115, 115mA through each output-transistor Q116-Q119 and finally 40mA through each CFP-secondstage output-transistor Q120-Q127.
I read about some people who where bumping up the current to gain more class A sound. Eventhough the heatsinks seems to be able to handle it, I will strongly recommend you to keep the original settings. The CFP/sziklai output stage is superstable and seems in perfect symmetry at these settings. But if mess with it, bad things could happen.
Here is how to do it.
no it's okay.I never found any servicemanual, schematic or adjustment procedure, so I had to reverse engineer the whole shabang and calculate decent standing currents myself.
Note the schematic and adjustments are somewhat different for the other models PA5, PA7 and PA7mkII, so please use this only with PA5EII and maybe the non-european version PA5 mkII.
So I will here share my findings in case someone else will need to adjust his/hers Namaichi PA5EII.
This procedure gives approximately 10mA through drivers Q114+Q115, 115mA through each output-transistor Q116-Q119 and finally 40mA through each CFP-secondstage output-transistor Q120-Q127.
I read about some people who where bumping up the current to gain more class A sound. Eventhough the heatsinks seems to be able to handle it, I will strongly recommend you to keep the original settings. The CFP/sziklai output stage is superstable and seems in perfect symmetry at these settings. But if mess with it, bad things could happen.
Here is how to do it.
Attachments
be nice to people here ...most of the times are very helpfull .... your post has 139 views including mine ...that also means that i took a few minutes to check my resources and had the same results with you(138 other people did the same !!! ) ...seems that documentation for your amp is very hard to get .
your procedure is correct and the information you provided is the best so far ...t5hank you for that
kind regards
sakis
your procedure is correct and the information you provided is the best so far ...t5hank you for that
kind regards
sakis
Best I can offer other than basic specs if needed.
Doc
http://i1112.photobucket.com/albums/k485/machinebuilderdoc/NakPA7.jpg
Oops... not much help. But since I set up the link I'll leave it.
Doc
http://i1112.photobucket.com/albums/k485/machinebuilderdoc/NakPA7.jpg
Oops... not much help. But since I set up the link I'll leave it.
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slow or low ?
Don't mind the temperature - it doesn't need to be anything specific, and if you play some music with moderate volume the temperature will increase. The temperature is a biproduct of the standing current, and this is the important parameter.
If you have the indicated voltages +50%/-30% at the testpoints, then your amp is working as it should.
Don't mind the temperature - it doesn't need to be anything specific, and if you play some music with moderate volume the temperature will increase. The temperature is a biproduct of the standing current, and this is the important parameter.
If you have the indicated voltages +50%/-30% at the testpoints, then your amp is working as it should.
...NEW TO HI-FI REPAIRS?
If you are in anyway not absolutely sure what you are doing, then leave it to an experienced technician!
BE AWARE that the above mentioned adjustments must be made in VERY SMALL increments, and with slow movements!
The output is a Sziklai / Complementary Feedback circuit and it is very delicate, so even if you are an experienced technician you should be very careful.
And do not be too obsessed with getting within +/-40% of the values anyway, since it is not always possible.
This is a DIY site, and I will bear no responsibility whatsoever to what you do to own equipment.
Sorry that I have to bump this old threat but the adjustment image comes up in google searches, and I had replies from an obviously inexperienced guy guy who just turned the pots up and down hastily, and his amp burned all the output transistors.
If you are in anyway not absolutely sure what you are doing, then leave it to an experienced technician!
BE AWARE that the above mentioned adjustments must be made in VERY SMALL increments, and with slow movements!
The output is a Sziklai / Complementary Feedback circuit and it is very delicate, so even if you are an experienced technician you should be very careful.
And do not be too obsessed with getting within +/-40% of the values anyway, since it is not always possible.
This is a DIY site, and I will bear no responsibility whatsoever to what you do to own equipment.
Sorry that I have to bump this old threat but the adjustment image comes up in google searches, and I had replies from an obviously inexperienced guy guy who just turned the pots up and down hastily, and his amp burned all the output transistors.
nrik
If your counting your approach as an experienced technician then read the manual once more ( or just look how the amp was made ) cause i thing that even though you measured most of things correctly there is one thing that you missed and you need to verify your readings again ...
There is minor flaw in your sayings that after all may make the amplifier actually run colder than is supposed to be .
TBH though this is not your mistake its a thingy that is planted inside the amplifier probably a twist or perversion of the designer ...look again ....
If your counting your approach as an experienced technician then read the manual once more ( or just look how the amp was made ) cause i thing that even though you measured most of things correctly there is one thing that you missed and you need to verify your readings again ...
There is minor flaw in your sayings that after all may make the amplifier actually run colder than is supposed to be .
