# [Impression] JDS Labs C421 (OPA2227 vs. AD8620) featuring cmoyBB, O2, T5 and UHA-4.



## ClieOS

I have to admit that I took immediate interest when JDS Labs announced their C421 project. Not only because their cmoyBB has impressed me before, but the fact that they are offering C421 alongside with the much acclaimed NwAvGuy’s open source Objective 2 (O2) amp (*End Note 1) is a great sign that they are confidence about their own design. 

C421 came in three flavors at first – you could select OPA2227, AD8066 or AD8620 as the main opamp, which are also the choices JDS Labs offered for their cmoyBB and some of the most popular opamp choices for DIY amps. The option for AD8066 is later removed since not many buyers ordered it, but it is still available under special request.







*Spec & Features*
Main opamp choice: OPA2227 or AD8620
Run-Time: 11+ hours 
Charge Time: 2 hours to 80%, <5 hours to 100% 
Frequency Response: +0.01, -0.41 dB (20Hz-20kHz) 
SNR: > 110 dB (20-20kHz) 
THD: < 0.0041% 
Crosstalk: < -57dB 
Output Impedance: *See ‘Impedance Talk’ section for more detail
Enclosure Size: 97.5 x 14.0 x 62.5mm 
Dual Gain, 2.3x or 7.0x (+7.2dB or +16.9dB) 
Bass Boost, +8dB peak 
Low Battery Indication 
0.1% Thin Film Resistors 
1200mAh, 3.7V Li-Ion Battery 
USB Powered Smart Charging 
Synchronized +/-7V rails
Aluminum Enclosure
Price: US$184 for OPA227 or US$189 for AD8620






*Build Quality and Accessories*
Like everything JDS builds, the C421 has excellent build quality. The black aluminum case has the same texture as the Meier Audio Corda 3MOVE / Stepdance’s case, which almost feels like sandpaper in finish. It looks classy but not that type of surface you will want to put an iPhone’s smooth back cover against it without something sandwich in between. But then, it really isn’t that big of a deal. The face place is quite good as well, but I wish the logo / letter marking should have been darker and bolder. That is mainly just aesthetic and doesn’t affect the value of the amp in anyway. If I were to compare, I’ll say Leckerton Audio UHA-4’s casing finish would be something I am more preferred. It is ultra-smooth without any corner and all the cutting and holes for the switches are just about perfect. Not that C421 is bad in anyway, but there are still room for future improvement no less. 

Accessories include a good quality USB cable for charging and 4 rubber feet – that’s something nice for JDS to include.





Would have been better if power LED is on the front plate

*Layout*
The front layout is nice. I generally prefer the input and output jack being further apart than they are together like the UHA-4. It gives more space for plug orientation as oversized and L-shaped plug isn’t that uncommon in the audiophile world. 

One thing I’ll like to see is having all the switches (bass boost, gain and power) placed just a little inward on the PCB so they won’t stick out as much on the casing. Two or three millimeter more inward will be all there is needed.

The second thing I’ll like to see is the front facing LED indicators instead of the rear facing. On a few occasion I have forgotten to switch the amp off because I didn’t notice the LED is still lighted up since it is on the back of the amp. It would be nice to at least have the power led facing forward.

*Battery life*
The listed battery life is over 11hours, which is about right as I can regularly get between 12 to 14 hours out of it before needing a recharge. The overall length of time of course will change depends on both the load and the volume. When the battery is low, the battery indicator on the rear will light up, warning you there is less than an hour of battery left and it is about time to recharge the amp.

The internal Li-ion battery is identical to that of the old iPod 4G battery so replacement is totally possible, but the stock battery should at least last you a few years before you need to replace it. 

*Hissing + EMI*
C421 is close to completely silence even with some of the most hiss prone IEM. There is virtually no hiss. Click and pop are also close to minimum. EMI, or cellphone interference, is also close to being perfect as the amp remains totally silence right next to a cellphone that is receiving incoming call (which EMI is at its worst). All and all, C421 passes the real world tests with flying color.





Size comparison: (top, left to right) iBasso D-ZERO, C421, iBasso T5; (bottom, left to right) FiiO E11, digiZoid ZO2.3, FiiO E6.

*SQ*
Both version of C421, as well as cmoyBB and O2 have been given at least 50 hours of burn-in before the review – no audible difference was detected on any of them.

