Channel Islands Audio PC4 MK II passive controller and C100S amplifier

The Channel Islands Audio PC4 MKII passive controller and C.100S stereo amplifier is comprehensively analyzed by Howard Milstein

The “Audiophile World” has recently broken outwith a plethora of Class D designed amplifiers. I’ve just recently spent some long and intense listening periods with the modestly priced Channel Islands Audio PC4•MK II passive controller and the C•100S Stereo Power Amplifier. These “Class D” designs offer far greater efficiency as well as some superb performance capabilities, combining high power efficiency and output without the “humongous” prices that dominate the ‘high end’ world with, in most cases, all the performance of the latter. “Class D” efficiency is typically in excess of 90% compared with 60% for a “Class AB” amplifiers .

If you look back to the past year, The Sound Advocate has literally had our hands on some of the best of these amplifiers. My previous experience with Class D shows that in no uncertain terms, all of these products, be it ICE or Hypex modules, are truly first-rate sounding pieces of equipment. Let’s be a bit more specific here, shall we?  As I have proclaimed, “A properly designed Class D amplifier can compete with the best Class A in performance”. This, thankfully, is what Channel Islands Audio is after. Indeed, they have most certainly succeeded in this venture!

To quote Dustin Vawter, designer and CEO of CIA, “we follow the ‘straight wire with gain’ philosophy in all of our products… with a high input impedance”. The amplifier also displays an ultra-low output impedance, barely perceptible THD+N & IMD, and a really flat frequency and phase response.


Channel Islands Audio C100S Power Amp back

The C•100S Stereo Power Amplifier is compact, exceptionally well built, and great looking. Its class D design utilizes patented technology by Hypex.. However, Channel Island only use the Hypex output/modulator circuit; having designed their own input circuit. Its small size belies its honest useable power abilities: 100w per channel @ 8 ohms/200w per channel @ 4 ohms of amazingly clean power.

At the start, I began auditioning the C•100S power amp on its own; inserting it between the Preamp out of the Peachtree Nova 300 DAC into the C•100S inputs using the latest Wire World Eclipse 8 speaker cables, interconnects and their brand new coaxial 75-ohm digital cable. Digital sources were both a Marantz SA10s1 or Metronome Le Player 2s CD/DAC. (review forthcoming).

While virtually all of the finest ‘high end’ amplification being built today could hardly disappoint today’s audiophile and music lover, certain products will most definitely match better with a given set of components and wires allowing them to offer certain over the top “qualities” that once implanted in your system, can become exceptionally captivating to the listener. Along with ones preferred loudspeaker system, front end and most importantly, the quality or, accuracy of your ROOM ACOUSTICS, this can make all the difference in the world, to say the least!

On top of that, sometimes a particular amplifier will display certain sound qualities that can be startlingly unexpected while recognizing its established set of design parameters. In the case of the C•100S power amp, it most definitely has the exceptional ability to exploit the best of tubes and solid state at the same time, while leaving behind all of the inherent problems and distortion that tubes have to offer. I say this without the slightest amount of hesitance whatsoever.

Some designers and enthusiasts say Class A solid state amplifiers sound like tubes due to their grain free sound, excellent dynamics, and life-like body and textures. However, tube amplifiers in most instances, exhibit poor performance at both ends of the audio frequency range.


In the case of the C•100S, tube enthusiasts will most definitely be getting the best of both worlds in this little amplifier. (not sure if Dusty thinks this?). The more I listened to it and the more program sources that I threw at it, the more it took on qualities of the most majestic solid-state amplifiers along with the lush ‘liquidity’ of the best tube designs. Though other high-end products may have these inherent qualities, none that I have heard has done it at Channel Island Audios’ relatively minuscule price point!

If you have a (‘great- ‘accurate’) pair of loudspeakers that are properly set up in a well-treated room, the C•100S will give you a soundstage width and depth perception that is quite magnificent. I would presume that if other high definition loudspeaker designs do not give you this type of performance, somewhere they have messed up bad! The mid-high frequency balance is where this amplifier shows its supreme dominance. Smooth, airy, creamy– yet decisively fluid and detailed sounds emanate and hang between the speakers and beyond its boundaries while in my case, to the limits of the end of my front wall. The ambience of well recorded classical orchestral recordings dissipates even slightly beyond the corners.

At the same time, imaging remains crystal sharp and in focus, (again…providing your loudspeakers are up to it). Unfortunately, if you cue up just a decently recorded pop, metallic or rock recording, you might be left a bit disappointed (not at the C•100S!). This amplifier was made to exploit the finest recorded program sources—many of which are fully attainable and quite prominent, either in analogue vinyl, CD or the many HD streaming sources currently available. When engaged as such, there is no stopping the truly beautiful sound of the C100S!



Now the enjoyment starts to build up even more. The mid and deep bass of the C•100S is quite splendidly reproduced, with all the benefits of a great solid state design. Cellos, bass drums, double bass—you name it; the C•100S reproduces these frequencies with a deep impact and wonderful ambience. Pop and rock recordings are no threat to this amps bass response. The bass guitar’s fundamental tones and interesting overtones include frequencies from about 60 Hz up to about 1 KHz. With that classic “tube”midrange quality, it was a bit unexpected to be able to hear such deep bass fundamentals from the C•100S. On another level, when listening to some well recorded live or studio FLAC 24-bit file, 192kHz download files or streams, the CS100S can exhibit a huge ‘walloping’ impact with the orchestral bass drum, portrayed way back center of the soundstage!

