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[review] Nuforce HAP-100

post #1 of 34
Thread Starter 



This is a companion review to my DAC-100 review here: http://www.head-fi.org/t/645068/review-nuforce-dac-100


Coming from the same stock, they share many of the same characteristics in terms of build quality and sound.


On the surface:

- four selectable RCA inputs via button or remote

- digital volume control, 100 steps, logarithmic

- headphone and preamp out (volume controlled): ~7.8V at max (fed 2V at input)

- preamp output can be disabled

- Class A headphone output

- wireless remote



Build and Aesthetics


Ok what I said about the DAC-100 being a little black box, I take it back, this one has that title. With the power off, there's almost nothing to see. With the power on... there's still almost noting to see unless you're looking at it fairly head-on. The front face plate is solid, with tiny perforations behind which mini led lights will show your selected input and volume setting. It's got a retro-ish vibe to it, and that's cool. More than 30° off axis though, and the lights almost disappear behind the grill.


The only real feature on the front is the volume knob, which serves additional duties as the on/off switch (primary power switch at the rear) and input selection. A quick press of the knob will turn the device on. If this is the first power on after the rear switch was flipped, then the HAP-100 automatically goes to input 1 and volume 0. If this is not the first time switching in on, then it remembers the previous setting. Successive presses of the knob will cycle through your four analog inputs (all RCA). Turning off the HAP-100 is done by pressing and holding down on the knob for a couple seconds. Of minor note, the triggers for switching inputs is actually the release of the knob. If you're intending to shut off but release before it triggers, you will switch inputs instead.


The knob turns with minor clicks to it, each one indicating a single step on the volume dial. Interestingly, this is not a standard potentiometer like the DAC-100. The knob can freely spin ad infinitum, and in fact does take several full rotations to go from 0 to 100. Spinning further has no effect. While this is very nice for minute volume control, it does make rapid volume changes impossible. A very minor quibble, but it bears mentioning. The only time this may be an issue is if you have a tendency to leave the volume settings very high, in which case some prudence of turning it down before your next session is generally a good form to take. The feel of the knob itself a little bit loose, much like the DAC-100. While not flimsy, a bit of extra firmness here would have made the HAP-100 feel more refined.


The rear panel has your four RCA inputs and the volume controlled preamp output. The jacks are all screwed in to the rear panel, so they feel extra secure when plugging things in, unless like some other amps where the jacks are only pcb mounted and there's a bit of uncomfortable give. Power input is via typical IEC power inlet (with a switch for 120V or 240V), and the HAP-100 ships with a rather beefy powercord that's a nice step up from your standard cord with some extra heft and a large ferrite attached.


As for the remote, meh. I'm pretty sure those were my exact words in the DAC-100 review. The remote is functional, doesn't feel particularly fancy, but it gets the job one. The volume knob isn't motorized, so there is no visible turning when you adjust the volume. Unlike the DAC-100 though, there is no danger of the volume jumping to the dial position when you touch it. Of important note: the HAP-100 remote is the exact same as the DAC-100 remote, own to the frequencies used. If you have both devices, you will not be able to control them independently. After speaking with Nuforce customer service, apparently you can get different codes/remotes, but you must indicate so during ordering.


Temperature-wise, the HAP-100 heats up a little bit but is actually cooler than the DAC-100. According to my temperature reader, it reaches roughly 30°C along the back and right edges, where the class A amp and power supply are located.





In terms of layout, once again there is a strong family resemblance to the DAC-100. The power supply occupies the entire right side of the chassis, with a toroidal transformer behind some shielding, and the regulators and hefty bank of capacitors and heatsinks in front of it. This power then feeds back to the front panel and amp circuitry.


The front panel contains the volume control and input switching, nothing out of the ordinary there. This connects back over to the main amp board which itself is fairly simple and a bit smaller than the DAC-100 board (since there's no dac section obviously). Most notable next to all the inputs are the socketed LM4562 opamps and class A buffers (there are no markings on the transistors). The bottom of the board is mostly bare save for the volume controller chip.


A quick note on the opamps:

From emails with Nuforce, each opamp handles one channel separately, with one half of the opamp feeding the preamp and the other half feeding the headphone amp. Nice; minimizes crosstalk that way. I will add at this point that Nuforce does not officially support users rolling their own opamps. If those sockets are just too tempting, then proceed at your own risk. That's all I can officially say on the matter.