Before we go ahead and discuss C421-2227 or C421-8620, I think it is important for us to reference back to other two amps JDS Labs is making, the cmoyBB and O2:

I have reviewed the cmoyBB almost 2 years ago and quite impressed by it (see the review here). It is one of the most impressive cmoy variance I have ever heard and well worth the asking price. Still it is not the reference portable amp of my choice as it sounds just a bit upfront and lush in a way – almost ‘fun’ sounding. It has more to do with the OP2227 used in cmoyBB as I have made note that AD8066 and (especially) AD8620 both sound more neutral (and have overall better performance) than OPA2227. For a very large part, I think I can say I have observed the same difference in the two version of C421. Since everything is equal in both versions except for the opamp, I think that is to be expected. Now let’s leave that part of the discussion for a later time and focus on the O2.

O2 is designed to be as good sounding to the ears as it is good to the measurements. You might not like NwAvGuys’ attitude and approaches toward some of the well established DIY’ers, but it is hard to argue that O2 isn’t an excellent amp of its own right. It is by far one of the most transparent amps I have heard of any price range yet it is not short on anything performance wise – soundstage, power, control and faithful to the source without any sense of coloration. It has become my reference of what neutral amp should measure up to, and naturally it is what C421 should measure up to as well.

Both version of C421 are easily some of the best sounding sub-$200 portable amp I have heard and without a doubt can compete with more expensive portable amp. Regardless of which opamp, they are powerful and close to being transparent. RMAA test reveals that both versions do measured very well. In fact, some of the best I have even measured and even close to (but not beating) the performance of O2 in most area. The results either mirror those that have been published by JDS, or close enough to O2 that would not worry me. The only area that isn’t impressive, so to speak, is the crosstalk measurement, but it is outperformed the published spec. One thing that RMAA doesn’t measure is the output impedance, which will be further discuss on the second to last section of the review.





C421, on top of O2.

I have made a few observations in the forum on both which I think are still very relevant and thus I am going to quote them instead of rewriting.



> …It is almost like the last time I compared the stock cmoyBB (which is OPA2227 based) to the AD8620 rolled cmoyBB, except this times both C421 sound much better than both the cmoyBB in every way. Like last times, the AD8620 wins over OPA2227 for me again. Not something night and day, but enough to call out a winner.
> 
> However, this is not to say AD8620 crashes OPA2227 in every way. I love the AD8620, but I can understand why someone would find it V-shaped sounding and prefer the OPA2227 instead. It has more to do with the slight difference in presentation between the two opamps (and I had observed the same in cmoyBB as well) - AD8620 has really great soundstage and portrays the image in a very 3D fashion. In a way, it is almost better in imaging (especially in depth) than the O2 and that's quite an amazing feat on its own. OPA2227 on the other hand puts everything upfront with a sense of rich and warmness between the tones. If we were to take O2 as our reference for what 'totally neutral' / standard should be, then AD8620 would be the equivalence of what 3D TV meant to normal TV (where you get the surreal 3D effect) while OPA2227 would be equivalence of sitting close to a HD TV vs. at normal distance (where you get to see the fine detail in individual element but not quite so over the whole picture).
> 
> ...




I think the above sum-up well how I feel about the two version of C421. Both are excellent amps but my preference goes to AD8620 because it has the resolution not found on OPA2227. It is the closer amp to O2 of being neutral and transparent. But as I have said in my sub-$100 amps shootout and as a general observation in the forum, I do notice people tend to opt for a warmish sound when it comes to amp because neutral is ‘sterile’ and ‘does nothing’ to improve sound. It is a strange thing that sound must be richer and lusher to consider improved, but that’s a choice I’ll leave for you to decide on your own - or choose your own poison, so to speak.



> *C421 vs. Ibasso T5 vs. Leckerton Audio UHA-4*
> …Volume matched using a SPL meter to wihtin 0.3dB of each other, I'll say there is no distinct advantage in SQ for T5. Overall, C421 (both AD8620 and OPA2227 version) sounds more detail and specious than T5, while T5 has the unique rich and smooth tone that usually associated with balanced amp (T5 has BTL ground, a type of active balanced ground). Technically, I'll say C421 is slightly ahead of T5, but the difference is small and quite subtle IMO…
> 
> …But as far as hearing goes, I have to say UHA-4 and C421 are very close in performance. Note, I choose OPA209 in my UHA-4 instead of the default AD8610 as I want to try a new opamp. I already have several AD8620/8610 amp in my collection and OPA209 seems to be very popular and well recommended.
> ...




