[project86]

 
 
 
[size=small]NuForce has an interesting history of success. On the one hand, they became famous on the strength of their relatively high end amps and preamps. They still sell plenty of models in their "reference" line, most of which cost at least several thousand dollars. In more recent times they seem to have focused on the opposite end of the market - the budget end - and have achieved success there as well. Products like their HDP, the various Icon compact amplifiers, their NE series of IEMs, and of course the uDac, have cemented their place as a popular maker of affordable gear. [/size]
[size=small]  [/size]
[size=small] I've often wondered what happens to sales on the higher end gear, after a company begins offering budget products. Musical Fidelity did it with their V-series, AMR is doing it through their iFi line, and I'm sure there are other examples that I'm forgetting. Does it drag down the prestige of their expensive products? I can see the awkward feeling when someone buys a $5K amp only to see that some kid down the street has a $200 headphone amp from the same brand. Or does it boost the prestige of the budget line, with the idea of trickle down technology and all that? Or maybe it's a bit of both? Ultimately the budget gear must be profitable or these companies wouldn't be bothering with it. [/size]
[size=small]  [/size]
[size=small] But what about the middle? Gear that costs more than a few hundred dollars but less than several thousand? That's a key area where the price to performance ratio is often at its best. And at $1095, the NuForce DAC-100 fits squarely into that "in between" category - not cheap nor massively expensive. But do they have the price to performance ratio in place? Interestingly, NuForce has other "100 series" components at various prices including the DDA-100 integrated ($549) and the HAP-100 headphone amp ($595). The DAC-100 is the most expensive product in this line by a significant margin. But overall I still categorize the series as  falling somewhere in between budget gear and high-end gear (but I refuse to use the term "mid-fi" as it brings too many implications). [/size]
[size=small]  [/size]
[size=small] DESIGN[/size]
[size=small] The DAC-100 is nicely sized for a headphone based system - 8.5 inches wide, 9 inched deep (but deeper if we count the volume knob and RCA jacks), and about 2 inches tall. This means it will handily fit into most systems, where bigger units from Audio GD and Bryston may have trouble. Weight is about 3 pounds which reflects the enclosure being less overbuilt than some competitors. But it is made of what appears to be copper-plated metal, like an old school Pioneer Elite or Marantz component, so the overall quality seems right. [/size]
[size=small]  [/size]
[size=small] The front panel is simple: 1/4" headphone jack, volume knob which doubles as a standby switch (just press it), 4 dedicated buttons for input selection, and sample rate indicators for 44.1kHz through 192kHz. The back panel is equally straight foward: IEC power receptacle with an actual power on/off switch, voltage selection switch for worldwide compatibility, RCA outputs, and 4 inputs total: Toslink, USB, and a pair of coaxial SPDIF. The unit comes in black or silver, with the silver model still having a black "stripe" across the front panel. The top portion of the enclosure has two sections of venting - one above the headphone amp section, and one above the power supply. The unit doesn't run overly warm but the venting is still a good thing in my book - just in case.[/size]
[size=small]  [/size]
[size=small] Inside, the DAC-100 "guts" are divided into several distinct sections. The relatively large torroidal transformer gets isolated from the other components, walled off by a metal shield. The power supply section has 4 voltage regulators attached to a beefy heatsink, augmented by a rather healthy collection of 17 capacitors. Next comes the main board which handles several functions: the actual DAC section based on an AKM AK4390 32-bit DAC chip, the output stage based around dual socketed LM4562 opamps combined with discrete transistors operating in Class-A, the AKM AK4118 24/192 capable digital receiver, a Xilinx Spartan FPGA, some local voltage regulation, and a few other odds and ends. It sounds complex but the layout is actually rather simplistic - not that simple is necessarily bad. The last "section" is the USB board, which appears very similar to the USB implementation I've seen in other NuForce products like the DAC-9, but different than my NuForce DDA-100 where USB is integrated into the main board itself. USB operates in asynchronous mode and the chip itself has NuForce labeling rather than one of the usual suspects like XMOS, VIA, C-Media, or Tenor. [/size]
[size=small]  [/size]
[size=small]
 
 
 

 
 

 
 

 
 

 
 

