If you've laid down serious cash for a great pair of headphones but they're plugged into your phone or computer, you're missing out on a lot of the sound quality you paid for. Don't get me wrong, phones and tablets can sound acceptable, but their designers didn't focus on sound quality -- that's the last thing they worry about. The cure for so-so sound is straightforward: invest in a high-performance digital converter/headphone amp, like the Cypher Labs Theorem 720. It can be used with iPhones, Android phones, or computers via USB connection with up to 192-kHz/24-bit resolution files.
Priced at $799, it's intended for use with state of the art headphones, so I tried out my Audeze LCD-X, Grado RS-1, and Sennheiser HD 700 full-size headphones, and my 1964 Ears V6 Stage, Jerry Harvey JH-13, and Shure SE846 in-ear headphones. In every case, the Theorem 720 demonstrated their full potential. The digital converter/headphone amp is made in Portland, Ore. and San Diego, Calif. The Theorem 720 measures 1.2x2.5x5.4 inches and weighs 10 ounces, and it's offered in black or copper finishes.
The Theorem 720 converts the digital output of iPods, phones, and computers to analog audio, and then amplifies the signal to play headphones. A full set of cables are included, Cypher Labs even throws in a Lightning cable for use with the latest Apple devices. The Theorem 720's powerful lithium-polymer battery fully charges in four hours, provides 18 hours of play time, and is potent enough to charge your phone's battery on the go.
Listening with my 1964 Ears and Jerry Harvey in-ear headphones, I heard a small amount of hiss and noise coming from the Theorem 720's amplifier, but I was only aware of the noise when music wasn't playing. Shure's SE846 flagship in-ear headphone sounded significantly more transparent and clear with the Theorem 720 than it did with my iPod Classic. Dynamic punch and impact was improved, soundstage dimensions were expanded, and bass was more visceral and potent with the SE8846 and Theorem 720 combination. Plugging that headphone into the V-Moda Vamp Versa digital converter/headphone amp, the sound was clearly better than the iPod's sound, but the Theorem 720's dynamic range, bass oomph, and transparency pulled ahead of the Vamp Versa's.
My low-impedance (32 ohm) Grado RS-1 headphones really clicked with the Theorem 720, and so did my high-impedance (150 ohm) Sennheiser HD 700 headphones. While I was listening to those two headphones I compared the Theorem 720 with the Centrance HiFi M8 digital converter/headphone amp. Thom Yorke's "Atoms for Peace" CD's pulsing beats had even more impact and weight over the HiFi M8, but the Theorem 720's more vivid sound quality made it a very close race. Both amps sounded dramatically better than my iPod Classic's headphone jack.
I also compared the Theorem 720's sound over its balanced and 3.5 mm headphone jacks with my Audeze LCD-X headphones. I've tried balanced connections with other amps, and they don't always sound better than the regular 6.3- or 3.5-mm connections. But the Theorem 720's balanced connection yielded superior resolution of fine detail/clarity, so I could hear more subtle stuff, like the room reverberation cues on classical and jazz recordings. Check with your headphone's manufacturer to see if your 'phones can be used with a balanced amplifier.