So which amp to choose? O2 is the obvious choice if performance is the only concern. You'll have to look pass its bulky size, the need of a dedicated AC charger and the relatively shorter battery life. It is really more like a transportable than it is portable. T5 is a good choice but it has problems of its own - overly loud click-and-pop during start-up and mediocre built quality when compared to other amps of the same caliber. The one advantage its has is its BTL ground, which gives a balanced-like output and plenty of power, probably the most powerful portable amp under $200. UHA-4 is by far the toughest challenger - slimmer and smaller than C421, it measures just as well as C421 under RMAA, no impedance issue at all, has a crossfeed circuit and USB DAC. Most importantly, it sounds almost as good. Well, the key word is 'almost' - as a pure amp, my ears fall for the C421-8620. I know I can be happy with UHA-4, but that is if I haven't heard the C421-8620 in the first place. But as far as value-for-money is concerned, I think UHA-4 does beat C421 by a hair with its included USB DAC. That is, if you do need an USB DAC.






Family portrait of JDS amps.

*Bass Boost*
Bass boost is what makes JDS Labs’ cmoyBB famous in the first place so naturally it is a ‘must-have’ feature on the C421. If you take a look at the two frequency graphs below, it is very apparent that the bass boost is more of a deep bass boost (*center around sub-bass, below 100Hz) that give rumble and body rather than a boom bass boost (*center around mid-bass, 250Hz region) that gives quantity. Both version of C421 has similar FR curves, starting under 1Khz, reaches 1.5dB @ 250Hz and 3dB @ 150Hz, then finally peaks at over 6dB @ 20Hz – which is quite impressive. While 6dB isn’t as high as the listed 8dB peak, it is still quite a lot and frankly enough for most.








Bass begin to roll-off under 20Hz, but that is out of hearing range.

*Impedance Talk*
With all the praise, it is time for the bad news.

Just a rule of thumb, I’ll generally do some basic measurements when evaluating portable amps. RMAA will give some reference points for comparison but it is generally not detailed enough to give the full picture, and I can’t really afford (or know how to use) an oscilloscope or audio analyzer. But as far as RMAA goes, as I have mentioned, C421 is doing very well. The ‘problem’ is when I started to measure the output impedance - which I generally carry out using a 1kHz test tone and a 47ohm fix load, then calculate output impedance using the voltage difference between loaded and unloaded output. The first measurement is so wild that I thought my multimeter was broken and I have to get a second, more precise multimeter to confirm the measurement. The final output impedance is calculated at around 10.5 ohm. The test was repeated using a different source with 100Hz and 500Hz test tone and the results are similar. That’s quite different from the >0.1ohm once listed in spec.

I have contacted JDS Labs for my measurement result and they later confirmed my result that the output impedance is indeed significantly higher than what they have previously estimated on the simulator during prototyping. I think it is only fair if they have the chance to explain it to you and not through my words, so I am not going to elaborate too much on the detail. But so far, I think the smoking gun for the high output impedance is an unforeseen compromise arose from trying to design an amp that protects itself from user error, which ends up making it less than ideal. However, like I have said to John @ JDS Labs, I really have nothing bad about C421 to say. It is an excellent sounding amp before I know about the output impedance issue and I don’t see why I would want to change my opinion over it just yet. Yes, C421 will not have nearly as good a electronic dampening as many other amps, but it is not like HeadRoom Total BitHead (which also has high output impedance, though not as high as C421) where the lack of control and bass roll-off really bothers me. It is definitely a weak spot but it is also only a single aspect of C421 and overall, I am still very happy at what I have listened for the last few months - and I’ll keep listening.

*Ending*
Oh, C421 (or more precisely C421-8620) would have been the most perfect slim portable amp I have ever used so far with the right combination of performance and value for money, but it is not to be. Well, not 100%. It will be silly to say people won’t start to worry about output impedance at this point even though some of them might have been very happy with their C421 before reading this review. No, this is not a witch hunt and frankly, I am not that worry about output impedance myself, though I should have - you know, being an IEM user and all with a large collection of IEM that are low in impedance. But I also know my IEM sounds great with C421 and see no reason why it shouldn’t be recommended as one of the best sounding slim amp in the sub-$200 category. That’s my opinion.

*Thanks to JDS Labs for the C421-2227 loan unit.

(*End Note 1: in case you have no idea who NwAvGuy is – he is the ‘mad scientist’ equivalent of electronic engineer who took upon himself the duty to debunk all audiophile electronic myths and expose the dark underside of audio business using measurement and science. While I did just refer him as mad scientist, I don’t mean anything ill toward him, just his rather radical approach to the problem and how he poses himself to the world. While there might be a lot of madness in his work, there is undeniably a lot of goodness as well. For example, O2 is his challenge to both mainstream and DIY amp designer for designing a reference quality portable amp that is both affordable and purely based on objective criteria/measurement.)

