Qutest: everything he said

126 posts and passages, oldest first, as one-line summaries in our words. Each link opens the original.

2018-01-09Watts says Qutest ships with a 2A supply but works on 1A 5V; pressing both buttons during the rainbow start-up sets output voltage, otherwise it changes display brightness. Head-Fi, Jan 2018
2018-01-09Watts says Qutest is now in production, with delivery to dealers in February. Head-Fi, Jan 2018
2018-01-10Watts lists noise and distortion pass criteria, says Hugo 2 and Qutest are within 0.5 dB of theoretical noise, and explains setting pulse array resistors at a distortion tipping point. Head-Fi, Jan 2018
2018-01-10Watts posts his Hugo 2 presentation updated to include Qutest, with the Qutest-only slides to follow. Head-Fi, Jan 2018
2018-01-10Watts explains the boost-voltage and linear-regulator supply that isolates the amplifier gain section from the output stage in Hugo 2 and Qutest, and the digital DC servo replacing coupling capacitors. Head-Fi, Jan 2018
2018-01-10Watts says John did a great job on the Qutest chassis, which feels substantial; he expects it may help sound quality but has not yet listened to it. Head-Fi, Jan 2018
2018-01-10Watts says the quartz oscillator and some parts are slightly microphonic: clicks are audible when the PCB is struck, and a mounting screw couples the oscillator to the chassis. Head-Fi, Jan 2018
2018-01-10Watts says 2Qute's discrete stage was never meant for low impedances; Qutest uses the Mojo output stage with more drive but is a DAC only, its impedance unmeasured. Head-Fi, Jan 2018
2018-01-10Watts says Qutest remembers all configuration settings, and its BNC inputs are individually selected and switch automatically into dual data mode. Head-Fi, Jan 2018
2018-01-10Watts says Qutest was designed mainly for speaker systems; it suits those who like an external headphone amp's coloration, but for transparency with headphones he recommends Hugo 2 or Dave. Head-Fi, Jan 2018
2018-01-11Watts says Dave's DX output is a 705/768 kHz signal with volume data embedded, making Dave a DX pre-amp; Qutest accepts DX data but ignores the volume. Head-Fi, Jan 2018
2018-01-11Watts says Qutest is a fixed-level DAC, not a DX pre-amp: it has no DX outputs and will not decode volume on a DX input. Head-Fi, Jan 2018
2018-01-11Watts explains Qutest feeds linear power amps, Hugo 2 suits 1W/8 ohms and Dave 2W, while planned DX amps are pulse array DACs delivering 20W to hundreds of Watts. Head-Fi, Jan 2018
2018-01-11Watts says a supply meeting USB specifications will not void the warranty, expects no gain from other supplies as the design is supply immune, and calls a USB battery ultimate. Head-Fi, Jan 2018
2018-01-11Watts says supercaps lower PSU impedance and distortion crosstalk, but Hugo 2 and Qutest avoid that by regulating from a boost voltage, and a DAC needs no supercap current. Head-Fi, Jan 2018
2018-01-12Watts says USB power was chosen partly because batteries are cheap; Qutest draws 2.5W so 100Wh lasts 40 hours, and batteries give the lowest RF and LF noise. Head-Fi, Jan 2018
2018-01-13Watts says it is done digitally with Hugo 2's volume control, whose aggressively noise-shaped truncation gives -400 dB accuracy, and 0dBFS is below the noise shaper's maximum modulation. needs context Head-Fi, Jan 2018
2018-01-15Watts says upsampling PCM to DSD256 will sound much worse than feeding the original PCM to Qutest, for several reasons. Head-Fi, Jan 2018
2018-01-16Watts says the finish is a Chord (John Franks) decision, but he understands Qutest will only be black. Head-Fi, Jan 2018
2018-01-16Watts says his listening tests support this but others differ; some amplifiers may be sensitive to Qutest's PSU, so try a USB battery and skip upgrades if no difference. Head-Fi, Jan 2018
2018-01-17Watts says Qutest's noise is identical at every output setting and the 3V figure reflects distortion; the best setting depends on the amp, e.g. 1v for a 1.2v-rated amp. Head-Fi, Jan 2018
2018-01-18Watts says the 0.025 ohm output impedance figure is incorrect as it has not been measured; the 300 ohm load represents the worst-case amp input impedance. Head-Fi, Jan 2018
2018-01-18Watts says 300 ohms is the measurement load, not the minimum load impedance, and the output impedance is too small to matter. Head-Fi, Jan 2018
