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Avondale NCC300 amp project ..

flashgo said:
Here's the next NAP135 prior to the rebuild. Of the original Naim amps, the 135 was always my favorite. There were only a few modest changes on the original board in this photo. When seen side-by-side with the NCC300/SPM1 rebuild, one can appreciate the brilliance of Les' repurposing.

NAP135_2018_0316_beginning.jpg
Click to expand...

One of the contributing factors (I believe) there must be others...:) is that the NCC300 is only regulated at the front end..leaving the raw to do its work only on the outputs, unlike the 135 which regulated as a whole.

The NCC300 has such 'grip and control' and the added bit of magic I feel is texture. Now only a few days in (still early for a complete comparison of NCC220s I know) but the 300s have a warmth and emotion to the presentation that I didn't hear or notice before or others more of it. Its the little things that are there now and weren't before...Im still just running the JR149's for now.

Like you Flash, I do have an issue with my second board which I need to sort when time permits, is a low bias of 1.4v pot at max. Strange as the second board is identical to the first in every component. The first board I had no issue with and could drive it to 2.4v of bias with ease (swapping the 2k7 for a 3k3) and settled with 2.2v as this is were it runs just warm after an hour or two. It'll have to wait now till next week before I can fathom it out.

Graham
 
Les's boards make the original Naim boards look like a DIY job :DLOL its like Ferrari parked next to a Lada
Graham I agree that Les has captured the best of both woulds with the magic of regulation and current mirror on the front end and the raw supply to the output stage that supply's the welly :cool:

Alan
 
Yes Alan couldn't agree more...

40803417391_2435e4d215_h_d.jpg


Work so far on the next pair. I'm using what I have knocking about to build these, bit of a mix and match but I'm sure will be just as good as the first pair.
 
Work looks good from here 'harmuph' ... I always refer to the NASA standards. It's public info.

Never go in raw, especially ... well hopefully you get ny point.
 
I could not find a fault anywhere or rather my expertise in diagnosis is not up to snuff...So I changed all the transistors in the front end anyway.

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Result, the second board is now at 2.2v bias steady state. (more if I want) Offset is 10mv ....All good I thought..:) but when plugged in, it works but with a buzzy distortion. ??
Time to power up the scope and sig gen....The sign wave is perfect up to the front end side 28k but after its horrible...and is the some anywhere on the output side. If its not one thing...errrr.
 
There's not a lot on the output side. You know all this, but hearing it from someone else could trigger a thought:
  1. check for AC on the power coming in or swap with the other channel's PSU
  2. remove the 2.2 & 10uF caps
  3. check for accidental contact with the heat spreader
Good luck!
 
Bingo....

While taking another look...as you do, I double checked my soldering .....what a plonker, a bad joint to an 0R22 (meter all over the place) as they all looked suspect (the 0R22 that is) under the lens...I re flowed with a dab of fresh solder. Power up ..woo hoo... sweet undistorted music. You think you check everything 10 times but you can still miss the simplest things.

Thanks all....Sadly, I'm away for a few days as of tomorrow so won't be able to hear both channels firing at once. (unless I'm up with the lark) :)
 
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I was up with the lark....

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A quick double check that all was as I left it last night. Bias on both boards 2.2v... The offset after a short time (5mins) is near as +-0.1mv at 0.0. on both channels. At first I thought there was another problem cos the offset was so low but a power off-on proved all was well initally rising 10mv then settling down very quickly to around this 0.0mv.

These are stunning amps. Ive been running them for 4 hours now with a pair of heavily modded (work shop) JR149s These could be my last amps. (What a statement). Grunt, grip, control, with loads of texture as Ive never heard before. No tweaks and nothing in the way of special components...Just straight board build.

In a day or two I'll get them into the main system, then I'll be able to access there ability far better.

Many thanks Les.
 
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Well done Graham, I'm well pleased for you.

This design is a league on from the Voyager where the strategy of treating the front
end is akin to giving a pre-amp its own power supply. The limiting factor of the
Voyager is the safe operating area limits of the output devices and whereas the
NCC200s will take the BUV20 series which, on copper heatspreaders will top out
at over 100Watts, the NCC220s are somewhat limited by the non-availability of
high current PNP devices.

I have looked at overall regulation over the years and whilst it offers some degree
of protection for the output devices, the supply of current at every part of the
frequency band is a hit-and-miss affair once the speaker impedance is taken into
account and the intermod products are difficult, if not impossible to remove, possibly
another contributor to the characteristic 'Naim sound'.

The NCC300s have no such hobbling as the paralleled devices easily outstrip the
SOA of a single pair of TO3s and interestingly, fail to exhibit the sonic horrors once
predicted by Naim when using such topology. I point of fact, the newest amps
appear to use series/parallel configuration to achieve their output figures.

It is possible with the NCC300, if I rejig the drive circuits, to up the power
considerably by using output devices in triplicate - 2SA/2SC series for instance.

It seems I have a NAP300 slayer in the stable and that's the beast I'm gunning for.

The earlier NAP135s are in abundance and well loved by their owners who, when
faced with the prospect of stumping up many £thousands for the NAP300, would
rather soldier on with their 135s. These amps were built with totally overkill
power supplies of which only a miniscule fraction of their capability is used
during operation. The build of the amp with the large toroid, big-can caps and
a fan assisted heatsink seems to promise a staggering performance.

Nothing can be further from the truth - it's only a few hops ahead of the NAP250
and as with most amps of the era, fails to get a grip on the popular speakers of
the day such as Linn Isobariks.

Listening to the needs of the market here's a more economical way of upgrading the
135 at a fraction of the factory alternative plus, adding what Graham has described
as texture but retaining the grunt and control - mainly I reckon, the result of the
front end regulator system. One of the first pairs of so-converted 135s are being
auditioned by a specialist in Briks and I'll be posting reactions on here.

I'll watch the project roll on as it gathers pace and with more results yet to come
in it seems this project is going to give many enthusiasts a great deal of pleasure.

Job done.!
 
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I really hope these boards become available. I’ve got four monobloc HackerNaps each with 500vA and 35vA R-cores for output and front end respectively
 
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