*[UPDATE]* Oct. 2012
A reversion with new parts (but same PCB) has lowered the output impedance to 2ohm, which should avoid most of the issue I have discussed above.


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## Mutnat

Wow, thanks for that detailed comparison!  I don't think I knew about the UHA-4 when I bought my C421-2227, or the decision might have been pretty tough!  None-the-less, I have been very, very happy with my amp. 
   
  I was wondering if you could point me to something I could read to understand what output impedance is and what the effect is on the end sound.  I know that headphones are rated at a certain impedance, and that the impedance and efficiency ratings on a given pair of headphones can roughly tell you how much voltage and current is needed to drive them (I may have those backward), but I've read very little about output impedance of the amps themselves.  Does a 10 ohm impedance mean that some of the power it generates is essentially wasted before the signal even makes it to the headphone cable?


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## omelette

http://www.head-fi.org/a/headphone-impedance


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## ClieOS

omelette said:


> http://www.head-fi.org/a/headphone-impedance




That is for headphone impedance, which is not the same as output impedance for amp. I can't point you to the page due to some forum rule, but google 'NwAvGuy amp impedance' should land you on the right place to explain all about output impedance and how it matters.


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## jseaber

Great work, ClieOS. As you asked:
   
  We measured every published characteristic of c421 and documented the test setup, except for output impedance ("output-Z"). The output-Z spec was listed without test setup notes, as it was a theoretical figure from our simulated LTSpice IV model. The entire c421 circuit, from the power stage, through the opamp output stage, was simulated before we built a prototype.
   
  Outputs of c421 are coupled to the headphone jack using strong SMT ferrites. These are the components responsible for output-Z. The purpose of these parts is twofold. First, they result in stable opamp phase response well into MHz territory (as gain naturally diminishes), even when loaded with a long or messy audio cable.
   
  Second, it's critical in a voltage boosted design to minimize radiated emissions in accordance with international guidelines. We spent months getting this right. c421 is clean and well behaved because we sought design advice from an expert in EMI regulations. This engineer was singly responsible for saving a multimillion-$ audio company from huge FCC fines about a decade ago. He asked that I keep his name anonymous. Anyway, output ferrites are an easy way to keep MHz+ noise from escaping a circuit. While c421 is measurably clean, we left these parts in place after prototyping because they're low cost and keep EMI noise to a minimum. Win-win...until ClieOS measured a specification we had not confirmed.
   
  DC resistance of these ferrites is R < 0.1 ohms. But impedance is |Z| = |R+jX|, and it was my failure to verify the true output-Z by measurement. The manufacturer supplied datasheet and LTSpice simulations made the reactive component appear insignificant. Unfortunately, that was not true at all. Actual impedance is right around 10-11 ohms, as ClieOS measured. We immediately revised c421's listed specifications.
   
  If by chance this specification error bothers someone, there's any easy fix to yield the expected value. Shorting out the ferrites will result in output-Z of < 0.1 ohm. But considering the tone of this review (and others), we will not alter the design of c421. The amp is well established and it would be confusing for units to exist with different specifications. And as explained above, the parts exist for a reason.
   
   
  Finally, I think there is some slight confusion when ClieOS mentions "the high output impedance is an unforeseen compromise arose from trying to design an amp that protects itself from user error". I believe this comment is in reference to a PM discussion we had about a feedback loop resistor, which does not affect output-Z. Here's the PM I sent in response to ClieOS's question about the purpose of resistors 14 and 15:
    
   


> c421 was designed to minimize failures due to customer error. R14 and R15 are for IC protection when an input cable is mistakenly connected to the output jack. This happened frequently before endplates were manufactured. The OPA2227 survives, but AD8620/AD8599 and others are not always happy (usually, but not always).
> 
> R801 and R802 further protect the IC mechanically, via 150 ohm resistive load when the output/headphone cord is unpplugged. But mechanical protection obviously cannot protect against reversed cables.


