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I have a a balanced stereo audio source, being fed into a headphone amplifier. Both source and amplifier are connected via a pair of 3-pin XLR cables, one for each channel. The amplifier then outputs to some studio monitor headphones.

Due to some hearing loss, my right ear has about a 1.5dB loss over the left. As such, I need to cut the left speaker down by around 1.5dB. Neither the source or amplifier have balance/panning controls.

I want to build a resistor-divider circuit that would sit between the source and amplifier which does the job of attenuating the left channel.

  1. How do I calculate the resistor values needed to reduce the left channel by 1.5db?

  2. Are there any special considerations required given that I'm using a balanced (positive, negative, ground) configuration for each channel?

XLR

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  • \$\begingroup\$ Given the reactive load of the speaker, you'll need a voltage divider before the PowerAmp. Otherwise the frequency response will become ugly peaky, dippy. \$\endgroup\$ – analogsystemsrf Dec 9 '18 at 13:36
  • \$\begingroup\$ The above is correct due to loss of dampening factor using an L pad attenuator for any given headphone load that requires the drive impedance to be much lower (<2% of load during bass series anti-resonance (high current) But if that doesn't matter then are these 8 or ? Ohm headphones? electronics-tutorials.ws/attenuators/l-pad-attenuator.html \$\endgroup\$ – Sunnyskyguy EE75 Dec 9 '18 at 15:26
  • \$\begingroup\$ Headphone and speaker impedance is never flat \$\endgroup\$ – Sunnyskyguy EE75 Dec 9 '18 at 15:31
  • \$\begingroup\$ Agreed with the comments that the pad needs to be before the amp, but it sounds like that's what the OP's proposing ("a resistor-divider circuit that would sit between the source and amplifier"), so I see no problem here. \$\endgroup\$ – Nate Strickland Dec 11 '18 at 0:17
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As Tony mentioned, the configuration you're looking for is called an L-pad attenuator (or for its balanced cousins, the H-pad, U-pad, or O-pad). These are pretty easily built in-line in XLR barrels.

1.5dB is small enough that all the online calculators I could find were giving negative resistor values, so you'll probably have to do the calculations by hand. This page explains the calculations you'll need to select resistor values: http://www.uneeda-audio.com/pads/. It also has info about building the circuit inside an XLR housing.

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