I own or have access to a large variety of high end amps. In comparison, the NAP250 is surprisingly capable, despite it's technical shortcomings. The regulated supply does indeed limit its bass and dynamics and the tantalum caps are certainly not what i would use, but in a sympathetic system this amp is really capable. Wish i knew why.
Most of vintage Japanese Amplifier of the 70's+ had the tone control based on the feedback node Now days this is presumed as a bad practice and tone controls are made better ways. Though the particular "mistake" or "bad practice " if load was easy and cables proper an short , produced unbetable sonics not easy to be produced by accurate amplifiers of today .
I belive that those sonics include distortions and often oscilations in the signal but somway somehow that was very frindly to listen to
Probably the identity of the NAIM and the way its made produces a particular sound that might sound well no matter what mistakes we see in the circuit and think that is wrong .
seems to me that a better implementation of the same circuit will sound by far beter .
Kind regards sakis
terrible things ....
when you design an amplifier that is based on a regulated power supply that regulates both voltage and current what is the point of adding a VI limiter also ?
It could work much better with unregulated psu and a Vi limmiter ...
Guys dont start a war on me now ....This just an opinion ...
I hope Salas is not emailing the 2000 Naimists against me as we speak....
when you design an amplifier that is based on a regulated power supply that regulates both voltage and current what is the point of adding a VI limiter also ?
It could work much better with unregulated psu and a Vi limmiter ...
Guys dont start a war on me now ....This just an opinion ...
I hope Salas is not emailing the 2000 Naimists against me as we speak....
Although its quite a while back I've last time listened to the NAP 250 I'm still pretty sure that they can compete to many nowadays designs.
The sound pattern they are/ were famous for will most certainly be destroyed if you don't know nor like the ancient Naim sound and nevertheless are carrying out what you think should be considered as "upgrades".
There is a "balance" in each and every mix of sound patterns *any* gear presents, that easily can move from charming towards unamusing.
🙂
Michael
The sound pattern they are/ were famous for will most certainly be destroyed if you don't know nor like the ancient Naim sound and nevertheless are carrying out what you think should be considered as "upgrades".
There is a "balance" in each and every mix of sound patterns *any* gear presents, that easily can move from charming towards unamusing.
🙂
Michael
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As I already said - there is way more to "sound" than what you present as technical basis for your verdicts
🙂
Michael
no probs ....this is a place to share opinions ...everyone has one ...
on the other hand the "technical basis" many reasonable things are said above
spare me a moment though ...
I have no problem to accept the design as an aspect that also means that i dont have to like it also ..
down to theory one amplifier with unregulated power supply will suffer from problems only and ony when the demands of power are high ... In casual listening i dont think that a regulated psu is a benefit but that also is just an opinion
On the contrary in low power and demanding music or load the same regulated supply probably will not provide enough current to perform properly ( since also the specific power supply will aaso regulate or limmit if you want, current )
similar things are said from Salas but also in the NAim forums where people noticed or compaired things like that .... obviously those people placed there ...their opinions ..
so all the above is just a question of aspect ...
kind regards sakis
on the other hand the "technical basis" many reasonable things are said above
spare me a moment though ...
I have no problem to accept the design as an aspect that also means that i dont have to like it also ..
down to theory one amplifier with unregulated power supply will suffer from problems only and ony when the demands of power are high ... In casual listening i dont think that a regulated psu is a benefit but that also is just an opinion
On the contrary in low power and demanding music or load the same regulated supply probably will not provide enough current to perform properly ( since also the specific power supply will aaso regulate or limmit if you want, current )
similar things are said from Salas but also in the NAim forums where people noticed or compaired things like that .... obviously those people placed there ...their opinions ..
so all the above is just a question of aspect ...
kind regards sakis
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Yeah - and as those Amps have had quite a community of fans, this tells at least something .
The no-nonsense black design of that uninspired boxes are hardly been the root cause...
🙂
Michael
The no-nonsense black design of that uninspired boxes are hardly been the root cause...
🙂
Michael
quted from the acoustica.org enjoy
Regulator board descriptions
Pretty simple discreet power opamp design and essentially very crude- fig 6. Based on an old old design by Anthony Holton if an old schematic and notes don't deceive me. Doesn't take much to jazz this up e.g. decent current source at the base of the long tailed pair, decent voltage reference, filtering and internal regulation etc. This was done by someone a few years back (current source anyway) who made favourable comments of the results. Reports are generally that the regulator is responsible for the slightly 'darker' and more detailed sound of the old 250 upwards but also damped the dynamics somewhat? It also has current limiting circuitry which puts a fat bit of impedance (0.1ohms) on the power rails and is generally not a good idea sound wise imo, which might have been responsible. Also its apparently a bit of a noisy bugger so not that great performance though it probably cleans up the rails a tad.
