# c421 vs O2  - home amp?



## Kanashimu

I plan to use an amp with my Miracle. It'll probably be paired with the DX100 if I can get one. I've heard of lots of good things about the Objective 2 / DX100 pairing, but how does the c421 compare?

 Its strictly for home use - I won't carry and amp + a brick for portable use, so disregard the portability or battery life of the amps.

 Thanks.


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## F900EX

I have asked the same question myself. If anyone in the USA is going to buy and O2 and interesting doing a loan swap just to hear the difference, I'd be interested.


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## syphen606

Have a C421 at home now.. and will get the last of the parts needed to finish my O2 this week.  I'll let you know my opinion between them soon.


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## Kanashimu

Interesting, thanks.


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## ahntorage

Was there an update on the difference you experienced between the two?


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## i_djoel2000

i've tried both. o2 is just the better amp, no competition there
   
  o2 sounds much smoother, balanced, and more bodied


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## deviusdragger

I like my O2 amp!!!!


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## KGee

Headfonia also said that the O2 beats the c421 in terms of sound.  If you have no need for portability, I think buying or building an O2 would be the right choice.


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## jseaber

The difference isn't too pronounced. If you only need a home amp, then by all means go for the O2. The price is lower and it will out-benchmark anything in its class. But that's where Voldemort cheated: designing in batteries doesn't make a device portable. Portability is about size. O2 is _not _small!
   
  c421 sacrifices very little in terms of SQ to gain a great deal in features and portability. It's hard to go back to the O2 after listening to c421 with bass boost.


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## F900EX

See, this is were I am more undecided after reading the above .... I could buy the 2 amps, I just don't need 2 amps. I feel the one that I do like, I will use all the time. The other one will sit in a draw forever. I look at it as a waste.
   
   
  Seems like sound wise the O2 beats the c421. Were the O2 does not beat it, is in the bass and portability dept. 
   
  I'm going to assume the c421 will beat the O2 in terms of sound stage and clarity/details.  O2 sounds like a more natural sounding Amp.


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## deviusdragger

f900 i say just buy 2 used ones, keep the one you like. Im sure youll have no problem selling either of them on here. Unless your like me and just keeps both of them, just to say you have them both :-/


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## syphen606

In listening to my 8620 C421 and O2 with my HD650's back to back, they are very similar sounding to MY ears. I will admit that the O2 is ever so slightly better but like has already been said loses out for me once the bass boost gets turned on!   A few of my headphones sound much better with bass boost like mt 558's or my RE-262's.


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## Mozu

Weird. The AD8620 C421 sounded so v-shaped to my ears.


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## ClieOS

mozu said:


> Weird. The AD8620 C421 sounded so v-shaped to my ears.




If you are comparing AD8620 to something like OPA2227, then I would understand why you will find AD8620 to be V-shaped - well, perhaps V-shaped isn't the word I would use. OIPA2227 is a fairly flat and forwarded sounding opamp to my ears. AD8620 has much better depth and image in comparison. I would think those who rather prefer an upfront presentation might find the more specious AD8620 unappealing. I am more of fan for the AD8620 myself.


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## jseaber

Quote: 





clieos said:


> If you are comparing AD8620 to something like OPA2227, then I would understand why you will find AD8620 to be V-shaped - well, perhaps V-shaped isn't the word I would use. OIPA2227 is a fairly flat and forwarded sounding opamp to my ears. AD8620 has much better depth and image in comparison. I would think those who rather prefer an upfront presentation might find the more specious AD8620 unappealing. I am more of fan for the AD8620 myself.


 

  
  It's difficult to understand interpretations like this, considering audible range frequency response is flat for c421 and the O2. Mozu must be describing something else, as you suggest.
   
  This would be easier to settle if we could place the O2's output opamp in a c421. Alas, NJM4556 isn't available in the SOIC-8 package.


