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I need to use a HPF for my headphone amp and I want some suggestions about at what frequency I should place the cutoff frequency.

Currently I want to use a HPF with a fc=15~20Hz but this gives me -3dB at 20Hz.

Is this acceptable or do I need to go lower to get not dump the "bass" so much? The one I have is made with a 1uF polyester cap and a 10k ohm resistor (I also have a 50k potentiometer that drops that resistance to about 8.3k.)

Also I might fiddle with the negative feedback path of the opamp to boost the "bass" by adding a cap and resistor in parallel with the feedback resistor.

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  • \$\begingroup\$ How far down can your ears hear? How far down can the speakers in your headphones go? \$\endgroup\$ – JRE Dec 18 '19 at 11:48
  • \$\begingroup\$ Why do you need to use a HPF is my question. \$\endgroup\$ – Andy aka Dec 18 '19 at 11:59
  • \$\begingroup\$ I use HPF to block DC and anything too low to care about.Also i asked about the cutoff because i'm afraid that if it's too high i might loose some important signal (like the lowest notes of the instruments) \$\endgroup\$ – Andrei112 Dec 18 '19 at 12:30
  • \$\begingroup\$ The lowest note on a bass guitar is 41 Hz so, what cut-off do you require? \$\endgroup\$ – Andy aka Dec 18 '19 at 12:36
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When designing your HPF remember that the headphone impedance is part of the circuit, and it's probably around 16-32 ohms. In that case a 10K shunt resistor will have a negligible effect. A series capacitor giving you a 3dB point of 20Hz would then be around 250-500uF.

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    \$\begingroup\$ The question is about a filter at the input of the amplifier. \$\endgroup\$ – JRE Dec 18 '19 at 13:19
  • \$\begingroup\$ I took it to mean a DC block for the output; it doesn't seem definitive either way. Any idea what the input impedance of the amplifier is? \$\endgroup\$ – Cristobol Polychronopolis Dec 18 '19 at 13:30
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If your aim is to make a high quality headphone amp, consider that the HPF causes phase shift at lower frequencies, even significantly above the 3db point, and phase shifts are subtly audible. I'd go seriously low (below 10hz) or not at all.

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