Alpine PDX-F6 Amplifier

Product Name: Alpine PDX-F6 Amplifier
Product Type: Amplifier
Price: $999.00
Reviewed By: Marty Price
Magazine: Incar entertainment:#3 2010
Distributor: - Select Distributor -
Who Sells What/Website: Alpine

The stunning evolution of a proven range.


Because Alpine is just about everywhere these days many people, especially younger folk, have absolutely no idea just what vast accomplishments lie in Alpine’s past. Therefore I’m going to start this review with a little history lesson. Alpine is a subsidiary of Japanese electronics manufacturer Alps Electric Company Ltd and although it started out in 1967 as Alps-Motorola, it became Alpine Electronics Incorporated (or Alpine for short) in 1978. Alpine has been credited with many accolades in relation to its source units, from the first in-car equaliser in 1982 to the first triple disc head unit in 1993.

But did you realise that its amplifiers are also something special too? Alpine has been designing amplifiers for more decades now than I care to remember and this goes largely unnoticed because of the sheer amount of amplifier brands available today. When Alpine first started manufacturing amplifiers the market was very sparse and many didn’t seem to work for extended periods. But soon enough Alpine units became well known for their reliability in the face of such adversity. This is what has kept it at the

forefront of design and the new PDX range should continue that tradition.


When Alpine released the first range of PDX amplifiers a couple of years back, they were initially received with much excitement. However in this day and age, where there are plenty of dedicated specialist manufactures that are true masters of their trade, this enthusiasm began to wane a little in comparison to the hot competition.

So Alpine returned to the drawing board a year ago, taking the basic PDX design and re-developing much of the technology until it was ready to release the new design as the 2010 PDX range – a vast improvement on the older series and easily on par with the best amplifiers in the car audio world today. I’d heard rumours that the specifications of the new PDX amplifiers were impressive but when the new PDX-F6 hit my desk I must confess I too seemed to have underestimated Alpine’s ability to create a superb amplifier on a tight budget. It seems Alpine is determined to revisit its former glory days as these amplifiers boast the best specs since the F#1 amplifier was available. The PDX-F6 is the larger of the four channel amplifiers (there is a smaller PDX-F4) and there are also two monoblock variants available. It’s a high power digital class-D design and each of its channels is rated at 150 watts continuous at 4 ohm (in compliance with the CES2006 standards). The birth certificate included with this particular one stated that it had been tested to output 182 watts per channel. In other words it’s no lightweight despite having a tiny footprint. Now I might just delve a little into the world of class-D digital amplifiers as the Alpine is a bit special. Most class-D (sometimes known as digital switching) amplifiers contain powerful MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors) that are switched (in that they’re either turned fully on or fully off) by digital control as opposed to raw voltage like say an analogue amplifier would have. This means theoretically that zero time is spent transitioning between the on and off states. In a perfect world this would mean 100% efficiency because if the switches are open then all of the power supplied to them is delivered to the load and none is converted into heat (remember you cannot eradicate energy, only convert it). When the switches are off they’ll have full supply voltage standing across them but no current flowing so again, no heat is dissipated.

Now that is the somewhat simple explanation of the workings and it’s not a perfect world. Therefore, like anything electronic, anything above 90% is considered acceptable. If class-D is so good then why isn’t everyone using it? Well the issue is that the distortion and noise levels are usually higher because the output of a class-D amplifier is basically a square wave form and the smallest irregularity (noise, voltage ripple, etc) results in an irreversible change of the output. Low pass filtering tends to smooth these pulses out and helps to restores the signal shape on the output but only a company like Alpine has the technical ability to produce a full range class-D amplifier that doesn’t suffer from high distortion levels. So basically the PDX amplifiers are not completely ‘digital’ as such because all amplifier power output stages still deal in voltage and current. However the control is binary as opposed to analogue voltage wave forms. They basically keep the signal in the digital realm until just prior to output. They’re definitely full range too, with the frequency response running from 5Hz – 100kHz! The design offers a very respectable 0.003% (total harmonic distortion) taken at 10 watts and 0.05% THD at full song. Signal to noise ratio (which is A-weighted) is 116dBA and damping factor and slew rate are quite high too meaning the amplifier is more than capable of controlling unwanted cone movement and handling high speed dome transients respectively. Compare those specs to many other amplifiers on the market and see who comes out on top.