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## Roan3489

Well..... I guess I'll just have to buy both. Now I'll have all 3 amps from JDS Labs!


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## BGRoberts

I'm in the same boat..............
  I've got the JDS CMoy (2 versions) and the JDS O2.
  Now that little C421 is looking awfully nice.........
  Here we go again!


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## Raines

me too
   
  i have the jds cmoy and i love it
   
  I like the sound stage and the sound signature.
   
   
  I was getting the O2 as my cousin is coming from the USA to Portugal and could get me one
   
   
   
  Also thinking of the c-421  but .... the 8620 or the 2227???    people say one is better , others the other...
   
  going from the cmoy whar would be the diference for the 8620 or the 2227?
   
  thanks


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## Ultrainferno

Overal I prefer the C421-2227 over the O2. Yes, the O2 is the better technical amp, but to me it misses out on body, the mids are just too thin and the bass to my ears doesn't have enough impact and that's why I enjoy my music a whole lot more with the C421 even if the O2 has better spacing, detail and soundstage.
   
  I actually expected a better O2 after all the hype


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## syphen606

Quote: 





ultrainferno said:


> Overal I prefer the C421-2227 over the O2. Yes, the O2 is the better technical amp, but to me it misses out on body, the mids are just too thin and the bass to my ears doesn't have enough impact and that's why I enjoy my music a whole lot more with the C421 even if the O2 has better spacing, detail and soundstage.
> 
> I actually expected a better O2 after all the hype


 

 An O2 with similar bass boost to the C421 would be pretty awesome. You can't really compare them directly when using the bass boost of the C421.     
  I still think the C421 is awesome due to its portability and USB charging. When I'm on the go, I listen to music off my iphone. I usually have the means to charge my Iphone while I travel and thus have the means to charge my C421 without bringing a big power adapter.
   
  I still have both though and think they are a great combo.


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## Raines

got the c-421 2227
   
   
  LOVE IT


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## jschristian44

You guys do know that the Objective 2 can have a bass boost in it as well right?


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## ClieOS

jschristian44 said:


> You guys do know that the Objective 2 can have a bass boost in it as well right?




If you want to add a bass boost yourself, sure. But I think JDS probably can't add a bass boost in it, since the current licensing does not allowed any modification to the design and I don't think NwAvGuy is much of a bass boost believer anyway.


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## Ultrainferno

Quote: 





clieos said:


> If you want to add a bass boost yourself, sure. But I think JDS probably can't add a bass boost in it, since the current licensing does not allowed any modification to the design and I don't think NwAvGuy is much of a bass boost believer anyway.


 
   
  And you're being very polite stating it that way


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## Mutnat

Quote: 





raines said:


> got the c-421 2227
> 
> 
> LOVE IT


 
   
  My sentiments exactly


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## guhmo

I've got the c421 8620 and I love it too!


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## tomllm

Is there any hiss with the C421 and sensitive IEMs?


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## guhmo

Quote: 





tomllm said:


> Is there any hiss with the C421 and sensitive IEMs?


 
   No hiss whatsoever. Completely (audibly) black. However there is some channel imbalance at low volumes.


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## Grizzlymann

Would you guys recommend getting a c421 or Objective2 to go with an ODAC?  Or is there another DAC that you would recommend all together?


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## mmayer167

just ordered a c421 2227. I will compare it to my o2 source being the odac from jds. Look for a brief opinion next week.
   
  -M


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## alphaphoenix

Quote: 





grizzlymann said:


> Would you guys recommend getting a c421 or Objective2 to go with an ODAC?  Or is there another DAC that you would recommend all together?


 

  The C421 and ODAC pairs very, very well, both aesthetically and sonically.  My Yuin PK1 never sounded so good:


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## Ultrainferno

I have to give that a try...


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## guhmo

Wow, that combo looks good!


