Pro Amps in Stereo and Multichannel Home Systems


The problem

Despite the lamentable ubiquity of integrated amplifiers, there’s a perennial demand among cognoscenti for modestly priced, reference-level power amplification.

No-frills ‘straight wire with gain’ is often on the shopping list when smart system-building decisions are made: it’s mandatory for DIY speaker activation; it’s essential when eschewing a preamp for DAC-direct connection, and it’s multiply inevitable when taking the vital step of separating processing and balanced amplification for multi-channel systems.

Dedicating an amplifier to a driver yields insuperable advantages; the next best thing is to dedicate an amplifier to a speaker. All of which is expensive. When building a Linkwitz LX521 (8 channels), or an Atmos system (11+), even going to the go-to people for inexpensive amplification, such as Wyred 4 Sound and Emotiva, racks up the cost – especially considering their cheaper options are not differentially balanced – a key objective here.

The solution?

The advent of PWM and ‘chip’ amps (variously inaccurately known as Class D, Class H, switching, digital and Tripath) conveniently packaged in modules for DIY (Hypex, ICE, etc), or installed under the hood of an increasing number of off-the-shelf amplifiers, has improved the price/performance ratio. However, it’s surprisingly hard to find good power amps under £500, or even in the £500-1000 range. The plethora of £100-300 boutique single-chip amps are for high-efficiency or small room systems only, and 100W+ modular amps tend to arrive on the shelf at £1000+ when packaged and sold through a dealer network.

You, like me, may have wished: “If only someone made an audiophile-grade stereo power amp for around £500 – it wouldn’t have to be crazy powerful – just clean-sounding and affordable enough to buy a bunch of them.”

Truth is, someone does. In fact, lots of someones do: the market is teeming with them. They’re better and more powerful than you need, and they start at about £250. They’re just not where you’re looking.

The surprisingly ‘in plain sight all along’ solution

In the pro audio world, switching power amps came out of the blocks quicker than on planet audiophile. For PA and commercial installations, the two (or more) channel powerhouse is a workhorse not a thoroughbred – low status animals sold at tiny margins through pro retailers, not hi-fi shops. However, in the last decade, developed by tech giants like Yamaha and the JBL/Harmann Kardon group, they have become absurdly capable, given their price relative to audiophile-branded products. And they’re not all new-fangled digital critturs: many still rock Class A/B like it’s 1984.

If you can overcome the mental barrier of buying a ‘pro’ product for the home, on a budget of £500 per channel, you can go shopping at the top end of this market. And you won’t go far wrong at a third of that price.

This isn’t a novel secret: in quiet corners of home theatre and audio forums across the web, you’ll find a contented (drive)core of users who have ended their audiophile wanderings with a rack full of ugly boxes that sound better than they should.

The best-known contender

Thanks to one influential review, the best known of these is the Class D Crown XLS series, now in Gen 2 (less ugly) fettle. If your brain already hurts from the long intro, you could do worse than go buy that XLS 1502 at under £500, or its big brother the 2x 775W XLS 2502. They weigh 5kg and sound great. You can run them bridged. They have single-ended and balanced inputs, dual volume controls and even in-built DSP and configurable high/low pass filters. They will not break. To an audiophile buyer, they’re essentially witchcraft.

The competition

As stated, this is fertile ground for the canny but impecunious audiophile – though it’s rarely explored from the perspective of critical listening. If it feels like you’re exploring off the beaten track, rest assured that the major players aren’t men in sheds lovingly crafting objects that sound great when they work  but fail in endlessly surprising ways. RCF, K-Array, Yamaha, JBL, QSC, Peavey, Lab Gruppen – these are proper companies with rich pedigrees.

This kit (power, installation, or PA amps) is built to do a punishing job, not draw attention to itself. Mainly, they’re built to go loud, not sound awesome. It’s somewhat accidental that technology has improved to the point where they’re sonically credible.

The risk

Having said that, Behringer has the flakiest reputation in this field for reliability. The lower-end models are certainly built to a price point and on average will not outlast the equivalent, but more expensive, Crown amps. Having said that, Behringer iNuke amps are now firmly (deservedly)cemented in position as the model of choice for the DIY subwoofer community. Such an application plays to all its strengths and dodges its weaknesses. But there’s no need to scrape the bottom of this barrel when sweeter fruit bobs above . . . .

Most offerings in this ballpark do share a common fault: whether Class D or A/B, they aren’t the last word in refinement. If you’re very susceptible to sibilance or have high-efficiency speakers, they may not be ideal. Some models have noisy fans. Some aren’t well shielded and emit powerful local RF fields. All sound open and truthful, with huge power reserves (therefore being very dynamic), and throw wide/tall soundstages, but they don’t do front-to-back staging tricks like valve amps. They don’t deliver richly upholstered timbre. And they are all on the ‘clinical’ side of linear, with varying degrees of hashiness introduced by their relatively low rent power supplies.

To some extent you get what you pay for: better pro amps have fewer vices. When you spend £250 for that much power, don’t expect perfection. Used as primary amplification on the back end of a DAC, with revealing floorstanders fed a diet of MP3s, you can only expect such an amp to be better than any other £250 model. Mindful of what you’re actually buying, there’s no downside other than the agricultural appearance (quite en vogue just now).

