Buckeye Nc502mp Review (6 Channel Amplifer)

[rdenney]

Please explain why this is so...if both channels on the board are active, what practical difference does it make if the module is running in bridged mode or stereo?

Bridging cuts the impedance seen by each channel in half, which increases the current for a given voltage. More current = more heat. 8-ohm speakers draw from the bridged amp like 4-ohm speakers from an unbridged channel. The 502 is rated for 4-ohm speakers when bridged and 2 ohms unbridged, but be sure they are really 4-ohm speakers. My Advent NLA from the old days, for example, are rated at 8 ohms but dip to less than four ohms in one spot on the spectrum. They would pose a problem for many amps when wired in parallel (which was a thing in the day with Advents).

Rick "same effect as wiring speakers in parallel" Denney

 

[Buckeye Amps]

Bridging cuts the impedance seen by each channel in half, which increases the current for a given voltage. More current = more heat. 8-ohm speakers draw from the bridge amp like 4-ohm speakers for the unbridged channels. The 502 is rated for 4-ohm speakers, but be sure they are really 4-ohm speakers. My Advent NLA from the old days, for example, are rated at 8 ohms but dip to less than four ohms in one spot on the spectrum.

Rick "same thing with wiring speakers in parallel" Denney

Was just replying but Rick said it perfectly.

It's also why Hypex discourages pairing a 4ohm speaker to a BRIDGED 502MP module.
It can be done (and has without issue) but only if you really know the speaker isn't dipping under 4ohm.

 

[livinon2wheels]

@Rick Sykora - Thanks for posting that graph showing all those anomalies Rick, that is truly surprising for what I call a truly high end amplifier. This makes much of what I have seen in class D look better by comparison. Obviously no matter what you choose compromises are part of the package. As my dad used to say, "you pay your money and take your choice" $1500 for the class D vs 10k for the Trinnov makes it pretty easy to choose.

 

[livinon2wheels]

Bridging cuts the impedance seen by each channel in half, which increases the current for a given voltage. More current = more heat. 8-ohm speakers draw from the bridged amp like 4-ohm speakers from an unbridged channel. The 502 is rated for 4-ohm speakers when bridged and 2 ohms unbridged, but be sure they are really 4-ohm speakers. My Advent NLA from the old days, for example, are rated at 8 ohms but dip to less than four ohms in one spot on the spectrum. They would pose a problem for many amps when wired in parallel (which was a thing in the day with Advents).

Rick "same effect as wiring speakers in parallel" Denney

point taken Rick and thanks Buckeye, I suppose there really is no free lunch. If you want more power in the same size case, temperatures will be higher. The question is how high is the temperature inside the devices at the junction at any given case temperature? Thinking in the computer industry, if the cpu gets to 160 C in most computers the fan runs at max and the operating frequency gets throttled back until things cool down. Since amp case sizes are standardized for a given manufacturer, putting a 500 watt amp in the same case a 125 w amp uses will make a huge difference in case temperature I would guess. Buckeye, do you take those kinds of measurements for your amps? I realize heat is relative to the average power the amp is producing at the time of measurement, but is there any measurement standard that exists nowadays? I think back in the 80s they used to test amps at 1/3 power for an hour, which seemed to be reasonable to ensure longevity. Also, is there any possibility of thermal runaway with today's designs?

 

[rdenney]

These amps at full power are about 90% efficient. A bridged 502 feeding 900 watts continuously to a 4-ohm speaker will make about the same heat as a 100-watt incandescent light bulb.

Driving two 4-ohm speakers at full power output will make 450 watts in each channel, so about the heat of two 50-watt incandescent bulbs. So, the same heat production. The output sound will be the same, too, if they are both playing the same input channel.

What makes BTL more powerful is you have two stereo amps for two speakers. But in terms of loudness, it’s only a 3-dB gain.

I ran into this when I was using stacked Advents. I had them paralleled on a 125-watt B&K amp, but those amps didn’t really like impedance that low. So I added a matching amp, and each amp drove two speakers without bridging—like two speakers with a 250-watt amp in terms of loudness. The 502 into two Revel towers nominally has a bit more power (maybe 325) but is probably constrained by the speakers. It’s no louder, but it sounds better in most other ways, particularly as one moves around the room.

Rick “whose speakers probably can’t make 115 dBA SPL with any power input, but the 502 in stereo was enough for the 110dB target” Denney

 

[DonH56]

Bridging ideally yields twice the voltage swing and thus four times the power or 6 dB gain.

 

[pma]

Bridging ideally yields twice the voltage swing and thus four times the power or 6 dB gain.

Exactly.

 

[antcollinet]

Bridging ideally yields twice the voltage swing and thus four times the power or 6 dB gain.

*If the amps are also capable of delivering twice the current.

 

[DonH56]

*If the amps are also capable of delivering twice the current.

Thus the word "ideally". This place is pretty pedantic even for me. I was correcting the 3 dB number for an IDEAL amplifier in bridged mode.

 

[antcollinet]

Thus the word "ideally". This place is pretty pedantic even for me. I was correcting the 3 dB number for an IDEAL amplifier in bridged mode.