 
[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] Other random bits worth mentioning: [/size]
[size=small]  [/size]
[size=small] *The DAC-100 also works as a preamp. The RCA outputs are variable, being adjusted in conjunction with the headphone amp. Max output is 2 Vrms which is "redbook standard". It's generally best to keep the volume knob maxed for regular DAC use unless you have some need for more attenuation based on the amp being used.[/size]
[size=small]  [/size]
[size=small] *Volume adjustments are handled in the digital domain via 32-bit processing for a total of 100 "steps". This could be accomplished through one of two ways - by using the built in volume adjustment in the DAC chip itself, or else by the Xilinx chip seen on the PCB behind the front panel; I'm not sure what route NuForce took here. The adjustment has a somewhat "cheap" feel to it, based on both the physical knob itself (which feels like plastic to me) as well as the action which has little resistance. I've got other DACs with digital volume control that feel great, but somehow in this case the lack of resistance feels weird. It might just be that the knob has more play than I'm used to thanks to the required "push" action for standby activation. Apart from that complaint, the actual functionality of the volume control is excellent. Perfect channel balance, totally free from static or other potentiometer artifacts, and as far as I can hear, no obvious loss of resolution even at lower volumes. Nice. [/size]
[size=small]  [/size]
[size=small] *The DAC-100 ships with a small remote, which I never use. I did try it once and all worked well. It doesn't move the actual knob which means using a combo of remote and physical adjustments will make things confusing. I figure someone will either use one or the other the majority of the time - remote if you mostly use the unit as a preamp, and knob if you tend to use headphones. But my Matrix Quattro DAC, at $400 less than the DAC-100, does manage to have a motorized volume knob. Make of that what you will.[/size]
[size=small]  [/size]
[size=small] *NuForce offers drivers for Windows XP, Windows 7, Mac, and Windows 8 (currently in Beta as I type this). No Vista? Not a problem I suspect... I used 2 different computers running Windows 7 and had zero issues. I have read several complaints about static and stuttering though, and even some BSOD crashes. But USB issues can be common with a variety of DACs and I'm hesitant to blame NuForce for what could be a system issue with a few users. All I can say is that everything worked for me, just as it should have. [/size]
[size=small]  [/size]
[size=small] *The design uses oversampling but no upsampling. NuForce refers to it as "questionable data manipulation". Can't say that I agree 100% but that's fine. This means a 44.1kHz signal (for example) will be presented to the DAC chip at the native data rate rather than being upsampling to 192kHz or some other arbitrary sample rate, as done by many competitors. [/size]
[size=small]  [/size]
[size=small] *The single-ended Class A headphone amp is interesting in that it has a constant current source and as such doesn't have an easily definable output impedance. I tried measuring it and got weird results (negative numbers), which echos the findings of user Amaegis (who has also reviewed the DAC-100 by now, though I deliberately skipped reading it until mine is posted). Apparently the Class A design is to blame, in addition to a resistor on the output for protection. In any case NuForce lists the "recommended headphone impedance" as 120-600 ohm. I'll discuss the practical application of this in my listening section.[/size]
[size=small]  [/size]
[size=small] *Specs for the headphone amp  - 10.4Vpp 3.7Vrms, 500mW into loads ranging from 300 ohm to 600 ohm (NuForce doesn't list current delivery into lower impedance), 80mA constant current. See extensive measurements of the DAC-100 HERE. [/size]
[size=small]  [/size]
[size=small] *The DAC section uses some type of buffering which helps with jitter rejection. NuForce doesn't really talk about this much, but it was pointed out to me (by Armaegis) that there's a slight "delay" to the sound being processed - I verified this by connecting the same transport with dual SPDIF outs to the DAC-100 as well as some other DAC, both feeding the same amp. Switching back and forth on the fly, the DAC-100 is maybe a second or so behind. Weird. But it makes sense that they have some type of system in place for jitter reduction since they frown on ASRC. I don't know exactly what the FPGA does in this design but chances are good it plays a role in this delay. [/size]
[size=small]  [/size]
[size=small] *The DAC chip itself is somewhat rare - the AKM AK4390. By specs it is very close to their AK4399 which is used in the Schiit Bifrost, Cary Xciter, and a few Hegel DACs. The only examples I can find using the AK4390 are the Fostex HP-A3 ($499) and the SOtM dAC-200 HD ($2199). Neither of those is very widely used around here. The AKM marketing literature really talks up their minimum-phase FIR filter but the datasheet shows the truth - default setting is a short delay filter, with minimum phase being optional. NuForce doesn't tell us which one gets used in this device. [/size]
[size=small]  [/size]
[size=small]  
 

 
 
 

 
 
 

 
 
 

Toroid is by Noratel, who also supplies Benchmark for their DACs
 
 

Xilinx Spartan FPGA
 
 

USB section
 
 

AKM digital receiver towards the bottom, AKM DAC on the left (sorry for the shadow)
 
 

 
 
 

 
 
 

Socketed opamps
 
 

 
 
 

