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Avondale NCC300 amp project ..

Hi Alan,

I don't think that will help. Q6 is providing bias voltage for the drivers and the o/p devices (and the drops across the 0.22Rs).
Like most people I have Q6 embedded in the T section alu. This means that Q6 is only (directly) correcting for the o/p devices, it cannot correct for the driver temperatures. This means that the hotter the drivers get, the more that Iq increases. In my stacked arrangement, airflow for the lower board driver heatsinks is impeded by the upper board.

It runs perfectly fine with no lid. I've had it playing for the last hour and everything is below ~40C.

She is just going to have to stay topless, unless she gets a complete new outfit! :)

I could fix it by:
- Mounting the drivers on the T section (there are already some holes which look like they could be for this purpose)
- Some sort of diode arrangement which includes sensing the driver tr temp (see http://leachlegacy.ece.gatech.edu/lowtim/2ndstage.html)
- Redirecting some air to the driver heatsinks on the lower deck
- Full reboxing and ditch the stacked arrangement (although I prefer compact amps).
 
Ah sorry David by your pictures I thought you still had your Q6 in its standard position, if they are already on the Tee section then that's fine
For me though you cant beat the Modushop dissipante cases 3U x400mm and you can get everything in one box with an amp board on both heat sinks and no fan
Alan
 
Yes, sorry Alan, the location of TR6 is masked by the wiring in my pics. Actually you can just see the legs of the TO92 poking into the T section if you look very closely.

I did expect some bugs with this build, as I've not done a fan cooled amp before.
BTW, no criticism of Les's boards is implied here!! I chose to use them "incorrectly".
I'm rather enjoying this nice little challenge to refine the thermal performance. As it is now, I am 99% certain my amp will not suffer from thermal runaway and that no parts can be operated at anything like a problematic temperature. The thermal trip, which is intended to protect against fan failure, will save the day if things did go badly wrong.

Having slept on it, I think I will try some ventilation holes in the bottom of the case under the drivers, to see if I can encourage a bit of convection. Les included some ventilation holes in the PCB to assist with this.
If that doesn't have sufficient effect then I will add a larger fan and allow it to "leak" around the sides of the heat pipe, Ironically I spent considerable time making an adaptor plate for the existing small fan to direct all the airflow into the rectangular cross section heat pipe. Overall I am very happy with the fan cooling, my tiny 7V fan run at 4.5V provides very little airflow and is almost silent but keeps the output devices at "comfortable" temperatures for all conditions of normal use.
 
He said many times he will not sell boards for this amp you can only get it ready built.
 
No fully built amps,have a look at his Facebook page he has explained this many times.
 
At the end of the day its Les's design and his call, even a built up pair is and excellent set of starting blocks for a superb set of amps :cool:

Alan
 
At the end of the day its Les's design and his call, even a built up pair is and excellent set of starting blocks for a superb set of amps :cool:

Alan
I'm not sure he's even selling built boards at the moment. AFAIK he's flat out doing fully fitted Naim upgrades.

BugBear
 
In case anyone is interested here is a plot of the distortion profile of one channel of my NCC300 running at approx 1W into a 10R resistor.:

NCC300-Left-at-2-983-V-into-10-R.jpg


TBH, there is nothing unusual here - perfectly decent performance.

For comparison, here is the same for my 50W JLH Mosfet amp:

JLH-MOS-Sikorel-Left-at-2-879-V-into-10-R.jpg


Perhaps the only point of note is that I used a non-standard grounding scheme in the NCC, where I moved the speaker return/star ground to one of the faston terminals on the pcb for each channel. Seems to have done no harm judging from the pretty respectable(ly low) 100Hz peak.
The JLH is a stereo amp, so it a bit harder to keep the supply ripple out.

For reference my Rotel RB850 has the 100Hz peak at -80dB (with the 1KHz signal at the same -12.6dB)
 
In case anyone is interested here is a plot of the distortion profile of one channel of my NCC300 running at approx 1W into a 10R resistor.:

NCC300-Left-at-2-983-V-into-10-R.jpg


TBH, there is nothing unusual here - perfectly decent performance.

For comparison, here is the same for my 50W JLH Mosfet amp:

JLH-MOS-Sikorel-Left-at-2-879-V-into-10-R.jpg


Perhaps the only point of note is that I used a non-standard grounding scheme in the NCC, where I moved the speaker return/star ground to one of the faston terminals on the pcb for each channel. Seems to have done no harm judging from the pretty respectable(ly low) 100Hz peak.
The JLH is a stereo amp, so it a bit harder to keep the supply ripple out.

For reference my Rotel RB850 has the 100Hz peak at -80dB (with the 1KHz signal at the same -12.6dB)
Could you describe your measurement setup please? I would like to be able to do something similar.

Ta.
 
Anyone intereted in comparing the distortion spectrum of a NAP200 clone with the NCC?:

NAP200-C-Left-at-2-860-V.jpg
 
Anyone intereted in comparing the distortion spectrum of a NAP200 clone with the NCC?:

NAP200-C-Left-at-2-860-V.jpg

Interesting comparison - the headline THD numbers are actually marginally better on the NAP200 clone but the products below 1KHz are significantly better on the NCC300 (and the JLH). I'm no expert in interpreting these plots but I guess these are intermodulation products?
 
Well I've said it before, more than once, and I'll say it again.... this is a stupid hobby!!!

I have built and modified more amps than I care to remember over the last 30 years. I have owned NCC200s twice, wondering each time what all the fuss is about.
Alan (337) brought his NCC300 round to my houe about a year ago and it sounded pretty good - slightly clearer than my Leach amp, but I felt my system needed further optimisation to get the tonal balance to my taste.

Some time later, Les kindly offered me a set of boards. It took me ages to get round to building them and as per the last few pages I decided to do my own implementation.

Some might have noticed that I have been very quiet concerning the sound of this amp. That's because I was far from impressed. I wondered if the issues I was hearing were because I had implemented a different grounding scheme - and yet the measurements indicated this was not an issue - or the titchy smoothing caps compared to many builds (i also don't like inductors anywhere near my supply rails).
The amp languished on the floor for long periods of time. I kept trying it to see if it had miraculously mended its sound quality, but after about half an hour reverted to other amps. I got to wondering if I should dismantle it and build something better in the chassis. Then a few days ago, I though it sounded rather decent and enjoyed listening to it for a couple of hours. Then it changed!!!!

And OMG has it changed. What on earth has happened? It sounds absolutely wonderful now.
This amp is a masterpiece.

Thank you Les!!!
 


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