Amplifier upgrade for Kef Reference 4c trio and matching surrounds

[JD_Spoon]

I recently took the leap to make a major upgrade to my living room (17' x 17' x 10') audio quality and jumped on the current KEF promotion to get a trio of Reference 4c as part of a larger 5.2.2 setup that's using an Anthem AVM 70 for a processor. Thus far, they have been an astonishingly good sound, and I couldn't be happier with what I'm getting from them. My concern is that I am not sure my current amp, an NAD M27, is going to be up to the task of driving them. The Reference 4c are nominally rated at 8 ohms and 90dB, but their impedance can go as low as 2.9 ohms (per the recent ASR review). Based on the KEF recommended power spec, I should be looking for amps that are over 240W per channel. The M27 can totally handle my surround/height speaker can't quite cover that for the front three. My equipment space limitations mean I really can't fit more than about 10u of amplifiers total, and the WAF for this project does not extend to having full-size monoblocks out on the floor. The other major consideration is that I need to keep my amplifier budget under about $13k. To satisfy providing 7 channels and ensuring the front three have adequate power, these are the options I've identified that can work in my space.

1. Legacy Audio iV3 Ultra paired with either the existing M27 or an iV4.
2. Bryston 21B^3 paired with the M27 (this handily beat out the McIntosh MC303 at the same price point in a back to back listening test with some Contour 60i speakers, so I've stricken the latter from the list of options.)
3. 3x Benchmark AHB2 as bridged monoblocks paired with the M27.
4. 2x Parasound Halo A51, bi-amping the front LCR and using the remaining 4 channels for the surrounds (Technically their A31 could handle the front three, but I'd be less nervous about handling the transients with a little more breathing room.)
5. 3x PS Audio M700 monoblocks paired with the M27.

Have I missed any viable options here? If so, what might they be? The bi-amping option for the front three intrigues me, but I'm not sure how much power headroom I need to account for in that construct. Specifically, I'm not sure if a 200Wx5 channel would be enough, which is why I erred on the side of caution with the A51. If not, are there any of these combinations that are likely to significantly outshine the others given the speakers they'd be powering?

Thanks,

 

[AcuDefTechGuy]

Have you already tried using the speakers with your current amp?

I think it's mainly about the volume. If the volume is sensible and everything sounds great, then I say it's all good.

 

[ryanosaur]

How about trying Purifi or Hypex based Amps which can offer gobs of power and are stable to 2 ohms. They also rate highly on Amir's bench.

 

[JD_Spoon]

Have you already tried using the speakers with your current amp?

That's a fair question. Yes, I am currently using it to power the L/R pair, and it seems to be... okay, I guess? Qualitywise I don't have any complaints, other than an admission that based on my auditions I might like the sound of good Class AB amps a little more than the one Class D option I've heard (and own). I admit I don't fully understand the implications of the numbers, it's a little hard for me to understand why I'm likely to need more than 50W per channel to handle a 90dB volume (which for me is right on the edge of uncomfortably loud for sustained listening) to a seating position 11' away from the speakers. That said, I'm not comfortable squaring off my rudimentary understanding of this stuff against what KEF has written for their specs. My concern with pursuing a power upgrade was more about hedging against premature wear from underdriving the speakers on those transients and the assurance that the amp is not actually clipping some elements that I'm not aware of.

 

[JD_Spoon]

How about trying Purifi or Hypex based Amps which can offer gobs of power and are stable to 2 ohms. They also rate highly on Amir's bench.

The M27 currently in place uses Hypex amplifiers. I'm intrigued by the Purifi options, just haven't seen much in the way of ones that are at the power ratings that I've estimated I need. The Legacy Audio iV3 Ultra isn't based on a Hypex or a Purifi, but certainly seems to have power to spare, at 610W per channel.

 

[Verdinut]

IMO, your NAD M27 amplifier is amply capable of driving your KEF speakers. I am convinced that you wouldn't be able to hear a difference with any other good amplifier, even expensive Krell, Benchmark or Accuphase products, with the SPL at which you listen to your system.

You say that you're getting astonishing sound with your KEFs with the current amplification. You don't listen to music at insane high sound pressure levels. KEF speakers are designed to operate well with amplifiers with power ratings starting from 50 watts and up to 240 watts. They don't require 240 watts to be properly driven. No commercially sold loudspeaker does require that much power to perform adequately. For instance, pro audio speakers output more than 100 dB with only 1 watt input. The 240 watts rating actually is most likely the maximum wattage which they will stand for a peak SPL of one second or so, beyond which they will be damaged.

If you want to spend on improving your system, then look for speakers to replace your KEFs with better ones. In any system, the speakers are the weakest link. With electronics, you get diminishing returns rather fast with more spending.

 

[JD_Spoon]

IMO, your NAD M27 amplifier is amply capable of driving your KEF speakers. I am convinced that you wouldn't be able to hear a difference with any other good amplifier, even expensive Krell, Benchmark or Accuphase products, with the SPL at which you listen to your system.

You say that you're getting astonishing sound with your KEFs with the current amplification. You don't listen to music at insane high sound pressure levels. KEF speakers are designed to operate well with amplifiers with power ratings starting from 50 watts and up to 240 watts. They don't require 240 watts to be properly driven. No commercially sold loudspeaker does require that much power to perform adequately. For instance, pro audio speakers output more than 100 dB with only 1 watt input. The 240 watts rating actually is most likely the maximum wattage which they will stand for a peak SPL of one second or so, beyond which they will be damaged.