Front panel PCB including separate Xilinx chip
[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] GEAR[/size]
[size=small]  [/size]
[size=small] I used the following gear during my evaluation of the DAC-100, down to the last excruciating detail for those who are interested:[/size]
[size=small]  [/size]
[size=small] Source: Cambridge Audio 840C, Acer laptop with and without an Audiophilleo AP1 with PurePower, Auraliti PK90 with NuForce LPS-1 power supply [/size]
[size=small]  [/size]
[size=small]
 
 

PK90 with 2TB G-Technology drive for storage
 

LPS-1 power supply
[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] AMP: Analog Design Labs Svetlana 2, Icon Audio HP8 MkII, Violectric V200, Auralic Taurus, Stax SRA-12S[/size]
[size=small]  [/size]
[size=small]
 

 

 

 

 
[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] Headphones: Sennheiser HD800, Audeze LCD-2.2 (with C3 Auric Ohno cable), Thunderpants, HiFiMAN HE-400 (CablePro Earcandy) and HE-500 (Toxic Cables Hybrid cable), beyerdynamic T1, Heir Audio Tzar 350, Westone ES5, Sensaphonics 3MAX[/size]
[size=small]  [/size]
[size=small]
 
 

 
 

 
 

 
[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] Power Conditioning: CablePro Revelation, Yulong Sabre P18[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] AC Cables: CablePro Reverie, Charlestone Cable Company Auric Ohno[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] Interconnects: NuForce Focused Field, Charleston Auric Ohno[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] Digital cables: NuForce Precision coax, Charleston Auric USB, NuForce Impulse USB, Signal Cable Optical Link[/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small]  [/size]
[size=small] LISTENING[/size]
[size=small] I first used the DAC-100 as purely a DAC. I used my Cambridge 840C as transport, and fed the DAC-100 RCA out to an Icon Audio HP8 MkII tube amp. I recently reviewed this amp and became very familiar with its sound signature, so I was fairly confident in the contribution of the DAC versus the character of the amp. My first impression: the DAC-100 sounded clear, natural, and detailed, with just a hint of added excitement as compared to a more flat presentation. Not that it's an unbalanced sounding DAC, but compared to something like a Benchmark DAC-1 the old standby term "musical" comes out to play. This implies excitement but also a lack of "digital" feel to the sound, especially on the top end.[/size]
[size=small]  [/size]
[size=small] Dynamics are a strong suit - if you dig listening to stuff like Holst, Dvorak, Rachmaninov, or other really dynamic classical, the DAC-100 is excellent. I threw in some of my Sheffield Labs test discs, the XRCD release "Dancing With Drums", and the Reference Recordings CD release of Stravinsky: The Firebird Suite. All sounded startlingly powerful and "large". Some DACs hit all the right notes but just don't sound as lively as they should in terms of macro dynamics - not so the DAC-100.[/size]
[size=small]  [/size]
[size=small] I later tried the Reference Recordings HRx hi-res version of the same Stravinsky album, and was able to compare the two versions back to back. I could really tell the difference between them in terms of fine detail as well as openness - the 24-bit/176.4kHz HRx files just sounded better to me than the already excellent CD version. Granted this was not a fair fight - the CD was played through my Cambridge 840C as transport over Toslink, while the HRx version came from a laptop by way of the Audiophilleo converting USB to SPDIF. To be completely thorough I'd have to rip the CD version and play it back to back but honestly I'm too lazy - I already have the HRx version on my HD and I'm not really here to test format differences. In any case, I suspect the power supply is mostly responsible for making this unit sound as "punchy" as it does.[/size]
[size=small]  [/size]
[size=small] From that point forward I played all tracks from the laptop. I switched to the Violectric V200 amp and heard the typical smooth, slightly warm presentation. It sounded very slightly more closed in as compared to when I use the Violectric V800 DAC, but the difference wasn't striking. The V200 isn't the most open sounding amp so it's not a major fault of the NuForce. But there was still a good amount of layering as I played "The Persuasions Sing U2", allowing me to pick out each member of the group as well as enjoy their collective sound. While it did sound slightly closed in compared to the V800, it also sounded more bold and energetic, so it was a trade-off. This applied universally whether I used my T1, or LCD-2, or Heir 6.A LE, or anything else. [/size]
[size=small]  [/size]