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## DanBa

The Android-powered smartphone Samsung Galaxy S III interworks with the ODAC:
  http://www.head-fi.org/t/595071/android-phones-and-usb-dacs-how-to-increase-the-issues-priority-with-google/60#post_8468969
  http://pastebin.com/Jjq4xnT3
   
  Samsung Galaxy S III > digital audio stream >> USB OTG cable >> USB DAC "ODAC" >> amp "O2" >> headphone


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## sashaw

Quote: 





alphaphoenix said:


> The C421 and ODAC pairs very, very well, both aesthetically and sonically.  My Yuin PK1 never sounded so good:


 
   
  Where do you get this ODAC?


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## alphaphoenix

Same place as the JDS Labs C421.


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## AstralStorm

Folks, what's the output impedance and real crosstalk performance of C421?
   
  (The measurements on JDSLabs page are useless - they don't have anything better than RMAA with a cheap soundcard?!)


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## elbastardo

Better specs posted here:
   
  http://www.sonicelectronix.com/item_46564_JDS-Labs-Inc-C421-C421-v1.01-Headphone-Amplifier.html
   
  Quote:


astralstorm said:


> Folks, what's the output impedance and real crosstalk performance of C421?
> 
> (The measurements on JDSLabs page are useless - they don't have anything better than RMAA with a cheap soundcard?!)


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## AstralStorm

This says 0.1 Ohm, but the thread: http://www.head-fi.org/t/615766/impression-jds-labs-c421-opa2227-vs-ad8620-featuring-cmoybb-o2-t5-and-uha-4
   
  Now that says 10.6 Ohm. 10 Ohm is unfortunately unacceptable for the annoyingly hard to drive IEM that is SE-5. 
  So, I've no choice other than fixing E17... (or rather, gambling it on the mail)
  O2 is not portable really.


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## ClieOS

astralstorm said:


> This says 0.1 Ohm, but the thread: http://www.head-fi.org/t/615766/impression-jds-labs-c421-opa2227-vs-ad8620-featuring-cmoybb-o2-t5-and-uha-4
> 
> Now that says 10.6 Ohm. 10 Ohm is unfortunately unacceptable for the annoyingly hard to drive IEM that is SE-5.
> So, I've no choice other than fixing E17... (or rather, gambling it on the mail)
> O2 is not portable really.




You can ask JDS to forfeit the ferrite which will of course worsen the EMI isolation, but you will get back the low output impedance. As my own pet DIY project, I am going to experience a variety of ferrite and see if a solution can be found where EMI isolation is still acceptable and output impedance can be lowered.


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## jseaber

Quote: 





clieos said:


> You can ask JDS to forfeit the ferrite which will of course worsen the EMI isolation, but you will get back the low output impedance. As my own pet DIY project, I am going to experience a variety of ferrite and see if a solution can be found where EMI isolation is still acceptable and output impedance can be lowered.


 
   
  Bypassing the output impedance (ferrites) shouldn't greatly impact audible interference. They improve phase response at high frequencies, blocking theoretical high frequency instability and interference. But these issues shouldn't be audible anyway.
   
  The 4-layer PCB is primarly responsible for EMI rejection and the great SNR.
   
   


astralstorm said:


> Folks, what's the output impedance and real crosstalk performance of C421?
> 
> (The measurements on JDSLabs page are useless - they don't have anything better than RMAA with a cheap soundcard?!)


 
   
  I won't defend RMAA, but we certainly did not use a "cheap soundcard". The RMAA test setup utilized a reference grade engineering sample of a high-end ADC and DAC. Most of our design reality checks are made on a Tektronix 100MHz digital scope w/FFT analysis function. Our reference ADC may not be a $10k audio analyzer, but I wouldn't call it useless. It at least provides a worst case picture of specifications. FFT analysis on a scope isn't as convenient or insightful as a dedicated audio analyzer. But again, it's not useless. Engineering is about designing the best solutions within a given set of constraints.
   
  Output impedance is 10.5 ohm. As mentioned above, we can set output-Z to 0.1 ohms if you will be using lower impedance sets and/or don't like the specification.


