NAP200 Clone materials

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Hi webfors, if it hasn't already been said a few times, welcome to DIY Audio :) Yes, apparently the all-important VAS transistors are even the correct type and that goes quite some way toward Naim sound quality - something none of the older NAP 140 clones ever came anywhere near to. However, this clone's schematic is simplified and doesn't really follow the NAP 200 any more than other NAP models from the 90s on. There are no phase correction networks at the base of the driver transistors and there is also the matter of speaker relays in lieu of the VI limiters. The biggest loss is that the magnificent NAP PCB is dumbed down and squashed into the old NAP 140 layout originating in the 1970s. I'm not sure that's a good thing.

I'm aware than some folk remove the limiters and networks on principle but that's not as useful as exploring the differences and deciding for yourself. I've heard NAP models with and without limiters and for most models, I'm quite happy and safe with the original amplifiers, as designed and manufactured. The NAP 200 actually has dual-slope type limiters that if checked out properly, perform much better than the original types and are silent even at moderately high listening levels. Relays are seldom a good idea for audiophile sound quality unless you spend a lot of money on them or, at lower cost but much better than the alternatives - go solid state, Mosfet.

The single pair of 2SC5200/A1943 output transistors may be good quality at low cost but they won't safely make the NAP 200's 100W/4R grade. Perhaps this clone would rate as a NAP160 though the sound may not be close enough to call it any kind of NAP clone.

Good points? low cost, smaller, easier to assemble. No mention is made of the of the power transformer so you may have to buy the complete and finished amp as a retail purchase and forget the DIY opportunity.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Hi zambox, congratulations on your finished clone. Unfortunately, I don't think you'll find any available specification for the internal operating temperature of Naim hi-fi power amplifiers of this general type and original design era.

This is mainly because within the amplifier's maximum power limits and recommended ambient temp. limits, the temp. is designed to vary safely, according to the signal level and safe output power limits. In the NAP models, the control of the operating temperature is initially set by the ambient temperature, then the heatsink cooling (that's the 2U, thick aluminium enclosure), the bias current servo controller and finally the VI limiter circuit for the output stage. Together, these maintain the temperature within a proven safe limit.

I think it is likely that the engineers at Naim nowadays, do have temperature specs for testing their products, since global markets may require it for safety reasons. However, I doubt that we are going to be told what they are or how they are measured and used for that purpose.
 
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zambox

Member
2013-01-23 1:11 pm
Hi Ian. Thanks for your response and sorry for all the typos in the previous messages (I switched to a new phone, New keyboard 😁).
Are you telling me that if the heating dissipator I'm preparing is not enough the amp will protect itself when the temperature reach a limit?
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
That may be so in some designs but reliable protection is not quite so simple. As said, there are several controls operating together to keep the amplifier thermally stable but limiters (assuming they have not been removed or disabled) are there to prevent damage due to abuse, overloads and accidents like shorted speaker leads. A heatsink is included to dissipate the heat produced normally, up to the maximum rated power but in original Naim amplifiers, the heatsink is also the chassis or case and you can see how large that thick 2U rack case is from the pics.

Usually, only large amplifiers, such as those for electronic instruments and public entertainment, have a thermal switch and fan controller that cools the amplifier as needed or shuts it down as a last resort. Domestic amplifiers avoid that abrupt type of safety switch and fans for obvious reasons. The VI limiter circuit or a similar control is there instead, to ensure that if you do overdrive the amplifier perhaps even for only a few milliseconds, whether or not it has time to become hot, the output will be reduced silently, to a safe level for the duration of the overload.
 

ochabot

Member
2014-08-29 7:39 pm
Anybody able to help me, 2 100 ohm resistor burn when I start up my Naim clone... Just after my first test...
 

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Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
The board appears to be a copy of the original so I assume the circuit is as the original NAP200. There are now a lot of "wannabe" NAP 200 clone kits that are nothing like any Naim product so we need to be certain what we're looking at.

The 100R resistors are connected across the output transistor base-emitter junctions so if they are burnt, it suggests the output current was flowing from the drivers through the resistors rather than the output transistors - perhaps because they have failed (shorted). This could have been caused by a few possible mistakes with speaker, output connector wiring etc. but I don't see any insulation pads or mica under the output transistors! - maybe there is insulation (note that the transistor backplate is also the collector) but I can't tell what is really the situation without a continuity or resistance test.
Shorting the collectors of the transistors to the chassis there would cause a big problem and blow some components for sure.
 
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