$60 Pack of Awesome: JDSLabs Cmoy


After finishing the portable amplifier shootout, a few people asked me if I could do a review on more affordable portable amps — additionally to see how the cheaper ones compare to the flagship $300 and upward-class amps. I’ve listened to a lot of entry level portable amps, and in my opinion the Cmoy design is still one of the best sounding sub $100 portable amp there is. I’ve listened to so many different Cmoys builds, from point-to-point, protoboards, dual layer PCBs, active ground cmoys, to dual mono builds running off of a Sigma11 power supply. Despite the large variance from one build to another, the Cmoys have maintained a good standard of musicality, and I’ve yet to find a Cmoy that sounds bad or unmusical.

The main problem about recommending a Cmoy is that it’s a DIY project, while most people look into buying a finished product. Then I found out about the JDSLabs Cmoys, and the fact that they sell either fully built Cmoys or bare PCBs really interests me. John explained that his Cmoys can be built as a standard build, or he can customize it to fit every individual’s needs better. The degree of customization is quite large, as he quoted some number of 200 possible different configurations. I thought, great! Send me one standard built, and send me another one with some customization on it.

When the Cmoys arrived, I quickly unpacked the mailer box to see two Cmoys neatly sealed in a neat anti-static bag, complete with the customization notes printed on them. One amp was labeled as the stock build, while the other is labeled as a Low-Z (low impedance) set. The Low-Z amplifier comes with a lower gain than the stock set (Gain 3 vs Gain 6), and also comes with two TLE2426CLPs that gives the Low-Z amp double the current capacity of the stock builds. The Low-Ω set therefore is useful not only for IEMs, but also for low impedance headphones such as the 32Ω Grados, while the stock set is better for the other 50Ω and up headphones with relatively lighter current demands.

This is the stock build. Everything is properly labeled on the PCB including the input and output switch. Power ON/OFF is integrated into the volume knob.


This is the low-Z build with two TLE virtual ground current sources. (The two black transistor likes left to the Bass-boost switch).


Although JDSLabs doesn’t guarantee perfect Altoids case on each of their amps, the two I’ve received are flawless and free from dents and chips in the paint. The holes for the in/out jacks, volume pot, LED, and power adaptor jacks are very precise with zero slack. The potentiometer knob is of high quality anodized aluminum knob with rubber trims and clear dot marking. As you open the case, you find the PCB taking up less than half the space of the Altoids case, components placed laid out very clearly on a high quality dual layer PCB with a separate ground plane. The supplied manual is printed on a piece of paper, but it’s probably one of the best product manual I’ve seen in terms of product information for the customers. JDSLabs also supplied print outs of the frequency response curves of the two different amps, along with the configuration notes.

There are no labeling on the exterior of the case, but if you open up the case, you’ll see that clear labeling printed on the PCB of what each jack does. Inside you will also find a toggle switch labeled “BASS”, which boost up the bass section by 9.4dB, or “just shy of a perceived 2x increase in bass volume”, as JDSLabs wrote. Next to the Bass boost switch is the op-amp mounted on a DIP format switch. Everything about the build indeed is high quality. The LED brightness is just right, the input/output 3.5mm jacks grips very well and likewise the the DC input jack. The power switch is integrated into the volume control, but another nice touch John added is the positioning of another switch in the headphone out jack. When there is no headphones plugged in to the output, the amplifier will turn itself off, regardless of the on/off in the volume knob. All these bits add up to an impression that John is not just trying to make a quick buck selling pre-assembled CMoys. He truly sets out to create one of the finest Cmoy builds out there.