TBH though this is not your mistake its a thingy that is planted inside the amplifier probably a twist or perversion of the designer ...look again ....
I just noticed what you wrote Don't mind the temperature - it doesn't need to be anything specific
You are clearly wrong about this ....
okay...then please share with me/us what the proper temperature is ?
The lack of public available information about these wondeful amplifiers can be helped if everybody would share what they know or think.
Just for info: What I meant was of course it needs to warm up to a stable temperature, but the main goal is to have some idling current through all transistors, but not too much as the sziklai risks going crazy and smoke will come out.
The lack of public available information about these wondeful amplifiers can be helped if everybody would share what they know or think.
Just for info: What I meant was of course it needs to warm up to a stable temperature, but the main goal is to have some idling current through all transistors, but not too much as the sziklai risks going crazy and smoke will come out.
...are you reffering to the thermonic resistor in the bias circuit?
Please be aware I still only have the schematic from PA-5 / PA-5E downloadable from hifiengine.com - I don't have the MKII schematic.
Since I had the PA5E-MKII for repair I needed to develop my own procedure.
So from this shortened servicemanual that I took the info of 40mA idle per output transistor, and I adjusted the PA5E-MKII for the same adjustment and ran it in my system for while with no problems. So I concluded that it must be okay.
But If you have the information about a specific temperature it should reach then please share.
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Hi Craig,
I'm late to the party, that's all. This thread started during a time when I was absent, so it's just now that I saw it.
Set the test point to 40 mV for output bias current. That's a fer sure thing. I can't remember this amplifier having two sets of adjustments for bias. I know for certain that the PA-7 MKII only has one bias set control, and you set that for 40 mV as well. It's important to note that this is the bias setting for only one output transistor. All the others are supposed to share equally. While it has a one ohm emitter resistor which should force them all to share nicely, you still need to make sure the outputs are matched roughly the same beta. If you are servicing one of these, check the current on each transistor (amp in service position). Once you have confirmed they are sharing current properly, you can set the bias.
The heat sink should be warm with the amplifier idling. Each channel should be about the same temperature as well.
These amplifiers are licensed Stassis designs, one of Nelson Pass' creations. I haven't any idea if he is aware of that additional adjustment on the PA5 MKII, but he might have an idea what that adjustment is all about. I don't think he actually designed these amplifiers, but that is another question for him I guess. Generally speaking, these amplifiers are extremely robust. I have only repaired a PA-7 that died because one of those copper box staples fell inside it. The staple did not survive either, in case you were wondering. I have checked a few for proper operation, but just that one for an actual failure. The CA5 and CA7 are really nice preamplifiers too. Just saying.
Manuals. I had to leave them when I sold the shop. The only thing that hurt was leaving 8 filing cabinets behind, each full of service information. If I had that manual now I could tell you more about that PA5 MKII.
Hi Henrik,
Did you ever attempt to contact Nakamichi for bias setting information, or one of their warranty shops? Nakamichi service used to be good about giving that information out as long as you were a service shop.
-Chris
I'm late to the party, that's all. This thread started during a time when I was absent, so it's just now that I saw it.
Set the test point to 40 mV for output bias current. That's a fer sure thing. I can't remember this amplifier having two sets of adjustments for bias. I know for certain that the PA-7 MKII only has one bias set control, and you set that for 40 mV as well. It's important to note that this is the bias setting for only one output transistor. All the others are supposed to share equally. While it has a one ohm emitter resistor which should force them all to share nicely, you still need to make sure the outputs are matched roughly the same beta. If you are servicing one of these, check the current on each transistor (amp in service position). Once you have confirmed they are sharing current properly, you can set the bias.
The heat sink should be warm with the amplifier idling. Each channel should be about the same temperature as well.
These amplifiers are licensed Stassis designs, one of Nelson Pass' creations. I haven't any idea if he is aware of that additional adjustment on the PA5 MKII, but he might have an idea what that adjustment is all about. I don't think he actually designed these amplifiers, but that is another question for him I guess. Generally speaking, these amplifiers are extremely robust. I have only repaired a PA-7 that died because one of those copper box staples fell inside it. The staple did not survive either, in case you were wondering. I have checked a few for proper operation, but just that one for an actual failure. The CA5 and CA7 are really nice preamplifiers too. Just saying.
Manuals. I had to leave them when I sold the shop. The only thing that hurt was leaving 8 filing cabinets behind, each full of service information. If I had that manual now I could tell you more about that PA5 MKII.
Hi Henrik,
Did you ever attempt to contact Nakamichi for bias setting information, or one of their warranty shops? Nakamichi service used to be good about giving that information out as long as you were a service shop.