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## mmayer167

I am really liking my c421 with the 2227 op. It is a little meatier sounding and maybe a bit more sparkly than the O2 at times. Detail retrieval is excellent and as good as the o2 imo. But, the previous statement may be due to the c421 seeming a bit more snappy in the treble. This amp is definitely worth it paired with the ODAC! Killer combo, looks, size, function, and build are excellent. It handles the Paradox, which can be hungry at times, pretty well (with bass boost on). The D2000 are excellent out of it as well, at times the treble can be hot with the Denon since I think the odac is a bit treble hot mixing with the Denon smiley face freq (note: my d2k are partial markl modded). For me the O2 still wins when I want truth, but dang is the c421 enjoyable.
   
  Thought I would jot down some impressions after 5 days with the c421. 
   
  -M


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## AstralStorm

Quote: 





jseaber said:


> I won't defend RMAA, but we certainly did not use a "cheap soundcard". The RMAA test setup utilized a reference grade engineering sample of a high-end ADC and DAC. Most of our design reality checks are made on a Tektronix 100MHz digital scope w/FFT analysis function. Our reference ADC may not be a $10k audio analyzer, but I wouldn't call it useless. It at least provides a worst case picture of specifications. FFT analysis on a scope isn't as convenient or insightful as a dedicated audio analyzer. But again, it's not useless. Engineering is about designing the best solutions within a given set of constraints.
> 
> Output impedance is 10.5 ohm. As mentioned above, we can set output-Z to 0.1 ohms if you will be using lower impedance sets and/or don't like the specification.


 
   
  That sounds decent, I'll strongly consider this amplifier then. (I'm getting a certain Audiotrak Prodigy Cube instead for non-portable use right now.)
  Using the ferrite... sounds to me like overcompensation at gain stage. Shouldn't be necessary indeed, including for the purpose of evening out phase response.
   
  Rather than the use of RMAA, I'm more worried that -57 dB crosstalk is the best your measurement setup can do...
  Heck, my old Aureon Space could do better than that and that's not exactly pro audio.


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## rudi0504

I have both amp O2 and C421 with op smp 8620 from Jds lab 

In my opinion : with standard version to drive UM Miracle , I prefer Jds lab C 421
 Jds lab C 421 with Opamp 8520 sound : more open and better bass.

With upgrade version O2 : with op amp 627 and black gate resistor , O2 sounding much better


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## ClieOS

rudi0504 said:


> I have both amp O2 and C421 with op smp 8620 from Jds lab
> With upgrade version O2 : with op amp 627 and black gate *resistor *, O2 sounding much better




You mean BlackGate _capacitor_. Those are a bit overhyped IMO.


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## AstralStorm

I'd be quite suprised if O2 sounded even a bit better with OPA627. That part would actually be inferior for IEM use due to higher current noise, similar voltage noise. It'd be "meh" for headphones.
  Changing the capacitor could've reduced ESR pushing the compensation a bit up in frequency, however this shouldn't have any audible effect, unless you've managed to make O2 unstable.
  Which is possible, OPA627 is faster and less stable than NE5532, it's also worse at driving capacitive loads, as typical.
  OPA627 is further from rails, so you're wasting quite a bit of gain capability. In case you run out, it clips pretty horribly.
  It's a part for the gain stage of an old-style analog scope and not audio.
   
  Summary: It might sound different, but that would mean it's introducing distortion - most likely ringing or oscillation. Not to mention forcing you to pay through the nose.


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## ddcpitt

Might I suggest the C421 for portable and the upcoming ODA (Objective Desktop Amplifier) for home use?  The ODA will take the objective design of the O2, and improve upon it, making it even better for home use.  Hopefully the design if finalized by late summer and will be released sometime during the fall (hopefully as a DIY and pre-assembled by places such as JDS Labs).


