T.H.E Show Newport 2015: Questyle QP1 and QP1R Digital Audio Players

I'm pretty sure the world doesn't need another digital audio player unless it's something unusual and different. Fortunately, Questyle is indeed "different" when it comes to their electronics design philosophy.

In a typical solid-state audio electronic circuit, the audio signal is a voltage going up and down in a rather jagged and complex manner. To ensure the stability of the circuit, negative feedback is used. A bit of the signal at the output is fed back in reverse polarity to nul the input signal. The problem is, because of the capacitive nature of solid-state components interacting with the voltage signal, it takes a small amount of time for the signal to travers the circuit before it gets fed back to the input. This propagation delay causes the negative feedback to not quite line up with the incoming audio, and produces transient intermodulation distortion—a particularly dissonant and unpleasant sounding type of distortion.

Many high-end audio designers choose to design amplifiers with zero feedback to get around this problem. Unfortunately, that produces problems of its own in that the output impedance of the amplifier can't be forced to a very low number, and zero feedback designs may become unstable and oscillate or make odd chips and tweets.

Questyle takes a completely different approach by converting the audio from a voltage signal to a current signal within their products—a technology they call current mode amplification. Current signals act quite differently and don't suffer the propagation delay problems of voltage based circuit designs. As a result, Questyle claims almost unmeasurable amounts of transient intermodulation distortion in their amps. The current signal is converted back to a voltage signal at the output of their amps—these are not transconductance amplifiers.

Current mode signals have been used, primarily for signal transmission, in high-end audio products before. Krell, for example, had CAST (Current Audio Signal Transmission) technology for audio transmission between components. But using current mode active amplification is rare as it is quite difficult to achieve the level of parts tolerance and matching needed to pull it off. And therein lies Questyle unique value proposition: they've figured out how to efficiently manufacture electronic circuits that require extremely tight tolerances.

And now, in the QP1 digital audio player, they've produced an all discrete component, class-A, current mode circuit small enough to hold in your hand. The QP1R uses the same design, but increases the quality of various critical components within. Output impedance is claimed at a remarkably low 0.19 Ohms.

I had a fun time playing with the QP1R for about ten minutes in the booth. The font size on the display seemed a little small and hard to read for me, but otherwise I found the user interface to work well and was rather more intuitive than many rotary wheel user interfaces I've experience previously. I'll certainly be hunting down a review sample for John Grandberg to include in his DAP round-ups.

For more info check out Questyle, the QP1 product page, and this (very slow to load) page describing current mode amplification.

Click here if you can't see the video.

ManiaC's picture

It gonna have digital or analogue volume control?

John Grandberg's picture
It will have digital volume control implemented via FPGA. So not the built-in volume functionality of the Cirrus DAC, but something else all together.
JinHit's picture

Looks good, rly interested in this one, though it's looking like FiiO X5 upgrade, cuz... u know, analog wheel with a button, dual microSD + usb at the bottom, 4 buttons at the corners having the same functions =)
I'm not blaming them, this DAP looks rly good and I think FiiO should have made their new X5 2gen like this, with new DAC and not leaving the same PCM1792A. New FiiO x3 2gen got CS4398 and sounds rly good for it's price, so looking forward to listen this Questyle QP1 if some of our shops in Moscow will have it.

P.S.: Sorry for my crappy English. Cheers. :)

WobblySam's picture

Tyl, while you were at the booth, did they happen to mention whether there was an actual U.S. retailer for their products?
I notice on the website, there is quite a bit of marketing flourish about the output amp but no mention of the output voltage or available output power in the specs. You know anything?

John Grandberg's picture
But I imagine the specs will be forthcoming. I'll have one of these sent over shortly for my big DAP review project, and will be sure to drag that info out of them if it isn't already available by then. The dealer situation is ever evolving. You have to email questyle@gmail.com and give them your location, they will then recommend the closest dealer. Not ideal, I keep telling them.
WobblySam's picture

It always concerns me when somebody has a product in production and won't provide basic operational specs. It makes you wonder what they're hiding while waving their arms and saying look over here at the cool marketing hype.
Thanks in advance for providing the info. I found out something a little disturbing about the DAP. It's line out really isn't. It's more of a preamp out with the volume control affecting the level. Que stated that if they implemented an equalizer, it's effects would be seen in the line out. I guess that's one of the down sides to implementing an amplitude control (volume) at the dac level instead of doing it in the analog domain. It bums me out as I wanted to use the Que as a portable source more so than an on-the-go player. I would use it with an external amp most of the time. Line out seems to be an issue (except for Fiio) with these Chinese dap makers - the iBasso DX-90 has the same problem.

John Grandberg's picture

I tend to think the lack of firm specs posted has more to do with the slight language barrier, as well as their marketing and design teams not being on the same page all the time. Notice the other products have a lot more specs listed - it's not like they are a company with a history of hiding that sort of thing. They provided extensive measurement info when I reviewed their desktop amp.

The line out issue, as you said, seems indicative of the topology. Honestly it doesn't bother me, assuming the built-in amp is of suitable quality.