Hypex Multichannel Amp for KEF LS50 Meta

[ClassicalDJ]

I'm in the market for a separate multichannel amp for my five LS50 Metas (I've been driving them with a Marantz SR7013 and previously a Denon AVR-4310, not necessarily displeased but some loud orchestral moments can seem "congested"). I'm thinking a Hypex NCORE-based model (Nord or Buckeye) might suit my needs nicely. My question is whether a NC252-based amp (250W 4 Ohms) will provide all the power I'd ever need, or if spending another $400 or so for a NC502 model (500W 4 ohms) would provide some upside for my room and listening sources?

Room & Speakers
_14d x 14w x 10h (loft area not completely closed off)
_MLP for music about 8ft equidistant from each LS50 Meta
_Rythmik F12 subwoofer
_In-ceiling speakers (4) for Dolby Atmos home theater content

Listening & Equipment
_Multichannel & stereo dsd & pcm downloads/SACD-rips, Qobuz streaming - mostly classical/orchestral, all controlled via Roon
_Topping E30 DAC via USB (stereo)
_Marantz SR7013 via HDMI (multichannel) - eventually would like a multichannel DAC (Okto8 Pro, etc)




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[AdamG]

IMHO, Buy once cry once. The Speakers may come and go but an amp is normally a keeper and who knows what they may need to drive in the future. So, my choice would be the NC502MP configuration. And I own a couple Buckeye 502 Amps, as a disclaimer of some bias in my advice. Very happy with them, thus the recommendation. They also performed well under Amir’s scrutiny and testing.

Buckeye Nc502mp Review (6 Channel Amplifer)

This is a review and detailed measurements of the Buckeye Hypex NC502MP based, 6-channel amplifier. It was kindly purchased and drop shipped to me by our dear moderator, @AdamG247. I don't know what it costs. Not sure what there is to say about the case: Or the back panel: Other than...

www.audiosciencereview.com

 

[Matias]

IMO NC502MP for the front trio, NC252MP for surround channels.

 

[ClassicalDJ]

So, my choice would be the NC502MP configuration. And I own a couple Buckeye 502 Amps...

I like Buckeye's pricing compared to Nord, but I'm concerned about integrating the balanced XLR inputs with the remainder of my system which, for now at least, can only output unbalanced RCA. To overcome this, is it simply a matter of getting correctly-wired RCA-XLR adaptor cables and increasing the volume to compensate for the lower voltage? I'd rather not have to take up more space with devices to step up the voltage.

 

[Everett T]

I like Buckeye's pricing compared to Nord, but I'm concerned about integrating the balanced XLR inputs with the remainder of my system which, for now at least, can only output unbalanced RCA. To overcome this, is it simply a matter of getting correctly-wired RCA-XLR adaptor cables and increasing the volume to compensate for the lower voltage? I'd rather not have to take up more space with devices to step up the voltage.

If power is an issue, determine your need first

Crown Audio - Professional Power Amplifiers | English (US)

www.crownaudio.com

What is you current crossover to the sub?

 

[ClassicalDJ]

What is you current crossover to the sub?

I believe it is set to 100Hz on my Marantz SR7013 (I'll verify when I get home this evening).

 

[AdamG]

I like Buckeye's pricing compared to Nord, but I'm concerned about integrating the balanced XLR inputs with the remainder of my system which, for now at least, can only output unbalanced RCA. To overcome this, is it simply a matter of getting correctly-wired RCA-XLR adaptor cables and increasing the volume to compensate for the lower voltage? I'd rather not have to take up more space with devices to step up the voltage.

Not sure I understand your concern about voltage? If you look through the thread I linked the XLR to Rca cable properly wired is listed with an Amazon link. If your still going to use the Marantz AVR, you just connect the new amp to the AVR preouts and run Audyssey again. Audyssey will reset all the channels trims to level match. Maybe I’m missing something here. If so, apologies.

 

[ClassicalDJ]

If power is an issue, determine your need first

Not sure if I'm doing this correctly, but to compensate for the 2.0 volt RCA signal I think I'd need an extra 6db to determine required amp power, so if my desired peak dBSPL was 90dB (96dB less 6dB for lower voltage) I'd need 358 watts of 4-ohm power?

Sensitivity and impendance per Amir's LS50 Meta review:

 

[HarmonicTHD]

Not sure if I'm doing this correctly, but to compensate for the 2.0 volt RCA signal I think I'd need an extra 6db to determine required amp power, so if my desired peak dBSPL was 90dB (96dB less 6dB for lower voltage) I'd need 358 watts of 4-ohm power?

View attachment 208523

Sensitivity and impendance per Amir's LS50 Meta review:

No the LS50 have a recommended max amp power of 100W and that will reach the ca 106dBSPL theoretically at 1m according to Kef website.

However, as you can see from Amir’s measurements they start distorting when playing really loud (96dB, 100%THD) They are not made for this.


A more reasonable assumption could be for example average 80dBSPL. And given their ca 85dB sensitivity according to Kef website. And even assuming the very worst case of 4ohms. However there won’t be any 20dBSPL headroom as the speaker does not play nicely at 96dBSPL or above. This calculator might help.

Peak SPL Calculator

So a 500w amp is way overkill for your speakers. Yes but might be future proof if you want get bigger ones later.

 

[ClassicalDJ]

As you can see from Amir’s measurements they start distorting when playing really loud (96dB).

According to dB measurements from my Apple Watch, I usually listen at peak levels well into the 80s at 8ft, probably topping out around 85 dB (of course this is usually orchestral music that doesn't normally blast at those peak levels for long), which would equate to around 94 dB at 1 meter.

 

[HarmonicTHD]

According to dB measurements from my Apple Watch, I usually listen at peak levels well into the 80s at 8ft, probably topping out around 85 dB (of course this is usually orchestral music that doesn't normally blast at those peak levels for long), which would equate to around 94 dB at 1 meter.

Very well. Plugging in these numbers at 1 m with 2 speakers requires ca 8W to get to 94dB peaks while assuming the worst case of 4ohms (hint: you need to double the wattage which you would get from the calculator).

 

[ClassicalDJ]

After reviewing Amir's video about sound levels, I'm going to do a remeasure tonight with the NIOSH app set to Z frequency weighting (no weighting = SPL) - I believe my Apple Watch measurements were dBA levels (A frequency weighting). This should a better approximation of dBSPL (I suspect peaks could reach into the 90s at my listening position).

 

[ClassicalDJ]

...while assuming the worst case of 4ohms...

I apologize as I'm not very experienced interpreting various audio measurement terms, but wouldn't 4 ohms be the best case vs. 8 ohm RMS - 4 ohm amp ratings usually (always?) being higher than 8 ohm ratings?

I still suspect 4 ohm is the appropriate case to use since much of the measured impedance is around that level.

 

[HarmonicTHD]

I apologize as I'm not very experienced interpreting various audio measurement terms, but wouldn't 4 ohms be the best case vs. 8 ohm RMS - 4 ohm amp ratings usually (always?) being higher than 8 ohm ratings?

I still suspect 4 ohm is the appropriate case to use since much of the measured impedance is around that level.

From an amps perspective 4 ohms is the worst case as the amp has to deliver twice as much current / power as opposed to 8 ohm.

The LS50 are rated as an 8ohm speaker, however you see in the impedance plot you posted that for some frequencies it drops to ca. 4ohm. The peak calculation assumes 8 ohm too (to keep it simple). So to be on the safe side I doubled the power requirement from 4W into 8 ohm to 8w. Still quite little as you see and often puzzling to people because not knowing how to use such a calc. But not you anymore. You know now.