Headphones, amps & a little tube glow
Two headphones, two amplifiers, each matched to the other for a reason. Here’s the setup and why the pairing matters.
Signal chains
Source
Computer / streamer
USBDAC + amp
JDS Labs Atom stack
Solid-stateHeadphones
HiFiMAN Sundara
Planar magneticWhy this pairing: The Sundara is a low-impedance planar that wants current. The Atom amp has near-zero output impedance and plenty of current to give, so it drives the Sundara cleanly.
Source
Atom DAC
Line outAmp
Bottlehead Crack + Speedball
Output-transformerless tube ampHeadphones
Sennheiser HD650
Dynamic, 300 ΩWhy this pairing: Output-transformerless tube amps have high output impedance and can’t supply much current, but they swing plenty of voltage. A 300 Ω headphone like the HD650 wants exactly that, which is why the Crack and HD650 are a classic match.
The gear
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image: for HiFiMAN SundaraHiFiMAN Sundara
- Type
- Open-back planar magnetic
- Impedance
- 37 Ω
- Sensitivity
- 94 dB/mW
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image: for Sennheiser HD650Sennheiser HD650
- Type
- Open-back dynamic
- Impedance
- 300 Ω
- Sensitivity
- 103 dB/V
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image: for JDS Labs Atom stackJDS Labs Atom stack
- Type
- Solid-state DAC + headphone amp
- Role
- Main DAC; drives the Sundara
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image: for Bottlehead Crack + SpeedballBottlehead Crack + Speedball
- Type
- OTL tube headphone amp
- Tubes
- 12AU7 driver, 6080 power
- Upgrade
- Speedball constant-current sources for lower noise and distortion
How much amp does a headphone need?
Pick a headphone or enter its specs, choose a peak loudness, and see the voltage, current, and power an amp has to deliver. The two presets show why the Sundara needs current and the HD650 needs voltage.
Voltage—V rms
Current—mA rms
Power—mW
P = 10(SPL − S)/10 mW for dB/mW, V = 10(SPL − S)/20 V for dB/V, then V = √(PZ), I = V/Z. Specs are the makers' nominal 1 kHz figures.