AmplifiersPortable Amplifiers

Cayin C9

Disclaimer:  Cayin needs little introduction as a long time player in the Tube amp, DAC and DAP market and this latest product combines some elements of all of that backstory.   I received the Cayin C9 as part of a review tour and spent 10 days with the C9 as my primary amplifier both home and portable to give it a good workout before sending it on to the next reviewer in line.    I have no financial interest in Cayin or any of its distributors, nor have I received any remuneration for this review.  I own several other Cayin Products and have reviewed several of their DAPs and IEMs previously in these pages.  If you have an interest in the C9 or other Cayin products, see their website and follow them on Facebook. 



The C9 is a premium product with a price tag to match so one expects a premium experience from start to finish and largely the packaging works although the sticker with the specs on the package reverse was not smoothed out well and air gaps can be seen in the photos, a little more care there would be appreciated.  Once the slipcover is removed, the packaging is nicely laid out with the C9 tucked in a foam surround in the top compartment and a pull out shelf with cables (3.5 interconnect and 4.4 interconnect), USB charging cable, disassembly tool, extra screws and storage container for same all hiding under the manual.   The kit is complete with everything one needs to take it out of the box and start using it without having to go search for a interconnect which is a nice touch. Likewise, my test unit came with the batteries at resting voltage (3.7V) so was usable out of the box even if not topped off before using. (How many of us resist the urge to try out a device before fully charging it?, I suspect many don’t).



The C9 uses a three sided (top and sides) cnc milled anodized aluminum housing with two oval openings cut in the top surface for tube visibility.   The bottom surface is a glass plate with a protective cover attached at the factory.  Unfortunately no feet are provided so it would likely be worth investing in some felt or rubber stand-offs to keep from scratching the unit on the desk.  Dimensions are about the size of an average cell phone in height and width (roughly 3.25 x 6.25 inches) and roughly 3 times as thick as phone (1 inch).  Heft is significant at just over a half kg.    Most of the controls are on the front panel except for a button on the left side that is used to activate pre-amp mode.  On the unit’s front there is a row of switches that sits atop a row of ports.  From left to right the top row is line/pre-amp, gain, volume knob, solid state/tube, and finally Class A/AB switches.    The bottom row contains the single ended 3.5mm input port, 4.4mm balanced input port, power button, 4.4mm balanced output port, and 3.5mm single ended output port.    Some of that heft is because of the battery arrangement.  Unlike most devices that use a LiPO foil pack battery, the C9 uses a removable battery tray with four 18650 Lithium Ion cells.   The unit ships with Murata (formerly Sony) VtC6 cells installed (more about these in the battery section later) and makes it easy for the user to carry a spare set when recharging is not an option or to replace the battery when the originals inevitably wear out.   The battery tray can be removed by using the provided tool to remove a screw from either side of the case about 1.5 inches from the rear, and then sliding the tray out of the rear of the unit.  Be sure the unit is off before doing so.    With the USB port and charging indicators being part of the battery tray, it may be used to charge the tray outside the unit.  Cayin offers spare trays as well for those who want a quick change option.   I’m glad to see a product that is acknowledges the need for user serviceable batteries as this is one of my biggest pet peeves with things like air buds.  Planned obsolescence due to not having the ability to replace a battery with a known life-cycle of 500 or so charge cycles has kept many products off my recommended lists.     One other note, this unit gets warm which shouldn’t come as a shock when you see class A and tubes in the mix, but Cayin has done a good job of controlling the heat build up and the unit while warm never got hot enough to be uncomfortable to touch or carry.




This is a loaded discussion as the c9 has so many different options.   The signal starts with the choice of tube or solid state balanced preamps (what Cayin labels as timbre circuits).  These are followed by a split.  One path remains balanced while the other is converted to single ended.  From there both paths pass through the primary gain stage (voltage gain 6dB) followed by the secondary gain  and a Muses 72320 electronic volume control (±18V).    After leaving the volume control, the signal passes to two fully discrete headphone amplifier circuits in opposite phase (Those familiar with the Cayin N6ii and particularly the E01 module will recognize the discrete amplifier design as it seems to be a near copy of the one used in that module.  Both of those circuits pass output to the balanced port while only one (the positive side) is used to feed the single ended circuit.     This can all be seen in the attached diagram below.  Just remember this is for a single channel so in reality the diagram would be doubled if looking at the entire C9 design.   On top of that, the unit is capable of impressive power (4,100mW (at 16Ω) or 2600mW (at 32Ω) per channel) which makes cooling those amplifiers even more of a challenge.