Sound and stuff


I suggest taking a look at my DAC-100 review, as my impressions of sound here are very very similar. I will make some comparisons in just a second.


The HAP-100 is designed for headphones of impedance 100ohm and up. It has a fairly substantial voltage gain, but limited current capacity which is why high impedance headphones are recommended. Low impedance loads will clip if driven too high. Of quick note however, the HAP-100 appears to have some kind of clipping protection which softens the effect. On the DAC-100 the clipping is very harsh, but here it is much more gentle and in regular music might actually go unnoticed. It feels a little bit like a compression effect, but I'm not entirely certain of that.


The power on thump from the switch at the back is quite strong. I would recommend not having headphones plugged in when you flip the switch. The power on with the front panel makes no noise however, so that should be fine.


The volume is digitally controlled through 100 steps, and it does a fantastic job of it. The transitions are nearly seamless with music. You have plenty of play and room on the knob to find your exact volume spot, and the values are displayed as well. Unity gain on the preamp outs is at 89%, and unity gain for the headphone output is ~84% with high impedance headphones.


In terms of noise... none. Nothing at all. Feeding it a source with noise will obviously result in an amplification of the noise, but feed it a silent source and you'll get a simply black background. This alone is probably the most notable difference from the DAC-100 and allows you to use headphones with low impedance and high sensitivity, even though the literature says you should stick to 100 ohm and up.


The amp has a series resistor on the output of the headphone jack for short circuit protection, same as the DAC-100. There is an optional headphone module with jumpers that can let you bypass these resistors. My impressions here are almost exactly the same as on the DAC-100. With the resistors in, the sound is a little warmer. Headphones with high impedance swings will show a variance in frequency response. Changes in damping factor are noticeable, though not as huge as some may lead you to believe. Unlike the DAC-100 where the output resistors actually helped lower the noise floor, the HAP-100 is quite clean so even with the resistors bypassed there is no noise. Bypassing the resistor also allows greater voltage swing into lower loads. However, as the amp is current limited I find this to mostly be a moot point as it has more than enough headroom with the resistors in place anyways unless I'm trying to push something like the HE-6.


Preamp functionality is excellent. Switching inputs is smooth with no clicks or pops, and is handled purely within the digital domain. In fact, when comparing dacs that are simultaneously feeding the same signal into the HAP-100, were it not for the fact that I pushed the button myself I might not have even noticed that it changed. It's that smooth. The volume remains the same regardless of input selected. Personally I would have liked to see some memory that maintained different volume settings for each input, but that's just a passing thought. I feel like I should be saying something more about the preamp, but what else is there to say? It works well, it's clean, no hassle. The preamp output also offers some active gain. It's unity at ~89%, and gives you 3x voltage gain at full volume (that's about 10db). This can be quite handy if you're using a particularly weak source. I would have perhaps liked to see a set of balanced (XLR) inputs, but seeing as there is no NuForce gear that does balanced out, I suppose it doesn't fit within the family of gear.


vs DAC-100:

The HAP-100 is more strident in the highs and a tiny hair cleaner in the bass with more kick but trading away some of the rumble. Very similar in most other respects, though obviously with more gain. The DAC-100 has a softer tonality to it and richer mids, and matches better with headphones that have sharp treble peaks


vs Lyr:

The HAP-100 has more rumble but a bit looser bass, better mid-treble snap and definition, yet does not feel “cooler” in the stereotypical sense. The Lyr is more impactful, but feels dull in comparison. Lyr soundstage is wider, but feels boxy and has a “wall of sound” feel. Lyr has far more headroom, but most of it is really unuseable as it gets far too loud too quickly. I find the HAP-100 just about right and allows a much greater use of the gain for fine control.



I actually prefer the sound a bit more from the DAC-100, which softens some of the treble zing and gives it a bit more fullness to the low mids.



I think the HAP is better than the DAC here as the HD600/650 are already fairly warm sounding, so the extra energy in the treble gives them a better sense of balance. I feel like there's slightly better dynamic range and layering, with more gripping vocals. It reminds me just a little bit of the Bottlehead Crack.



Passable, and better than the DAC-100, but still a bit lacking. The Lyr obviously has far more power on tap.



