Buckeye NC502MP 8-Channel Amp Review

[IAtaman]

Wow look at that Power Cube measurement. The most perfect one I've seen. All you folks with "difficult to drive" speakers need this. I wonder if connected to my Soundlab ESLs if the near/sub 1 ohm impedance with very high phase angle near 20 khz would cause it to shut down?

You have the brilliancy control turned to max?

 

[TNT]

The load box is not designed for this purpose. It limits you to max and peak power measurements in Audio Precision. I can bypass that and test it for distortion but that is "off label" use for the box. My own dummy loads are used for precision measurements of distortion. I can parallel the loads to get to 2 ohm but only one channel.

I don't understand the rest of your comments. I measured with 2 ohm with +-60 degree phase angle. What else do you want to see there? The loadbox goes to 1 ohm but as I reported, the amp instantly shuts down. The performance that I measured is already superb as hardly any speaker goes down to 2 ohm with that kind of difficult phase angle.

The rest where: could we see distortion also in complex loads - not just output power. The "only" thing we see now is how the DUT keeps up the voltage in tricky reactance situation. Maybe it starts to distort like crazy in 3 ohm - 30 deg Cap even if it manages to keep the voltage/power. Btw - isn't it also interesting to see how it behaves in inductive reactances? Now it seems to be only cap.

And while at it... I'd really like to see a 18+19kHz test for power amps so that the meas. filter don't come into play suppressing creation of sum/diffs occurring in the passband or the multi-tone without the measurements filter at 25k so that we can see how the amp would behave with our amps/speakers - this would be more helpful in choosing power amps from specs I believe.

Tnxs!

//

 

[Mkaram]

They have indeed been addressed. See the teardown: https://www.audiosciencereview.com/forum/index.php?reviews/

Many thanks for looking into it!

 

[xaxxon]

I own a PA5.

ah i guess yours just hasn't broken yet.

 

[SuicideSquid]

And while at it... I'd really like to see a 18+19kHz test for power amps so that the meas. filter don't come into play suppressing creation of sum/diffs occurring in the passband or the multi-tone without the measurements filter at 25k so that we can see how the amp would behave with our amps/speakers - this would be more helpful in choosing power amps from specs I believe.

Tnxs!

Can you explain why this is a relevant measurement?

 

[TNT]

Can you explain why this is a relevant measurement?

Any non linearity will produce harmonic tones (2nd 3rd etc....) if the DUT (device under test e.g. an amp) is offered one (1) single signal (like a 1 kHz sinus). This is not a problem as the 2nd for say a 18kHz tone is 36k. When the same DUT is offered more than one signal, it will create IMD which arise as both unwanted summa and difference signals from the involved stimuli. In the situation of offering the DUT 18 kHz and 19 kHz, the difference signal is a 1 kHz signal which is frequency wise audible if loud enough (while very few hear 18/19k) - this contribution to music is not desired.

Now, THD and IMD are tightly related - their is no way of designing a low THD amp with high IMD - the problem with the LP filter at 25 kHz that is used when measuring THD / Sinad is that the high overtones are attenuated so one cant judge the amount of THD and thus, also not estimate the IMD problems of an amp. NB that here I stil only talk about one signal stimuli measurement. By using a 25kHz filter, one hide distortion above 12,5kHz.

So, either introduce a 18+19k stimuli or remove the LP filter so that we can see how much THS there is up high - why? Either of these 2 would reveal the IMD situation. Combine it over a reactive load so it represent real life and we are good. No need to do it for max power - I think at -10dB would be OK to save involved gear.

//

PS. Perhaps is it difference produced IMD products that lies as a faint correlated non-harmonic noise in the midrange making violins sound harsh and nasty... would be nice to find a correlating measurement for such nasty faults in reproduction - truly music killing sh*t.

Unfortunately, due to measurement protocols - we are denied to understand this property of amps.

 

[Ron Texas]

This is a nice piece of kit. For someone who wants a superb HT setup, the main difficulty is finding a front end for it.

 

[pma]

No THD+N vs. power plots at frequencies higher than 1kHz, @amirm ? Or THD+N vs. frequency plots?

 

[Prince Valiant]

No THD+N vs. power plots at frequencies higher than 1kHz, @amirm ? Or THD+N vs. frequency plots?

I believe he said he'd post them (post 41). I guess he's forgotten or been too busy?

 

[375HP2482]

The rest where: could we see distortion also in complex loads - not just output power. The "only" thing we see now is how the DUT keeps up the voltage in tricky reactance situation. Maybe it starts to distort like crazy in 3 ohm - 30 deg Cap even if it manages to keep the voltage/power. Btw - isn't it also interesting to see how it behaves in inductive reactances? Now it seems to be only cap.