The C9 ships with four VTC6 cells made by Murata of Japan (formerly Sony).  These are 3000 mAh cells that are slightly lower capacity than the market leaders, but lead the market in sustained current throughput with a 20Amp rating.  That combination of 8.4V (2 in parallel 2 in series) at 20Amps gives the C9 the ability to run without needing a boost converter to dirty up the output.   While 18650 type batteries can be found at pretty much any vape shop, there are very few cells currently on the market capable of support 20Amp continuous power draw so when sourcing replacement batteries, ask for the Sony VTC6 by name or make sure to purchase cells capable of sustaining a high current load from a reputable seller.   Other compatible batteries include the Sony VTC5 cells, Samsung 25R, the LG IMR 18650 HE4, and Sanyo NCR2070C but all except the Sanyo have lower capacity than the VTC6 so will result in shorter battery life than the table below shows.   The Sanyo NCR2070C is actually a bit higher capacity than the VTC6 cells (3475 vs 3000 mAh) so will extend charge life by rough 15% when using the 2070C cells in the C9.    Also note that when charging lithium ion cells they will take an initial charge of 4.2V but will slowly self-discharge back to a resting voltage of 3.7-3.8V where they will then stabilize and can sit for an extended period at 3.7V.  A cell that self-discharges below 3.7V is going bad and should be changed.   When replacing batteries in the C9, always replace all four with a new set at the same time, do not mix old and new as this can have disastrous results.   I found the numbers provided by Cayin on battery life to be pretty accurate and while 5.5 hours is a little disappointing as one can’t get through an 8 hour work-day on a single charge, switching to class AB loses very little performance and nearly doubles that so is an acceptable trade off.


Korg NuTube 6P1:

I gave the tubes used here their own section as they are quite a departure from the tubes I grew up with and most here recognize.  The Nutube looks like an IC with a couple blue/green LEDs embedded.   In reality, it is a modern vacuum tube with improved power handling and microphonics and it behaves similarly to a 12ax7 in use.    The 6P1 is a directly heated dual triode tube using vacuum fluorescent display technology and is made under license by Noritake Itron of Japan for Korg.   Compared to the 12Ax7 that has a heater voltage/current of 12V/0.15A, the Nutube uses a heater voltage of  0.7V/.017A.   Likewise plate voltage of a 12ax7 is usually somewhere around 200-250V vs the nutube’s 12V.  One big difference though is mu (kind of gain in the tube if you will) where the 12ax7 is a good bit higher output than the Nutube.  Still we don’t see 12ax7’s used as pre-amp tubes often due to the fact they are too high powered for that role and instead they often are the 2nd tube in a circuit following a 12au7 or 6922 preamp tube with a mu similar to that of the Nutube.     So here we have a modern take on the classic preamp tube with lower power requirements, better stability, and a 30,000 hour rated life.    For more information, see Korg’s guide.



There really is no way to discuss the C9s sound in a single section as it has too many options to tune the sound to do that.  I have broken it down a bit based on modes so I can cover at least most of the options.   So first lets look at  Class A vs Class AB as that actually makes more difference than many will expect and will impact our tubes vs solid-state discussion that follows.   The C9 in class A mode is a bit less impactful than in AB mode but remains a little closer to neutral as well.    AB mode is more aggressive from bottom to top with more impact in the sub-bass and more shimmer in the treble range, but a bit less warmth than in pure A.   This is particularly notable in the mids and lower treble with AB having a bit tighter sound with a bit more edge to it.  The Class A by comparison is a bit warmer in the mids, but a  bit more laid-back as well.   These qualities show through in both solid-state and tube modes.   For example in class AB switching from Solid state to tubes doesn’t make this huge jump that many will expect, instead it softens the sound a bit and gives the C9 a more relaxed feel with less of that assertive edge in the treble heard in solid state.   Overall the AB tube mode is probably the best combination of detail and euphony and is what I would leave the C9 set to were I listening for pleasure.    Class A tube sound is smooth, warm and provides that creamy signature that pure class A tubes are known for.  It is a little thinner than the Tube AB which I found carried a touch more weight in the mids compared to Class A mode.   I preferred the detail of the AB mode with the tubes but for those looking for pure tube sound, the Class A tube setting will provide what they are after.   In solid state, the Class AB mode has the most impactful bass and treble of all the modes but also has what I thought was the worst mid-range tonality with strings presenting a bit too much energy at times.   It would likely pair well with a headphone that needs a little mid push to do its best work.     Class A solid-state loses a little of the impact of AB but gains a better timbre to the mids and treble that makes it a better option to my ear.  Vocal performance was best of all 4 modes in my estimation in the pure class A solid state setting.    Class A solid state is a good pairing for headphones that already have a V-shaped signature where it calms it a bit.