[size=small] Bass hit very nicely on "Parallax" by Electronic Noise Controller. It's one of my reference bass tracks due to the deep extension yet natural feel, unlike a lot of "bass music" which is fun but way overdone. The Heir Audio 8.A and Thunderpants were both able to dig very deep to the point where I don't think much further could be accomplished - the DAC-100 approached reference level quality in this respect, and the sound was surely more limited by the amp or headphone rather than the DAC. [/size]
[size=small]  [/size]
[size=small] Vocals were nicely done as well, though not on the same level as the bass presentation. I found Livingston Taylor to sound clean and non-sibilant, but I've heard other DACs at this price which do better in terms of realism. Switching from my (more expensive) Resonessence Labs Invicta or Anedio D2 to the DAC-100 gave less of a sense of vocal projection, like I was still in the room with the singer but off to the side - his vocals projecting mainly to the side instead of directly toward me. This is not to be confused with a sucked out midrange or anything major like that - it just didn't quite have the same purity as those other DACs. I got similar results with various singers from Nancy Bryan to Norah Jones to Aretha Franklin. It didn't stick out as being terrible on its own but in comparison to other DACs I did notice it. I'd take care in mating the DAC-100 with certain gear (stock Denon D7000 for example) where the cumulative effect would be more significant. [/size]
[size=small]  [/size]
[size=small] Aside from that, I have nothing major to criticize. The unit has very good attack and decay, a nice even tonal balance with just a hint of excitement, and an impressively accurate imaging. Soundstage is roughly medium in size (among similar priced units), with horizontal spacing average for this class but depth being more impressive. Note that when I talk about the unit sounding "exciting", I don't mean it has some added zing up top. While the highs are certainly present, they sound fairly refined and "non-digital", and don't really shout at the listener as some DACs can. Background is reasonably black though I've heard darker. Microdetails are plentiful if not top of the class - my Violectric, Anedio, and Kao Audio DACs all do better in this area for similar cash. Yet this might actually work in favor of the overall presentation - the DAC-100 has a focus on being lively and dynamic, so it makes some degree of sense that low level detail retrieval is not the focus. If it were, I think some users might find the presentation a bit overwhelming - too much of "everything" all thrown up at once, resulting in a sound that becomes fatiguing over the long term. The DAC-100 is easy on the ears for extended listening, despite the dynamic presentation.[/size]
[size=small]  [/size]
[size=small] I did go back and forth between native USB and several USB to SPDIF converters. It was lengthy, time consuming process about which I'll spare you all the boring details. But in summary: the native USB solution is very satisfying. It held its own when compared to a Stello U3 and an Izmo M1 USB to SPDIF converters, both of which are very nice units. It fell slightly behind when compared to the Resonessence Concero, and further still in relation to the reference level Audiophilleo AP1 with PurePower battery option. That set costs more than the whole DAC-100 so the comparison is not really fair, but there it is. Overall though, I'd say the DAC-100 USB is just fine by itself and doesn't really need help from an external DDC. [/size]
[size=small]  [/size]
[size=small] AMP[/size]
[size=small] The headphone section on the DAC-100 is sort of a mixed bag for me. At times I find it brilliant, yet other times it is frustrating. Overall I'll still call it one of the better integrated amps out there and at times it goes from good to great with certain headphones. But it's definitely not without its drawbacks. I'll break it down in sections:[/size]
[size=small]  [/size]
[size=small] The good - it's clean, rich, and dynamic, with a great sense of timing and pace. This is one of the best integrated amps I've heard when used with the right headphones - I love it with the HD800, and LCD-2 and T1 sound very nice too. There is plenty of drive for all of these models and I never had issues with running out of headroom. The presentation has a sense of ease which is helpful on models like HD800 or T1 which can be edgy on the wrong amp. Despite that, it still matches well with the somewhat laid back LCD-2, not sounding overly dull. That's impressive. The HD800 is an especially good match - in this case it's right up there with the excellent integrated amps in my Anedio D2 and Resonessence Labs Invicta DACs. Those both have advantages with certain other headphones but with HD800 the synergy is undeniable. For someone looking to build a system around the HD800 I'd say give the DAC-100 a shot - seriously, it's that good. [/size]
[size=small]  [/size]
