audio_tony
Addicted to Fun and Learning
Another thought on the low input impedance.
In the quest for low noise, a lot of opamp circuits use quite low values in the feedback loop.
So if you have a source with an opamp in the output stage, and this opamp has typical values of 2k (Rf) and 1k (Rin) in the feedback loop, that opamp is already driving 3k.
Connect that source to this headphone amp, and you have 3k in parallel with the 2.7k input impedance, and your source is now expected to drive a 1.4k load.
I know of many opamps (OPA2134 which is a popular one) that have rising THD when driving loads below 5k or so - therefore in such a situation using this headphone amp is likely to result in higher distortion from the source...
In the quest for low noise, a lot of opamp circuits use quite low values in the feedback loop.
So if you have a source with an opamp in the output stage, and this opamp has typical values of 2k (Rf) and 1k (Rin) in the feedback loop, that opamp is already driving 3k.
Connect that source to this headphone amp, and you have 3k in parallel with the 2.7k input impedance, and your source is now expected to drive a 1.4k load.
I know of many opamps (OPA2134 which is a popular one) that have rising THD when driving loads below 5k or so - therefore in such a situation using this headphone amp is likely to result in higher distortion from the source...