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## stv014

Quote: 





> Originally Posted by *AstralStorm* /img/forum/go_quote.gif
> 
> Rather than the use of RMAA, I'm more worried that -57 dB crosstalk is the best your measurement setup can do...


 
   
  In my opinion, -57 dB, especially if it was measured at 10 kHz (so it is probably better at lower frequencies), is low enough not to be audible.


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## stv014

Quote: 





rudi0504 said:


> With upgrade version O2 : with op amp 627 and black gate resistor , O2 sounding much better


 
   
  I would recommend reading the article "Op Amp Measurements" from August 2011 at the blog that must not be named. The measurements there show that using expensive op amps in the O2, especially at low gain, is most likely a waste of money, if not worse.


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## ClieOS

stv014 said:


> In my opinion, -57 dB, especially if it was measured at 10 kHz (so it is probably better at lower frequencies), is low enough not to be audible.




I would say the same as well. I actually got lower number from RMAA on both C421, around -68dB or so. Not nearly as good when compared to O2 and such, but still decent enough.


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## stv014

Quote: 





clieos said:


> I would say the same as well. I actually got lower number from RMAA on both C421, around -68dB or so.


 
   
  How did you test it exactly ?
  Actually, the O2 is "only" -65 dB, but that is likely a reliable measurement, and also with a 15 Ohm load (lower impedance loads generally increase crosstalk and distortion).


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## ClieOS

stv014 said:


> How did you test it exactly ?
> Actually, the O2 is "only" -65 dB, but that is likely a reliable measurement, and also with a 15 Ohm load (lower impedance loads generally increase crosstalk and distortion).




That's the dark secret of RMAA. It should only be used to make relative measurement (against a known standard) because the number it puts out vary depends on the tools (i.e. sound card) you used for measurement and even different configuration. That's why quoting RMAA generally doesn't make it very helpful when you are comparing RMAA result from two different setups.


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## Raines

ODA + c-421 seems good idea


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## AstralStorm

Unsuprisingly, Audiotrak Prodigy Cube is more than enough of an amplifier for low impendances.
  Beatifully sharp sound on 0 Ohm output (big jack), about as extended as E17.
  (Maybe more, but I can't do A/B, need to finally send the FiiO devices for a repair)
   
  Of course it won't drive 300 and 600 Ohm headphones - not enough power for that.
   
  The sound is pretty suprising, since it uses the supposedly "warm" OPA2134. I hear nothing warm about that, correct (if not perfect) detailing and 0 noise instead.
  If someone likes muffled sound with their IEMs, they're free to use the 32 Ohm minijack.


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## stv014

Quote: 





clieos said:


> That's the dark secret of RMAA. It should only be used to make relative measurement (against a known standard) because the number it puts out vary depends on the tools (i.e. sound card) you used for measurement and even different configuration. That's why quoting RMAA generally doesn't make it very helpful when you are comparing RMAA result from two different setups.


 
   
  The most common problem with using sound cards for measuring crosstalk is that sound cards usually have unbalanced inputs and outputs referenced to a common ground (i.e. basically the metal chassis of the PC). Since with low impedance headphone loads much of the crosstalk occurs through the ground wire, the sound card loopback bypasses it, and the measured value is therefore better than it really should be. Also, for whatever reason, the crosstalk value (and the noise/dynamic range as well, by the way) printed by RMAA seems to be simply wrong; it does not agree with the value read from a real time FFT analysis while playing a test tone on only one channel under the same conditions as with RMAA.
  For reasonably accurate crosstalk measurement, one method is to simply use a DMM that works at the tested frequency on the resistor load (it does not allow for measuring very low crosstalk with most inexpensive DMMs, but if it is less than -60 dB, then it is not much of an issue anyway). For PC based measurement, software other than RMAA might be worth trying, and either two separate machines for playback and recording (I did not test this), or differential input for recording (I tried this with a DIY differential amplifier, and it did make a useful difference in some cases).