[size=small] The mediocre - despite the bass being punchy and very clean, it doesn't really dig as deep as it could. And those mids are still a bit laid back in terms of vocalists not coming to the forefront of the mix as much as they do with other amps. I suppose this could merely be the amp section acting transparent and serving up the presentation as given to it by the DAC section... I have no way to tell since there isn't an analog input, so I can't try feeding it with a different signal. Again, this is not a major problem, but worth noting nonetheless.[/size]
[size=small]  [/size]
[size=small] The bad - noise floor. Period. It's the biggest flaw here by far. It essentially makes this device unsuitable for most sensitive headphones. The Ultrasone Signature Pro is out, as are the Denon D2000-D7000 and the Audio Technica Woodies. Grados? Not ideal. IEMs? Forget it. All this assumes the listener is like me and prefers not to hear an annoying hash sound intruding on their listening. If this was a budget unit costing maybe a few hundred dollars, it would be one thing. But with a 4 digit price tag I expect much more. Once the music plays, the noise is less obvious, but it still takes away from the presentation by clouding the dynamics and micro details. I have no clue what causes this but I wish NuForce was able to address it. [/size]
[size=small]  [/size]
[size=small] As it stands, I certainly do enjoy the amp with the Audeze LCD-2, HiFiMAN HE-400 and HE-500, Sennheiser HD650 and HD800, Thunderpants, and Beyer T1. The low impedance of the planar models doesn't seem to be an issue, and there's just enough gain to drive even my difficult Thunderpants to high levels. I'm still perplexed by the odd output impedance but it ends up being a non-issue due to the high noise floor. Anything with low enough impedance to potentially cause interactions, is probably sensitive enough to reveal the noise problem anyway - with the exception of planars of course. [/size]
[size=small]  [/size]
[size=small] NuForce did send me a revised part for the headphone section. Apparently it allows a bypass of the 15 ohm resistor. Amaegis has tried it in his DAC-100 and doesn't seem super impressed. I'm exceedingly pleased with the synergy with my HD800 as it stands, so didn't bother to install it right away. When I finally got around to opening the case, I found out the newer part was already in there anyway. I haven't bothered playing with the jumper at this point and I'm not sure I ever will. [/size]
[size=small]  [/size]
[size=small] The fact is not lost on me that the above description sounds like it would be absolutely terrible with the HD800. Don't ask me why it works so well - it just does. Rather than sounding lively and exciting in a sort of "on edge" way, with heightened treble peaks, it actually sounds very smooth and controlled but still extended. It doesn't roll off or turn the HD00 into an LCD-2, but it does keep the treble in line with an iron fist. Perhaps the constant current design of the amp section is more capable than the average amp when it comes driving the HD800 and its "interesting" impedance characteristics. Whatever the case, I'll take it. [/size]
[size=small]  [/size]
[size=small] CONCLUSION[/size]
[size=small] DACs have really come a long way. In the past few years alone, I've seen the price of your average "really good sounding" DAC drop to between $1,000 and $2,000, where prior it had been several times that. Sound approaching state-of-the-art is now a lot more attainable. The only problem with this equation is the expansion of choices, which is not necessarily a bad problem to have.[/size]
[size=small]  [/size]
[size=small] So where does the NuForce DAC-100 fit in? I'd say it is definitely worthy of the price, and competes well with models in the same bracket. I definitely prefer it to numerous competitors such as the PS Audio NuWave (too bright and digital sounding), Rega DAC (fun but not very resolving and overly dark), W4S DAC1 (too clinical), and Musical Fidelity M1 (generally unimpressive on many levels). Does it beat out every DAC in the price range? No. The Violectric V800 ($1300) and Matrix X-Sabre ($1099), both offer slightly better overall sound quality. But each has its own unique presentation and neither has a built in amp section much less a (selectively) excellent one like the DAC-100. So it's a tradeoff. And the DAC-100 might actually be better than either of those in certain cases, if the user values a more engaging, lively sound in their DAC. System synergy would definitely come in to play here.[/size]
[size=small]  [/size]
[size=small] It's hard not to feel like the DAC market is a bit overcrowded at the moment. NuForce has a tough road ahead of them in terms of distinguishing their DAC-100 from the rest of the pack. Yet I think they deserve to succeed. It's not the perfect DAC but with an exciting, dynamic sound, and lots of functionality, this unit is truly worthy of consideration. That's not something I can say for many competitors. [/size]