Not my favourite pairing for the LCD2; I would easily choose the Lyr over it here which offers more punch and impact


w/Fostex T50rp

Pretty darn good. Lots of articulation and plenty of bass energy. Choosing between the DAC or HAP here is just a matter of taste with the HAP giving a bit more of a cleaner/dryer sound.


w/Amperior (low impedance, high sensitivity)

Not listenable on the DAC-100 due to noise, but sounds just great from the HAP-100.



random placements... not a final word on anything

bass impact: Lyr > HAP >= DAC

bass clarity (LCD2): DAC >= HAP > Lyr

bass clarity (HD600): Lyr > DAC > HAP

treble impact: HAP > DAC > Lyr

treble clarity: DAC > HAP > Lyr

midrange: DAC > Lyr = HAP

noise: HAP > Lyr > DAC





Voltage measurements, fed from DAC-100 with a 60Hz sine wave at full volume (~1.9V)


Unity gain for headphone output with the series resistor in place (stock config)

- with high impedance load ~84%,

- with 33ohm load ~89%

Unity gain for headphone output without the series resistor ~84%


HAP preamp RCA unity gain at ~89

HAP preamp full gain = 5.7V (that's 3x voltage gain, roughly 10dB)


full volume headphone output voltages, into resistor loads, with stock series resistor in place

- 33 ohm = 4.7 V (about 2.5x voltage gain, 8db)

- 180 ohm = 7.5 V

- 560 ohm = 7.6 V

- 1M ohm = 7.9 V (roughly 4x voltage gain, 12 db)


Measuring resistance (not impedance) with a resistor load in parallel:

- 1M ohm ---> ~2 ohm (wobbles a lot)

- no resistor ---> -0.8 ohm (0.5 ohm when turned off)


headphone: HE-6

full volume from DAC-100 feed into...

HAP-100 headphone output: clips at 90

HAP-100 preamp out to Icon2 speaker amp: clips at 85 (clips the Icon2 input circuit, not the HAP)



Weird things happen when I try to measure the output impedance of the HAP-100, much like when I tried with the DAC-100. Nuforce themselves say that a direct measurement is not possible due to the configuration of their class A circuitry, and I'm inclined to believe them. When going through some of the numbers, I was getting negative values in my calculations. If you check above, I even got a negative resistance reading just going across the outputs. So something nutty is definitely happening there. In any event, I did not find any issues with the output impedance. Changes in damping factor with noticeable when bypassing the series resistor, but it's not a huge difference particularly with higher impedance headphones.



Final Thoughts


At $600 the HAP-100 sits squarely in between the budget $100-200 range and the $1k+ powerhouses. It's headphone amp is more versatile than the DAC-100, with higher gain and a substantially lower noise floor. However, it has a limited amount of current on tap so ideal headphone pairings are those with higher impedances. The mid to low impedance headphones are fine; you'll get to loud levels no problem, just not ear-bleeding levels.


The sound of the headphone amp itself is excellent. It is superbly clean, and very *very* similar to the DAC-100. If I had to differentiate, I would describe it as the “technical” sibling of the DAC-100 which I would categorize more as “musical”. The output module to bypass the resistors is a nice option, though in practice I found myself leaving them in most of the time.


The preamp functionality is very nice. Where the DAC-100 offers four digital inputs, the HAP-100 has four analog (RCA) inputs. The two siblings together can handle just about any combination of toys and mishmashery one can imagine, and in fact I did just that while writing these reviews. Input switching on the HAP is seamless, with the only telltale signs being timing differences due to dac buffering. Four inputs and a variable output (with gain) offers a lot of flexibility.


Bang for the buck, I think this is a great piece of kit though with more of a niche market. If you don't have need of the preamp function, then some of the value will be lost on you. If you also like to rock out ridiculously loud with low sensitivity headphones, or want to drive heavy orthos, then this won't be for you either. But if you have a couple different sources that you like to switch between, have some high impedance headphones (so pretty much Sennheiser or Beyerdynamic, or some version of a modded Fostex T50rp), and perhaps would like to loop out to a speaker when you want to party, the HAP-100 will be a fantastic addition to your desktop rig.


