I don't understand how Benchmark can do what they purport to do without closed-loop control on the outputs.
Apologies for the ignorance, but do most amp output stages operate open-loop?
Benchmark referenced this paper: http://www.ti.com/lit/an/slyt630/slyt630.pdf, it propose a R/C network at amplifier frontend, figure 7 in the paper seems like mach Benchmark's amplifier behavior.When we change the load to headphones, the distortion profile wildly changes unfortunately. So there is some secret sauce in Benchmark headphone amps that the RME does not have.
Seems like a dream DAC.
I wonder:
1. If it can be stackable for doing multichannel (2 units or more) using the USB ASIO driver, the ADI-2 Pro manual hints little about this capability ("multi-interface", if I'm not confusing it) and the ADI-2 DAC hint even less. Could then be just about the best Multichannel DAC/opAMP at about $800 less than the closest contender (exaSound e38) if only 5.1ch is needed (or $1800 less for 2.2ch), with much more features and probably a better headphone AMP(s, as you get more than one unit at this price).
2. How would the $599 iFi Micro iDSD BL be compared in both DAC and headphone AMP section. Benefits are a native DSD to headphones (unlike conversion to PCM as in the RME) and MQA support.
I would guess that channel balance would be less performant due to an analog volume control, compared with the DSP based one in the RME.
The "diversion" is microscopic. Ohm's Law.
If the measuring instrument has an input of 1 megohm, which wouldn't be unusual, then the power going its way would be less than 0.01% even with the highest impedance 'phones, so nothing to worry about for the non-expert!
What are the implications on what the headphones actually output? Does higher distortion coming from the load make the load even more distorted?That variation in distortion measurement at the output is usually due to back emf from the load. The lower the amp's output impedance the less it should appear, but it is from the load, not the source.
What are the implications on what the headphones actually output? Does higher distortion coming from the load make the load even more distorted?
Impedance is a function of frequency. Doesn't mean it has to depend on frequency, but it can. If you have a capacitor in your output, you will get a higher impedance at low frequency, resulting in rolled off bass.The confusing thing to me is how benchmark says it affects amplifiers even though they have low output impedance, when it seems output impedance is the only thing affecting this. Is the idea that some amps have higher output impedance at certain frequencies and the specifications are misleading? Also, is the reason that the grado headphones do particularly poorly due to high resistance on the cable?
Benchmark referenced this paper: http://www.ti.com/lit/an/slyt630/slyt630.pdf, it propose a R/C network at amplifier frontend, figure 7 in the paper seems like mach Benchmark's amplifier behavior.
That is it! I had seen that link but somehow did not click on it. It fully explains the topic and solution. Here is the final THD graph matching the results we are seeing:Benchmark referenced this paper: http://www.ti.com/lit/an/slyt630/slyt630.pdf, it propose a R/C network at amplifier frontend, figure 7 in the paper seems like mach Benchmark's amplifier behavior.
Interesting that both Benchmark and TI give this solution away but it doesn't seem to be implemented elsewhere.
I was going to ask how widespread the approach in this paper may be.
Pessimistically, are most headphone amp makers getting this wrong?
That is it! I had seen that link but somehow did not click on it. It fully explains the topic and solution. Here is the final THD graph matching the results we are seeing:
Could be that it has been considered insignificant by the manufacturers who know about this. Getting -60 dB THD from your amp does not add much to the -20 dB you get from your Grado already. But this is just me guessing.Seconded. The levels we’re seeing here, even at this early stage of discovery, should have everyone asking this question. Still want to see more samples of various kinds, but I’d be lying if this whole thing isn’t making me look twice at all the amps I have.
you said that right...for 2 grand or more, a dac should come in at full fighting trim, primed and ready to go.Mytek are ok, but then their designer publicly states that the dac’s performance can be improved with a linear power supply!
For me that rules them out straightaway.
Keith