 

[Armaegis]

Very nice. I think we share many of the same sentiments. 
 
I just recently had a chance to try the DAC-100 with the Senn HD800 and quite enjoyed the pairing (though I find that I'm honestly not quite a fan of the HD800 itself). 
 
As for the jumper to bypass the output resistors, I'm of two minds. I find myself wishing there were actually an in-between option. In stock configuration, there is a 15ohm resistor in series with the output (plus whatever else the class A circuit does). It gives a nice sliver of warmth to the Sennheisers, and testing with the T50rp I can actually notice the effect of looser damping which again give a bit more oomph in the bass and play with the highs a little. With the jumper bypassing those resistors, the bass levels out on the Senns and the T50rp behave a little flatter and have less zing up top. Noise floor is also higher since you are no longer dropping output across the resistor, though that's only noticeable with unsuitable cans and doesn't really affect the likes of the HD800.

 

[lithium1085]

Hi John, 
Excellent review as usual. I have a feeling that the selectivity of the amp that you mention is because of the current drive nature of the amp. Current drive amps usually don't work well with varying impedance loads which are more common with low impedance headphones. This would also explain why it works well with orthos, inspite of their low impedance, as orthos don't vary their impedance much.

 

[mcullinan]

Project,
Excellent review! Per usual...In depth and gives me a good sense of the sound qualities. 
 
I had the Nuforce Reference 9 SEs up to version 3 for about 3 years. Up to version 2, the Class D amps were phenomenal. For me version/update 3 lost the magic they had in 1 and 2 and I went in a new amp direction.
 
What you describe as capturing the liveliness and macro dynamics might be the Nuforce house sound. The 9SE amps were very musical and lively, but definitely not the last word in micro details.
 
Thanks for a great review.
Mike

 

[project86]

Quote:

Project,
Excellent review! Per usual...In depth and gives me a good sense of the sound qualities. 
 
I had the Nuforce Reference 9 SEs up to version 3 for about 3 years. Up to version 2, the Class D amps were phenomenal. For me version/update 3 lost the magic they had in 1 and 2 and I went in a new amp direction.
 
What you describe as capturing the liveliness and macro dynamics might be the Nuforce house sound. The 9SE amps were very musical and lively, but definitely not the last word in micro details.
 
Thanks for a great review.
Mike

 
Thanks!
 
I've heard similar comments about the "new" sound from some of the later models. Apparently, if this is true, the DAC-100 has more of a "classic NuForce" sound. I'm not complaining though - it sounds really great in its own unique way. 

 

[project86]

Quote:

Very nice. I think we share many of the same sentiments. 
 
I just recently had a chance to try the DAC-100 with the Senn HD800 and quite enjoyed the pairing (though I find that I'm honestly not quite a fan of the HD800 itself). 
 
As for the jumper to bypass the output resistors, I'm of two minds. I find myself wishing there were actually an in-between option. In stock configuration, there is a 15ohm resistor in series with the output (plus whatever else the class A circuit does). It gives a nice sliver of warmth to the Sennheisers, and testing with the T50rp I can actually notice the effect of looser damping which again give a bit more oomph in the bass and play with the highs a little. With the jumper bypassing those resistors, the bass levels out on the Senns and the T50rp behave a little flatter and have less zing up top. Noise floor is also higher since you are no longer dropping output across the resistor, though that's only noticeable with unsuitable cans and doesn't really affect the likes of the HD800.

 
Finally read your review - excellent of course. Interesting how we came to many of the same conclusions, but not identical. 
 
I agree about the "sliver of warmth" with HD800. It's probably damping factor related but definitely still tight enough to sound clean. If removing the jumper doesn't take away most or all of the background noise, then I have no desire to mess with it. If it actually adds noise, then I really don't want to do it. 
 
I guess my expectations for good SS amps has led me to have certain expectations. I won't complain when a tube amp has a noise issue with sensitive headphones, but for some reason I get all indignant when it happens on a solid state amp. It's not exactly fair of me, but there it is. 
 
Quote:

Hi John, 
Excellent review as usual. I have a feeling that the selectivity of the amp that you mention is because of the current drive nature of the amp. Current drive amps usually don't work well with varying impedance loads which are more common with low impedance headphones. This would also explain why it works well with orthos, inspite of their low impedance, as orthos don't vary their impedance much.

 
I was thinking the same, except the HD800 has a wild impedance swing.... but perhaps it is so high as to be more benign. 

 

[lithium1085]

Quote:

 
Finally read your review - excellent of course. Interesting how we came to many of the same conclusions, but not identical. 
 
I agree about the "sliver of warmth" with HD800. It's probably damping factor related but definitely still tight enough to sound clean. If removing the jumper doesn't take away most or all of the background noise, then I have no desire to mess with it. If it actually adds noise, then I really don't want to do it. 
 
I guess my expectations for good SS amps has led me to have certain expectations. I won't complain when a tube amp has a noise issue with sensitive headphones, but for some reason I get all indignant when it happens on a solid state amp. It's not exactly fair of me, but there it is. 
 
 
I was thinking the same, except the HD800 has a wild impedance swing.... but perhaps it is so high as to be more benign. 

If you guys measured the output impedance to very low, how can the damping contribute? perhaps the synergy is because it was the reference headphone......so it was designed for the HD800

 

[Armaegis]

Quote:

 
Finally read your review - excellent of course. Interesting how we came to many of the same conclusions, but not identical. 
 