2018-01-19Watts reports measuring Qutest's output impedance at 0.042 ohms at the phono sockets at 1kHz and 20Hz, with no coupling capacitor thanks to the digital DC servo. Head-Fi, Jan 2018
2018-01-25Watts explains AES dual data mode, says Hugo 2 and Qutest auto-assign channels while DAVE needs manual connection, and says a Mojo with Nighthawks or Aeons beats far costlier systems. Head-Fi, Jan 2018
2018-01-25Watts advises comparing a USB battery pack with Qutest's included PSU, saying a battery pack outperforms a linear PSU by eliminating mains RF noise. Head-Fi, Jan 2018
2018-02-07Watts lays out the Hugo 2/Qutest signal path from 16FS WTA1 (49,152 taps) to 104 MHz pulse array, and explains noise-shaped truncation and the -301 dB test for depth. Head-Fi, Feb 2018
2018-02-07Watts says he cannot say whether someone will like a product, only that Hugo 2 and Qutest are technically, measurably and musically much more advanced than Hugo 1 and 2Qute. Head-Fi, Feb 2018
2018-02-22Watts says Chord announced at the Blu 2 launch that other M scaler units would come, but says no more; Qutest uses a 4-layer PCB of Hugo 2's spec. Head-Fi, Feb 2018
2018-02-28Watts says Hugo 2 and Qutest share circuitry and FPGA code but Hugo 2's output stage is more advanced; for headphones it outperforms Qutest with a separate amp. Head-Fi, Feb 2018
2018-03-06Watts says Hugo 2/Qutest use 67.5mS of data versus 1mS for conventional filters, minimum phase sounds soft, the M scaler uses 1.37 seconds, and more M scalers will follow. Head-Fi, Mar 2018
2018-03-06Watts says 2Qute outputs 3.0V RMS at 0dBFS, exactly the same as Qutest at its 3.0V setting. Head-Fi, Mar 2018
2018-03-06Watts says Qutest and 2Qute have identical discrete output stages and the same 3V output, suggesting Qutest's greater refinement may make a difference more apparent. Head-Fi, Mar 2018
2018-03-13Watts says Dave's superior transparency comes from many factors beyond its noise shaper, which dominate given Hugo 2 and Qutest's noise shapers, and both benefit enormously from an M scaler. Head-Fi, Mar 2018
2018-03-17Watts says Davina will use Choral metalwork and all new DACs will accept M scaler dual data, which is why Qutest and Hugo 2 have that input. Head-Fi, Mar 2018
2018-03-22Watts says Qutest has the same number and packaging of transistors as Mojo, and no power button because it consumes only a couple of Watts. Head-Fi, Mar 2018
2018-04-04Watts expects desktop models to stay ahead; on taps alone, Hugo 2 and Qutest have 49,152 versus Blu MKII's 1,015,808, which he calls 'a 20 times capacity advantage.' article, Apr 2018
2018-04-08Watts says the DPLL minimizes buffer delay while eliminating source jitter, so Hugo 2 and Qutest fed from one SPDIF source show no noticeable delay difference. Head-Fi, Apr 2018
2018-04-19Watts says the best output level depends on the pre-amp's topology, as 3v may cause distortion in some; without PA20 experience, he advises trying levels by ear. Head-Fi, Apr 2018
2018-04-25Watts says USB runs at 32 bits with 16-bit sources zero-padded; the source must not upsample, so check 44.1k files show red. Head-Fi, Apr 2018
2018-04-29Watts says he used a 100W/h battery bank with 5v/2.1A USB output, more than Qutest needs. Head-Fi, Apr 2018
2018-05-20Watts says it supports native DSD up to DSD 512 via the ASIO driver and DoP up to DSD 256; he does not know about Linux. Head-Fi, May 2018
2018-05-21Watts says Chord confirmed ASIO is Windows only, so on Linux DSD is DoP only. Head-Fi, May 2018
2018-05-22Watts says Linux needs varied drivers for native DSD while DoP is driverless but less efficient, capping it at DSD 256; his DSD 512 track sounds flat and soft. Head-Fi, May 2018
2018-07-01Watts says AAC, short filters, MQA, minimum phase, NOS and DSD sound soft and warm from transient timing uncertainty; turning off the incisive filter similarly sounds warmer. Head-Fi, Jul 2018
2018-07-05Watts says noise is identical across the three voltage settings because the adjustment is digital; the right setting depends on the connected amp's overload behavior. Head-Fi, Jul 2018