The contenders and A spec

Though specs don’t tell nearly the whole story, it’s a good place to start. Few amps that measure badly sound wonderful, and most great amps measure fairly well. For home or home theatre application, most of this kit is powerful enough. But not all are house-trained: quiet and couth. A useful indicator here are SNR and crosstalk figures.

For comparison, Wyred 4 Sound’s £2000 ST1000 Mark II stereo power amp records 108dB. Arcam’s current £4000 flagship AV Receiver reports a SNR of 100dB in regular modes, and 110dB in its optimal  ‘Pure Direct’ stereo mode. DSP and D-A stages tend to impact heavily on crosstalk figures, too.

Benchmark’s benchmark AHB2 amplifier scores a comparable 119dB at 1 kHz, 20 kHz LPF, at full rated output into any rated load. Or 132dB A-weighted, in stereo, relative to output noise, with inputs shorted. There are many ways to rate SNR (see here) and we’re left to guess whether the following figures are directly comparable or not.

It’s worth noting that pro audio manufacturers more rigourously conform to a comparable standard than the infinitely elastic methodology  of audiophile manufacturers. It’s also worth noting that Class D output figures notoriously fail to reach claimed levels when independently tested.

It’s furthermore worth noting that Nagra’s £62,500 monoblocks and

Price Model Power PC @ 4Ω SNR XT 1K
£1000 Apart Champ 3D 350W x3 Hypex 90dB 80dB
£500 Apart Revamp 2250 250W Class D >90dB >74dB
£700 Yamaha XP1000 155W Class D 96dB 70dB
£600 Peavey IPR2 DSP 535W Class D 92dB 70dB
£390 Crown XLS 1002 350W Class D >97dB 85dB
£360 QSC GX3 425W Class B 100dB NA
£370 Apart Revamp 2150 165W Class D >98dB >70dB
£475 QSC GX5 700W Class H 100dB NA
£460 QSC RMX 850a 300W Class A/B 100dB NA
£600 Yamaha PX3 500W Class D  100dB 60dB
£300 Behringer iNuke 3000 880W Class D 100B NA
£200 Behringer A500 185W Class A/B 100dB NA
£325 RCF IPS 700 250W Class H 100dB 75dB
£425 RCF IPS 1700 450W Class H 100dB 75dB
£570 RCF IPS 2700 1050W Class H 100dB 75dB
£300 Crown XLi 800 300W Class A/B >100dB 75dB
£535 Crown Xli 2500 750W Class A/B >100dB 75dB
£650 Peavey IPR2 3000 950W Class D 101.5dB 68dB
£1100 Yamaha XP3500 590W Class D 102dB 70dB
£220 Samson Servo 200 100W Class D 102dB 80dB
£250 Samson Servo 300 150W Class D 102dB 80dB
£1000 Lab Gruppen IPD 600W Class D 102dB 80dB
£470 Crown XLS 1502 525W Class D >103dB 85dB
£535 Peavey IPR2 2000 535W Class D 105dB 70dB
£125 Samson Servo 120A 60W Class A/B 105dB 80dB
£635 QSC PLX 1104 500W Class A/B 106dB NA
£500 ElectroVoice* Q44 450W Class A/B 106dB >80dB
£1000 QSC PLX 1802 575W Class A/B 107dB NA
£590 ElectroVoice Q66 600W Class A/B 107dB >80dB
£715 ElectroVoice Q99 900W Class H 109dB >80dB
£1000 Crown CT4150 150W x4 Class D 110dB 70dB
£890 ElectroVoice Q1212 1200W Class H 110dB >80dB
£1200 Martin Audio MA3 1500W Class D 112dB NA
£655 Lab Gruppen E4.2 200W Class D >112dB >70dB

The Shortlist

Drawing a shortlist from these contenders, it’s wise to omit any with very noisy fans: we need a cooling system smart enough to know the amp is pootling along driving ceiling speakers, not gigging hard, and to shut up accordingly. Also, the performance and noise characteristics of these amps improves significantly when bridged – that could be a dealmaker. You may wish to mark down those with ‘non-standard’ connectors: most of the 1U depth amps have Phoenix connectors – if you want to use exotic cabling, you’ll need combi or XLR inputs. You may want to exclude Behringer on reliability grounds. And more affordable is good, up to a point.

We’ve done a lot of listening to and lending of Crown products, so the XLi800 and DriveCore XLS1502 make it to any shortlist. The XLS1502 in particular ticks all the boxes: powerful, bridgeable, and with a recognisable connector set. If you need four channels, and can live with the Phoenix connectors, the CT4150 is very impressive, too. It comes it higher powered versions, at £250-500 per channel, and is the best amp Crown currently makes.

You could make an equally good argument for the ElectroVoice/Dynacord Q44: an older design, and not bridgeable, but doubtless a bit different tonally. The logical upgrade from the XLS1502, though, looks like the Class H EV Q99.

Peavey’s IPR2 2000 (not the hamstrung DSP version) is also worth auditioning back to back with the Crown. Also, to see whether Lab Gruppen’s crosstalk figure for the E4.2 translates into an audible issue.

For less demanding applications, the elderly Samson Servo models also look to offer killer value.

And, of course, don’t forget that you can always lash together a couple of Hypex modules and a stock PSU for less than £1000 that will be reliably transparent – or buy a Nord Acoustics amplifier that is essentially that plus a trick output stage: also reliably superb at £1500+.

Watch this space for future reviews and listening tests . . .

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