This is my second attempt at using a portable amp (I returned my Fiio E12A for this).
 
That was a good decision. The Cayin C5 is an absolute powerhouse. It can power IEM's and earbuds (what I use it for), but also large size over-ear headphones. I am very pleased by the sound. It is slightly warm with a really expansive 3D soundstage. But by far the best feature is the bass boost; the sub-bass really slams. The amp can also charge your other devices (like your phone etc.) which is an added plus. I got the black edition which aesthetically looks great.

I used it with my Astell & Kern AK Jr. player and Rose Mojito high-fidelity earbuds.

 
 

The Good.

 

1. It's an amp and it's job is power and it's got a lot of that. I would think it was more powerful than the e12 though the specs say otherwise. Bass boost matches graph
2. Bass!!

 

Bass switch demo

 
Source was an X5 using this slope on Low Gain

 
 

 

More Good

 
Overall sound on normal listening with a different or no eq and a pair of open back Sony ma-900 reveals that the hype was right. Out of the box it has a wider spacial presentation not found on the e12.
 
 
 
 
 
 
 
 
 

The Bad

 

1. Getting an amp  20-30% more expensive than the e12 that has no mini to usb like the e12 comes with is unacceptable
2. The volume which is numbered in off brown/champagne on a cream (not white) wheel is very hard to see. It's under a plastic cover...fine. MAKE IT READABLE 
3. Blue? Really?.....blue. Thick blue straps (e12 has black and I got 4 and I got a normal ready to charge setup.)

 
 
 
 
 
 
 
 
 
The e12 is the amp I built the Extremebasshead thread with which will soon be the largest Head-fi has ever seen. As powerful as that amp is the Cayin C5 puts out what seems like more power as it seems to be cleaner/wider and the bass slope is elongated. I can sculpt a bass curve with an eq and the C5 gives me quite a hill to carve.
It is the new official amp of the Extremebass thread. The amount of e12's moved by that threads rec/video displays is a large number. I have to explain the weakness of the item to as they say "Keep it real". I expect folks wanting a wider stage (How does an amp change staging??) I dunno but the e12 clearly sounds more closeted when compared directly with the Cayin C5
 
 
I think the mini to mini cord is a joke and the blue rubber and numbering on the dial...if it's gonna sit under a shaded tree (plastic) should be bigger with better contrast
 
 
 
 
Rocky start but I think the long term will prove to be quite fruitful for my ears.
 

 

I am penning down my opinion about the ‘most-buzzed-about’ C5 amp. I will try to keep this review simple as possible and I hope it would be easy to read, and will help fellow enthusiasts to know more about the mighty C5 amp.
 

 
 
 
Me : I am an 21 year old Engineering student living in a small town in India. I would like to call myself an music enthusiast, rather than an audiophile.
 
I was inspired by music since childhood, and as the time passed, the passion of music grew in me, and that subsequently led me to join Head-Fi. Eventually, I found the pleasure of listening to music mainly by the HD600 headphones, and realized the true components of recorded music. I usually like to listen to Indian Classical Music along with Bollywood songs.
 
 
Intro :  Spark Audio used to be a subsidiary electronics department of the Chinese Air Force. Its association with tube electronics and dates back to the old days when aviation technology employed vacuum tubes. After its privatization in 1993, Zhuhai Spark electronic equipment ltd. decided to apply its technical expertise into consumer audio, and has become one of the most reputable audio companies in China. It designs, manufactures and markets its own products under the name “Spark” in China.
 
 
“Cayin” is a brand under Zhuhai Spark electronic equipment ltd. They mainly manufacture desktop and tube amplifiers. Cayin was not renown to most of us, until it released its famous C5 portable amp. C5 is the flagship portable amplifier offering from the house of Cayin.
 
 
Packaging and Accessories : The C5 arrives packed inside an simple yet rigid golden coloured classic cardboard box. The box is plain with only ‘Cayin’ written over it. The box has an slide-able sticker, which needs to be slid to one side to lift off the lid of the box.
 

