Balanced version, THD and THD+N at 1kHz/4Vrms
THD vs. frequency (at 4V, @BW90kHz) is now mostly a copy of the measuring system plots.
THD vs. frequency (at 4V, @BW90kHz) is now mostly a copy of the measuring system plots.
Several shots of design creations of my similar headphone amp design - that never went into production 😉.
I find 10k totally adequate input impedance. All the digital sources can drive it without rise in distortion. CD players or DVD players can drive it easily as well. The only exception might be valve common cathode output. But .... why in such case to use this preamp?
You may of course use 100k input dual pot, if you like, and increase R4/R104 to 1M (and R1/R2/R101/R102 increased 10x, if used). You will have 100k input impedance then. With the only difference against the original design - you will get higher noise and less flat amplitude response, and probably slightly higher distortion. It is up to you.
In my design philosophy, I do not agree with such solution.
You may of course use 100k input dual pot, if you like, and increase R4/R104 to 1M (and R1/R2/R101/R102 increased 10x, if used). You will have 100k input impedance then. With the only difference against the original design - you will get higher noise and less flat amplitude response, and probably slightly higher distortion. It is up to you.
In my design philosophy, I do not agree with such solution.
I get your point, but the counter example you gave is a bit extreme. In my current calc, I have R1 == 12k, R2 == 68k and a 47k log pot. That gives about 31k input impedance. You think the noise will really be significantly raised?