Does the Bottlehead Crack 1.1 drive the Audio-Technica ATH-R70x?

Computed from rated specifications · target SPL 110 dB · load 600 Ω

Ample OTL-compatible pairing

The Bottlehead Crack 1.1 drives the Audio-Technica ATH-R70x with ample headroom (~10.2 dB headroom at 600 ohms; needs ~15.8 mW, delivers 166 mW). (Amp power at 600 ohms is estimated from its published figure at a nearby load.) This OTL tube amp suits the headphone's impedance (470 Ω) — a classically compatible pairing for high-output-impedance tube sources.

Headroom
10.2 dB
Required (110 dB SPL)
15.8 mW
Delivered (@ 600 Ω)
166 mW *est.
Required voltage
2.73 Vrms

Power Headroom

Headroom: 10.2 dB 0 · target 10.2 dB below target marginal adequate ample -14 dB +10 +20 +36 dB

Scale shows dB headroom above the 15.8 mW required to reach 110 dB SPL. Amp delivers 166 mW at 600 Ω (+10.2 dB above target). Power figure estimated from an adjacent published load.

Audio-Technica ATH-R70x Dynamic · over-ear
Impedance 470.0 Ω rated
Sensitivity 98.0 dB/mW rated
Driver Dynamic
Spec basis Rated
Rated: Audio-Technica official spec (470 Ω, 98 dB/mW at 1 kHz). RAA has no measurement page. · Source ↗
Bottlehead Crack 1.1 Desktop Tube · Single Ended
Output impedance manufacturer 120.0 Ω
Power @ 300 Ω 333 mW
Power @ 600 Ω 166 mW *est.
Power source Manufacturer
* Loads marked "est." are derived from the published voltage ceiling at a lower-impedance load (V = √(P·R) → P_higher = V²/R_higher). All derivations are upward only.
Bottlehead product page (bottlehead.com/products/crack-1-1-otl-headphone-amplifier-kit): output impedance 120 Ω (published). Power: '~10V into a 300 ohm load' → P = 10²/300 = 333 mW; the '~' qualifier makes this approximate. 600 Ω derived from 300 Ω voltage ceiling (~10 V). Designed for 300–600 Ω headphones only. · Source ↗
Impedance compatibility

This OTL tube amp's high output impedance (120 Ω) is a good match for the Audio-Technica ATH-R70x's 470 Ω impedance. The impedance ratio (3.9×) falls within the recommended range for high-output-impedance tube sources — a classically well-matched pairing.

Power figure note

The amp's power at 600 Ω was not published directly — it was derived from the voltage ceiling at a published lower-impedance load. The actual delivered power may differ modestly.

Where to buy

Bottlehead Crack 1.1 on Amazon ↗ Audio-Technica ATH-R70x on Amazon ↗

Disclosure: links above are Amazon affiliate links. As an Amazon Associate this site earns from qualifying purchases — at no extra cost to you. Affiliate commissions do not influence verdicts; all analysis is computed independently from the data.

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