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QUDOS - the brilliant new amplifier boards from Avondale

I know a few of you built NCC200s with BUV20 output devices so has anyone done a comparison between that and the NCC220?

I have ncc200's with buv20 and copper hear spreaders. Never heard the ncc220 so cant comment on that comparison. Pity there is npo pnp equivalent of the buv20:( or not one i know of anyway.
 
Hfe = 4 is very low. So at (say) 4 amps collector current, base current is 1 amp? Wow. (Not in any way disagreeing with Les, just surprised Hfe is that small - data sheet says ~55 typical @ 1amp Ic with Vce = 4v)
 
I'd presume to measure hfe properly, you'd have a set up that allows you to adjust the bias (e.g. combination of a fixed & variable resistor) to give a known collector current, then measure the voltage across the fixed resistor to get the base current. (Vce should not be critical, but I also assume you'd pick a collector resistor so that at the desired Ic, it sets Vce close to a known value.) Having a collector resistor also means you need only one multimeter, as you can get Ic from the current across this. But I'm sure you know all of this.
 
Built my Qudos today. Due to a faulty resistor which set fire to one of the NCC boards I needed to contact Les and rebuilt the charred board. Tempted, I also decided to take a plunge into the Qudos. No regrets. It sounds great -better than any of my power amps. I dared not bias them beyond 100mA as I I dropped the boards into my PFM Voyagers monos and the case has no external heatsink fins. Besides,they are customarily powered at front end via VBE at around 50v. Should I up the bias up to 140? Shall I get sufficient heatsinks first? It was easy to follow Les's schematics. I indulged in some exprensive resistors from HIFICollective. I'm hopeless at this.
 
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I run my NCC220 boards at 108mA bias with the front end running from Les's VBE board at 12mA making a total of 120mA. I think that's how it should be calculated.

My cases are aluminium with no external heatsink fins and yes the cases do get warm, but not hot .
 
When I got my Qudos boards from Les the printed bias instructions quoted 140ma total quiescent current so that's what I used.
They sound great!
As Les said when I ordered them "if you listen at moderate levels" - which I think I do, whatever my wife says! - "you might be listening entirely in class A".
The case does get a bit warm so I've taken Les's advice to turn it off when not listening and turn it on 30 minutes before settling down (when the wife's out!) for a good listen.
The heatsinks are the usual heat spreaders bolted to the chassis of a NAP180.
 
When I got my Qudos boards from Les the printed bias instructions quoted 140ma total quiescent current so that's what I used.
They sound great!

How strange. My Les supplied Qudos schematic shows a 120mA bias setting
 
"How strange. My Les supplied Qudos schematic shows a 120mA bias setting"
I received my NCC220s early February (just in time for my birthday - thanks Les!) and the schematic on the cd quoted 120ma - "do not exceed this"!
A printed sheet showing the bias setting procedure quoted 140ma.
That's what I've used.
 
What voltage swing can I expect across tp3/tp4? I have 1.63V right at the bottom end of the trimmer and can go over 3V towards t'other end. There are no output devices fitted yet and the supply rails are 45v-0-45v whilst on the bench.
 
What voltage swing can I expect across tp3/tp4? I have 1.63V right at the bottom end of the trimmer and can go over 3V towards t'other end. There are no output devices fitted yet and the supply rails are 45v-0-45v whilst on the bench.

Those readings sound OK to me, set each board to the lowest figure and then adjust them up when you have the output devices installed.
 
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