Infinity Reference 475a

A four channel amplifier with 4×75 watts of RMS power, verified by the USA CEA amplifier ratings system. This was brought in so that reputable manufacturers’ power claims could be believed. Some makers of cheap and nasty stuff, like the much-derided Koac, put silly claims on their products. This is simple fact. It has a set of RCA through-puts to obviate the need for Y leads if you have not got enough RCA line outs to also feed a separate subwoofer amplifier. It features switchable crossovers, one per pair of channels, that can be used high or low pass and can be set between 37Hz and 370Hz. A bass boost can add only a modest 6dB of boom at a slightly higher than normal 50Hz. Terminals are enclosed within clear plastic housings and are the bare wire grub screw type. Large illuminated blue LED strips run along the top of the grey finned extruded heatsink. It wears a cast metal trim panel that looks like a frame with end caps, secured on chromed Allen-headed bolts. From the side it is trapezoidal in shape, very smart. It is not supplied with a bass controller knob but has two ‘IMS’ sockets on the professional-looking control panel that are hidden behind a durable sticker-cover. These are multiple-wire input and output sockets on the RJ45 standard. Two more, smaller stickers are also placed over a single three position switch for each pair of channels. Once removed, you can see they are marked, not as LPF/FULL/HPF, as are the crossover controls, nor as Left/Stereo/Right as are the bridging switches but as Sub/Rear/Front. This is to select which channel feed on the RJ45 cable the pair of channels is to use.
The Harman Kardon Input Management System (IMS) is to be based on a hideaway box and small dash mountable screen and is to be used anywhere you would like to add lots of peripheral devices. Including adding onto OEM systems, Bluetooth and sounds from navigation etc. Even A2DP streaming is likely. You connect the sources to the IMS box and the system then feeds the signals to the amplifier via the RJ45 cables to input multiple channel information. This is to be launched under the Harman Kardon label in the future.
– Class AB
– 4 x 75w RMS @ 4 Ohms
– 4 x 90w RMS @ 2 Ohms (@14.4V)
– 2 x 180w RMS @ 4 Ohms bridged
– Finned Aluminium heatsink with dark grey finish and silvery metal trim panel
– 8Ga. Power Terminals with cross headed grub screw bare wire socket connection
– 12dB per Octave high/low pass crossovers
– 0 to +6dB Bass Boost @ 50Hz
– Adjustable input sensitivity 100mV to 6V
– Illuminated with blue LEDs
– four, three and two channel operation
– Frequency response 10Hz to 100kHz
– Signal to Noise Ratio 85dB
– High/Low Pass Filters 37Hz to 370Hz
– Fuse Rating 35A x2
– HxWxD(mm) 69 x 361 x 229mm
Review by Adam Rayner
This is a lovely product in most ways but despite its ‘Reference’ moniker, it has a fairly low signal to noise ratio of just 85dB and if you crank her up, there is a definite awareness of the noise floor. That said, the power output is correctly stated and is considerable for the price asked. Also, the high frequencies are fast-sounding, giving good detail retrieval overall and clearly coming through quality electronics. At only £150, this is a relatively midprice item and yet the two 35 A fuses required speak of the amount of current it can really chew on and turn into watts for your speakers. I gave the amp a lovely signal from a top-model Panasonic DVD deck. Playing CD as well as some movies, I checked out the sound quality via some Morel £1,400 component speakers that although not yet reviewed, I do suspect of being of reference quality. They were certainly good enough to listen to the amplifier rather than the limitations of the speakers. This is a crucial point in both reviewing and also considering what you want in your system. If you are partnering this amp with the high efficiency speakers that Infinity also make with great skill, you’ll get a result that’ll blow lesser branded kit into the weeds both for quality and potency. However, if you are a mad audiophile, you might want a higher-spec S/N/R product.
I absolutely loved the looks of the cover piece and the deep and bright blue LED illumination strips along the top. All held on with Allen headed bolts (which I am a sucker for, they look so, well engineeringy) and shaped to slant in at the ends as you look at the side of the amp. They hide what is a simple finned ally extrusion and give it the sort of descended from Pro-Audio look that Alphasonik are so famous for, too. There are lots of controls and the 12-language manual is brilliant (in English anyway, I cannot vouch for the Magyar or Russian translations) and also shows lots of hook up options. It covers the whole Reference range, which looks to include some huge mono bass amps. These big ‘uns come with a bass control knob but this 475a four channeller does not. Instead it has three stickers on the side. They do not feature in the manual except by illustration. Peel them off and you get two sockets and two switches appear. This is for the as-yet unreleased Harman Input Management System and is far more advanced than a simple pot-on-a-wire bass gain knob. It is a multi-channel system and will be useful for OEM integration. Watch this space – we’ll review it when it comes out!
There is a clear sticker cover over the Infinity logo on the top that you remove last of all upon fitting it to preserve the cut-look logotype’s bling appeal. A very posh looking amplifier with lots of flexibility and excellent system upgrade paths built in. Plenty of power but some small hiss in the back of the box when cranked right up.
Overall 8.2
Sound Quality 7
Power Output 7
Features 9
Build Quality 9
Value For Money 9