You can see that modes on the C9 are not gimmicks, they do actually give the user enough tuning options to use the C9 with a wide variety of sources and headphones and coax the most out of them.    Regardless of mode, the C9 had good clarity and instrument separation.   I have a hard time attributing things like stage and imaging to an amp as I find the headphone is mostly responsible for these qualities but I can say at the very least the C9 did nothing to detract from stage and imaging and in most cases it did seem to have a beneficial effect with improved stage dimensions.

The C9 also has the option of Line in or preamp input. The issue here is if using the line-input mode and accidentally switching to preamp input where the c9 is set to maximum possible output level one could destroy both the headphones and their hearing in a matter of seconds. For this reason, switching to preamp mode requires that the button on the left side of the unit be pressed and held as well as moving the switch to pre position on the front panel before engaging the preamp mode (smart!).    I tried the C9 in pre-amp mode and generally found that I preferred using line-in mode as essentially you are amping the sound twice in pre-amp mode coming from the likes of the WM1A or Cayin N3 Pro and in both cases I felt it lost a little bit of dynamic range as a result.



As mentioned earlier, the C9 is quite capable with nearly 2.7 watts into a 32Ω load so one would expect it to be best suited for full sized headphones or high impedance/low sensitivity in-ears.   I tested with the normal murderer’s row of 600Ω beyer dynamics, the He6 (balanced), and the HD800 (also balanced) and it handled all as well as I expected it would.   The tube mode seemed a particularly good match with the HD700 as it added a little body to the mids with its warmth.      Once I got through testing every headphone I could throw at it without finding any it really hated (from the Cascade and T5p at the easy to drive end all the way to 600+ Ohm AKG and power hungry T60rp and He6),  I turned to in-ears.  Surely this beast with enough power to light up an He6 was going to hiss when I plugged in something like the Andromeda and indeed it does.  Plugging in an iE-match solves the issue, but it is fairly clear that high sensitivity in-ears were not the intended target of the C9.



Let’s face it, there are not too many competitors for the C9 as most are either half the cost or twice it.   I used the two closest things I had at the house for comparison sake.  Those are an iFi micro iDSD Black label which puts out similar power to the C9 but lacks the modes and costs a good bit less, and the Chord Hugo 2 (a borrowed unit) which again, similar form factor and portability, but at a substantial increase in cost vs the C9.    The iDSD Diablo might be a fairer comparison but having not had the opportunity to get my hands on one yet, I’ll have to save that for a later date.


ifi Micro iDSD BL- 

These two have similar shapes with the ifi having a less convenient shape for stacking should the need arise.   The iDSD is a DAC/Amp vs the Amp-only C9, but offers similar power at 4 Watts into 16Ω (in turbo mode) and also has similar battery performance when set to equal output levels.  Sound wise the iDSD does not offer A/AB switching, or tube/solid state but does expose the dac filters and offers 3d and Xbass boost so does provide the end user some tuning ability.    The iDSD has an additional gain level that lets it drop lower than the C9 as the mid and high on the iDSD are roughly comparable to low and high on the C9.  iDSD also has the iE-match built in that will be needed for use with in-ears with the C9.    What the iDSD does not have is as rich and full a tonality as the c9 when on tube mode or the dynamic range of the C9 on solid state.   The iFi has become a very popular dac/amp for price performance, but Cayin clearly has outclassed it with the C9 and a quick listen will show any would be naysayer why the C9 commands the price it does comparatively.    The battery in the iDSD is non-removable and charging requires a male to female USB cable that is much more difficult to source than a replacement USB type C used with the C9.      While I still find the iDSD good value in the $600 range, it doesn’t fit in this comparison as build and sound both favor the C9 by a good margin.