post #2 of 34
Thread Starter 


front view




inner view: note the power supply which takes up the entire right side; large toroidal transformer and plenty of caps and several large heat sinks

power feeds to the amp board and front panel separately



closeup of the mainboard: note the four analog inputs at the rear, the opamps, and the class A components

a pretty clean layout al things considered





the rather hefty toroidal transformer, surrounded by a shield



power regulation, heat sinks in the middle and off the side





front panel



front panel



there is no potentiometer in the traditional sense




rear view



front naked view; the illumination for input and volume are very mild



close up



closeup of the opamps and mosfets

opamps: LM4562

mosfets have no markings; no way to tell if they are the same as the DAC-100


power cords 1

on the left is the beefy power cord that comes with the DAC-100 and HAP-100. To the right is a standard IEC cord. The difference is quite stark. 


power cords 2


power cords 3


output jack 15 ohm resistors in series

original headphone jack, with 15ohm series resistor



new headphone jack on the left, with jumpers for bypassing the resistor




underside view. The jumper is currently in the front position, which leaves the resistor in place (stock config). Moving the jumpers to the rear of the board will bypass the resistors. 

Edited by Armaegis - 4/17/13 at 11:30am
post #3 of 34
Thread Starter 

reserved for other notes

post #4 of 34
Thread Starter 

pics have been added

post #5 of 34
Thread Starter 

Whoa, I made front page... biggrin.gif

post #6 of 34

Front page, congrats!


Nice review, great pics wink.gif I love the look of this amp.

post #7 of 34

Congrats on another very nice writeup.

post #8 of 34

Loving all the detailed pictures! Very nice review.  Looks like a solid amp. 

post #9 of 34
Originally Posted by Foxjam View Post

Loving all the detailed pictures! Very nice review.  Looks like a solid amp. 


It was a very sweet review, as was the DAC-100 review that Project 86 wrote.  I love NuForce, but I am worried about the noise floor issues with my Grados.  My Icon HDP w/ LPS-1 has an absolutely black background and I am spoiled in that regard.

post #10 of 34
Thread Starter 

The HAP by itself is pitch black and will be fine with Grados if you have a quiet source. If you're feeding the DAC-100 into the HAP-100, then Grados are not your friend.

post #11 of 34
Originally Posted by Armaegis View Post

The HAP by itself is pitch black and will be fine with Grados if you have a quiet source. If you're feeding the DAC-100 into the HAP-100, then Grados are not your friend.


OK, thanks for the note.  Would you recommend a DAC to go with the HAP-100 and Grado?  Thanks, in advance.

post #12 of 34
Thread Starter 

To be honest I don't think the HAP-100 is really the best match with the Grado either as you'll clip the amp if you like to listen at high volumes. Just my thoughts on the matter. Dac wise, the HDP with LPS is already very good.


The only higher end dacs I have experience with are the DAC-100, Bifrost and Gungnir. The Bifrost is ok, the Gungnir is better though only balanced and I found the sound rather forward. Price to performance wise, I think the HDP is very good. The Centrance stuff is around the same league, maybe a touch better, but since you're already at the HDP I don't think it makes sense to spend the money on that sidegrade. It'd be better to ask project86 for some input on the matter.

post #13 of 34
Originally Posted by Armaegis View Post

To be honest I don't think the HAP-100 is really the best match with the Grado either as you'll clip the amp if you like to listen at high volumes. Just my thoughts on the matter. Dac wise, the HDP with LPS is already very good.


The only higher end dacs I have experience with are the DAC-100, Bifrost and Gungnir. The Bifrost is ok, the Gungnir is better though only balanced and I found the sound rather forward. Price to performance wise, I think the HDP is very good. The Centrance stuff is around the same league, maybe a touch better, but since you're already at the HDP I don't think it makes sense to spend the money on that sidegrade. It'd be better to ask project86 for some input on the matter.


Thanks for your thoughts, which sound like good advice.  To be honest, I replaced the u192s yesterday with the Bel Canto mLink and I'm in love with the new sound - you know, for the time being, of course.  I am getting the impression that the system I have is a good match for my level/type of phones, so I think I am going to refocus on adding to my music collection.

post #14 of 34
Thread Starter 

Right now, my "balanced" rig is the HDP as dac, feeding the Icon speaker amp to the HE-6, both powered from an LPS-2U which also acts as optical bridge for the HDP. 



Icon2 - speaker amp // RJ45CX - converter box // Icon HDP - dac and headphone amp

from left to right:


RJ45CX adapter box (discontinued), which I modded to have the 4-pin XLR in front


bottom: LPS-2U-192k

post #15 of 34

Have you tried He-4 with the HAP-100?? if so, what's your impressions, thanks. 

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