[watchnerd]

I'm currently using a Nuforce Icon HDP external DAC/Pre/Headphone amp.  But it's a little underwhelming in the power department and I'd like to have something with more juice for my AKG 701s, as well as possible additional, more demanding phones I might buy in the future.
 
While I believe a more powerful headphone amp may be beneficial, do I really need an external DAC?
 
Could I do just as well by running the line out from my Mac Mini into a headphone amp?  
 
[I'm going to assume for the sake of this thread that the internal DAC of the Mac Mini and an external DAC are both sufficiently proficient at actual digital conversion as to be indifferent and thus we're mainly comparing analog stages.]
 
Comparison Specs:
 
Mac Mini:
 
Frequency Response: 20Hz-20kHz, +0.5 dB/-3 dB
Maximum Output: 1.4V RMS (+5.15 dBu)
SNR: >90 dB @ 1.4V RMS
THD: <-80 dB (0.007%) @ 1.4V RMS
 
 
Popular Mid-Price External DAC:
 
Frequency Response: 20Hz-20KHz, +/-0.1dB
Maximum Output: 2.0V RMS
SNR: >108dB @ 2V RMS
THD: <0.003%, 20Hz-20KHz @ 2V RMS
 
 
So there is no doubt that the external DAC has better specs.  It's flatter, puts out more volts, has better SNR and better THD than the analog stage of the Mac Mini.  
 
But it if I'm driving an external amp, does it matter?
 
The only obvious thing I can think of is that 1.4 V vs 2.0 V means that the external amp will need to apply more gain, but with so many 1000+ mW headphone amps on the market, that doesn't seem like much of an issue.
 
And with the maximum theoretical 16 bit digital noise floor being -96db, and probably less than that in practice, does the theoretically better SNR make any difference?

 

[carlchip78]

Start with the amp that you think will have enough power for your needs and listen to that connected directly to your mac mini for a while. If you notice that there is a high noise floor or not enough volume then an external DAC may bring an improvement.
I added a dedicated DAC to my setup because the noise from my PC was clearly audible through headphones and speakers.

 

[watchnerd]

Start with the amp that you think will have enough power for your needs and listen to that connected directly to your mac mini for a while. If you notice that there is a high noise floor or not enough volume then an external DAC may bring an improvement.
I added a dedicated DAC to my setup because the noise from my PC was clearly audible through headphones and speakers.

 
Well that seems shockingly simple and common sense!
 
I suppose I could also start that experiment with my Icon HDP using its analog input and checking for noise on both the pre-out (via the desktop speakers) and the headphone amp circuit.
 
I was expecting someone to tell me that what I'm trying to do is ill-advised for some theoretical reason.

 

[carlchip78]

Yep, start with what you have and you may be satisfied with the sound quality. I had a pair of 701s a while back and I do remember they needed more of the volume dial than most of the other headphones I had tried.
If you're using more than 50% of the volume on your amp then the additional power from an external DAC may give you more headroom and less noise.
Remember, if it sounds good then it is good. I spent a tonne of money on this hobby when I first got started chasing solutions to problems that didn't even exist. Today my headphone rig is very, very simple and I don't feel like I'm missing out on anything.

 

[castleofargh]

if the max output of the mac is 1.4V pretty much any amp can take it without clipping, so there is no problem in trying to plug whatever you have to the analog output at any volume level.
most likely you will get a pretty clean sound with the mac maxed out(or very close to the max), and the external amp adjusted for your preferred loudness.
 
double amping(using the amp section of the mac and the external amp) is regarded as bad in the VIP audiophile club^_^,  because it's in theory not ideal. but in reality a lot of very good sound systems use a preamp, so it's really just a matter of what we want to achieve and how good are each amp sections. if the result sounds good to you and has enough power, then you have your system.

 

[carlchip78]

^ What he said.

 

[watchnerd]

 
double amping(using the amp section of the mac and the external amp) is regarded as bad in the VIP audiophile club^_^,  because it's in theory not ideal. but in reality a lot of very good sound systems use a preamp, so it's really just a matter of what we want to achieve and how good are each amp sections. if the result sounds good to you and has enough power, then you have your system.

 
I find that kind of ironic given that whenever one uses a phono stage with vinyl, especially an external one, there is definitely double-amping going on.  And how much more elite does it get than vinyl with an external phono? Heck, if you add in a low output MC cartridge with a CineMag step-up transformer one could even argue that it's triple amping.
 
But seriously though, my thinking is this:
 
-Most of my headphones have a max input of 100mW - 200mW; they have an impedance rating of 55-250Ω
-The amps I'm considering put out 1000mW-4000mW @ 50Ω and 320mW-660mW @ 250Ω
-Assuming these max ratings are for 2V input, 1.4V should give me ~70% of that max.
-But given the headphones I own need <60% (or way less than that in most cases), I should be okay
 
All of this is assuming that noise is at acceptable levels.
 
Does this logic magic sense, or is there a big hole?
 
The biggest issue I can think of is that the internal analog in the amp may be a bit weak on the power supply side, which might reduce dynamics. Then again, it might be switching mode and be just fine.

 

[castleofargh]

  I find that kind of ironic given that whenever one uses a phono stage with vinyl, especially an external one, there is definitely double-amping going on.  And how much more elite does it get than vinyl with an external phono? Heck, if you add in a low output MC cartridge with a CineMag step-up transformer one could even argue that it's triple amping.
 
But seriously though, my thinking is this:
 
-Most of my headphones have a max input of 100mW - 200mW; they have an impedance rating of 55-250Ω
-The amps I'm considering put out 1000mW-4000mW @ 50Ω and 320mW-660mW @ 250Ω
-Assuming these max ratings are for 2V input, 1.4V should give me ~70% of that max.
-But given the headphones I own need <60% (or way less than that in most cases), I should be okay
 
All of this is assuming that noise is at acceptable levels.
 
Does this logic magic sense, or is there a big hole?
 
The biggest issue I can think of is that the internal analog in the amp may be a bit weak on the power supply side, which might reduce dynamics. Then again, it might be switching mode and be just fine.

well it's hard to get a clear idea while playing with all those ranges of variables. 1 concrete situation with actual specs would be clearer. 
going from 1.4v to 2v will make your headphone 3.1db louder, so the chances that this would be the important factor are small ^_^.
 
about the max input you mention for the headphones, I'm not sure what those are and what use they have for you? is that the value for when a headphone blows up? ^_^

 

[watchnerd]

 
about the max input you mention for the headphones, I'm not sure what those are and what use they have for you? is that the value for when a headphone blows up? ^_^

 
Max input values are from the makers. Yes, I assume that's when the cans explode or burst into flame.

 

[watchnerd]

Update:
 
I got a 3.5mm -> RCA cable and am testing things out.   
 
The nice thing about the Icon HDP is that it has USB, coax, and analog inputs.  So I can use the same piece of equipment for evaluation without adding in new gear as a variable.
 
So far, bypassing the external DAC sounds pretty good.  The biggest obvious difference is that the gain is different when the Icon HDP is set to USB vs analog (the analog input needs to be dialed back relative to the USB).  The Mac OS volume setting is currently at 88% of max (leaving just a little overhead to avoid clipping).
 
Perhaps this weekend I'll get more scientific about things and use level matching and maybe even some blind testing to see if I can differentiate between the external vs internal DAC.
 
But the early returns are good, very listenable.  No noise or other badness.