If you want to spend on improving your system, then look for speakers to replace your KEFs with better ones. In any system, the speakers are the weakest link. With electronics, you get diminishing returns rather fast with more spending.

That's a reasonable point, and as I noted in a previous reply, I'm having trouble reconciling the math for why they call for such beefy amplification. I did want to clarify one thing, though. The Reference 4c and 5 recommended power spec for is 50 - 400 watts. I got the 240W number I mentioned by applying KEF's own rule of thumb (https://www.shop.us.kef.com/blog/recommended-amplifier-power) of setting a floor of 0.6 of that maximum 400W rating.

 

[Cos]

Congrats on the AVM70 purchase, I am just setting up mine now. I am only running 200Wpc ATI Class D amp driving my persona's in a room that is 19x22x9 and that is more than enough power to drive the front three. My 3Fs reach a minimum magnitude of 3.49 ohms I have my Halo's driving the rest. Based on the gear you are talking about, I agree with ATDG. You obviously have money to burn so I am going to assume you have solid subwoofers. After hearing the Focal Utopia's being driven my the Anthem 1140, I don't think more power will be a huge improvement unless you want your ears to bleed.

 

[JD_Spoon]

Congrats on the AVM70 purchase, I am just setting up mine now. I am only running 200Wpc ATI Class D amp driving my persona's in a room that is 19x22x9 and that is more than enough power to drive the front three. My 3Fs reach a minimum magnitude of 2.85 ohms I have my Halo's driving the rest. Based on the gear you are talking about, I agree with ATDG. You obviously have money to burn so I am going to assume you have solid subwoofers. After hearing the Focal Utopia's being driven my the Anthem 1140, I don't think more power will be a huge improvement unless you want your ears to bleed.

Thank you for your feedback as well. I hadn't brought up the specifics on the subwoofers because I didn't think they were particularly germane to the amplifier question, but I am running a pair of Fathom f113v2.

 

[Verdinut]

That's a reasonable point, and as I noted in a previous reply, I'm having trouble reconciling the math for why they call for such beefy amplification. I did want to clarify one thing, though. The Reference 4c and 5 recommended power spec for is 50 - 400 watts. I got the 240W number I mentioned by applying KEF's own rule of thumb (https://www.shop.us.kef.com/blog/recommended-amplifier-power) of setting a floor of 0.6 of that maximum 400W rating.

You can verify how much power you need taking into account the speakers sensitivity, using the following link:

Peak SPL Calculator

 

[lovinthehd]

I'd just use your current amp, little to be gained by changing, especially if its fine using them as is now....

 

[AcuDefTechGuy]

The M27 currently in place uses Hypex amplifiers. I'm intrigued by the Purifi options, just haven't seen much in the way of ones that are at the power ratings that I've estimated I need. The Legacy Audio iV3 Ultra isn't based on a Hypex or a Purifi, but certainly seems to have power to spare, at 610W per channel.

A friend of mine just got his Legacy Audio iV2, and he swears by it. His brother is also getting the iV2. But I just can’t see needing 610W-8-ohms/ 1000W-4-ohms. Seems way overkill.

 

[PENG]

That's a fair question. Yes, I am currently using it to power the L/R pair, and it seems to be... okay, I guess? Qualitywise I don't have any complaints, other than an admission that based on my auditions I might like the sound of good Class AB amps a little more than the one Class D option I've heard (and own). I admit I don't fully understand the implications of the numbers, it's a little hard for me to understand why I'm likely to need more than 50W per channel to handle a 90dB volume (which for me is right on the edge of uncomfortably loud for sustained listening) to a seating position 11' away from the speakers. That said, I'm not comfortable squaring off my rudimentary understanding of this stuff against what KEF has written for their specs. My concern with pursuing a power upgrade was more about hedging against premature wear from underdriving the speakers on those transients and the assurance that the amp is not actually clipping some elements that I'm not aware of.

As ADTG said if you are fine without cranking up the volume, then your M27 should be more than enough. I don't know the range of the AVM 70's volume, may be @Cos or yourself can tell us. If it is say 0-100 and you are getting loud enough spl at less than 70 then replacing it with any of the amps you listed won't do a thing for you. Power not required/used will not change a thing just because it is available, and we all know specs better than the level considered well below humans threshold of audibility is also not going to help. For example, the AHB2, under one test condition, has THD+N 10 dB less than the M27, but even golden ears cannot tell a difference, not in theory, all else being equal.

You can also use an online calculator to find out how much power you really need but again, going by the volume (actually would be better to have the level trim settings as well just to be sure).

The NAD M27 has great specs, the only amp you listed has a chance to beat it in terms of audio specs is the AHB2 but I think you know that already. The chart below only shows the results of one test, but the M27 did extremely well on the other tests performed on that review as well. If I agree with others, if you need more channels just grab another Hypex or Purifi amp. Even if you have money to burn, you can burn them on things that will actually make a difference, such as acquiring the best available source contents. In my experience, given the nice equipment you already have, top recording quality contents will give you the best bang for the buck, not a better/more expensive power amps.

Review and Measurements of NAD M27 PWR Amp | Audio Science Review (ASR) Forum