Regulator board descriptions
Pretty simple discreet power opamp design and essentially very crude- fig 6. Based on an old old design by Anthony Holton if an old schematic and notes don't deceive me. Doesn't take much to jazz this up e.g. decent current source at the base of the long tailed pair, decent voltage reference, filtering and internal regulation etc. This was done by someone a few years back (current source anyway) who made favourable comments of the results. Reports are generally that the regulator is responsible for the slightly 'darker' and more detailed sound of the old 250 upwards but also damped the dynamics somewhat? It also has current limiting circuitry which puts a fat bit of impedance (0.1ohms) on the power rails and is generally not a good idea sound wise imo, which might have been responsible. Also its apparently a bit of a noisy bugger so not that great performance though it probably cleans up the rails a tad.
now ...
according to this schematic that looks exactly like my amplifier http://www.acoustica.org.uk/t/naim/poweramp_pix/NAP250 schematic.jpg
i found the input capacitor to be of 470pf which seems to me quiet high for 22K
then again in the VI limiter area the two base resistors that will be R9-8 should be 47R and both the same .. actually the P side resistor is 100 R and the N side resistor is 47 ... That will result that in a limit condition P side will be limited more than N side any reason for that ???
now that is odd and any way the VI limmiter is completely removed but any comments on that could be usable to listen .
Keep in mind that eventhough amplifier looks repaired before the specific resistors looked mammy since we all know very well that in blown amps normally VI limmiters survive .
Kind regards sakis
according to this schematic that looks exactly like my amplifier http://www.acoustica.org.uk/t/naim/poweramp_pix/NAP250 schematic.jpg
i found the input capacitor to be of 470pf which seems to me quiet high for 22K
then again in the VI limiter area the two base resistors that will be R9-8 should be 47R and both the same .. actually the P side resistor is 100 R and the N side resistor is 47 ... That will result that in a limit condition P side will be limited more than N side any reason for that ???
now that is odd and any way the VI limmiter is completely removed but any comments on that could be usable to listen .
Keep in mind that eventhough amplifier looks repaired before the specific resistors looked mammy since we all know very well that in blown amps normally VI limmiters survive .
Kind regards sakis
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Hi Sakis.
In the schematic the input capacitor is 330pF (?)
Are you going to retain the the value of the TR1 collector resistor (=1000 Ohm)? This leg passes more than twice the current of the TR2 leg.
Also, most DIYers have not included the VI limiter.
Regards
In the schematic the input capacitor is 330pF (?)
Are you going to retain the the value of the TR1 collector resistor (=1000 Ohm)? This leg passes more than twice the current of the TR2 leg.
Also, most DIYers have not included the VI limiter.
Regards
correct in the schematic the capacitor is 330pf and looks quiet reasonable but in my amplifier is 470 pf and also looks mammy made
i am working as we speak
i allready used closelly matched BC 546 and thermally coupled as seen in the pictures ... just a few minutes ago measured ofset and that will be 9mv for left amplifier and 5 mv for right amplifier
( of course that happend after i tuned rails regulators to 40.1+40.1 volts since they had a diference of almost 1.5 volts )
i will look at the resistor issue and let you know
more to come in a while
kind regards sakis
i allready used closelly matched BC 546 and thermally coupled as seen in the pictures ... just a few minutes ago measured ofset and that will be 9mv for left amplifier and 5 mv for right amplifier
( of course that happend after i tuned rails regulators to 40.1+40.1 volts since they had a diference of almost 1.5 volts )
i will look at the resistor issue and let you know
more to come in a while
kind regards sakis
amp is up for about 30 minutes and ofset remains stable
though after half an hour amplifier is not warm at all ( temp in the shop is 22 due to heavy airconditioning ) so i suspect underbias i will see that also and proceed with the rest ....
though after half an hour amplifier is not warm at all ( temp in the shop is 22 due to heavy airconditioning ) so i suspect underbias i will see that also and proceed with the rest ....
Despite the NAP250 circuit not being the most advanced, it does sound nice. And they do seem to last a long time - probably because they are beautifully built. Having said that, I've been mulling the idea of replacing the innards of mine with more modern boards...
Hi Sakis,
there is no Naim amp that gets warm on the touch just by letting it switched on, especially not at 22 degrees ambient temperature. Naims work with a low bias current setting. No need to increase this.
One more thing. Please let us all stay at least a bit subjective when it comes to sound. For many people, Naim amps have a certain kind of musicality, drive and an overall pleasant character. These guys are often more involved with some music made at the time their amps have been made.
Other people are getting more touched by a sound that is more precise, clean and with maximum resolution. A matter of taste. No need to claim "this amp sounds good" or "that amp doesn't".
Regards!
Martin
there is no Naim amp that gets warm on the touch just by letting it switched on, especially not at 22 degrees ambient temperature. Naims work with a low bias current setting. No need to increase this.
One more thing. Please let us all stay at least a bit subjective when it comes to sound. For many people, Naim amps have a certain kind of musicality, drive and an overall pleasant character. These guys are often more involved with some music made at the time their amps have been made.
Other people are getting more touched by a sound that is more precise, clean and with maximum resolution. A matter of taste. No need to claim "this amp sounds good" or "that amp doesn't".
Regards!
Martin
Its not only due to low bias that NAIM amps stay cool, its also due to the heat dissipation system chosen.
Those "precise, clean and with maximum resolution" certainly wouldn't be attributes that I would exclude from characterization of NAIM presentation.
Those NAIM amps may add some SS coloration not everybody is happy with - but in terms of all the other high end audio buzz words - no concerns !
And again - I doubt that the intended "upgrades" can do anything to overcome that specific SS colorations.
More likely they will result in destroying a long grown and refined sonic balance.
IMO one would have to dig waaay deeper to make any significant progress sound wise.
🙂
Michael
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