I am an electronics hobbyist. After reading online my understanding is that an op-amp buffer or JFET pre-amp can be used to match a medium (lower) input impedance with a high output impedance. In my case need high-impedance output with attenuation or reduced voltage.

Sub woofer sounds hard hitting, bass too hard (high) thump at minimum volume in Sub woofer amp (Wharfedale).

For testing I connected line out of MP3 module with 10k resistor, bass response was good, smooth, no hard thumps.

I used resistor divider 42k and 12K, did not attenuate much, and felt it's effecting quality of sound (Low frequency response of subwoofer).

Media player Output:
Output Level / Output Impedance: Subwoofer(30Hz) - 4v / 470ohms.

Subwoofer amplifier line input:
Amplifier Power: 150W RMS
Input Sensitivity 200mV for 75W
Input impedance: 10kΩ
Frequency Response: 35Hz to 110Hz

Requesting guidance choosing from DIY circuits or designing one.

  • \$\begingroup\$ A resistor divider will be good enough. Or just output directly at reduced volume. In audio signal transmission, you don't match impedances..that is important only for maximum power transfer. instead you try to minimize driver impedance and maximize receiver impedance..Your equipment does that alread. \$\endgroup\$
    – tobalt
    Jan 8 at 9:10
  • \$\begingroup\$ I used resistor divider, 42k & 12K not much of difference. \$\endgroup\$ Jan 8 at 10:12
  • \$\begingroup\$ When there are multiple filters for the same frequency range (here: subwoofer), take care to set them octaves apart or accept unknown interaction. 30 Hz fixed with mediaplayer? Set Wharfedale to upper limit. \$\endgroup\$
    – greybeard
    Jan 8 at 11:54

1 Answer 1


That is not how line level connections work and you don't need to do anything.

Impedance matching between line out and line in to be equal is incorrect. Voltage bridging is used, not impedance matching. Line out should have as low impedance as possible and line input should have as high impedance as possible. Or whatever is practical.

470 ohm output driving a 10k input is good.

If you need to attenuate the signal, do not use high impedance resistors and try avoiding external reaistors.

Adjust the sub amp input sensitivity or preamp sub out amplitude if there are knobs for that.

  • \$\begingroup\$ Thank you for explaining I have better understanding, Sub amp woofer output too high even at low volume in sum amp, it hits hard or may be clipping, when I connected my headphone amp with 10k resistor output was smooth/ pleasing not hitting hard. \$\endgroup\$ Jan 8 at 10:37
  • \$\begingroup\$ (outout driving a 10k input is good outout is outright non-good as is reaistors.) \$\endgroup\$
    – greybeard
    Jan 8 at 11:43

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