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JBiser
31
Oct 24, 2018
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I verified 5 ohm output impedance with topping customer support. However, there are some language issues- I also asked whether OPA 1688 would be a good chip to roll (I believe used in nx4s and also super cmoy project) and they replied not useable because amp uses output transistors, which is wrong.
Anyway, should work great for 50 ohm and above, probably Ok down to 32 ohm.
What no one has mentioned, if global feedback is used, then equivalent output impedance should be lower.
The chip used has high bandwidth and slew. Usually designers add output resistance for stability, like with Topping A30. This is the trade-off. Up until a few years ago, no one would think of designing an amp without some output impedance. I think that owners of 16 ohm Iems or multi-driver iems with poorly designed crossovers, should look at something like O2. Of course, the result of using those with this amp would be flabby boosted bass, which some people like anyway. Also, if there is feedback, maybe this won't happen.
Oct 24, 2018
Caiz
23
Nov 9, 2018
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JBiser yes i was also told of the high output impedance, i was commenting about it on the last drop. I think it's really sad.., like you said, okay for 50 ohm and above, but some say a damping factor of even 20 can net noticeable improvements., so i dont know how great, a value when compared to something like an O2 for like a 50 ohm headphone, but also half the price, but I say that there are other things to consider. At the pricepoint; it's interesting i think but like you mention the output impedance, too bad about that.., ppl say use this with iems, but i think in all cases you'll be right, loose highly inaccurate base, poor impulse response, tracking issue/phase, and distortion.. That said, with something like a 150ohm headphone, but then you might consider topping's design and reliability issues, and just what your getting, And just who knows what voltages and standard theyre getting that 120 SNR figure at.. With the short warranty and poor returns compared to a deigned and assembled in america O2, with a 1ohm output (so useable with waaaaaay better headphone support) combined with 10 year warranty not sure just how great that value continues to remain.., The o2's snr is 115 a-weighted at @1v, it could compare differently at different voltages though, and with many sources the source becomes a bottleneck any extra wouldn't see. I've never heard the O2 quote at 120snr before, personally., Now, im not going to say; "theirs no application that the nx3s is "better" than an O2 at", especially given the price difference,. BUT THAT, the price difference can easily go in reverse and down the drain, either if the unit like many toppings, fail withing a year or two or six months, or the user moved to a balance armature or other 16ohm headphone where it's no longer useful at all for reference playback.., The high output impedance really does have a major affect on reproduction that which on-one would want occurring, and also the low high power limit for being so mobile means more headphones cut out, so applications are limited limited limited, to some headphones in a more narrow range, and not even target/average headphones.. that said in a proper setup, based on written specs alone and ideally, customer could be getting well served at that price, for some applications and personally, im not sure just how. "unrecommended" and "compromising" 5ohms would be for a headphone rated 32ohm nominal.., However i cant believe massdrop is hiding and withholding that figure, and misleading people into thinking this is just "great all around with IEMs".., without adding any kind of warning or addendum.., I guess sales are more important than community support and serving customers well? Is this place customer focused and products focused, or profits focused? you know, you can do good business serving customers transparently and see returns in the way of profits. That said, i dont put much stock in toppings products in terms of durability and reliability.., I was really looking at this amplifier at a recent drop, but yes, everyone's hiding that figure.., ;-) so, for economy i get it, 50 is half of 100 of the O2, having the O2 means UNDER 1 ohm output impedance, SO even if you switch to balance armatures or something low impedance; you don't loose the 50 bucks, so then your economy isnt gone.., And then what? Whats next if you get a balanced armature you really wanna use; buy an O2 for the low impedance iems? ohh geeze. But, yeah, im not going to say the nx3s is without a good application, just that it's pretty highly application limited and complicated. Cant do power hungry, cant do low impedance, or perhaps even target impedance fully "proper".., but like you said, 50 ohms, i would say for that scenario, with anything but the power hungry, might be quite good. Certainly looks good on paper given the SNR spec and the price, but that i really suggest like you forwarn; there are big issues even with the products described application; for "IEMs". Now if you cant afford an O2, i understand, but if you can, and your lining from something like an ipod, or a source with a SNR around 110., what would you gain but portability and limitations with the nx3s? you'd probably be netting major losses going with an nx3s with most headphones, and your really limiting yourself to a particular range of headphones, much more than an O2. That said, both amps, last i checked, can with some