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Old 28th June 2013, 02:16 PM   #6961
zhai is offline zhai  Denmark
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I have a dual mono nc400 (+2x smps600) box, and I have a couple of questions. A while ago, one of the channels started to exhibit some strange behavior. The volume would drop, and simultaneously either white noise or ~100-200 Hz noise plus high pitched noise would occur. This happens also if the source is turned off. Also, this seems to happen more and more often. Has anyone else had this happen?

I haven't yet tried to swap the modules around to isolate the cause. Will probably do so soon.

Another question: seeing as I'll probably have to send the module (+ probably also smps) of the offending channel to Hypex for repair, will I be able to just put both speakers on the good channel while I wait for the repair? If so, how should I make the connection? I have 8 ohm speakers.

I already sent these questions to hypex, but I guess they've shut down for the weekend and I'm slightly impatient, hope someone can help!
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Old 28th June 2013, 05:02 PM   #6962
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Default wiring speakers in series is safer than wiring in parallel

Quote:
Originally Posted by zhai View Post
I have a dual mono nc400 (+2x smps600) box, and I have a couple of questions. A while ago, one of the channels started to exhibit some strange behavior. The volume would drop, and simultaneously either white noise or ~100-200 Hz noise plus high pitched noise would occur. This happens also if the source is turned off. Also, this seems to happen more and more often. Has anyone else had this happen?

I haven't yet tried to swap the modules around to isolate the cause. Will probably do so soon.

Another question: seeing as I'll probably have to send the module (+ probably also smps) of the offending channel to Hypex for repair, will I be able to just put both speakers on the good channel while I wait for the repair? If so, how should I make the connection? I have 8 ohm speakers.

I already sent these questions to hypex, but I guess they've shut down for the weekend and I'm slightly impatient, hope someone can help!
Whilst your speakers are 8 ohm nominal, they may well drop down to a 4 ohm impedance at some frequencies. If you wired them in parallel then the impedance would be 2 ohms.

Better play safe and wire them in series so the nominal impedance will be 16 ohms.
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Old 7th July 2013, 04:56 PM   #6963
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Stupid question, are these modules one or two channel, would I need to buy two for stereo?
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Old 7th July 2013, 04:59 PM   #6964
Julf is offline Julf  Europe
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Quote:
Originally Posted by Ali Tait View Post
Stupid question, are these modules one or two channel, would I need to buy two for stereo?
As discussed 2 pages back, they are mono, so you need 2 for stereo.
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Old 7th July 2013, 05:00 PM   #6965
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I'd just waded through the first 200 pages of this thread, got tired of looking for the answer

Thanks.
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Old 7th July 2013, 05:07 PM   #6966
ro9397 is offline ro9397  United States
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Quote:
Originally Posted by EuroDriver View Post
Whilst your speakers are 8 ohm nominal, they may well drop down to a 4 ohm impedance at some frequencies. If you wired them in parallel then the impedance would be 2 ohms.

Better play safe and wire them in series so the nominal impedance will be 16 ohms.
The amp described by the poster is safe to 1 Ohm load (no power rating @ 1 Ohm, rated 600W @ 2 Ohms). Bruno replied re. Ncore driving the huge Apogee full range ribbon with 1 Ohm minimum impedance.

Compared to 4 Ohm 16 Ohm results in less heat (1/4 current requirement), lower distortion magnitude, less offensive distortion components, and 1/4 current capacity for the speaker wire. The only down side is 1/4 the power of 4 Ohm.
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Last edited by ro9397; 7th July 2013 at 05:20 PM.
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Old 7th July 2013, 05:29 PM   #6967
Julf is offline Julf  Europe
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Quote:
Originally Posted by ro9397 View Post
Compared to 4 Ohm 16 Ohm results in less heat (1/4 current requirement)
True, but only because of:

Quote:
The only down side is 1/4 the power of 4 Ohm.
(and of course the heat generated when driving 16 ohm won't be 1/4 of the heat generated when driving 4 ohm, so in that sense you lose more in available power (in proportion) than you gain in less heat).

