Hi! I need some help with building a balanced 2.5kHz highpass filter as a inline filter for my Xlr power amp. I have a Tpa3255 which have 20kohm input impedance. Source has low impedance so it shouldn't matter. I put in some values into a online lowpass calculator with 20kohm impedance, and it said that I needed a 900mH inductor?! I know I need 2 inductors(one on each conductor) and a cap in paralell with the input. If someone would bother to check the values or point me to cheap source of the such an inductor that would be great!
Typically a PLLXO is done with RC filters which means that you can only hae a 1st order filter (single cap) or a droopy” second order filter.
If you want an LC filter the inductor values become VERY difficult.
Marchand, in their LC PLLXO terminates the network with 5kΩ, meaning a high input impedance in the amplifier required and a REALLY low pre output.
dave
If you want an LC filter the inductor values become VERY difficult.
Marchand, in their LC PLLXO terminates the network with 5kΩ, meaning a high input impedance in the amplifier required and a REALLY low pre output.
dave
Thanks for clearing that up for me! I guess this option is out since the dac is already driving 2 amps so the combined impedance low already.
900mH inductor is quite doable with 18mm gapped ferrite cores. But you'd not want to rely on the input impedance of the amp as your loading because on-chip resistors typically have a tolerance of +/-30%. 5kohm does seem like a reasonable loading.
Thanks for the creative solution Abraxalito, but I hoped to avoid ferrite core since the midwoofer will be crossed so high.
An unwritten "rule of thumb" is that passive x-overs belong inside cabinets, active ones on the "electronics" side.
Maybe there´s a practical reason for that?
Maybe there´s a practical reason for that?
Sure looks like that in this case.. but I like to explore new possibilities. I have a class D amp which handles low impedance well so I'm rebuilding my bought speakers to be a low impedance higher sensitivity one. Getting rid of a 0.8Ohm series inductor with the woofer seems like a low hanging fruit. I would have gone active if I hadn't put so much effort into my diy dac last winter. I'm already doing triamping with active with eq below 300Hz.. But 3 good dacs is a lot of work, so a PLLXO looked at first glance a better solution.