2018-07-06Watts suggests sound differences between CD players into Qutest via optical likely come from differing error rates, or RF upsetting the headphone amp, and says rips give error-free data. Head-Fi, Jul 2018
2018-07-21Watts says he uses the M Scaler with Hugo 2 on planes, Hugo 2 and Qutest work fine, and he regrets not giving Mojo 768 capability. c w 29:47
2018-07-26Watts says Qutest, Hugo 2, TT2 and Dave share the post-scaler process (WTA2 to 256FS, third-order filter to 104 MHz), notes diminishing returns, and previews DX amps' transparency. Head-Fi, Jul 2018
2018-07-28Watts says flashing lights mean the FPGA failed authorization at power-up, likely from a power interruption; removing and reapplying power fixes it, and nothing is wrong. Head-Fi, Jul 2018
2018-07-29Watts says optical and USB sound the same on Hugo 2 with headphones but differ once grounded; coax lacks galvanic isolation, so RF raises noise floor modulation and sounds brighter. Head-Fi, Jul 2018
2018-08-08Watts says Qutest has no DX input but accepts dual-data 768 kHz, ignoring the volume information in the user data. Head-Fi, Aug 2018
2018-08-13Watts advises 75 ohm BNC cables matching the M scaler's output; scaled DACs still differ: Dave beats Qutest, with a 20-element pulse array and 30 times lower distortion. Head-Fi, Aug 2018
2018-08-20Watts speculates why the test filter is poor, and says the 16FS, WTA2 256FS and 2048FS path is identical from Qutest to Dave; noise shaper, pulse array and analog differ. Head-Fi, Aug 2018
2018-08-28Watts explains he uses no coupling caps but a digital DC servo trimming the noise shaper, which takes 16 seconds to stabilize, hence the rainbow start-up and Dave's turn-on delay. Head-Fi, Aug 2018
2018-09-14Watts says linear PSUs lack RF filtering and sound brighter, Qutest benefits hugely from the M scaler but an M-scaled Dave easily beats an M-scaled Qutest. Head-Fi, Sep 2018
2018-09-25Watts says the warmth heard is softness from transients misaligned by crude upsampling versus Qutest's WTA filter, and advises a bit-perfect source with no upsampling. Head-Fi, Sep 2018
2018-10-13Watts says Qutest sounds very different from the Yggdrasil, preference is the buyer's choice, and they measure very differently, with measurements mattering profoundly. Head-Fi, Oct 2018
2018-10-13Watts names the Poweradd Pilot Pro 2, which powers the M Scaler at 12 V and Qutest from USB; at 85 Wh it passes airports, giving 35 hours on Qutest. Head-Fi, Oct 2018
2018-11-11Watts says Qutest uses the same output stage as Mojo, so shorting it is a bad idea, and its powerful discrete stage gives lower distortion even into amplifier inputs. Head-Fi, Nov 2018
2018-11-11Watts says Hugo 2 is designed for negligible distortion change into low impedances, while Qutest driving amp inputs stays in Class A and needs no second-order analog noise shaper. Head-Fi, Nov 2018
2018-12-17Watts says 2 V is 3.5 dB and 1 V 9.5 dB below 3 V; non-WTA upsamplers cannot predict the M Scaler, as longer conventional filters add near-zero coefficients. Head-Fi, Dec 2018
2018-12-18Watts says Qutest can simply be unplugged; it is the laptop that needs correct disconnection, best done by powering it down before removing the USB cable. Head-Fi, Dec 2018
2018-12-19Watts says the poster needs to earth Qutest, really the power amps, since Qutest and the M scaler are both isolated from ground. Head-Fi, Dec 2018
2018-12-29Watts says Chord confirmed the BNC connector datasheet states 75 ohms, size differences come from dielectric constant, and 75 ohm cable is essential since M Scaler outputs are 75 ohms. Head-Fi, Dec 2018
2019-01-20Watts details WTA1 modes, WTA2 versus the three-stage IIR, the HF filter at about -1dB at 20kHz, and says Stereophile's Qutest frequency response was wrong due to latency. Head-Fi, Jan 2019
2019-01-20Watts says Qutest's output levels are set digitally through one noise-shaped stage at -400 dB accuracy, so audible differences come from ancillary gear; if unsure, use 2 V. Head-Fi, Jan 2019
2019-02-05Watts says Qutest has no coupling capacitors; it is fully DC coupled with a digital DC servo, and the capacitors are 200 V C0G parts for the analog filter. Head-Fi, Feb 2019
2019-02-19Watts says Qutest is designed to stay on 24/7 at 2.25 W, and rejects the idea he cripples products for upgrade paths, describing designing for maximum quality at each price. Head-Fi, Feb 2019
