Almost two years ago today I reviewed a brand new desktop headphone amplifier, the Questyle CMA800R. It was my first current mode amp, I loved it and if you read that review, everything I said stands to this day. It still sits on our Pride of Place and it still is the amp I go to when I fancy the very best of listens. Well to be precise it is half the amp I listen too. Since I originally reviewed it I have been yearning to try it in dual mono, placing two of these amps next to each and gaining access to the full balanced output. It might have been an impatient wait for me but boy was it worth it. You see, on purchase of the CMA800R you get a great SINGLE ENDED amp with just one 3 pin XLR balanced output. It is only when you cough up the cash for another unit that you can plug into this output and reap the full benefits and trust me, after being eyed up by the XLR output for almost two years, let me tell you it will drive you mad and get the better of you at some point! Whichever way you do it though, be it one at a time or going straight to the glory of two, owning a pair of Questyle’s CMA800R will cost you £3000. SCV Distribution have just become the UK distributor so picking one up for Brits is easier than ever, Questyle have grown hugely since I first dealt with them and I am so glad because their products need to be heard.
I really have covered a lot of this amp in my last review of it, including all the tech side of things such as the current mode technology it implements in a rather different way to Bakoon. Now the difference between this and Bakoon I did miss out last time around is that as far as I am aware, at the very end, this does still output in voltage. It does the amplification in current mode but then last seconds switches it back. It is only current mode between input and output, not all the way through output. How it does this is through a last minute I/V converter and I know that some of the benefits of this are the ability to have a lower output impedance. If the output is truly in current you will end up with around a mega ohm (MΩ) or 1000000Ωs. Basically a ridiculously high amount and while that bodes no problem for a planar magnetic can with a flat impedance plot, something like the HD800 will have its frequency response skewed. With the CMA800R that won’t happen and consequently, I don’t even have to think which I would rather have between a Bakoon or Questyle when it comes to pairing with a HD800, the CMA800R every day.
Time Doesn’t Change Us
Being two years apart in production there is two small design difference in my units and that is the thinner type font of my new unit and also a change in the RCA ports used. That being said I know a few more designs changes have been proposed such as markers on the volume knob, which will be handy for reasons we will get to later. There is also an upgraded “Golden” version on its way that I saw at the High End Show Munich. Also comparing the two we can look at the included measurements taken by Questyle before they are shipped out and while the presentation of the graphs have changed a little the results have not. If I am not mistaken my original CMA800R is the original test sample which the results were based off of and every unit strives to achieve. That being said comparing the THD vs Power graph while they seem identical from 10m to 2, the new unit continues very smoothly until 10 while my old unit is a little more rollercoaster-esque there and hits points a little differently, like having a touch more distortion at 3. Looking at the frequency response graphs it also seem the new unit rolls off a little earlier, at 100kHz instead of just after, so a technicality that does not matter really. The new unit also seems to have small swoop up at 30Hz where my original unit stayed flat, interesting.
So why should we go balanced? A few reasons, first and foremost for the general benefits of balanced such as separating the channels with an extra ground but we also get more power and lower distortion. THD goes from 0.00038% to 0.00026% into 300 ohms, Signal to Noise Ration goes from 114dB to 1118dB and output power basically quadruples. Into my 300ohms HD800 and HD580 we go from 180mw to 710, quite dramatic but these aren’t really headphones that need huge wattage. Now the CMA is unlike more traditional balanced amps that share the same housing etc, as normally circuitry does not change when you go balanced. Here it really does, an entire amp is now dedicated to each channel and each channel as its own power supply cutting noise, this is clearly the ideal way to go about balanced drive. Inefficient models though, like my ZMF Blackwood get a huge helping more and going dual mono certainly seems to help my planars more. They are 50 ohms and while I am not sure on the power for that, I am sure it gives out plenty.
So configuring your monos into action can be done a few ways and you can even have your system set up so you have 2 (or 4) single ended outputs available if you want to share music. Every CMA800R has a set of 3 inputs, a pair of RCAs, a pair of XLRs and then a single 3 pin XLR. It is that single XLR that gives us access to the full balanced mode and whichever channel XLR you plug into that the amp becomes. Now if your DAC has enough outputs, you can still have them going into one of the pairs of the amp, so you flick the amp into “stereo” mode and listen from the two SE outputs and then go back to “mono” to enjoy an amp per channel. So once you have your DACs balanced outputs plugged into your CMA800R and they are both set to “mono” mode you are good to go.
But you then have volume control to deal with and depending on your DAC you may get too choose or have a method handed to you. Now if your DAC only has a true line out (and XLRS) with no volume control you will have to use the units volume control and match them manually, this is why I said the new design units with a reference on the volume pots is so needed as matching right now is a little bit annoying, especially if you want to quickly tweak the volume level, it is needed to be done on both units. Then again some companies choose to do this by default with the single ended Tektron Head Amp I have using separate channel volume knobs by default, but it is freaking annoying! The other method is my preferred way of controlling these amps and that is using a DAC that doubles up with pre amp functionality and of course has XLRs out, then you can set the Questyle’s to max volume purely as power amps and the attenuate the volume on the DAC. Honestly this is the best method and every one of the last ten or so DACs I have reviewed double as pre amps, even the cheaper ones so is not a hardship to find. I personally use my totaldac d1-tube-mkII and its gives me tight volume control even with lower impedance cans, which is handy due to the high gain of the CMA800R.
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