 
   
   


  Quote: 





clieos said:


> *Impedance Talk*
> I have contacted JDS Labs for my measurement result and they later confirmed my result that the output impedance is indeed significantly higher than what they have previously estimated on the simulator during prototyping. I think it is only fair if they have the chance to explain it to you and not through my words, so I am not going to elaborate too much on the detail. But so far, I think the smoking gun for the high output impedance is an unforeseen compromise arose from trying to design an amp that protects itself from user error, which ends up making it less than ideal. However, like I have said to John @ JDS Labs, I really have nothing bad about C421 to say. It is an excellent sounding amp before I know about the output impedance issue and I don’t see why I would want to change my opinion over it just yet. Yes, C421 will not have nearly as good a electronic dampening as many other amps, but it is not like HeadRoom Total BitHead (which also has high output impedance, though not as high as C421) where the lack of control and bass roll-off really bothers me. It is definitely a weak spot but it is also only a single aspect of C421 and overall, I am still very happy at what I have listened for the last few months - and I’ll keep listening.


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## ClieOS

Thanks for chiming in for an explanation, John. Those ferrites do their job well to make the C421 immune to EMI as I have not been able to detect any interference placing it next to a cellphone.


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## Mutnat

Wow, thanks for the detailed explanation, John!  I'm no expert on electronics design and electrical engineering concepts, but what I distill from what you've said is essentially that the higher output impedance is a result of some choices made to minimize interference from and to phones and other devices.  This does seem consistent in that nobody has complained of any interference from phones, which is common with many models of portable amps.  Since the end result sounds so good, I think this was definitely a worthwhile trade-off. 
   
  I did read in the link that omlette posted:
   
  Quote: 





> As a rule of thumb, the load impedance (headphone) should be at least ten times higher than the amplifier output impedance.


 
   
  And I was a bit worried, since that sound seem to indicate we should only use 100 ohm of higher headphones with the C421, and my HD25-1 II's are only 70ohm.  But I can't argue with the results.


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## Cassadian

Nice review.


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## s0lar

Nice review. There are some very good amps available for not that much money!
  I can also confirm the O2 is very transparant.


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## leothurpv

I'm wondering what the situation is with output impedance - on both your profile and the website it still is listed as 0.1 rather than 10-11 :/ urm.
   
  Also I'm new to this entire thing - anyone know how the MG6Pro would perform with the C421? It's 32ohm if that's helpful (lol see how new I am? xD)


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## ClieOS

leothurpv said:


> I'm wondering what the situation is with output impedance - on both your profile and the website it still is listed as 0.1 rather than 10-11 :/ urm.




Are you addressing me or John? I'll guess you are referring to John but I remember the incorrect output impedance spec has been removed from JDS Labs's website even before I posted this review and thst'd almost 3 months ago.


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## jd4091

Great reading in this thread. Thanks to ClieOS and John.  I have Cmoy BB 2.03 and c421. Was condsidering O2, but really happy for now with the c421. Really nice amp.


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## cyberalpha11

Hi ClieOS.
  I need your opinion about the performance between JDS Labs C421(OPA2227) and GoVibe VestAmp by Jaben Australia.
  Which is a better amp to drive Beyerdynamic DT880/DT990, and also which one has the wider sound stage, better separation, and good punchy bass?
  Thanks.


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## ClieOS

Quote: 





cyberalpha11 said:


> Hi ClieOS.
> I need your opinion about the performance between JDS Labs C421(OPA2227) and GoVibe VestAmp by Jaben Australia.
> Which is a better amp to drive Beyerdynamic DT880/DT990, and also which one has the wider sound stage, better separation, and good punchy bass?
> Thanks.


 
   
  Sorry, I have heard neither of the Beyer nor the VestAmp, so I can't really tell you anything.


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## rhapsodicboom

would the jds c421 be "good enough" to drive the he-500 ?


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## ClieOS

Quote: 





rhapsodicboom said:


> would the jds c421 be "good enough" to drive the he-500 ?


 
   
  I don't have a HE-500 to confirm, but I know it has a very low sensitivity. C421 might do the job but the new C5 is probably a better choice.


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## rhapsodicboom

What happens when lets say you have an amp which has a frequency response of 20-20kHz jds c4and headphones are of different responses like 14-29kHz. gradops500 Would that amp not be suitable for the headphones since its only giving 20-20 range and headphones not driving those higher frequencies because its connect to that amp ?
   
  looking into getting the grado ps500 but think my amp jds c421 may be limited


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## ClieOS

Quote: 





rhapsodicboom said:


> What happens when lets say you have an amp which has a frequency response of 20-20kHz jds c4and headphones are of different responses like 14-29kHz. gradops500 Would that amp not be suitable for the headphones since its only giving 20-20 range and headphones not driving those higher frequencies because its connect to that amp ?
> 
> looking into getting the grado ps500 but think my amp jds c421 may be limited


 
   
  Nothing will happen.
   
