Headphone Calculations for Amp Matching

[Shannon Parks]

Working on a spreadsheet to help make decisions on headphone matching to amps, particularly small tube amps (like my Budgie SE). For reference is my old 20/20 circuit post: viewtopic.php?t=5239

So I chose 100dB SPL as the listening level as we need a target level to compare all these apples and oranges. I figured out what the volts required for 1mW and then adjusted that voltage to 100dB. I then chose 1/3 rotation of the volume log pot as the area used for this level. 1/3 rotation is -20dB lower than max rotation (0dB attenuation), so full rotation must be 120dB SPL (theoretical not actual - more concerned about the amp doing its job).

My Budgie SE is about a 3W amp for 8 ohm loads, or about a 5Vrms output. With the 20/20 headphone circuit, the voltage divider cuts this in half, to 2.5Vrms. This is good, as it makes sure our output to our headphones is a useful range with our volume pot and also ensures that we don't blow them up accidentally. Looking over the headphone list I've started, it looks like only the Audeze LCD-2 and LCD-3 would work best without the 20/20 circuit. For those two Audeze headphones, small tube power amps can have the headphone TRS jack directly connected to the standard 8 ohm output transformers (i.e. no dropping resistors or funky ratio transformers needed). Possibly parallel power resistors might be useful (40 or 50 ohms), particularly with amps with feedback.

Happy to embiggen this list as requested.

[EWBrown]

Great information, thanks!

/ed B