I agree about the "sliver of warmth" with HD800. It's probably damping factor related but definitely still tight enough to sound clean. If removing the jumper doesn't take away most or all of the background noise, then I have no desire to mess with it. If it actually adds noise, then I really don't want to do it. 
 
I guess my expectations for good SS amps has led me to have certain expectations. I won't complain when a tube amp has a noise issue with sensitive headphones, but for some reason I get all indignant when it happens on a solid state amp. It's not exactly fair of me, but there it is. 
 
 
I was thinking the same, except the HD800 has a wild impedance swing.... but perhaps it is so high as to be more benign. 

 
I think the warmth would be more the impedance peak of the HD800 at ~100Hz. The damping factor is already 20+ with the resistor in place, so I don't think it should make much of a difference.
 
Shifting the jumper to bypass the resistors does increase noise, but really only with headphones that shouldn't be used to begin with.
 
Anyhow, here's a comment from my email exchange with Nuforce regarding the noise floor of the DAC-100 vs the UDH-100 which is reportedly quieter.
 
Quote:

There are some tricks we used to create a sweeter sound in DAC-100 that are not in UDH, they have different positioning, the trade off is higher noise floor in DAC-100 but to have utmost musicality and  because the noise is not an issue with headphones like HD800, while UDH are lower end and the headphone compatibility across lower impedance phones are the design objective.

 

[project86]

Quote:

If you guys measured the output impedance to very low, how can the damping contribute? perhaps the synergy is because it was the reference headphone......so it was designed for the HD800

 
But the output impedance didn't just measure low. It measured negative, which makes me wonder what the heck is going on there. 
 
NuForce did deny having the HD800 as a design reference. I suppose it could just be by chance. Guess it doesn't matter, as long as it sounds good.
 
Quote:

 
I think the warmth would be more the impedance peak of the HD800 at ~100Hz. The damping factor is already 20+ with the resistor in place, so I don't think it should make much of a difference.
 
Shifting the jumper to bypass the resistors does increase noise, but really only with headphones that shouldn't be used to begin with.
 
Anyhow, here's a comment from my email exchange with Nuforce regarding the noise floor of the DAC-100 vs the UDH-100 which is reportedly quieter.
 

 
So is there anything you like better about bypassing the resistor? 
 
As we discussed before via PM, the UDH-100 is the sort of black sheep here. It's either a stripped down version of the DAC-100 without any of the same magic.... or else it's a steal of a deal, essentially a DAC-100 minus legacy SPDIF inputs and fancy casing. 

 

[Armaegis]

Quote:

 
But the output impedance didn't just measure low. It measured negative, which makes me wonder what the heck is going on there. 
 

 
I suspect that the class A circuit is pulling current from anything nearby, which happens to include the multimeter when you're doing measurements and would undoubtedly result in very odd readings. Turn the amp off and the readings change significantly.
 
 
Quote:

NuForce did deny having the HD800 as a design reference. I suppose it could just be by chance. Guess it doesn't matter, as long as it sounds good.
 
So is there anything you like better about bypassing the resistor? 
 
As we discussed before via PM, the UDH-100 is the sort of black sheep here. It's either a stripped down version of the DAC-100 without any of the same magic.... or else it's a steal of a deal, essentially a DAC-100 minus legacy SPDIF inputs and fancy casing. 

 
There's only anecdotal heresay that the HD800 was used as the design reference. Then again, what the R&D guys know vs what athe PR guys know is probably quite different as well.
 
Bypassing the resistor did make a noticeable difference in damping with the T50rp. I'll give it a try with an LCD2 hopefully tomorrow, though I'd suspect a similar effect. The better damping offers a more accurate bass. The lower damping is not bad at all and gives the music a bit more oomph, but obviously isn't as precise.
 
I don't really know what to make of the UDH-100 now. The literature says one thing, but their PR rep says another. You can't even say that the dacs are the same and amp sections differ, because the noise is present on the preamp outputs of the DAC-100. So I can only (maybe wrongfully) assume that the dac sections do differ between the DAC and UDH-100.

 

[project86]

Could be. I know their DAC-9 used a pair of TI DACs, PCM1798 if I recall correctly. I think they usually deface the chips to keep it secret. But some units slipped through where they missed it - both on that model and the DAC-100. Speaking of the DAC-9 ---- I heard it once not too long ago, and honestly I think the cheaper DAC-100 might just be the better sounding DAC. The DAC-9 has a nicer look to it but the DAC-100 is either right up there with it or possibly surpassing it in SQ. I'd have to get one here to directly compare, but I'm pretty confident in my memory of it.

