HD 650 from a Galaxy S25: every 2 V dongle lands one decibel short
The HD 650 needs 2.24 V. A FiiO KA17 gives 1.993 V and reaches 109.0 dB against a 110 dB peak target; the cheaper KA13 stops at 104.7 dB. The only source here that clears it is a battery-powered DAC at 5.2 V.
Signal Chain Compatibility Matrix
Select gear and parameters for live gain, impedance and SPL calculations.
Input Equipment Setup
PASS: Optimal Signal Chain
Requires minimum +60dB of clean pre-amp gain. Most budget entry interfaces max out at +50dB to +56dB and introduce hiss at max pot. An inline preamp booster (Cloudlifter CL-1 / FetHead) is strongly recommended.
The interface preamp provides sufficient headroom.
$538
$405
-25%Tonal & acoustic characteristics: Flat, wide-range frequency response for clean music and speech. Smooth, warm acoustic character with air-suspension shock isolation.
Technical advisory: With +69dB max gain, the Gen 4 Solo can drive demanding dynamics like the Shure SM7B natively without requiring an external inline booster.
Physical Interconnect Topology
Shure SM7B
Direct Cable Connection (No Intermediate Box)
1x Shielded Balanced XLR Cable (3-Pin XLR Male to XLR Female)
Focusrite Scarlett Solo (Gen 4)
Host: Apple MacBook Pro (M1/M2/M3/M4)
Almost. The KA17 reaches 109.0 dB where the target is a 110 dB peak — a shortfall of 1 dB, which the calculator counts as «enough, no headroom» and which in practice means the volume control lives at maximum.
Sennheiser rates the HD 650 at 103 dB per 1 V into 300 Ω, so a 110 dB peak needs 2.24 V, 16.71 mW and 7.46 mA. Against that, the whole class of phone dongles clusters in one place: KA17 and Qudelix 5K at 2 V (1.993 V delivered, 109.0 dB), Hidizs S9 Pro Plus Martha and DragonFly Cobalt at 2.1 V (109.4 dB), TRUTHEAR SHIO at 2 V. The cheap end fails outright — the KA13 at 1.22 V reaches 104.7 dB, 5.3 dB short. The only source in this catalogue that takes an HD 650 to a genuine 110 dB peak from a phone is the Chord Mojo 2, which publishes 90 mW into 300 Ω as 5.2 V RMS: 117.3 dB, 7.3 dB spare, at eight times the price of the KA13.
Why they all sit at 2 V. Every bus-powered dongle in this catalogue lands between 1.22 and 2.1 V, and the only source that goes past that from a phone carries its own battery — although a battery is no guarantee either: the Qudelix 5K is battery-powered and still stops at 2 V. The gap between 2 V and the 2.24 V the HD 650 wants is the whole argument, and it is 1 dB wide. A 1 dB shortfall on peaks is not audible as distortion — it is audible as never being able to turn it up on a quiet recording.
The pearl: Samsung never publishes the port current. The specification sheet gives the port version — USB Type-C, USB 3.2 Gen 1 — and stops. The 4.5 W in this catalogue is derived from what the USB Type-C specification defines as Default for a single-lane USB 3.2 port, 900 mA at 5 V, so it is a floor rather than a measurement; the phone may advertise 1.5 A or 3 A and only a measurement would say. And the switch that actually stops most people is not power at all: USB host mode has to be enabled, and some carrier builds hide the setting.
What we cannot check. FiiO publishes <1 Ω for the KA17, which against 300 Ω is a ratio of 300 and safe. Qudelix, Hidizs and AudioQuest publish no output impedance at all for their 3.5 mm outputs, so for those three the 1/8 rule — 37.5 Ω or less for a 300 Ω headphone — cannot be verified in either direction. It matters more than usual on this headphone: the HD 650's impedance peak near 100 Hz means a high-impedance source adds bass instead of merely taking level away.