 

 
Once the lid is lifted off, The C5 is seen to be resting on an pseudo-base, packed inside an soft cover. The pseudo-base can be lifted off to reveal the storage compartment, in which all the included accessories are present.
 

 

 
 
List of accessories in the box, which include the following:
 

 
1) 3.5mm interconnect cable: For attaching to an DAP, as its of short length and connects are 90 degree angled.
 
2) Micro-USB interconnect cable: To utilize the power bank feature of the C5, by connecting to DAP or smartphone.
 
3) Rubber feets: To attach to the C5 amp for getting better grip and for avoiding scratches.
 
4) Rubber bands: For binding the C5 with the DAP. Hence attaching them both as one whole unit.
 
5) Velvet pouch: To store the C5, and therefore avoiding dust and scratches.
 
6) Manual:  Contains the instructions for C5 amp and warranty details. The entire manual has recently been updated to English language.
 
Overall, the packaging and accessories gives an positive first impression. Packaging is secure and practical, with accessories provided being plenty and made up of good quality.
 
 
Design and Build : The C5 has an excellent build quality and has been built with professional grade materials. Metal panels, high quality audio jacks, switches and reliable overall sturdy construction. The C5 is roughly about the size of a 5 inch touchscreen smartphone, and is convenient to attach to most of the smartphones and DAP’s making it perfectly portable.
 

 
On the top part of the amp, Volume control, LED indicator and input, output jacks are present. The volume knob is embedded inside the main body of the amp, and feels comfortable to turn. The jacks are perfectly positioned and don’t cause hindrance of space.
 
 

 
On the bottom side of the C5, an micro USB charge inlet and an charge outlet are present. An 3 LED charge indicator is present on the front-bottom side of the amp. Bass-boost and gain switches are on one side of the amp, and feel ‘solid’ and smooth to switch. The C5 includes OPA134 as Op-Amp and LME49600 as prower driver, Alps pot as volume control, among other good quality interior components. 
 
Overall the C5 has solid exterior construction, along with well designed interior circuitry, which ensures in its long life and reliable consistent performance.
 
Here is the schematic of C5 as per Cayin:
 

 
 
Specifications of C5 as per Cayin:
 
Rated output power: 800mW + 800mW (32Ω load)
SNR: ≥101dB (A-weighted)
Life time: about 12 hours (32Ω load)
Frequency response: 20Hz-100kHz (± 1dB)
Sensitivity: ≤500mV (gain H)
Charge limit voltage: 12.6V
Charging time: about 4 hours (off state, using DC5V / 2A charger)
Total Harmonic Distortion: ≤0.02% (1kHz)
Lithium battery capacity: 1000mAh / 11.1V
Size: 136x63x15mm
Weight: about 185g
 
 
 
Portability and Features : 
 
The C5 is fairly light in weight, sleek in thickness, and is well designed, with controls and switches placed at right places in right manner. It slides in easily inside an jeans pocket.and hence be considered as completely portable. It gets charged by standard 5V micro-USB cable, and that gives it an worldwide charging opportunity.
 
Headphone protection relay : The C5 employs an smart relay, which ensures one does not hear any noise or EMI apart from the music itself. The relay automatically switches on when the amp is turned on/off, and absolutely no pop/click is heard from the C5. EMI pickup is absolutely Nill.
 
Power of Zeus : The maximum output power of the C5 is 800mW@32ohms. Which is an advantage for driving full size headphones. This amount of power is more than sufficient to drive anything from IEM’s to headphones to their very loud listening levels, and the C5 does an excellent job here.
 
Smart charging indicator : An 3 LED mechanism shows the level of charge in the amplifier and the current charging status in Low-Medium-High fashion, which I find is very convenient and well implemented. The LED's blink one by one when charging and also indicating the charge level simultaneously. I should also mention that, C5 can be switched on and used during charging also, and has no audible noise even during charging.
 