modification and perhaps without; be used in BTL, bridge tied load, which when using two of the amps, would put both these amps at being able to put out over 1.2watts @32ohms, i understand, which means either could fully drive any headphone to above reference power requirements, but then at half the price and then twice the output impedance of the nx3s in normal mode; (10Ohm in BTL) the nx3shas again highly limited application Now, if you JUST want to power a single heapdhone, like you suggest at 50 ohms, or like 120 or 150ohms, with a moderate power requirement headphone, and are willing to go with a risky company(high nominal faults) and practically no warranty, then by all means, you could end up very well served.., ! That said; the O2 has user-replaceable batteries, and wih the warranties, can last like 5 times longer than an nx3s, which has a capacitor life of only maybe 1000-5000 hours, afaik. Mayflower electronics will repalce caps when they fail, JDS labs will replace caps with fresh ones whenever you want(at least if you purchase through them, but for a small service fee) even outside warranty, . the nx3s will die out way before, but of course if your into electronics you can solder in some new ones to the nx3s, if your into that., Or you can socket mod your o2, and simply un-pressfit your caps when your done their useable life, no soldering needed.., swap em' just like the batteries, which by the way are user-replaceable with the O2... when your looking at price, this is kind of a HUGE value difference here, in favor of the O2 in terms of life, reliability and support., i think topping makes thier batteries unavailable and un-serivceable so that users have to buy a new amp every year or two like a commodity, whereas a slightly modified O2 is good for life, maybe even 10, or 100 times longer. so hows your disposable value purchase looking now? Still an economical purchase? Even the mayflower comes with a 10 year warranty and jds will send you a pcb ready for in-pcb press-fit socket's, for end-of-life capacitor swapping.. just a thouhgt for value/economy.., Now, if you need to drive some shr840's and you know; THATS IT. Maybe the nx3s can get you there for a year or two, or three, or depending maybe even a few years if you use it lightly and that might be all you want and need, and fit nicelier in your pocket. ;-) So yeah, possibly good deal for that, just saying though, the impedance and risky business makes the "value" less bright, i figure, fellow. then again, i dont know many other amps signing off on a 120SNR figure,.
Nov 9, 2018
JBiser
31
Nov 9, 2018
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CaizHi there. What a detailed and thoughtful response. I'm still digesting this. Please don't think that I am some kind of expert, but like you, have been trying to inform myself, mostly because audio interest me. That said, we're kind of comparing two things - a desktop amp (O2) with a portable one. Even though O2 has the portable option, its runtime is short. This unit, I would say, is more optimized for portable operation, has relay switching to minimize turn on/off "pops", and better cutoff of the circuit when the batteries get low than the O2. I really do view the O2 as a desktop amp. Conversely, as a desktop unit, the Nx3s has a volume control that is not so easy to get at, nor am I sure that you can operate it continuously off the charger, or would want to. (I myself would). I don't know about any quality issues with Topping, and actually they have been designing well engineered designs, are honest and complete in their published specs, are reaching out to reviewers and others, who for example are developing Linux drivers for their DACs. They appear to be be a real audio company, as opposed to one-man boutique operations. Check out audiosciencereview.com It is difficult to implement a DAC correctly. They seem to nail it every time. This product is certified to the Japanese Hi-Rez standard. It used to be that anything around 98DB THD+Noise was good enough for CD audio, but people are using Hi-Rez formats nowadays. If you see a measurment in the range of -115DB, by the time they A-weight it, it is in the ballpark of 120DB. This is what everyone is shooting for. This is an order of magnitude better (or more?) than any headphones it will be driving. NWAVGuy designed the O2 to be used with CD audio. The IC's are much older. The O2 output is slew-rate limited about 3V/uV. Is this a problem? Probably not. He was also designing for stability and purposely did not use the ultra-fast chip available at the time, because he needed to fit a lot of stuff in a relatively small box, and genuinely did not believe any audio signal needs the higher slew. His amp is stable with a low output impedance. Job well done. The Topping NX4 DSD, this amp's big brother basically measures like a desktop amp, give or take. This one should measure just as well. It appears to be that quality, minus the DAC. For $50? It is a great time to be an audiophile. I would like to know what Massdrop's warrantee policy is, though.
Nov 9, 2018
JBiser
31
Nov 9, 2018
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CaizLet me add: Expect 50 - 70 clean mW output at 300 ohms. That is one "limitation". Also, despite prodigious output at 32 ohm, we have the output impedance issue. Or maybe non-issue. Anyway, I'm only interested in 300 ohm, so not an issue for me. If you are using on a desk, a desktop amp is definitely better. May I also suggest Topping A30, again with the output impedance issue, but otherwise great.
Nov 9, 2018
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