2019-02-20Watts says Qutest is surge protected, element count does not set resolution, Davina has no date, DSD sounds unnaturally soft, and explains FIR for reconstruction versus IIR for EQ. Head-Fi, Feb 2019
2019-02-27Watts says all his galvanically isolated designs power the USB decoder from VBUS, isolating it so the DAC sees only I2S data without decoding noise. Head-Fi, Feb 2019
2019-03-11Watts says Qutest isolates USB with RF digital isolators of 2 pF coupling plus GHz filtering, not transformers, so added USB devices raise system RF noise rather than improve isolation. Head-Fi, Mar 2019
2019-03-12Watts explains how a mains-powered USB reclocker creates intersecting ground loops that defeat Qutest's isolation, and weighs an M Scaler against removing an external amp, advising a dealer trial. Head-Fi, Mar 2019
2019-03-13Watts lists TT2's advantages over Qutest: better noise shapers, DAVE reference circuitry, a second-order analog noise shaper, and a far simpler path than Qutest plus headphone amp. Head-Fi, Mar 2019
2019-03-16Watts says one earthed component on each side of Qutest is fine, because problems need current flowing through a Qutest output loop intersected by a source loop. Head-Fi, Mar 2019
2019-03-17Watts says Qutest's supplied PSU is ungrounded, and SMPS have low coupling capacitance and RF filters linear supplies lack; a USB battery pack removes mains coupling, with tiny differences. Head-Fi, Mar 2019
2019-07-20Watts says Qutest, like all his DACs, decodes DoP over SPDIF, so DSD64 works over optical, which is its maximum there. Head-Fi, Jul 2019
2019-08-01Watts says better transients make tempo seem faster while less dominance effect makes it seem slower; an M Scaler on Qutest mostly reduces dominance, sounding more measured. Head-Fi, Aug 2019
2019-09-20Watts says Qutest uses Mojo's Class A stage for easy loads, while Hugo 2's noise shaper output is crossover-distortion free into 33 ohms, with 120 dB feedback at 20 kHz. Head-Fi, Sep 2019
2019-09-30Watts says Qutest's optical input runs at 192 kHz if source and fiber allow, but replacement optical parts for discontinued Toshiba devices are less reliable at 192 kHz. Head-Fi, Sep 2019
2019-11-18Watts confirms the manual: red is 1 V, green 2 V, blue 3 V. Head-Fi, Nov 2019
2019-11-22Watts says 4.9 V on the micro USB supply is fine, since all rails are regulated internally, so long as it meets USB's 5 V +/- 0.25 V spec. Head-Fi, Nov 2019
2019-12-16Watts says he wanted DSD's single-element benefit without signal-dependent switching, leading to the pulse array; Qutest has ten PWM elements arranged so one rises as another falls. Passion for Sound 3:58
2019-12-16Watts says eight or ten elements (ten on Qutest) give a 4-bit signal and better small signals, then starts explaining how a noise shaper maps 32 bits to 4. Passion for Sound 6:09
2019-12-19Watts says the timing error degrades timbre, soundstage and bass, which improve as taps increase; Qutest's 48 thousand taps are about 12-bit sinc accurate. Passion for Sound 19:15
2020-01-02Watts says the needed timing accuracy cannot be stated, and cites Qutest, where switching between white/green and orange/red filters switches a 256FS WTA filter. Passion for Sound 2:54
2020-01-02Watts says the two Qutest filters measure identically yet sound different; WTA1 outputs every 1.3 microseconds and a second WTA stage outputs every 88 nanoseconds. Passion for Sound 3:38
2020-01-02Watts says more is going on, since Qutest always needs an amplifier for headphones or loudspeakers. Passion for Sound 23:05
2020-01-02Watts says TT2 is more transparent than Qutest (better noise shapers, components, supply, output stage), but the M Scaler uniquely brings timbre, pitch, separation and musicality. Passion for Sound 23:33
2020-01-02Watts says DAVE is much more transparent than even an M Scaler-fed TT2, the choice is personal, Qutest with another amplifier loses transparency, and many Qutest owners add M Scalers. Passion for Sound 24:58
2020-01-06Watts says Qutest drives any amp input above 100 ohms, but an unpowered connected amp's clamp diodes may degrade linearity, so compare on, off and disconnected. Head-Fi, Jan 2020