 
 
Memory volume knob : The volume knob is practically designed, and the knob has a slight play in horizontal movement, which ensures, the volume does not change, if the knob is accidentally jerked or turned unintentionally. It also has numbers imprinted on it, to remember the position of the knob and level of the volume.
 

 
 
Power bank : This is an interesting yet very useful feature which Cayin has incorporated inside an portable amplifier, The C5 has an charge out port, from which one can charge DAP or smartphone. Though it is not a very strong power bank, but it can be very useful in emergencies.
 

 
 
Bass boost : This feature is found in almost every portable amplifier, in C5, the BB feature is better implemented than most of the rest. BB switch in C5 Provides an fuller pleasant sound instead of solely extending and loosening the bass quantity. The bass boost performs very well without an hitch.
 

 
 
 
 
Sound : The C5 is overall ‘clean and clear’ sounding with excellent sound stage depth ( along with very good width), imaging and detail retrieval. Considering the C5’s overall neutral sound quality, It can match up with any genre and any headphone without sounding bad in particular. C5 is not as transparent as the O2 (as a reference) but is very close in terms of sonic performance. Sound stage width is very good especially in this range, and depth is phenomenal. Detail retrieval is excellent. Imaging and dynamics live upto expectations, giving an circular spacious surround sound. C5 can overall be considered as having holographic soundstage along with incredible neutral sonic performance.
 
C5 pairs very well on an dynamic Sennheiser HD600 and Planar Magnetic Audeze LCD2. It drives both HD600 and LCD2 with authority and with plenty of power to spare. The pairing results in an pleasing and clear non-fatiguing sound to our ears. Enthusiasts who wish to drive Summit-Fi headphones on an sub 200$ portable amp, C5 is the answer.
 
 

 
Gain setting (high/Low) is very wisely implemented, with low gain specifically implemented for IEM’s and high gain for headphones. Gain setting provides more than adequate output power. An slight hiss is noticeable with IEM’s on high gain, but that can be expected as high gain would be too much and not recommended for IEM’s. Low gain is more than sufficient for IEM’s, in this state, there is no sign of hiss.  With headphones, there is absolutely no audible noise, hiss, EMI in whatsoever configuration!  
 
Impressive indeed.
 
 
Comparison with fellow amps :
 
Since Objective2 and FiiO E12 are the top contenders in 200$ category portable amps, they are chosen for comparison with C5. Lets see how they put up against each others;
 
Objective2 : The O2 wins in terms of sheer transparency. C5 is close behind on its heels. The C5’s sound stage is massive, O2 also provides a very natural and effortless soundstage. O2 ‘sounds’ transparent, whereas C5 is also transparent sounding, with being a touch ‘bright’. Though O2 definitely Lacks output power, features and portability factor of the C5.
 
FiiO E12: The E12 has upper hand in output power with 880mW@32ohms and also has an slightly better build quality than O2 and C5. But E12 is noticeably warmer and is more forward sounding than both O2 and C5, which makes the E12 to possess a narrower soundstage. It is easy to conclude that C5 is a step ahead in terms of sonic qualities when compared to E12.
 
O2 offered supreme sound quality but suffered practically. E12 was designed practically, but sound quality was forward, and hence the sound felt compromised compared to O2 and C5. I feel the C5 delivers best of both worlds, with sonic quality very similar to O2, and with features and portability similar (or even better!) to an practically designed amp like E12.
 
 
Conclusion : Cayin C5 is an truely amazing, If not an mesmerizing portable amplifier. The C5 offers phenomenal Sound quality along with excellent portability and features, in an decent price bracket. It is an easy recommendation for an portable amp. I can safely bet on C5 as the best sub-200$ portable amplifier. 
 
 
 
Not to mention, the C5 amp has won my ears.