Sorry - I interpreted the word "ideally"as meaning "without voltage losses"

 

[cavedriver]

Maybe but you'll spend more for quality Class AB and still may have challenges at some frequencies. Would not trust gross generalizations when I have real measurements to compare. Here is a solid Class AB design (almost $10K) that Amir recently tested...

View attachment 411528

View attachment 411527

Rick, isn't the Trinnov a Hypex amp? From their product page:

"Like its big brother the Amplitude8, the Amplitude8m is designed to deliver spectacular performance in a luxury home theater but at a fraction of the price. Using the Hypex N-Core Class D output module, each of the eight channels can deliver up to 300 watts RMS at 4Ω."

 

[RickS]

Rick, isn't the Trinnov a Hypex amp? From their product page:

"Like its big brother the Amplitude8, the Amplitude8m is designed to deliver spectacular performance in a luxury home theater but at a fraction of the price. Using the Hypex N-Core Class D output module, each of the eight channels can deliver up to 300 watts RMS at 4Ω."

Actually, (thought) I used the Amplitude 16 and it is ICEPower. So is Hypex. Thanks for catching my mistake. Fortunately the principle still applies. I had a Class AB amp shown but deleted to keep the post simpler.

P.S. Apologies again as did use the Amplitude 8m.

 

[RickS]

To exemplify that the principle still applies, here is a Class AB amp that Amir tested…

 

[Sokel]

To exemplify that the principle still applies, here is a Class AB amp that Amir tested…

View attachment 411744

It's usually this what the AB is famous about:

(link)
(this one is no cheap of course)

 

[livinon2wheels]

One could make the argument that class AB generates more distortion in the low bass region and class d in the upper frequencies. I am considering that class D has probably matured enough that class AB is likely on its last legs except perhaps for diehard tube enthusiasts. (I wonder if anyone has ever done a class d amp with tubes or if such a thing is even possible?) I bet within a decade there will be very few class AB amps manufactured.

I have a couple of cheap (under a $100) class d amps in service, one is an FX-audio brand that was used by my wife as a keyboard amplifier before the house burned, the keyboard didnt survive but the little amp did. Currently on my desktop connected to my Macbook Air via headphone jack for background music and watching videos. IF pushed it doesnt sound good at all but at lower levels its good enough for that application. Definitely far from hi resolution and most likely pretty high distortion at anything approaching loud levels. Its got a 24 volt supply so I am guessing its likely about 10-15 watts maxed out. Just as an experiment yesterday, I turned it up to the maximum clean level I could get out of it and let it cook for an hour and the case never got above ambient temperature which is probably what I should have expected with such low power capability.

 

[RickS]

It's usually this what the AB is famous about:

View attachment 411747
(link)
(this one is no cheap of course)

Yes, is not cheap but does represent the pinnacle of Class AB and some might infer other Class AB amps are similar. As I mentioned, prefer to stick to individual measures whenever possible. This particular test is fairly recent addition and so Amir’s older reviews do not have it. As more of his Class AB reviews are older, is harder to compare. Getting back to more affordable Class AB amps…

Also want to be careful about chasing numbers as in many cases, the distortion is still quite low in many of these amps. Even the best speakers have much more harmonic distortion across the audio spectrum and also get even uglier when pushed harder.

 

[Sokel]

Yes, is not cheap but does represent the pinnacle of Class AB and some might infer other Class AB amps are similar. As I mentioned, prefer to stick to individual measures whenever possible. This particular test is fairly recent addition and so Amir’s older reviews do not have it. As more of his Class AB reviews are older, is harder to compare. Getting back to more affordable Class AB amps…

View attachment 412309

Also want to be careful about chasing numbers as in many cases, the distortion is still quite low in many of these amps. Even the best speakers have much more harmonic distortion across the audio spectrum and also get even uglier when pushed harder.

Agree about speakers.
AB done right can be really good allover and even affordable if one does not want much power.Look at the SINAD champions for example,both cheap and class AB.

As for the pinnacle of class AB's (for me) is still the Halcro Eclipse which is insane all over but even more expensive (fun fact,it comes from non-audio people,they make the world's best metal detectors,at least prior to this design)

 

[EJ3]

Yes, is not cheap but does represent the pinnacle of Class AB and some might infer other Class AB amps are similar. As I mentioned, prefer to stick to individual measures whenever possible. This particular test is fairly recent addition and so Amir’s older reviews do not have it. As more of his Class AB reviews are older, is harder to compare. Getting back to more affordable Class AB amps…

View attachment 412309

Also want to be careful about chasing numbers as in many cases, the distortion is still quite low in many of these amps. Even the best speakers have much more harmonic distortion across the audio spectrum and also get even uglier when pushed harder.

This may (or may not) be relevant her (but I'm pointing it out in case it might be). I had this issue in an APT/Holman Preamp of mine that Amirm tested. It turned out to be a Volume pot adjustment for both channels to be tracking the same & an unknown to be missing resistor in the circuit for the peaking above 10K.