I have a set of Sen HD560s that are great aside from a little too much energy in the upper mids. There's a passive filter here HD 560S | DIY-Audio-Heaven that is designed to address that. It states it needs a lowish output resistance (impedance?) amp to work correctly, but I'm running mine from a mixer that most likely uses a couple of 4580 sections per side through 2 120 ohm resistors. Example here Screenshot 2021-10-04 151854.png - Google Drive (Mine is a different model but it will be similar).
I'm wondering if it is possible to predict the effect of those resistors on the filter? Or is there a close to drop in replacement for the 4580 that doesn't need such high value output resistors? I'm pretty terrible at theory but can wield a soldering iron no problem.
Thanks for any help!
I'm wondering if it is possible to predict the effect of those resistors on the filter? Or is there a close to drop in replacement for the 4580 that doesn't need such high value output resistors? I'm pretty terrible at theory but can wield a soldering iron no problem.
Thanks for any help!
The headphone driver you've shown has two 4580 op amps in parallel with 120Ω resistors in series with each, so the output impedance will be >60Ω, and too high to drive the recommended filter network for the HD560s.
Best option is to swap out the 4580s with NJM4556s which have >>double the output drive capability, then swap out the 120Ω resistors with 1Ω resistors for >16Ω headphones or 10Ω resistors for >8Ω headphones (the HD560s are 120Ω). This will be the perfect drive for the filter network and will also reduce the HD560s broad bass peak centred on ~60Hz by around -2.5dB. Personally I'd use 1Ω resistors for the best damping factor.
Best option is to swap out the 4580s with NJM4556s which have >>double the output drive capability, then swap out the 120Ω resistors with 1Ω resistors for >16Ω headphones or 10Ω resistors for >8Ω headphones (the HD560s are 120Ω). This will be the perfect drive for the filter network and will also reduce the HD560s broad bass peak centred on ~60Hz by around -2.5dB. Personally I'd use 1Ω resistors for the best damping factor.
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Thanks John. Would they drop straight in aside from the output resistor swap, or would other resistors values need changing also? Cheers
NJM4556s are used as output drivers in high quality headphone amplifiers and measure better in every significant specification than 4580s. They are unity gain stable stable, so as far as I am aware you can just drop them in without any circuit alterations. Their ability to deliver more output current means you can drop the value of the output resistors to benefit the headphones and filter circuit.
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