Crossfeed problem (Jan Meier's design)


2010-11-26 7:33 pm
hey guys
i thought i could have better sound through my Sennheiser HD212Pro + iPod Nano 5th gen combo, implementing crossfeed. for the simplest circuit, i went (attached), all the components were used as specified in the circuit, 470nF Polypropylene cap (100V), 1k resistors 2.19k resistor. My headphone specs are 32ohm impedance, 20Hz-19000Hz, 112dB senstivity. the problem is, the crossfeed i built is not working as expected, its killing the bass, giving me a tweeter overall rather than headphones.
please note that i wanted a spatial effect, which lead me to the above schematic, taken from

HeadWize - Project: A DIY Headphone-Amplifier with Natural Crossfeed by Jan Meier

what have i done wrong? why is the sound more crappy? i ensured good caps and resistors, nothing is shorted, there's no crossfeed (i feel). what should i do?


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Ensure that R2 is only 2K2 and properly connected. Check the values of the other resistors and capacitors. In the circuit description it acts as a ~2.5dB shelving high pass filter on the direct side, cutting bass. If the resistor values are off it could result in a higher center frequency and higher cut.

The other possibility is that there is an issue with the opamp part of the circuit. Temporarily solder a piece of wire across one or both of the 470 nf caps. Is the sound OK now? You will get unfiltered cross feed, but the bass should return. If you get the bas back you now have isolated the problem to those 5 parts that make up the crossfeed. If the bass is still lacking, look at your connections elsewhere in the circuit. What opamps did you use? (can they deliver the required current? ) Are you using the high or low Z output?
The crossover circuit cannot drive your phones. Add an opamp type buffer like the C-Moy or follow the whole circuit in the article in your link. Those triangles in the schematic are opamps. Your Nano's output can replace the ones on the left, but you need an opamp per channel after the crossover circuit. The Cmoy will give you that in a battery operated package so you don't lose portability. You can probably build it in an Altoids can.