-Chris
Hi Chris
That is some goooood info you are sharing already.
No I am sorry didn't, and my PA5E-MKII is sold long ago.
So currently I have no PA5X bias-problems, but from time to time someone asks me for help, because they have found my drawing on the first page.
...And as you can see Mr. East Electronics starts playing hard-to-get
dropping a comment as if he knows a little secret ...and I am trying to make him share it (if it exist) for the benefit of those people who needs to adjust - or just check - their PA5-MKII.
So thank you for chiming in, really good info.
Anyway: My experiences with that one PA5 is at least shared.
Man those Nakamichi-boys made some nice gear back then.
That is some goooood info you are sharing already.
No I am sorry didn't, and my PA5E-MKII is sold long ago.
So currently I have no PA5X bias-problems, but from time to time someone asks me for help, because they have found my drawing on the first page.
...And as you can see Mr. East Electronics starts playing hard-to-get
dropping a comment as if he knows a little secret ...and I am trying to make him share it (if it exist) for the benefit of those people who needs to adjust - or just check - their PA5-MKII.So thank you for chiming in, really good info.
Anyway: My experiences with that one PA5 is at least shared.
Man those Nakamichi-boys made some nice gear back then.
Since I have been gathering information on the Nak PA amps, I thought I would share this quote from Nelson Pass regarding bias setting on PA5:
"Arrange to get the amplifier some serious ventilation and then raise the
bias until the heat sinks run at 50 deg C after an hour of operation."
Classic NP advice
It is from this thread:
http://www.diyaudio.com/forums/pass-labs/218270-nakamichi-pa-5-upgrades.html#post3134189
"Arrange to get the amplifier some serious ventilation and then raise the
bias until the heat sinks run at 50 deg C after an hour of operation."
Classic NP advice
It is from this thread:
http://www.diyaudio.com/forums/pass-labs/218270-nakamichi-pa-5-upgrades.html#post3134189
..... Thinking that a CFP pair or set will oscillate if biased hard is wrong my estimation is the totally opposite the harder you bias them the more stable they get ....
I am not playing hard to get but nothing in this life comes for free ... That means that try to put your brains to work first and if you don't manage i will let you know what i have in mind ...I dont like to give fast food solutions Point is for all of us to learn something more not to just fix or tune one amplifier .
Then again if i am the one "hard to get " you are the one that complained about available solutions from the forum members even though 138 ppl read your post and then i actually find kinda insulting calling someone you don't really know "new to hifi repairs? "
Point of the forum is learning not bragging ...
Spent some time around vbe multipliers
Kindest regards
Sakis
I am not playing hard to get but nothing in this life comes for free ... That means that try to put your brains to work first and if you don't manage i will let you know what i have in mind ...I dont like to give fast food solutions Point is for all of us to learn something more not to just fix or tune one amplifier .
Then again if i am the one "hard to get " you are the one that complained about available solutions from the forum members even though 138 ppl read your post and then i actually find kinda insulting calling someone you don't really know "new to hifi repairs? "
Point of the forum is learning not bragging ...
Spent some time around vbe multipliers
Kindest regards
Sakis
Hi Sakis, before you and Nrik start arguing over nothing, I just want to point out, that what he wrote about "..New to Hifi repairs" was not to any specific user, and not as a response to prevoius post. I read as a headline to a general warning to anyone inexperienced that happen to find his bias illustration on the web. So I think perhaps you have misunderstood his intention there.
Btw: I don't actually know Nrik, even if we both happen to be from the same country.
Btw: I don't actually know Nrik, even if we both happen to be from the same country.
I am in two moods about your position:
Firstly I understand exactly your point, and yes - it is better in the long run to learn slowly and by experience.
But when you are in a situation of trying to repair an expensive piece of electronics, you are not really in the mood for some wizard to teach you long term zen-approach ( zen the philosophy, not the amplifier).
Now it is 5 years ago that I had the problem and fixed it myself using my experience, but one year ago a rookie read this thread and blew up his amp, and right now I am emailing with a guy who needs help. I am sharing everything I know and trying to help everyone. I am sorry that you prefer to keep valuable adjustment information to yourself ( if you really are doing that) instead of sharing it with people who needs it. I encourage you to rethink your position based on the values of this forum.
And by the way I have also spent quite some times with VBE's, but as you yourself points out, it is always better to start from the producers own recommendations.
Please understand that I find the tone in this forum often to be lovely informal. That statement was a joke...danish sarkasm...followed by a smiley and a subtle disclaimer ... you misunderstood it. I am sorry - in the future I will try to be more serious and not the funny helpful guy.
Sakis I never meant to insult anyone, that message was not meant for you.
Exactly jvhb
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