I recently started looking at crossfeed circuit designs to work with a headphone amp and came across a relatively simple design by Jan Meier. I liked its relative simplicity compared to a number of other versions but realized that even his design could be further simplified. His approach requires changing 4 component values for each cross feed setting, going from "low" to "medium" to "high" (which are the frequency crossover points). I skipped the "low" setting based on his comments in another of his posts regarding a bass-enhanced version, so my version below just implements the "medium" and "high" crossover points. That only requires changing ONE resistor value, compared to two capacitors and two resistors. This version does not implement the bass-enhanced frequency-gain profile. Noodling around while trying to achieve that using my simplified scheme quickly showed that it wasn't going to be quite as straightforward to implement as I was hoping for.
I have NOT realized this design, that will come soon. I used easyEDA to do the schematic capture, and as it is, not suitable for directly driving headphones. Anyway, for viewing/comments:
I have NOT realized this design, that will come soon. I used easyEDA to do the schematic capture, and as it is, not suitable for directly driving headphones. Anyway, for viewing/comments:
Just in from JLCPCB...
The design was changed to eliminate the on-board RCA connectors. Using panel-mount versions makes the wiring a little more complex but vastly opens up choices for enclosures. I learned this the hard way on a phono preamp design.
I didn't see any point in making the crossover point(s) selectable by an external switch. Once I find the setting I like that's the way it's going to stay, so an on-board jumper is fine by me.
The board is a 4-layer, pure overkill for a simple design like this -- but it did simplify the layout a bit. Anyway, I always like ground planes due to all the RF designs I laid out in the past. Thank goodness I don't have to think about controlled-impedance traces for stuff like this. Other things, instead.
The "AS:===:IS" logo on the board is a pure conceit on my part, has nothing to do with a commercial enterprise 😉. I thought up the name decades ago and just recently resurrected it. Currently it's on three different boards -- this one, a phono preamp board and an HA board. The latter two are up & running.
The design was changed to eliminate the on-board RCA connectors. Using panel-mount versions makes the wiring a little more complex but vastly opens up choices for enclosures. I learned this the hard way on a phono preamp design.
I didn't see any point in making the crossover point(s) selectable by an external switch. Once I find the setting I like that's the way it's going to stay, so an on-board jumper is fine by me.
The board is a 4-layer, pure overkill for a simple design like this -- but it did simplify the layout a bit. Anyway, I always like ground planes due to all the RF designs I laid out in the past. Thank goodness I don't have to think about controlled-impedance traces for stuff like this. Other things, instead.
The "AS:===:IS" logo on the board is a pure conceit on my part, has nothing to do with a commercial enterprise 😉. I thought up the name decades ago and just recently resurrected it. Currently it's on three different boards -- this one, a phono preamp board and an HA board. The latter two are up & running.
I finally was able to get this thing going. The last hiccup was a brain-fart on my part -- I mis-labeled the power supply connections. I reversed Vcc and Vee but fortunately the OPA1656 appears to have survived my bench test. I'm glad I decided to be smart and bench test the thing before connecting it to my JLH-ish headphone amplifier. It seems to be quite unforgiving regarding what sort of device that is connected to it. In fact, it wanted to oscillate until I inserted some damping resistors in its input lines. Wide-bandwidth amps can be picky! Anyway...
It's working OK now!
