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AnalogRelic
74
Mar 21, 2021
I got an email saying this amp was 'Now in Stock' but when you go to the product page it says '2 months left'. ??? Also, wassup with the specified 1KΩ input impedance? That's extremely low, enough so to cause problems with many line level sources. To adhere to the 1:8 standard rule of thumb for this ratio, the source impedance would have to be no higher than 125Ω. If I can get answers to these questions, I might be a customer for this amp.
(Edited)
Michael-Q
243
Mar 22, 2021
AnalogRelicI'm not an expert on the matter but here's my thoughts. When I think of the 1:8 standard rule of thumb for source to load that has more to deal with actual headphones. (trying to keep my explanation simple) Headphones have a frequency response that isn't flat (they're not purely resistive -> they're transducers with inductance). When the source impedance is high it can alter the frequency response of the headphones making them sound different. Now, amplifiers have a flat frequency response. The input resistance is dominated by the real resistance. Sometimes there is reactance (capacitor in signal chain to prevent dc voltages) but it's mostly real resistance for frequencies above like 20Hz. What I'm trying to get at is even if the 1:8 rule is broken the frequency response will be the same (amp will sound the same regardless of the source.) The only issue I see is the fact that the voltage drop on the source impedance might be larger -> you might notice one DAC is louder than another DAC even they both technically output 2.15V max. Sort of a non issue for an amp. I don't know everything though so maybe I'm missing a concept.
AnalogRelic
74
Mar 22, 2021
Michael-QUnderstood about the frequency response part but I was under the impression that too low of a load impedance can ‘load down’ the source- too low looks almost like a ‘short circuit’ to the source. For a line level input, 10k ohms is considered low, and 25k to 50k ohms more typical. My previous DAC had an output impedance of 75 ohms- that would have been no problem. I don’t know the output impedance of the one I have now.
Michael-Q
243
Mar 22, 2021
AnalogRelicFew closing thoughts: So yeah, I forgot about the 'short circuit' idea. If the dac is at 2.15V and it feeds into about 1k ohms load -> ~ 2.15 mA. DAC's output often comes from decent enough op amps that I'm fairly certain don't struggle unless it's more like 20mA. Perhaps some DAC's can't provide 2.15mA while maintaining a high performance. Certainly worth taking a look at. I want to say enough people have had a chance with this amp that if this were an issue, it would have been noticed. Buyer beware i guess >.>. Things change -> you're right the input impedance is absurdly low for what's typical. I'm not so sure it matters though. (wording on this next sentence doesn't quite say what I want it to but I'm short on time :D) The standard 20 or so years ago was to plan around 120 ohm output impedance for headphone amps. That was the 'standard' model/design (not saying this was a good thing they tried to achieve- it was the baseline to what to expect). Not sure where that came from? perhaps just a legacy concept from dealing with tube amps idk. For modern headphone amps 120ohms output impedance is ridiculous. What I'm trying to say is that perhaps modern sources/dacs no longer need to feed into such high impedance loads. /Shrug
AnalogRelic
74
Mar 22, 2021
Michael-QThe 120 ohm standard, nobody seems to know where it came from! Apparently it emerged when the first FTC regulations for amplifiers took effect in the 1970s. My first Sennheiser phones were 2KΩ impedance (not a typo) probably to make them an easier match to the tube amps that were still prevalent then, as you suggest. On the discussion boards for the well known O2 DIY amp, the 10KΩ input impedance of the amp is discussed as a concern. This amp is 1/10 that (unless there's a typo). By contrast, the other amp I'm considering- the Schiit Magni Heresy- has an input impedance of a more typical 25KΩ. Since that amp is half the cost of this one, and seems to be competitive, my question may be moot anyway. I'm not convinced that the difference between .008% distortion and .0008% is meaningful in a listening situation, at least not enough to justify a doubling of the cost. The three gain settings (not three gain 'stages' as stated in the description) is an attractive feature though. If there were to be a problem, I would expect it to show up in the form of increased distortion, especially at the frequency extremes (in which case, why pay extra for the better 'spec'?)
(Edited)
Michael-Q
243
Mar 22, 2021
AnalogRelicPersonally I'd just go with the Heresy. The three gain options, specifically the bellow unity x0.25 gain certainly could prove useful for some people -just not for me. As far as the distortion goes, if I remember right, the 789 had a noise floor that puts in on par with the Heresy's SNR. Seems like kind of a gimmick to report just the THD numbers and not THD+noise like most amps. Granted the harmonic distortion peaks above the noise floor for most amps. Amazing accomplishment but ultimately just a gimmick. Maybe I'm miss understanding something... With that said, ignoring cost I like this amp much more than the Heresy. The Heresy is just a tad small and the gain selector and power switch is in the back. Also, the volume knob is far more accessible than Heresy's with the headphone jack right next to the volume knob. It all makes sense from a design perspective but not so much for a customer with high expectations/standards.
IvanDaTerrible
0
Apr 28, 2021
AnalogRelicI don’t think you would ever be a happy customer for anything but here’s hoping you prove me wrong. I doubt it.
AnalogRelic
74
Apr 28, 2021
IvanDaTerribleI have nothing to ‘prove’ to you (or anyone else) here and will keep my thoughts to myself (or at least off this ‘community’ ) in the future. Quite pleased with what I chose. Have a nice day. Actually, one closing thought: Many people seem to be unaware that when encountering something on the internet that you disagree with or find annoying or offensive- stupid, even- one can simply scroll right past it or go to another page without responding, especially if you have no real contribution to make to the discussion. Just for future reference.
(Edited)
Joe405
353
Jul 17, 2021
Michael-QMan it's pretty weird how Drop never addressed the input impedance.
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