Back in Issue 133, we reviewed Questyle’s excellent CMA800R headphone amplifier. At the time, we suggested there would be a follow-up review of a pair of CMA800Rs for balanced operation. But then, an idea was hatched… why not go for the full stack? In fact, why not go for gold?
Questyle’s first electronics stack (not including the company’s clever wireless power amplifiers for loudspeaker users) features the aforementioned CMA800R headphone amplifier – two of them, in fact – the CAS192D DAC, and the CMA800P preamplifier. There have been just two significant changes since these products were released three or so years ago; the CAS192 DAC became the CAS192D model when it began supporting DSD replay, and the changes made between the standard and ‘Golden’ Reference editions. As the name – and the pictures – suggest, the Reference models differentiate themselves externally from their standard siblings through the use of a gold finish. It’s an all-over gold finish, too, right down to the feet. This might be a little ‘bling’ for conservative British tastes, and yes… confronted with the full four-box gold stack, I do feel a sudden, burning desire to drink Cristal from the back seat of a Maybach. Word!
There is more to the Reference Edition than just the gold finish, however. Each model takes the basic circuit design of its standard issue model, replaces the standard components with selected components, and swaps out the standard circuit board for a custom thick film ceramic PCB made by Roberts. The products are still constructed in the Foxconn factory, however. Think of this process like blueprinting for an engine; the standard model is built with some wiggle-room thanks to variations in component value. Questyle’s Reference series products use more carefully selected components throughout, so component values are precisely those laid down in the original circuit design. When you think that each component in a circuit could have as much as a 10% variance on its actual rating, shaving ±5% down to ±0.5% across hundreds of components should make a substantial difference in performance.
This ‘blueprinting’ practice is common in high-end audio, but with a twist; instead of using the right components for the job and hand-selecting the best versions of those right components (which takes time), many companies take the easier option of specifying more expensive components with more precise tolerances (which costs money) from the outset. Typically, this means an expensive product bristling with ‘big name’ components and no real way of determining whether they make the product sound better, because there is no basic version made available. Although Questyle also uses big name components in its construction, the company also gives you the option of the standard and ‘blueprinted’ versions, so you can directly hear if there is a difference and decide for yourself. This is almost unique in the audio world. Each Reference model commands an £800 premium over its base model, and I wouldn’t be surprised if anyone who tried both in quick succession develops a sudden lust for lustre…
Of course, high spec products are as nothing if the basic circuit design is not up to scratch. Fortunately, in each case, these golden products justify their place in the hierarchy extremely well. The core technology in the preamplifier and headphone amps is Questyle’s Current Mode Technology, a four-stage transconductance amplifier circuit, which we discussed in some detail in our Issue 133 review of the standard, solo CMA800R. Essentially, however, this is an amplifier circuit that ends up with extremely low levels of measured distortion and wide bandwidth, using a negative feedback circuit that works at far higher speed than is usually found in audio amplifiers (thereby reducing potential slew rate problems to the infinitesimal). In this setting, the preamp ‘simply’ takes over the gain control and source switching (of sorts; it’s more a balanced one-input active gain control with an optional single-ended input than a full-blown line stage), while the pair of CMA800R take over left and right channel amplification, if you have a pair of headphones (and the right set of cables) that can be driven balanced. This is kind of financially self-balancing, however, because no-one willing to spend over £10,000 on a headphone DAC and amplifier stack is going to use a headphone that cannot be run balanced.