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## dannyd123

is the c421 a better version than the cmoybb v2.03?


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## tzjin

You could say that, but it's a completely different amplifier. A Ferrari is basically a better version of the Camry. Both cars, but completely different performance levels. Read here: http://www.headfonia.com/flyin-high-jdslabs-c421/
   
  While Mike and L enjoy the 2227 opamp, many on Head-fi enjoy the 8620. Just something to think about.


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## Ultrainferno

Quote: 





tzjin said:


> You could say that, but it's a completely different amplifier. A Ferrari is basically a better version of the Camry. Both cars, but completely different performance levels. Read here: http://www.headfonia.com/flyin-high-jdslabs-c421/
> 
> While Mike and L enjoy the 2227 opamp, many on Head-fi enjoy the 8620. Just something to think about.


 
   
  Many on Head-fi also prefer the 2227. Just something to think about.


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## dannyd123

what is the difference between the 2227 and the 8620 versions?


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## ClieOS

dannyd123 said:


> what is the difference between the 2227 and the 8620 versions?




I reviewed both versions here: http://www.head-fi.org/t/615766/impression-jds-labs-c421-opa2227-vs-ad8620-featuring-cmoybb-o2-t5-and-uha-4


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## dannyd123

thanks for the link


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## cyberalpha11

I need other opinion about the comparison in term of performance between JDS Labs C421 against Headstage Arrow 12HE 4G. Which is a better amp to drive Beyerdynamic DT880, DT990?


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## Headzone

Quote: 





cyberalpha11 said:


> I need other opinion about the comparison in term of performance between JDS Labs C421 against Headstage Arrow 12HE 4G. Which is a better amp to drive Beyerdynamic DT880, DT990?


 
  Since you're using them with DT880 and DT990, you don't need a portable amp? Look at the new Schiit Magni, it should be awesome and run them very well.


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## Puppysmith

I would take a look at Shiit's stuff. Good reviews.


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## rtaylor76

My question is: Has anyone attempted to put in another chip in the O2? Say a 2227, 2228, 8066, or otherwise? Someone may have already posed about this, so I apologize.


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## ClieOS

Quote: 





rtaylor76 said:


> My question is: Has anyone attempted to put in another chip in the O2? Say a 2227, 2228, 8066, or otherwise? Someone may have already posed about this, so I apologize.


 
   
  Of course it has been done before. But O2 is designed specifically with NE5532 in mind, so using another opamp might not actually make it better.


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## JakeJack_2008

Quote: 





syphen606 said:


> An O2 with similar bass boost to the C421 would be pretty awesome. You can't really compare them directly when using the bass boost of the C421.
> I still think the C421 is awesome due to its portability and USB charging. When I'm on the go, I listen to music off my iphone. I usually have the means to charge my Iphone while I travel and thus have the means to charge my C421 without bringing a big power adapter.
> 
> I still have both though and think they are a great combo.


 
   
  Well, I am not an expert, but I've read on this site that,  in general, an AC powered amp is  better  than an USB powered amp _in terms of sound quality._
  (The electric power via USB port is more poluted than the AC power from the wall.)
   
   
  Obviously, we assume that both ways are well implemented.


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## jseaber

Quote: 





jakejack_2008 said:


> Well, I am not an expert, but I've read on this site that,  in general, an AC powered amp is  better  than an USB powered amp _in terms of sound quality._
> (The electric power via USB port is more poluted than the AC power from the wall.)
> 
> 
> Obviously, we assume that both ways are well implemented.


 
   
  AC vs. USB power is irrelevant when both circuits are properly implemented. Sound quality will be identical, unless the designer has failed to do his job. Yes, it's more difficult to build a clean USB power supply--not impossible. With a large battery and proper design, you can still crank out incredible power at ultra low ripple that doesn't even begin to impact the PSRR spec of the amplification circuit.


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## iguanajm

What did you end up getting?


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