  Any well designed amp can outdo 20Hz-20kHz, but they only list 20-20 because that's what is important to human hearing and it is convenient (*and because many customers expect a number, even though most of them have no idea what that number actually mean).
   
  The so called 14-29 is also a marketing trick. First, you likely can't hear pass 20kHz, so what good 29kHz does to you? Second, the headphone is likely never be able to produce even 20kHz in enough loudness to make it to the +/-3dB (reference to 1kHz) tolerance. So why list 29kHz? Well, it looks good on paper, and most people will not consider it a fraud when a manufacturer exaggerate the actual performance in headphone (or at least they don't know about it). That's why the officially listed frequency response for most headphone are totally useless, and only intend to mislead the public who lack the knowledge.


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## rhapsodicboom

Thanks that was really helpful i guess its similar to marketing peak watts to RMS watts. So what exactly do you look out in an amplifier to pair it with a headphone which is meaningful, guessing it would be the power output listed. Or would it just be the matter of trying it out and hearing what you feel pleasing.


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## ClieOS

Quote: 





rhapsodicboom said:


> Thanks that was really helpful i guess its similar to marketing peak watts to RMS watts. So what exactly do you look out in an amplifier to pair it with a headphone which is meaningful, guessing it would be the power output listed. Or would it just be the matter of trying it out and hearing what you feel pleasing.


 
   
  The first few things to look for are the headphone impedance and sensitivity. These often are enough to tell you whether a headphone can be driven well by a portable source or an amp might be beneficial. High impedance (i.e. 80ohm or over) or very low sensitivity (under 90dB) means higher gain / volume might be needed. Too low of an impedance (under 16ohm) means more current output is likely needed. High sensitivity (110ohm or over) means you want to look for an amp or source that is hiss-free and low in gain. Of course, sometime synergy also matters if you are looking for a particular sound signature.
   
  Most of the time it is not what is needed that dictates what gear to get, but what we believe that is 'missing' that makes us want to upgrade. Unfortunately there is hard to know whether what we believe in is actually real or not.


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## hilosxdd

Are these suitable for CIEMs ?


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## ClieOS

Quote: 





hilosxdd said:


> Are these suitable for CIEMs ?


 

 Most CIEM have too low of an impedance to be used with C421 because of the possibility of coloration. Unless we are talking about single driver, I'll suggest the new C5 instead.


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## hilosxdd

Quote: 





clieos said:


> Most CIEM have too low of an impedance to be used with C421 because of the possibility of coloration. Unless we are talking about single driver, I'll suggest the new C5 instead.


 

 I see , thanks for the tips , since when they're out ? Have not seen these models before , only have seen like O2 and C421 . Are o2 suitable for CIEMs too ?


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## ClieOS

Quote: 





hilosxdd said:


> I see , thanks for the tips , since when they're out ? Have not seen these models before , only have seen like O2 and C421 . Are o2 suitable for CIEMs too ?


 
   
  O2 will works with CIEM without any problem. C5 has been out for a few months now, replacing C421.


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## hilosxdd

clieos said:


> O2 will works with CIEM without any problem. C5 has been out for a few months now, replacing C421.



Is an odac relevant for a (frequent) traveller ?


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## ClieOS

Quote: 





hilosxdd said:


> Is an odac relevant for a (frequent) traveller ?


 
   
  That depends how much you value a good sound out of your laptop and how much improvement there is going from the internal soundcard to ODAC. It will be easier just to look for a portable amp with built-in USB DAC even though it might not be as good sounding as ODAC + amp for the same budget.


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## hilosxdd

Quote: 





clieos said:


> That depends how much you value a good sound out of your laptop and how much improvement there is going from the internal soundcard to ODAC. It will be easier just to look for a portable amp with built-in USB DAC even though it might not be as good sounding as ODAC + amp for the same budget.


 
  Do any of the JDSLab amps have a Odac+amp ? Do all ODAC's need power supply ?


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## ClieOS

Quote: 





hilosxdd said:


> Do any of the JDSLab amps have a Odac+amp ? Do all ODAC's need power supply ?


 
   
  ODAC is powered directly from the USB connection, and it is a standalone unit. You can buy a O2+ODAC combo (where ODAC is fitted into the O2 casing) from JDS Lab, but it is non-portable and must be powered by a wall adapter.


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## elfary

Quote: 





clieos said:


> Most CIEM have too low of an impedance to be used with C421 because of the possibility of coloration. Unless we are talking about single driver, I'll suggest the new C5 instead.


 
   
  As a multidriver balanced armature iem user (Shure SE420, Westone UM3x, Shure SE535) i wonder what's the ear sensivity to frequency response deviations caused by output impedances drving swinging impedances.
   
