[Armaegis]

Interesting. So you've had a discussions with them where they said they tuned the headphone output according to the HD800?
 
One possible advantage of output paralleled resistors is that the amp will see a fairly consistent load regardless of the headphone impedance curve. A downside would be reduced power (possibly a negligible concern), and I'm not sure how damping factor is affected here.
 
Typically a higher output impedance can give a looser or warmer sounding bass. Not a hard rule, but it depends how the amp interacts. I also have a Bottlehead Crack which has a 120ohm output impedance and I think it sounds fantastic with my Sextett and Sennheisers.

 

[HeadphoneAddict]

Quote:

Interesting. So you've had a discussions with them where they said they tuned the headphone output according to the HD800?
 
One possible advantage of output paralleled resistors is that the amp will see a fairly consistent load regardless of the headphone impedance curve. A downside would be reduced power (possibly a negligible concern), and I'm not sure how damping factor is affected here.
 
Typically a higher output impedance can give a looser or warmer sounding bass. Not a hard rule, but it depends how the amp interacts. I also have a Bottlehead Crack which has a 120ohm output impedance and I think it sounds fantastic with my Sextett and Sennheisers.

 
Yes, they told me they voiced it for the HD800, and I think they made the right choice.  There are loads of amps out there that sound great with everything but HD800, so it's about time.  While it's not as good of a choice to listen with the low impedance LCD-2 or and HE-500 that need more power it's the best SS amp I have at home for the HD800.  Actually, the only amp listed in my profile that is better with my HD800 than this is my Eddie Current ZDT.  The Luxman P-1u I had on loan from TTVJ a while back was a great SS amp with the HD800 and similar to my ZDT, and I sometimes wonder if the DAC-100 might be on that level of performance with the HD800.
 
The HAP-100 amp sounds almost the same as DAC-100 when driving the HD800, but with more volume available (not needed).  However, the HAP-100 drives low impedance phones better than the DAC-100, with at least 4-5 dB more headroom and a stronger bass kick.  With low impedance phones the HAP-100 also seems to have a little more forward mids than the DAC-100.  That part I'm not sure how I feel yet.  It's still burning in and I'll give it it's own thread later.  I also have to try it with IEM.
 
And don't get me wrong, the DAC-100 can still be enjoyed with the other headphones that I used, but it's just not optimal for those vs other amps I have that are a great match. And it's not a looser or boosted bass that I hear with LCD-2 and HE-500, but rather just a lesser punch, weight and kick do to lower voltage swing and limited current with low impedance phones.  I do hear the mid-bass boost in my V-MODA M-100 34 ohm phones, and the DAC-100 has gobs of power to drive those efficient phones.  
 
I also noted that my second best headphone with DAC-100 is either my re-cabled HD600 and the LCD-2 rev2 (but not the old rev1 I tried at first).  I'm going to unbox my Stevie Wonder owned AKG K240M 600 ohm this weekend and try them out as well, to see how these do with that kind of load. 

 

[Armaegis]

I too find the HAP-100 amp section to sound very similar to the DAC-100. With my Sextetts, I find the DAC-100 amp section has a little more bloom in the lower end (not necessarily cleaner, just more energy), while the HAP-100 seems to give a bit more edge to the treble transients. The differences are very minute however, and it's possible I may just dismiss that due to headroom or placebo after more listening.
 
For those who like numbers, here are a few measurements:
DAC-100 headphone out, max volume, 1M load, 60Hz sine wave at -1dB =  3.4V
HAP-100 headphone out, max volume, 1M load, fed the 60Hz from DAC-100 = 7.8V
so that's a bit more than double the voltage swing, which equates to roughly 6dB more headroom (more like 7, but we'll go with 6 for simplicity and calculation sake).
 
The output impedances are wonky and seem to wobble a bit. At best guess, there's a resistor running in parallel with the headphone load, and I've measured them both to be roughly 16-17 ohm. Considering that they recommend headphones with 100ohm impedances or higher, I might theorize that someone on the design end literally took the 8:1 rule of thumb to heart.
 