And while at it... I'd really like to see a 18+19kHz test for power amps so that the meas. filter don't come into play suppressing creation of sum/diffs occurring in the passband or the multi-tone without the measurements filter at 25k so that we can see how the amp would behave with our amps/speakers - this would be more helpful in choosing power amps from specs I believe.

Tnxs!

//

Amir's multitone test is more taxing than a CCIF two-tone IM test. It even teases out the broadband effects of power supply leakage ("bad" channel).

Expecting a reviewer to measure SINAD not only at all power levels and frequencies, but with multiple power factors added, is a lot to place on a reviewer, though the Loadbox does a decent job. The excellent performance at 2 ohms infers wide phase margins at higher load impedance.

 

[TNT]

Agree - the multi-tone is good. I forgot about that - sorry Amir. But please run it also with a reactive load - this is the reality an amplifier faces.

0,1-5W multitone into a reactive load - this is the every day situation for an amp. Please test for that also and not only the clinical tests (which are good also!).

//

 

[Hipster Doofus]

how about a denon with pre outs and audyssey 32 and 3 or 4 FOSI amps instead.

 

[Julf]

If your DAC or preamplifier can spit out more than 2.9V and you (or your device) accidentally turn the volume all the way up, your speakers will get burned.

Just a small reminder - what burns speakers is not clipping, but too much power.

 

[Sokel]

Just a small reminder - what burns speakers is not clipping, but too much power.

I will quote:

A hidden consequence of clipping is that, while high frequency drivers are more efficient in converting electrical power to sound, they have less mass than low frequency drivers.


Mass translates into thermal inertia. The higher the thermal inertia the more it takes to change the temperature of the mass. This means that high frequency drivers can heat up faster than low frequency drivers.


This is especially true during clipping because the driver is converting all its input power from the amplifier into heat while the signal is clipped.

Why Should We Care About Power Amplifier Clipping? - ProSoundWeb

Causes of clipping, thermal inertia, and more...

www.prosoundweb.com

 

[Julf]

This is especially true during clipping because the driver is converting all its input power from the amplifier into heat while the signal is clipped.

That is pretty much true even without clipping.

I will quote:

"The hazard with allowing an amplifier to clip is NOT that there is anything inherently evil about a clipped (or square) audio frequency wave but simply that the effective power output has increased - often dramatically!"

Speaker Failure: The Truth

 

[Sokel]

That is pretty much true even without clipping.

I will quote:

"The hazard with allowing an amplifier to clip is NOT that there is anything inherently evil about a clipped (or square) audio frequency wave but simply that the effective power output has increased - often dramatically!"

Speaker Failure: The Truth

So clipping DOES destroy speakers,often without the amp working at full power.

(It's a given that too much power can destroy a speaker (even if experience shows that amps with high power are safer) but that is more than evident,clipping is sneaky and damage is done when it's too late to do something about it)

 

[Julf]

So clipping DOES destroy speakers,often without the amp working at full power.

Clipping CAN destroy speakers because the amp working at more than rated full power.

(It's a given that too much power can destroy a speaker (even if experience shows that amps with high power are safer) but that is more than evident,clipping is sneaky and damage is done when it's too late to do something about it)

Right. If you drive a speaker with a 10 W amp driven to clipping, or by a 100 W amp fed with heavily distorted (guitar and synthesizer) music to full power (but below clipping), which one is more likely to burn the speaker?

 

[Sokel]

Right. If you drive a speaker with a 10 W amp driven to clipping, or by a 100 W amp fed with heavily distorted (guitar and synthesizer) music to full power (but below clipping), which one is more likely to burn the speaker?

Depends on the speaker but I would bet that the 10 watt one heavily clipped would be the joy of a tweeter manufacturer.
Just have a look at these all-in -one cheap (100-200$) "stereo" which it's exactly the case (10-30 watts at most).
It's hard to find any without it's tweeters burned.

I have never managed to burn any even with 600 watts on tap,it goes so loud that you have to lower it long before.

 

[Julf]

Depends on the speaker but I would bet that the 10 watt one heavily clipped would be the joy of a tweeter manufacturer.

Do you have any rational (as opposed to anecdotal) justification for that bet?

 

[Sokel]

Do you have any rational (as opposed to anecdotal) justification for that bet?

Other than experience and a ton of explanations from experts like the one I posted,of course not.
I know what I don't know so I rely on experts,and most of them agree.

The one thing not mentioned is that the article states that it doesn't matter where clipping occurs (can be before the amp),it's its shape that makes unproducable by the drivers and so converted to heat.