Chord Hugo 2 –   

Here again, its dac/amp vs amp with the Hugo 2 having  Chords FCPGA as its centerpiece that operates as both dac and control unit.   Unlike the previous compare, the Hugo 2 comes in at roughly $500 more than the C9 so we have both a functional and price disparity.  I might have mentioned the market for $2k amps is pretty thin.    In order to do a valid compare I used the Hugo 2 dac output to the C9 via a 3.5mm to RCA cable so as to only compare amp to amp.    Both are more transportable than pocket material with the Hugo coming in at 400 grams and the C9 at 550, neither is a lightweight and both are fairly large footprints for portables as well.  Construction favors the C9 as it looks more premium while the brushed  shell of the Hugo 2 looks a bit unfinished by contrast and don’t get me started on the controls on the Hugo.  Whoever thought it was a good idea to wrap controls all the way around the unit has obviously never tried to use the Hugo 2 on an office desk where you either expose the controls or the headphone jack.  And on top of that you have to wrap the USB cables around the front to connect a source via USB or charge the unit.  Ergonomics very much favors the C9.     The Hugo 2 is a class A only amp with no option for tubes or class AB so the ability to change its tonality is only through the dac filters and changes are more subtle compared to mode switches on the C9.    Power handling is quite similar in single-ended between the two units with a slightly advantage to the Hugo as we get above about 300Ω headphones.   Having said that, the balanced output on the C9 is not even an option on the Hugo and easily outperforms the Hugo’s single ended output (even including 300-600Ω models that slightly favor the Hugo2 on single ended).     The other oddity here is despite power being roughly equal, the C9 has less hiss and noise when using things like the Andromeda or K5 and the Hugo 2 is about unusable with these same in-ears without adding the iE-match to the mix.

Soundwise, the star of the Hugo 2 is the DAC as it is super detailed and very near neutral so sorting out the amp differences was a bit of a task.  The c9 has more weight and a bit more low end grunt with either a slight sub-bass emphasis or simply enough power to get all of it out of the connected headphone.  The Hugo2 is slightly less impactful, but a little tighter and a little more linear.  Above the lows, the Hugo 2 seems a bit thinner while the C9 is a bit fuller and more lush.  The Hugo 2 is the better technical performer but the C9 is more engaging of the pair with vocals being notably more musical via the c9 and more analytical via the Hugo2.      These two obviously target different things with the Hugo going for absolute neutrality and cleanliness and the C9 going for a more organic musical experience.    If listening for review purposes, I’d choose the Hugo 2, if instead listening for pleasure, I’d use the Hugo 2 dac output to the C9 and pair it with the HD800 all day.

As a final note, the Hugo 2 battery life is even less than that of the C9 so if you plan on using the Hugo 2 for any extended period, plug it in.



Cayin has been in this game for more than a few years and has made premium products in the tube amplifier space for years.  More recently they got heavily into the portable space and have now produced some fantastic products in that space with innovations like being the first premium DAP with modular dac/amp modules,  the first budget DAP with tube/solid state amplification options etc.    Seeing them combine their design chops from portables and tube amps into the C9 was a natural extension of their business and it shows.  There is nothing about the C9 that isn’t well thought out, well designed, and equally well implemented.    From the removable, replaceable battery pack, to the location of all controls centrally, to the options of sound signature, the C9 shows that Cayin did their homework.    The C9 is expensive for sure, but it shows all the polish and capability we expect from a product in that space and for those who can afford it, it’s a helluva product.   I was honestly sad to see this one go as it rivals the best options I have on hand and is more portable than things like my Auris Euterpe that compete with it in performance.    The other nice thing is being a pure amp  with a tube lifespan of 30,000 hours of continuous use, and replaceable batteries, this could well be the last amp you need to buy for the foreseeable future since while DAC and OS functionality seems to change weekly, a pure Class A tube amp has been around since the 1940s and is still going strong today.

  • 8.5/10
    Packaging - 8.5/10
  • 9/10
    Accessories - 9/10
  • 9.5/10
    Build Quality - 9.5/10
  • 9.5/10
    Sound Quality - 9.5/10
  • 8/10
    Battery Life - 8/10


Pros –  great musicality with good power and dynamics.  replaceable battery, spare battery packs available.

Cons – middling battery life, slight non-linearity in signature, some hiss with iems.