PinkyPowers
Reviewer: The Headphone List
I use the NFB-28 with my 64Audio U12 and Rhapsodio Solar CIEM. In Low Gain you get decent volume control and no hiss.
It depends on the impedance of your IEM. A rule of thumb is that optimally, we want a damping factor of >= 8. The damping factor is the ratio between the nominal impedance of a driven load and the output impedance of an amplifier. The NFB-28 has an output impedance of 2 ohms, and if I use the JH13 as an example, it has an impedance of ~28 ohms. That provides a damping factor of 14 which comfortably satisfies requirements. A low damping factor often shifts HP/IEMs towards a warmer signature as bass becomes less controlled.
An output impedance of 2 ohms is not bad, and is sufficient for most applications, it's just that 1 ohm output impedance leaves a bigger margin. In my opinion, the output impedance is likely a tradeoff for the non feedback topology of AGD amps. The noise floor on the AGD kit is generally very low, so it should play well enough with high sensitivity low impedance HP/IEMs.
If your setup is mostly single ended, you should give the NFB-29 some consideration. I don't understand why it never took off, but it should be just as capable as the NFB-28 for most uses. I don't know your situation, but I only went balanced because I wanted a balanced preamp for a stereo setup that I'm now building (with long cable runs). I'm also a one headphone guy, so I don't have to worry about the costs of rewiring a whole collection of headphones.
Optical would isolate the electrics between your computer and your DAC, however if you happen to have the USB cable plugged in at the same time you have any other electrical connection to the computer, it will pick up noise. I'll give you an example, I had a FIIO amp which also had a DAC so it has USB and analog inputs. I went with an external DAC and connected the analog out from it, to the analog in on the FIIO and the noise was awful. The reason for it was the RCA connections shared a ground between the DAC (and therefore the computer) and the Amp which still had it's own USB cable plugged in. Simply unplugging the amp's USB cable fixed the problem immediately.I'm getting a strange problem on my NFB-28 I was wondering if y'all could help me out with. I run optical from my computer's Xonar DGX into my 2014 model NFB-28. Sometimes I'll get a lot of popping/crackling, that usually fixes itself if I just cycle around all the inputs back to "2 (optical)". Could that be a sound card problem, drivers, or something in the NFB-28? I'm not sure if cycling the inputs resets the connection with the computer or not, or it'd be easier to narrow down what's going on.
Headphone balanced is a COMPLETELY different thing than traditional balanced for stage equipment. Read up on it. This stuff has only been around for a few years. Old-school balanced has been around for ages.