There must be some other resistor or interaction in there though, since the HAP-100 is affected more by different loads. With a 560ohm resistor load the DAC-100 output measures the same, but the HAP-100 measures 7.5V, and at 33ohm the numbers drop to 2.3V and 3.6V (note that this is into distortion range of the HAP-100 since we hit the current limit of the amp). So we can see that the effect of lowering load impedance is more drastic on the HAP-100, which is usually indicative of a higher output impedance, but there are other factors at work here too.
 
edit: hmm some preliminary number crunching does not work if I assume a "simple" resistor in parallel and in series with the load... I actually wind up calculating a negative output impedance or something like that

 

[Armaegis]

A few more...
 
DAC-100 RCA out at full volume with 60Hz -1dB tone  ~1.9V 
feeding into HAP-100, achieves unity gain at:
~89% for preamp out
~84% for headphone out (with 1M resistor load)

 

[HeadphoneAddict]

Thanks for all the measurements.

 

[Armaegis]

So both the DAC-100 and HAP-100 have two socketed DIP-8 LM4562NA opamps (debatably the same as the LME49720/LME49860... I wonder what kind of rolling possibilities there are...
 
edit: I have no idea if it's one chip per channel, or if one chip drives the pre-outs, or maybe one is a servo... *shrug*

 

[Armaegis]

Larry, does your DAC-100 run hotter than the HAP-100? Mine is noticeably warmer all across the case.

 

[HeadphoneAddict]

Quote:

Larry, does your DAC-100 run hotter than the HAP-100? Mine is noticeably warmer all across the case.

 
They are both fairly warm, but the DAC-100 does seem a little hotter on the right side.

 

[Armaegis]

My HAP only gets slightly warm to the touch, while the DAC is quite a bit warmer especially at the right and back sides. I send an email to Nuforce earlier today about that, along with a whole slew of other questions. 

 

[HeadphoneAddict]

It's a class-A amp, and they said it's supposed to run warm.  It's not hot enough to burn me, so that means it's warm.  But very warm.  
 
People with the Schitt Asgard were complaining that the volume know was over 120 degrees, and at least this doesn't do that.

 

[Armaegis]

Oh my concern isn't that it runs hot. They are both warm-ish at best. I was more curious why the DAC is so much hotter than the HAP when the HAP has a stronger headphone output (and I assume must pull more heavily into class A than the DAC). 

 

[HeadphoneAddict]

Quote:

Oh my concern isn't that it runs hot. They are both warm-ish at best. I was more curious why the DAC is so much hotter than the HAP when the HAP has a stronger headphone output (and I assume must pull more heavily into class A than the DAC). 

 
Because one is both a class-A DAC as well as a class-A amp?
 
All I can say is, if I had an HD800 and I only wanted a good value DAC and amp combo for them, I'd buy the DAC-100 and close my head-fi account before my wallet committed suicide.  If I already had a good DAC I'd buy the HAP-100 and close my head-fi account.

 

[Armaegis]

I wasn't aware the dac in the DAC-100 runs in class A... I don't see anything about it in the literature. But even then, the psu on the right side is hotter in the DAC. Maybe that's because it has to power more components in the DAC-100 compared to the HAP-100? Just curious about it, that's all. 
 
Later this week I plan to borrow a Schiit Bifrost and Lyr (and if my friend is feeling generous maybe his LCD2) to do some comparison. 
 
I have the Nuforce power supply with the 192k usb converter as well, which can feed the DAC-100 and Bifrost simultaneously, and feed those both into the HAP-100 (and possibly into the Icon2 into HE-6 later on). for a good head to head of the dacs. I might throw the iBasso D10 and some others into the mix if I'm not worn out of listening by then. Heck I could do a FiiO e10 coax out into one of the dacs as well... 

 

[Armaegis]

edit: I have pictures of the internals for the DAC-100, HAP100, and LPS, but will wait for permission before I post them all up

 

[HeadphoneAddict]

Quote:

I wasn't aware the dac in the DAC-100 runs in class A... I don't see anything about it in the literature. But even then, the psu on the right side is hotter in the DAC. Maybe that's because it has to power more components in the DAC-100 compared to the HAP-100? Just curious about it, that's all. 

 
I put a question mark on that.  I don't know if the DAC is also class-A.  Looking through my conversations with Nuforce, and a Q & A I go this.
 
[size=medium]"Q: Does the DAC/amp run too hot to stack other components on top?[/size]
 
[size=medium]A: You can probably stack something, but need to have ventilation.  It does run warm due to the 10W idling current for the Class-A headphone stage."[/size]