OK, I have to admit this review of the Questyle CMA800R had a painfully long gestation period, due to me getting it colossally wrong at the outset. You see, my ‘go to’ place for running headphone amplifiers in involves connecting them to a decent DAC and using my pair of ever-reliable Sennheiser HD-25-1 II ENG/Studio cans. This is because the HD-25 design is sufficiently sensitive to be driven by anything. And in the CMA800R, that wasn’t like putting the headphone amp in low gear; it was like switching it off!
So, when the CMA800R returned the sound of the Sennheiser HD-25-1 II, I made a rookie error: I expected ‘magic’ and benched the Questyle. And it stayed benched. It was only reading just how much the company’s QP1R digital audio player took our Publisher Chris Martins that I remembered this was lurking in the back of our storeroom. In fact, there were two of them, because one of the great joys of this headphone amp is it lends itself very easily to monoblock use. In fact, the CMA800R now forms just one part of the company’s top four-box desktop stack, comprising DSD-ready DAC, preamp, and mono headphone amps (the preamp, originally commissioned by Stax and designed to complement the Stax SR-009 Earspeaker/SRM 727MkII, can act as a useful controller in its own right, both improving overall performance and bringing one volume to rule them all). There is also a special Golden version, which uses higher specified components, as well as the gold finish. We’ll look to the full stack in a later issue – first it’s time to catch up with the CMA800R as a one-box headphone amplifier.
This is a pure headphone amplifier, without a DAC. The CMA800R has one stereo balanced and one stereo single-ended input (with a small toggle switch on the front panel, it’s almost best to think this a one-input amplifier), and a pair of single-ended outputs to a preamplifier. There is also a single full-balanced XLR input, should you decide to use the CMA800R as a mono pair of headphone amps. There are two single-ended ¼” TRS jack sockets for single-ended headphones, and a balanced headphone output XLR for one half of a true balanced headphone output.
The ‘CMA’ in the title stands for ‘Current Mode Amplifier’. This is the defining aspect of the headphone amplifier, and in many ways shows why Questyle chief designer Wang Fengshuo (Jason Wang) is so highly respected in the audio field that a company like Stax would approach him to build an amplifier. And it owes its development at least in part to a failed experiment. While still at university in 2004, Wang was debugging a failed current mode circuit that should have been processing communications signals, but was instead acting as a high-speed amplifier with vanishingly low intermodulation distortion. Wang, already a music loving audiophile, hit the books to see if this circuit had been used in audio amplification, and fortunately his teachers saw the innovator rather than the failed circuit, and let him run with the concept.