 

[Armaegis]

So yesterday I got to play with the HD800, LCD2/3, HE-500, T50rp. Tried them out with the DAC-100 and HAP-100, as well as experimented with the output impedance. My impressions went pretty much as expected in regards to damping.
 
With the orthos which are all low impedance, the difference in damping was noticeable when you know to listen for it but it's not huge. Bass thumps a bit more, which can be good or bad depending how you like the sound. With the T50rp the extra oomph was a nice touch. With the LCD2/3 it was hard to tell as they are already kinda rumbly. The HE-500 falls somewhere in the middle and I liked it with the extra energy. Treble differences were much harder to tell but lower damping does seem a bit zingier (yeah I just made up a word). I didn't like that with the Audeze's which are already kinda shouty.
 
I do think the Senn HD800 sounds better with the stock config. Overall sound is blacker, slightly warmer tilt, and a slightly looser sound gives it some groove and takes away some of the hard bite
 
tl;dr... my opinion:
stock config: I like the Hifimans, Fostex, HD800
jumper bypass: better for the Auduzes, HD600/650
 
I've got a few more notes over in my review: http://www.head-fi.org/t/645068/review-nuforce-dac-100

 

[DBB1]

Thanks for a thorough review. I have been running my Nuforce DAC-100 through a modified Marantz 7025 power amp for over a month now. No headphones. I am listening through Green Mountain Chroma speakers. My experience with this configuration is diferent. First, I am using Windows 8 and found the beta driver a complete failure. I had to switch to the 24/48khz maximum resolution on the optical out from my computer's mother board to get digital into the dac.(I have a USB to SPDIF card on order) Once achieved the sound has been detailed, clear, neutral, somewhat dynamic, but, after hours and hours of listening, lacking in musicality. It is some how not musically satisfying to me. Not nearly the soul of my Neko D100.I recognize the problem could be the lack of a preamp. I have a used McIntosh preamp on order. This may add the weight and musicality I think it is missing. 

 

[project86]

Quote:

Thanks for a thorough review. I have been running my Nuforce DAC-100 through a modified Marantz 7025 power amp for over a month now. No headphones. I am listening through Green Mountain Chroma speakers. My experience with this configuration is diferent. First, I am using Windows 8 and found the beta driver a complete failure. I had to switch to the 24/48khz maximum resolution on the optical out from my computer's mother board to get digital into the dac.(I have a USB to SPDIF card on order) Once achieved the sound has been detailed, clear, neutral, somewhat dynamic, but, after hours and hours of listening, lacking in musicality. It is some how not musically satisfying to me. Not nearly the soul of my Neko D100.I recognize the problem could be the lack of a preamp. I have a used McIntosh preamp on order. This may add the weight and musicality I think it is missing. 

 
I love GMA speakers! Used to have the Europa for a while, and once had the pleasure of using the Callisto for a while in my system. Very nice speakers.
 
I see several potential issues here. First, the Windows 8 driver issues. I haven't tried Windows 8 yet but I can imagine how frustrating that would be. NuForce needs to get on top of that ASAP. Second, optical out from my desktop PC sounds horrible, so that could be part of the problem. I've had other computers which did a decent job but I'd say there is definitely some room for improvement once you get USB up and running, or USB to SPDIF. That could solve everything. 
 
I'm not sure about adding a preamp to fix the problem. It could certainly add flavor, but I would think the DAC-100 should be able to to a good job by itself for the most part. At least, it did in my humble speaker setup. I hope you get it straightened out. 

 

[DBB1]

Quote:

 
I love GMA speakers! Used to have the Europa for a while, and once had the pleasure of using the Callisto for a while in my system. Very nice speakers.
 
I see several potential issues here. First, the Windows 8 driver issues. I haven't tried Windows 8 yet but I can imagine how frustrating that would be. NuForce needs to get on top of that ASAP. Second, optical out from my desktop PC sounds horrible, so that could be part of the problem. I've had other computers which did a decent job but I'd say there is definitely some room for improvement once you get USB up and running, or USB to SPDIF. That could solve everything. 
 
I'm not sure about adding a preamp to fix the problem. It could certainly add flavor, but I would think the DAC-100 should be able to to a good job by itself for the most part. At least, it did in my humble speaker setup. I hope you get it straightened out. 

I hope you are right. I should add that I when I listen using headphones the missing element is back even though it is fed via toslink cable. My comment is strictly in a direct to amp set up with optical out. The texture, space, and weight sound right through the heeadphones.  
 
3/31/13 I need to ad an ademdum: Today I moved the computer and TV cable box further away from the Nuforce DAC and Marantz power amp. It sounds much better. The problem might have been EMI/RFI interference.