As is common in many of the latest Class D designs, The C•100S is priced so attractively, you wonder how an amplifier such as this can be designed with such an exalted, musical sound reproduction quality. It is so easy to listen to, fundamentally and tonally exact, and music just simply flows from your loudspeakers; and all types of music at that. The unit is essentially “neutral” in its musical reproduction. This is what a concerted and dedicated audiophile should be begging for; and here it is, at a price that is quite an amazing bargain visa- vie the audio reproduction qualities it offers. Indeed—a true steal!!


Channel Islands Audio PC4.2 passive controller

The debate over passive vs. active preamps continues on within the audio community with the prevailing wisdom being that an active preamp is better than any/all passive preamps. What about this? As with so many things in audio the answer is…it depends.

Channel Islands new PC•4 MKII Passive Controller is a tiny, minimalist passive audio system controller. The new model builds on the popularity of prior VPC models with its new machined aluminum chassis and laser etched graphics. The non-magnetic stainless-steel hardware and high-grade circuitry give this little guy more prominence than its outward appearance would suggest.

Just as all active preamps are not the same, the performance of passive controllers can range from just ok to exceptional. The PC•4 MKII controller is definitely an unadorned designed unit. It provides two standard inputs as well as two outputs and a mute switch.

The small, solid, machined aluminum box also includes internal jumpers that allow Output 2 to be configured for “variable” or “fixed” settings. I listened to the PC4 Mk II in its default output1– which was connected between the Peachtree Audio 300 DAC or the Wyred4Sound Anniversary DAC (review forthcoming). These were mated together with the newest Wireworld Eclipse 8 Cables.. Towards the final auditioning week with the CIA amps, the newly obtained INAKUSTIC LS-4004 loudspeaker cables were also introduced to the mix. These speaker cables brought the C•100S to even greater heights of intricacy, depth and exciting musical detail and accuracy. For vinyl recordings, I was able to switch to the Peachtree phono stage all though I must admit, I used very little vinyl for this review.

Having been totally impressed with a direct connection from the above DAC’s married to the C•100S directly, quite naturally, I wanted to see if there was any difference in sound quality or otherwise when the PC4• MKII was inserted into the existing system. Initially, careful analysis divulged very little difference here. Everything the C•100S portrayed without its mating controller was preserved with the controller inserted. The music’s tonality, harmonic structure, and beautifully preserved airy and spacious midrange were explicitly captured. 

Interestingly, within about 2 weeks after listening to the CIA pre/power as a combo, I did start to hear small improvements in the combination’s overall performance and my enjoyment of the two pieces used together became more engrossing. The main improvements I noticed, although very subtle, was a slightly “smoother” and sweeter tonal balance throughout the full frequency spectrum. However, I cannot say this with total certainty. Nevertheless, I kept the controller in for the remainder of the reviewing process.

Looking for a possible explanation for this, I asked Dustin about it and he observed that there can be some big differences between driving the amplifier directly from the source, and with PC•4 while acknowledging that the PC•4 has a perfectly flat frequency response, zero THD, and no phase error. So, what could be the possibilities?? The source usually has a low output impedance (200 ohms or lower), the amplifier has a high input impedance (100k ohms). To quote Dustin, when Inserting the passive (PC•4):

“A typical active preamplifier is similar to the above… high input impedance/low output impedance. Passive units do not have input and output impedance/or at least shouldn’t be viewed this way. In the case of PC•4, we use a 10k potentiometer, which is basically in parallel with the 100k input impedance. So, when driving directly from the DAC, the source will see a 100k load. When going through the passive, the source will see 9.1k. In fact, the source sounds very much the same driving 9k~100k”.

It would appear that this may have been a system or synergy interaction, and could very well turn out to be the opposite with another source component.


There is no denying that the Channel Islands Audio newly introduced C•100S stereo power amplifier and PC4• MK II passive controller are true ‘State of the Art’ components and much more so at its excellent points! They combine a great tube-like midrange and terrific mid to lower bass response, while the steady state 100 watts per channel can drive most loudspeakers to very high levels, while at the same time sounding clean and unfatiguing throughout. Totally musical, detailed and lush sounding, the more you listen to these units, the more you crave their sound attributes.! In fact, I can think of NO downsides to the C•100S and PC4 Mk II, unless of course, you demand much more power.

If you think you need a bit more power, CIA offers some other higher power amps including a few mono-block offerings to round out their portfolio. The CIA PC•4 MKII also has a sister unit, the PLC•1 MKII Passive Line Controller, which includes a few more features, including a remote control ($995).

This is a fantastically designed, simply executed, musical pre/power amplifier combination that I’m finding hard to give up. Any music lover worth his salt should try to seek them out for an audition!   

CIA C•100S – Power Output: 180 watts per channel @ 4 ohms (both channels driven)
100 watts per channel @ 8 ohms (both channels driven)
THD + Noise @ 1kHz: <.006% (1 watt/1kHz)
IMD: <0.005%

  • CIA PC•4 MKII Passive Controller
  • $495.00
  • CIA C•100S Stereo Power Amplifier                                   
  • $1,495.00

Channel Islands Audio
567 W. Channel Islands Blvd. PMB #300
Port Hueneme, CA 93041
(805) 984-8282

Associated Equipment engaged for this review:

Digital front: Marantz SA10s1, Metronome Le player 2// Analogue: Linn Lp12/ Naim Aero/ Ortofon Cadenza Bronze Amplification: Peachtree Audio Nova 300, PS Audio Gain Cell preamp/ DAC /700 monoblocks Wyred4Sound 10th Anniversary DAC // Loudspeakers: Kef LS 50, Spendor BC1, Spendor SP1, Quad ESL63 USA, Cables-Conditioners: Wireworld 75-ohm coax, Wireworld Eclipse 8 interconnects and speaker cables, Inakustik LS-4004 Power Station and LS-4004 speaker cables.


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