  I wonder if is there any well established convention that states 1 decibel, 2 decibels or...kind like the 1/8 rule.


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## ClieOS

Quote: 





elfary said:


> As a multidriver balanced armature iem user (Shure SE420, Westone UM3x, Shure SE535) i wonder what's the ear sensivity to frequency response deviations caused by output impedances drving swinging impedances.
> 
> I wonder if is there any well established convention that states 1 decibel, 2 decibels or...kind like the 1/8 rule.


 
   
  That really depends on the impedance interaction between the amp and the specific IEM. Since every IEM has its own impedance curve, interaction will be different as well. But the general consensus is that 1dB variance is enough to be noticeable for most human. Of course, whether the coloration is a good or bad thing is largely a personal opinion. But in the quest of fidelity, the goal is try to avoid unnecessary colortion as much as as possible.


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## reff

great review


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## iguanajm

The O2 is definitley a beast!  (Not very portable)


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## rudi0504

Anybody know about battery replacement for this Jds labs amp C421
I have long time not use it , now the battery is dead
I write email to Jds , but the price included shipping is vey expensive about 50 USD 
If I sell my C421 only 90 USD 
Thank you


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## ClieOS

rudi0504 said:


> Anybody know about battery replacement for this Jds labs amp C421
> I have long time not use it , now the battery is dead
> I write email to Jds , but the price included shipping is vey expensive about 50 USD
> If I sell my C421 only 90 USD
> Thank you


 
  
 It is the standard iPod 4G battery IIRC. Here is an identical one you can get from eBay for under $20: http://www.ebay.com/itm/Fit-Apple-iPOD-Photo-4th-Generation-U2-battery-/360205622821?pt=Battery_Chargers&hash=item53dded9e25


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## jseaber

rudi0504 said:


> Anybody know about battery replacement for this Jds labs amp C421
> I have long time not use it , now the battery is dead
> I write email to Jds , but the price included shipping is vey expensive about 50 USD
> If I sell my C421 only 90 USD
> Thank you


 
  
 Hm, did you request USPS Express shipping? Cost of the battery is under $10 USD.
  
 Here's the part on eBay for $16.95 shipped:
 http://www.ebay.com/itm/Fit-iPOD-4th-Generation-battery-1200-mAh-new-/181328437577?pt=Battery_Chargers&hash=item2a38046149


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## rudi0504

clieos said:


> It is the standard iPod 4G battery IIRC. Here is an identical one you can get from eBay for under $20: http://www.ebay.com/itm/Fit-Apple-iPOD-Photo-4th-Generation-U2-battery-/360205622821?pt=Battery_Chargers&hash=item53dded9e25




Thank you ClieOS for your info


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## rudi0504

jseaber said:


> Hm, did you request USPS Express shipping? Cost of the battery is under $10 USD.
> 
> Here's the part on eBay for $16.95 shipped:
> http://www.ebay.com/itm/Fit-iPOD-4th-Generation-battery-1200-mAh-new-/181328437577?pt=Battery_Chargers&hash=item2a38046149




Hi jseaber
Yes I have requested with the cheapest shipping , they said normally they used fed ex 
Thank you for your info


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## rudi0504

I just got the iPhone 4G battery from my friend 
How can I replace the battery just plug and play or I must solder ?
Please advise 
Thank you


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## ClieOS

rudi0504 said:


> I just got the iPhone 4G battery from my friend
> How can I replace the battery just plug and play or I must solder ?
> Please advise
> Thank you


 
  
 Plug and play. It should have a socket on the battery cable.


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## rudi0504

clieos said:


> Plug and play. It should have a socket on the battery cable.




Hi ClieOS

Thank you for your help , I will try to open by my self , I got the battery now


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## Bassman999

How will this do with DT900 600OHM?


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## ClieOS

bassman999 said:


> How will this do with DT900 600OHM?


 
  
 By spec, it should do well enough. But any time with a 600ohm headphone, you are probably going to get better result with desktop amp.


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## Bassman999

clieos said:


> By spec, it should do well enough. But any time with a 600ohm headphone, you are probably going to get better result with desktop amp.


 
 From my reading so far, it seems tube driven might be the best bet for the really high ohm phones.


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## ClieOS

bassman999 said:


> From my reading so far, it seems tube driven might be the best bet for the really high ohm phones.


 
  
 Not really. It is not about tube vs. solid state but more about competent vs. incompetent design. Tube amps have their own problems, and often more so than solid state design and requirement more attention to get it right (= cost more as well).


