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Old 24th June 2012, 10:26 PM   #4571
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Quote:
Originally Posted by DavidT View Post
...The 85 C measurement on the UCD TO220's bothers me, but hey, my various UCD amplifiers have survived 6 summers just fine...
Everybody and his cousin mounts TO220s without heatsinks, in spite of the 85% or so reduction in rated dissipation. So the heatsink police won't come knocking at your door... this time.

Thanks for posting these measurements. You can use a q-tip to press the probe tip against a surface.
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Originally Posted by serengetiplains View Post
Beautiful casework, JT.
No kidding! Got to hide those photos from the children!

Last edited by Sam Lord; 24th June 2012 at 10:31 PM.
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Old 25th June 2012, 02:36 AM   #4572
DavidT is offline DavidT  United States
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Now for the electrical tests.

The UCD400's performed with aplomb as they normally do, however the NC400's show a ringing of about 4 cycles @ 62.5 kHZ on a 10kHZ square wave with an amplitude close to the carrier amplitue of 300mv rms. It shows a resemblance the to ultrasonic transformer ringing in some (famous, shh )tube power amplifiers...

Other than the ringing, the NC's perform as expected. The ringing is not audible to me in a short test with Joshua Bell playing the Tchaikovsky. The amps present a very clean sound with mesmerizing detail...

I tried to upload photos to show this, but no joy, as this message came up:

"Your submission could not be processed because a security token was missing."

Does someone know a work-around to upload photos?

Also, is it normal for NC's to ring?


Regards,

DavidT
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Old 25th June 2012, 06:22 AM   #4573
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Bruno explained it above as corresponding to a local minimum in the loop gain. See post #1014.

Mesmerizing detail, I like that.
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Old 25th June 2012, 07:33 AM   #4574
DavidT is offline DavidT  United States
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Hello Serengetiplains,

Thanks, what a relief. I was not looking forward to going round-and-round on that issue...

That BP post was so many moons ago in December, that I forgot about that 62 kHz wrinkle...I have been enjoying this adventure in real time and started building around January... BTW, my saucer-sections are from the second build, I believe.

I can also add that the detail retrieval is trancendent to me because I do get flashback-glimmers of the feelings of my time as a youth as 1st stand viola. THAT is mesmerizing....Bravo Bruno!

Thank-you again,

DavidT
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Old 25th June 2012, 08:23 AM   #4575
pos is offline pos  Europe
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Here is Bruno's quote from #1014 (to save some searching) :
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Originally Posted by Bruno Putzeys View Post
The frequency response plot is given in the data sheet. It shows a ripple around 60kHz (corresponding to a local minimum in the loop gain, see the white paper) and for no reason other than ordinary time-frequency duality this means that the impulse response (and its integral, the step response) must have a corresponding wrinkle as well.

DavidT, with what load did you measure the ringing?
Looking at the ~60khz glitch of the response curve in the data sheets it looks like it gets lower when the impedance rises (and it is also much lower in the NC400 compared to the NC1200).
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Old 25th June 2012, 09:54 AM   #4576
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Ncore consists of a simple self-oscillating amp (inner loop) with an outer loop wrapped around it, whereby a distortion-free linear model tries to model the closed-loop response of the inner loop as closely as possible and whose output is subtracted from the feedback before it's fed into the outer loop. This way the outer loop sees only the difference between the two (i.e. distortion). As a necessary byproduct of making a lot of extra loop gain in the audio range, the outer loop introduces introduces the loop gain minimum near 70kHz and hence potentially ringing. The closer the model matches the inner loop, the less signal the outer loop sees and hence the smaller the ringing.

As it stands the model accuracy is limited by component tolerances and on the output impedance of the inner loop. So if you were to take a family of curves on a whole lot of NC400's you'd find that the shape of the "blip" varies from unit to unit, with some not showing any at all at 4 ohms. Those units have no ringing either (at least at 4 ohms).

A more sensible way of looking at it is output impedance, since the model gets no feedback from the output. There, you won't see much variation across units. All have a maximum at sixty-something kHz. This peak corresponds to the Z of the output inductor divided by one plus loop gain. It's a cosmetic disadvantage of Ncore vs UcD, which has a famously tight squarewave response. It just goes to show that squarewave response only says so much about sound quality, which is not much
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Old 25th June 2012, 03:15 PM   #4577
yetis is offline yetis  United States
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Hi,

Being as I don't seem to get many answers emailing the HQ, can anyone please let me know what sort of wait time they have experienced after sending back their amps for adjustment? I am well into month number two at this point, having been assured they would ship last Monday, after much prodding. I am so glad I spend the $ to get them to Ncore quickly...
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Old 25th June 2012, 03:23 PM   #4578
jtwrace is offline jtwrace  United States
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Quote:
Originally Posted by yetis View Post
Hi,

Being as I don't seem to get many answers emailing the HQ, can anyone please let me know what sort of wait time they have experienced after sending back their amps for adjustment? I am well into month number two at this point, having been assured they would ship last Monday, after much prodding. I am so glad I spend the $ to get them to Ncore quickly...
What kind of adjustment? I didn't know that Hypex had a Chriopractor on site.

DC Offset?
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Old 25th June 2012, 03:28 PM   #4579
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Quote:
Originally Posted by yetis View Post
Hi,

Being as I don't seem to get many answers emailing the HQ, can anyone please let me know what sort of wait time they have experienced after sending back their amps for adjustment? I am well into month number two at this point, having been assured they would ship last Monday, after much prodding. I am so glad I spend the $ to get them to Ncore quickly...
Please send me all info (info at hypex dot nl), some guys are on holiday now...
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Old 25th June 2012, 07:19 PM   #4580
DavidT is offline DavidT  United States
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Sam Lord: "You can use a q-tip to press the probe tip against a surface."

Nice idea, thanks!


pos: "DavidT, with what load did you measure the ringing?"

8.1 ohm (via Fluke 179), 10.9 uH (via Extech LCR 380193), 50W resistor, both channels driven into two resistors at various levels up to clipping.

8 ohm is the average measured impedence of my SS 18W/8531-g00 mid-woofer centered around 330 Hz, which appears to be the rough center of power in most symphony music. Of course, it does dip to around 5 ohms around 200 Hz...

Regards,
DavidT
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