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Originally Posted by ro9397 View Post
lower distortion magnitude, less offensive distortion components
Curious about what that is based on.
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Old 7th July 2013, 05:56 PM   #6968
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Quote:
Originally Posted by EuroDriver View Post
Better play safe and wire them in series so the nominal impedance will be 16 ohms.
Avoid this for bass speakers unless they are mechanically coupled. Awful damping and strange results around resonance, specially with bass reflex.
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Old 7th July 2013, 08:08 PM   #6969
ro9397 is offline ro9397  United States
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Quote:
Originally Posted by Julf View Post
True, but only because of:



(and of course the heat generated when driving 16 ohm won't be 1/4 of the heat generated when driving 4 ohm, so in that sense you lose more in available power (in proportion) than you gain in less heat).



Curious about what that is based on.
IIRC independent test by Audio Circle member "mgalusha" revealed NC400 distortion increased and distortion components worsened (both very little) with falling load impedance. Sorry no link. Bruno's spec sheet shows only 2 Ohm load for THD+N...I presume readers are to infer 2 Ohm is worst case scenario and all higher impedance loads yield better results.

AFAIK this is universal SS rule. Please correct if wrong. Audibility obviously varies per many variables.

My system employs two high resolution stand mount monitors per channel, each monitor is 8 Ohm nominal, 5.3 Ohm minimum. I auditioned at length NC400 mono driving two loads identical except for 2.7 Ohm minimum (parallel) vs. 10.6 Ohm minimum (series...speaker wire was the only other variable...in every other respect identical loads...I adjusted the preamp for 6 dB gain difference in the amp).

Trying to avoid going OT, but this is noteworthy (I discussed it with Bruno): With too small AWG (larger numeral) the latter performed better. With appropriately large AWG the former worked better. Results were not marginal, but rather very audible. Even with monitors active HP crossed 2nd order @ 80 Hz.

NC400 has huge current capacity greater than anything else lb for lb. Some applications (low Z) require much larger AWG than expected to hear the amp perform properly.

For speaker wire on the 2.6 Ohm load I used short runs of high quality fine strand copper 4AWG (car audio power cable, super soft touch rubber jacket, highly pliable) with a parallel 30AWG wrapping wire to compensate for high self inductance.
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Last edited by ro9397; 7th July 2013 at 08:14 PM.
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Old 8th July 2013, 03:40 AM   #6970
Julf is offline Julf  Europe
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Quote:
Originally Posted by ro9397 View Post
IIRC independent test by Audio Circle member "mgalusha" revealed NC400 distortion increased and distortion components worsened (both very little) with falling load impedance. Sorry no link.
I see you edited your response. I have seen mgalusha's FFT plot for 8 ohm, but not ones showing lower impedances.

Quote:
AFAIK this is universal SS rule.
I am always sceptical towards "universal" rules. What, in your view, would be the cause for higher distortion (and especially for a different distortion spectrum) as current increases (in a class D amp such as nc400)?

Quote:
Trying to avoid going OT, but this is noteworthy (I discussed it with Bruno): With too small AWG (larger numeral) the latter performed better. With appropriately large AWG the former worked better.
I find AWG a very confusing measure - partly because it is *american* wire gauge and incompatible with any other measuring systems, partly because it is an arbitrary scale, but mostly because it is an inverse scale - smaller numbers mean thicker wires. Wire thickness (be it in inches or mm) or area (mm2) are much better descriptors.

I agree that the nc400's benefit from low-resistance (thick) wires, and I do have a bit of a concern with some of the thinner "audiophile" wires.

Quote:
NC400 has huge current capacity greater than anything else lb for lb. Some applications (low Z) require much larger AWG than expected to hear the amp perform properly.
I agree. I am using 4 mm (equivalent to AWG 6) for mids and tweeters, and 6 mm (AWG 2.5) for the woofers in my system.
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