How to pick the right headphone amp
Jan 8, 2015 at 3:47 PM Thread Starter Post #1 of 10

longtalltechsan

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Hey everyone.  I have really enjoyed the wealth of information from this website.  Based on what I read here, I bought a pair of RHA M750i's several months back and have been really happy with them.  
 
Now, I am an audiophile on a budget.  Spending the money on those is something I never thought I would do.  But I am extremely happy with them.  Just after Christmas, I bought some Audio Technica ATH-M30x over the ear monitors and am happy with the sound I get from them as well.  However, I have been thinking I would like to get a small amp to either hook up to my laptop or iPod for better sound.  
 
This is where I need your help.  I don't know how to pick an amp that will be good for the headphones.  What do I look for in amps?  I believe I would like to get one with DAC as well as amplification.  I just don't know how to select one.  Starting out, I don't want to spend much, maybe $75 or so.  But I would like the information I need in order to make an informed purchase.  
 
So what kind of advice can you give me?
 
Thanks in advance.
 
Jan 8, 2015 at 11:08 PM Post #2 of 10

ProtegeManiac

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This is where I need your help.  I don't know how to pick an amp that will be good for the headphones.  What do I look for in amps?  I believe I would like to get one with DAC as well as amplification.  I just don't know how to select one.  Starting out, I don't want to spend much, maybe $75 or so.  But I would like the information I need in order to make an informed purchase.  
 
So what kind of advice can you give me?

 
Add a little bit more to your budget and get the Ibasso D-Zero MkII. Anything you can get for less than that is likely not as good, and noticeably too.
 
Jan 9, 2015 at 1:02 PM Post #3 of 10

longtalltechsan

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Thanks for the recommendation, but can you tell me why that is a good amp for my situation?  What I am looking for is what specs should I be looking for in an amp that will make it a good pairing with my headphones?  The specs of the ATH-M30x's are:
 
TypeClosed-back dynamic
Driver Diameter40 mm
MagnetNeodymium
Voice CoilCopper-clad aluminum wire
Frequency Response15 - 22,000 Hz
Maximum Input Power1,300 mW at 1 kHz
Sensitivity96 dB
Impedance47 ohms
 
Jan 9, 2015 at 10:52 PM Post #4 of 10

ProtegeManiac

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D-Zero MkII specs:
 
Power Source:Built-in 4.2V Li-polymer battery
Frequency Response: 17Hz~20 KHz +/- 1.0dB (DAC), 17Hz~100 KHz +/- 1.0dB (AMP)
Signal to Noise Ratio:108dB (DAC), 102dB (Amp)  
Total Harmonic Distortion: 0.002%@1kHz/0dB (DAC), 0.003%@1kHz/-10dBV (AMP)  
Output Power:Up to 120mW+120mW into 16Ω  
Output Impedance:  <0.5ohm
Gain:  +3dB/ +9dB (AMP)
Battery Life: 120 Hours (AMP), 10 Hours (DAC+AMP)
Battery Charge Time: 5 Hours
External Power supply: 5V DC
Recommended Headphone Impedance: 8~300Ω
Case dimension: 2.17W x 3.98L x 0.44H (inch)
             55W x 101L x 11H (mm)
Weight: 95g or 3.35oz
 
The problem with amp specs is that they are general output figures with less regard to each individual headphone - in some cases manufacturers either make overkill amps or they advertise the amp's compatibility with the specs of a particular hard to drive headphone. Here we can see the power output is 120mW per channel at 16ohms, but we can't see what the output power is at 32ohms, let alone at your headphone's 47ohms. Ditto the THD - it says 0.003% at 1khz, but we don't know at what output power and at what impedance. That's the same with every amp btw, unless the manufacturer is pushing it for those who own a popular but hard to drive headphone.
 
However, I have tested the MkI with 32ohm Grados, 50ohm AKGs, and 300ohm Sennheisers, and it has no glaring difficulties driving any of them. My reference desktop amp has tighter bass at louder volumes, but for example at lower volumes for extended listening (like while working in my home office computer) the sound is pretty much identical. Not sure how well the battery life stacks up, but I've used the MkI as a DAC-HPamp for over a month (roughly 2 to 3 hours daily on average) and I only plugged it in to charge. I've had the chance to listen to the MkII and the amp is even better, but I have no idea about the battery life.

 
 
Jan 27, 2015 at 10:24 AM Post #7 of 10

RRod

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  Again, thanks for the replies, but why are these amps compatible with my setup/usage?  I would like to know what specs to look for in an amp based on my music source and the specs of my headphones.  

 
You need the amp's power output at your headphone's nominal or maximal impedance, and you need your headphone's efficiency. See http://www.audiobot9000.com/ for some suggestions based on these types of numbers.
 
Jan 27, 2015 at 11:30 AM Post #8 of 10

billybob_jcv

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Most mfrs, especially budget amp mfrs, do not publish enough specs to really make a good selection based on the numbers. For example, your M30X are a nominal 47 Ohms. If I look around on the 'net, I can probably find the actual impedance curve vs frequency for the M30X. It might be a perfectly flat line at 47 Ohms, or it might be a curve that varies by a large amount around 47 Ohms. As RRod just said, what I really want to know about the amp is the actual power output and THD along the impedance curve of the headphone. If the headphone impedance curve is perfectly flat at 47 Ohms, then if I know the amp's power output is high enough at 47 Ohms, and the THD is low, the amp will power the headphones adequately. If the headphone impedance curve peaks at 225 Ohms, and the amp has little or no power output and/or high THD at 225 Ohms, then it's probably not going to work well with the headphones.

However - I typically don't have all that information. So, I will probably have to infer and guess. If the amp spec shows it has decent power output at 300 Ohms, and my headphones peak at 225 Ohms, then I'm probably OK. If the amp spec only shows 5 mWatts at 16 Ohms, and I need good power at 300 Ohms, it's doubtful the amp will be able to do it. If it shows 1 Watt at 16 Ohms, then maybe it can (but just maybe) - I have to guess.

With all that said, at $75, you should just be looking at whether the amp is reliable and puts out a relatively clean signal. There just isn't that big a difference between the amps that have already been suggested to you. Any of them will do nicely.
 
Jan 27, 2015 at 11:45 AM Post #10 of 10

Rearwing

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My advice would be to try to listen to as many as possible and then make a judgement based on sound and synergy. The music you listen to, your headphones, your dap, will all influence what sounds right to your ears.
 

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