Like most Cmoys I have listened to, the JDSLabs Cmoy take on roughly the same kind of tonality. Overall the tone is medium warm, semi relaxed and smooth, emphasis around the lower mids to midbass with a relaxed treble. Especially worth mentioning is that the JDSLabs is extremely smooth, and above average when compared to the other Cmoy builds I know. I listened to the JDSLabs with the Audio Technica M-50 and the Sennheiser HD650, and the JDSLabs were able to make good music out of both headphones. After spending a few hours with it, I noticed that this Cmoy is totally smooth from top to bottom with no discernible flaws, spikes, uneven transitions, or distortions, anywhere in the frequency range. I got even more curious and so I plugged in the Sennheiser HD800 to it, and like what I noticed earlier, I could not detect anything unnatural or unpleasant throughout the frequency range. The JDSLabs Cmoy was just smooth from top to bottom — and that is very impressive considering the HD800 often still find faults on much more expensive desktop amps. To have such as smooth tonal balance from top to bottom is truly phenomenal, as this little Altoids-cased amp costs merely $60!

Perhaps if I were to nit-pick, I would complain about the relatively weak low-bass performance of the amp. But personally that’s just asking for too much from a Cmoy design, as many other more expensive portable amps still have a relatively weak low-bass. The semi-relaxed pace, and the midrange emphasis makes it a good all-rounder amp with a wide genre bandwith. However, heavy fast-paced music fans would probably want a faster-paced amp than the JDSLabs Cmoy.

It’s a very clean build in and out.


The JDSLabs come with a stock op-amp OPA2227 from Burr-Brown. The stock op-amp is very good and natural sounding. It’s what’s responsible for some of that smooth sound I described in the previous paragraphs. However, I have other potent op-amps that I would like to try on the JDSLabs Cmoy. At first I tried replacing the stock op-amp with the famous OPA627. The 9V battery that comes with the amplifier barely meets the minimum specified operating voltage of the OPA627, and so I found distortions on semi-loud passages. A better idea is to use an external DC power adaptor, which not only eliminates those distortions with non-stock op-amps, but also increased the dynamic range of the amplifier, even on the stock OPA2227. I didn’t use anything fancy here, just a plain 12V wallwart from my Hewlett Packard Printer re terminated to the proper 1.3x3x5mm DC connector. The JDSLabs Cmoy accepts a range of DC power adapters from 9-24V DC, either linear/switching or regulated ones. Seeing that DC Power adapter costs as little as $5.93 from DigiKey.com, it’s probably a good idea to have one around because not only does the 12V external supply gives a better dynamic range, but you can run the amplifier 24/7 without worrying about replacing batteries. You don’t need to unplug the batteries when using a power adapter (what a nice convenience!), but you need to plug the adapter when the amplifier is OFF.

Replacing the stock op-amp to the OPA627 improved the sound, though not by a large margin. A tad better micro detail, and a more weighty lower bass region, though soundstage was not as spacious as on the OPA2227. Another op-amp that I tried was the OPA2111KP, which performs at roughly the same performance level as the OPA2227, but with slightly different tonal balance than the OPA2227 and the OPA672. The OPA2111KP creates a more linear frequency balance that is less mid-centric, but improving the midrange clarity from the OPA2227/OPA627. With a Class-A biasing on the OPA627, the treble becomes very smooth and lush, something treble lovers should try. Class-A biasing is not a recommended configuration if you are using the amplifier without an external DC power supply, as the power drain on the battery would be pretty rapid. Moving around the different op-amps, I really am happy with any of the three I tried: the stock OPA2227, OPA2111kP, or the OPA627 (class-A biased or not). The JDSLabs Cmoy manages to give out a solid and musical presentation regardless of which of the three op-amps I use — though at the end I do think that the stock OPA2227 is my favorite out of the bunch (probably why John shipped the Cmoys with these).

Another thing that I discovered is that the JDSLabs Cmoy is very revealing of the original source. Some amps are not as transparent, and this makes source upgrades to better players like the Hifiman HM-602 less audible. But with the JDSLabs Cmoy, that congested midrange out of the Ipod Classic’s DAC always shows itself very clearly, making the HM-602 a much better player for pairing with the Cmoy.