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## Bassman999

clieos said:


> Not really. It is not about tube vs. solid state but more about competent vs. incompetent design. Tube amps have their own problems, and often more so than solid state design and requirement more attention to get it right (= cost more as well).


 
 I know little about amp designs, and was under the impression solid state make more power with lower loads..only problems are heat, and less cone/driver control.
 Making them sound better with higher loads, but with way less output power.
  
 I also thought somehow tubes put out more current with higher loads, and this was just based on specs from a few designs I saw.
  
 I also have no idea what amount of V or I is required to drive headphones or even mine specifically 990 600ohm to full output without clipping.


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## ClieOS

You might find this useful: http://www.head-fi.org/t/668238/headphones-sensitivity-impedance-required-v-i-p-amplifier-gain
  
 Not a direct answer regarding your headphone, but it should give you some idea on what kind of parameters you should be looking for.
  
 Don't really think the heat/current issue is correct with headphone. The power requirement on headphone is usually so small that the heat generated is negligible. With a 600ohm headphone, the current needed is also less demanding than, say, a 12ohm headphone. It is not the same compared to speaker.


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## Bassman999

I read the graph, and different pairs draw such different numbers like this one
  

Audio TechnicaATH-ANC7B1183050.3981.3050.52-14
 compared to this one

 Hifiman
HE-6894311.22260.9352927.734 15


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## ClieOS

It is not about individual headphone, but overall trend. If you look closely, you will see in many cases, high impedance headphone often requires higher voltage swing and lesser current draw than low impedance headphone.
  
 Also, HE-6 is a bad example for you to look at, as it is planar magnetic and not dynamic. You simply can't compare apple to orange.


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## Bassman999

clieos said:


> It is not about individual headphone, but overall trend. If you look closely, you will see in many cases, high impedance headphone often requires higher voltage swing and lesser current draw than low impedance headphone.
> 
> Also, HE-6 is a bad example for you to look at, as it is planar magnetic and not dynamic. You simply can't compare apple to orange.


 
 Ok yeah that one threw me, and didnt seem to fit the otherwise noticeable trend


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## H20Fidelity

My Studio V / JDS C421 rig.


I use this for driving full-size headphones mostly, with the likes of:  SHR440, ATH-M50, Klipsch Image One, MDR-V6.


Switching to 'high gain' it will drive 250ohm DT880 without any fuss.


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## Redcarmoose

I just picked one of these guys up on the used market for a song. Reading the OPs original review was impressive to me. When I saw this amp company's products recommended on Head-Fi to drive the AKG k701s my jaw dropped. Actually if I was outside a small fly could have quickly flown in.

Upon spending a couple days with it, I'm quietly amazed. I was looking for an amp to take with me around the house and into the yard with full size headphones. I know, I'm strange. But having a really small amp and DAC/file player and being able to walk around with great sound is of value to me.


I really can't add anything to the review on page one as it being so complete. I want to thank ClieOS for his PM about charging style, battery life and battery replacement.

So this amp does run the k701s to a point. I was listening to the Beatles " Here Comes The Sun " in Apple lossless with an iPod Classic and Fiio LOD and it was maybe just there in the volume dept. Mind you these little portable amps are not suppose to even come close to running a beast like the k701s and most readers here would see it as an exercise in futility. Obviously this little amp has way enough power for a lot of headphones out there. I'm primarily using it with full size Denon AH-D 7000 headphones. The 7000s are actually easy to drive and even though I have other amps which drive them better I just don't have extension cords that long or the interest to use them around water. Lol

My normal modus operandi is straight out of an iPod Touch 5 gen. So even though the JDS c421 is noted at ruler flat line transparency in the frequency response dept., I believe the iPods to be even a little more ruler flat. That said the JDS adds a tiny warmth to the combination that is an added surprise. That along with getting the added power to make the bass respond with more authority while using full size AH-D 7000s.

I'm sure added juice in the 5C newer model amp would benefit any asylum members attempting to drive the k701s. For the price and what I'm doing things are fine.



The 8620 chip dug it's way into my very rare and sonically demanding Pete Namlook & Klaus Shulze Feat Bill Laswell test CD. Most members use DSOTM I use The Dark Side Of The Moog VII.

Here. http://m.youtube.com/watch?v=5mHlBNIPTz0



I gotta say it's the way this handles the mids that makes the magic. Added the bass detail from such a funny little box the size of a pack of cigs. The great part is it is the most dead silent amp I own. Those magnets! I wish I had magnets to silence the hiss from my Wife.


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