Alpine-PDX-F6-S2 The Arc Audio KS125.4Mini at $999 is another option from a lesser profile company
Alpine-PDX-F6-S3 For those with a smaller budget, the Focal FPS 2160 at $649 is a worthwhile option

The physical design of Alpine amplifiers over the years has been clean but these latest PDXs look downright sexy. They’re finished in a blend of machined black anodized aluminum (on the top and sides) and a stamped steel back plate. Located in the centre of the top plate is a neat square Alpine logo that is backlit in traditional blue. Around the perimeter of the top is a 16mm wide black Perspex insert that adds a nice touch to the look when it’s seated alone. However Alpine has also incorporated a very neat design aspect where this insert can be swapped out for another set of feet and additional PDXs can be stacked vertically. I’d say this is the best looking amplifier Alpine has produced, although I do have a soft spot for the old black fin covered heat sinks of the late 80s.

The overall foot print is small measuring 257mm x 192mm x 57mm; slightly smaller than the older PDXs. Weight is a measly 2.88kg. Lined along the front end are all the connections for power and signal plus four ports for the speaker plugs supplied. Alpine has designed a system where the speaker wires are terminated in plugs. The plugs are similar to RCAs (but rectangular) where the positive is in the centre and the negative on the outside. An appreciated design if you’ve had your amplifier in a tight spot at night and are trying to see which terminal is positive and negative – it doesn’t matter which way you put them in because the result is still the same!

Amplifier controls aren’t overflowing compared to some on the market but all the useful ones are there. In addition to the usual gain controls you also have an adjustable crossover with high, low or full pass on each channel. There’s a fair bit of dismantling in order to get to the internals, and once in, all looks very high quality. There are thick fiberglass circuit boards, robust power components including two enormous power caps, and four large solid core transformers. The serious power handling components are kept well away from the signal path – the signal input and circuit board are attached to the top plate. That’s what I call maintaining a distance! The 12 MOSFETs are lined-up along the sides and are attached firmly to the heatsinks just for those hot moments… Overall it’s a very clean design and testament to Alpine’s design ability.


In the box you get all the mounting screws, tools, spacer plates for stacking and the plugs for the terminals. Using these I mounted, connected and set up the amplifier before beginning the auditioning. Comparing it to other high-end amplifiers with its outputs directly connected into the real time analyzer, its frequency response does exhibit a little rise in the bass and treble but overall it’s a very smooth amplifier.

When auditioning amplifiers I also like to test their noise levels first with the car engine turned off, before I go anywhere. In my opinion an acceptable level of noise is where one cannot hear anything from the seated driving position when playing a zero bit track. I’m happy to report that the PDX-F6 passed with flying colours remaining noiseless right up until maximum gain was reached. With that promising start I grabbed a pile of CDs and headed off. The PDX-F6 is an extremely accurate amplifier that remained well defined no matter what genres of music I threw at it. During pieces containing complex high frequency sound such as the flute and cymbals from Vivaldi and Dragonforce respectively, the amplifier was superbly precise. When pushing it throughout the lower regions it also sounded strong and controlled even with hard hitting bass tones. So how about I couple these two aspects together? When setting gains on amplifiers I often use bands like Fear Factory because the accurate double bass drumming means the midrange driver has to move a long distance while changing direction very fast – this reveals weaknesses in most amplifiers very quickly. The PDX-F6 is a very strong amplifier playing Raymond Herrera’s bass drum combinations (affectionately called machine gun drumming) accurately and loud, with breakup and eventual distortion only occurring at the most ridiculous levels. However; if you really require that much bass then get yourself a PDX-M6 or PDX-M12 mono-block.


In conclusion, there are a myriad of amplifiers available on the market today offering all kinds of fancy abilities and features. You’ll have a hell-of-a search before you find one that is as powerful, as accurate and as good looking as the PDX-F6, especially for the $999 asking price!


TYPE: Class-D 4/3/2 channel amplifier
CONTINUOUS POWER RATING: 4 x 150 watts at 4 ohm (CES2006)
FEATURES: Adjustable crossover, stackable
COST: $999
CONTACT: Alpine Electronics Australia
PHONE: 1300 765 760
DISTRIBUTOR: Alpine Electronics of Australia Pty Limited


Beautifully designed Superb sound quality Innovative technology


Less overall features compared to some