Comparing between the standard build version and the low-Z version with double TLE2426CLP, I did notice that the low-Z version handled my 32 Ohm MS-Pro better at loud passages, where the standard build distorts earlier — but this was at extremely loud levels. When I using the more average headphone such as the ATH M-50, HD650, HD800, or the HD598, or even the JH16Pro, I find the standard build version to give a more spacious and open sound, and this was the version I prefer for most of my listening. I am not sure if the difference was caused by the op-amp’s performance at the different gain levels (Gain 6 vs Gain 3), or the different components used to populate the boards, or perhaps because of the addition of the extra TLE2426CLP on the low-Z version. Anyway, I’m sure that John can give a better insight into this, and perhaps even make a low-Z version while still retaining the same sonic performance of the stock build. John mentioned that he is able to do 200+ different types of customization, so I’m sure that the choice is plenty. But if you’re in doubt, just order the stock build version, as I never really had volume control problems (though the range was a bit limited) even with the JH16Pro.

The bass boost switch can be found when you open the lid of the case. It’s a toggle switch, and it adds a solid boost to the bass that extends quite low. It’s one of the better bass boost I’ve heard, as many bass boost often just lingers around the midbass area, while others tend to lose control of the bass. The bass boost on this amp actually goes fairly low, and the boosted bass remains fairly tight. It does color the bass area a bit and makes the frequency balance less smooth, so I actually use the JDSLabs Cmoy without the bass boost OFF mostly.

Slightly shorter and narrower footprint makes a nice stack together with the Ipod Classic 120GB.


One of the thing that people always wonder is how good these Cmoys are compared to the premium brand portable amps. I no longer have most of the amplifiers I reviewed on the Portable Amp Shootout, but comparing the JDSLabs Cmoy to the HeadAmp Pico Slim (with the JH16Pro) reveals that though the Pico Slim has better micro detail, the JDSLabs Cmoy is more spacious in the soundstage. Also comparing the JDSLabs Cmoy to the Ibasso PB2 (single ended) out to the HD800, I found that the tonal balance and the overall sound is not as smooth on the Ibasso compared to the JDSLabs Cmoy. Of course there are other differences such as tonal balance, presentation, or the accuracy of the digital volume control on the Pico Slim, or the power output of the Ibasso PB-2. But for the general headphones out there without any specific power demands, I think the JDSLabs Cmoy can hang out with the general crowd of the premium amps.

When I emailed John asking about his Cmoys, I was merely looking for a Cmoy that I can recommend to the Headfonia readers: a Cmoy with a good build quality, good sound, and at a good price. But after spending time with the JDSLabs Cmoy, I was truly blown away with the sound that I’m hearing. Not only is this one of the best Cmoy I’ve listened to, but the sound is actually very good that I know other people would be blown away when they listen to this $60 amp. It is a really good amp, and I recommend it wholeheartedly.

Extra Documents:


System used for review:
Headphones: Sony PFR-V1, Audio Technica M-50, Sennheiser HD598, HD650, HD800, Beyerdynamic T50P, Alessandro MS-Pro, Superlux HD440, Jays Q-Jays, JHAudio JH16Pro
Amplifiers: JDSLabs Cmoy Normal build, Low-Z build, HeadAmp Pico Slim, Ibasso PB-2
Source: Hifiman HM-602, Ipod Classic

$60 Pack of Awesome: JDSLabs Cmoy
5 (100%) 2 votes



  • Reply December 31, 2015


    Hello, I have a question. Spec wise, what would be a better bang for the buck? JDS Labs Cmoy or Topping NX3?

  • Reply May 26, 2015

    Eugenio Opazo Rosselot

    What about pairing a pair Beyer Dynamic DT 770 Pro 80 Ohms. Would it be a better match than the JDS 02?

  • Reply November 29, 2014


    I own the Sennheiser HD 600, which version should I buy? Thanks

    • Reply November 29, 2014

      Dave Ulrich

      The regular build will do just fine. It is a nice amp for the Senn.

  • Reply June 13, 2014

    electronic cigarette

    electronic cigarette

    JDS Labs Appreciation Thread!

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