2020-02-03Watts says Qutest's 2 V and 3 V settings do not differ significantly internally, so audible changes come from the pre-amp or power amp. Head-Fi, Feb 2020
2020-03-09Watts says Qutest has no volume control, explains truncation, Gaussian dither and 11th-order noise shaping at 705/768 kHz, and prefers Roon volume over a pre-amp. Head-Fi, Mar 2020
2020-06-25Watts says Qutest's BNC inputs take 768 kHz without transformers at 75 ohms, it was not designed for slow-ramping PSUs, and non-stock supplies void Chord's warranty. Head-Fi, Jun 2020
2020-08-03Watts says PSU leakage current causes the amp issue, which a battery avoids; earth Qutest via BNC, RCA, an earthed USB PSU or a chassis bolt, or earth the amp. Head-Fi, Aug 2020
2020-12-14Watts says 6 V would destroy the FPGA; the supply must be USB compliant at 5 V +/- 0.25 V. Head-Fi, Dec 2020
2020-12-15Watts says it probably makes no difference, but he would put the BNC on the Qutest side, where mis-termination reflections have less effect. Head-Fi, Dec 2020
2021-01-25Watts says the treble extension and tighter bass heard with an Sbooster supply are noise floor modulation from more RF, and SMPS RF filters give softer, warmer, less fatiguing sound. Head-Fi, Jan 2021
2021-09-28Watts says Qutest shares Mojo's discrete output stage, pure Class A into 300 ohms or more; on Hugo 2, TT2 and DAVE a second-order analog noise shaper eliminates crossover distortion. Head-Fi, Sep 2021
2021-09-28Watts says loads below 300 ohms give Qutest some small measurable crossover distortion; Qutest was designed to drive amplifiers, so use Hugo 2 for headphones. Head-Fi, Sep 2021
2021-10-18Watts says idle Qutest draws 2 W and was meant to stay on, as cool electronics are more reliable; no affordable FPGA for 0.5M taps exists or is coming. Head-Fi, Oct 2021
2021-10-22Watts says supplied BNC cables are starters; 2GHz ferrites, Wave cables or battery power cure ground currents; Qutest uses Mojo's output stage; M Scaler was developed with TT2 and DAVE. Head-Fi, Oct 2021
2022-01-31Watts says other reasons were simplifying setup alongside the new DSP and that Mojo's 3 volts is too much for many amplifiers, hence Qutest's 1, 2 and 3 volt settings. Darko.Audio 17:48
2022-02-09Watts declines to name consulting clients for confidentiality, repeats he has not started a DAVE replacement, and says likewise for Hugo 2, Qutest and TT2: no Hugo 3 next. Head-Fi, Feb 2022
2022-02-09Watts says the power bank would run Qutest about 100 hours per charge but is too powerful for flying and lacks 12v for M scaler; he suggests a Krisdonia 25000mAh. Head-Fi, Feb 2022
2022-03-27Watts recounts redesigning Qutest's regulation after Qute proved PSU sensitive, admits his 2016 USB preference on Dave was RF brightness, and calls optical the reference input. Head-Fi, Mar 2022
2022-05-23Watts says DAVE's DX outputs carry 705/768 kHz from its 164,000-tap WTA1 filter and should sound better than Qutest's 48k taps; Qutest ignores the embedded volume data. Head-Fi, May 2022
2022-05-28Watts attributes a 1 kHz measurement artifact to APx555 ground currents over USB, discusses ground loops and optical as reference, and gives settings for noise floor modulation tests. Head-Fi, May 2022
2022-06-27Watts says pure DSD and R2R DACs are fundamentally limited, DAVE's noise shaper is not capped at 17th order, the HF filter sits after WTA2, and car batteries are ideal. Head-Fi, Jun 2022
2022-08-02Watts confirms orange and red filters bypass WTA2, with the following filters running 16FS to 2048FS, and green/orange removing more HF noise and distortion above 50kHz. Head-Fi, Aug 2022
2022-11-09Watts says Qutest uses the same output stage as Mojo and will safely drive 25 ohm loads, so a TH-600 is no concern. Head-Fi, Nov 2022
2023-02-05Watts says around 2016 people began using linear supplies with 2Qute, illustrating how forums help his work. Soundnews 37:22
2023-02-05Watts says 2Qute was supply-sensitive, which does not mean linears beat switching; for Qutest he improved regulation and RF filtering so a switching supply matched a 12-volt battery. Soundnews 39:49
2023-02-05Watts says Qutest's supplied unit equals a 12-volt car battery, so linear supplies that sound different degrade it; TT2 runs ten seconds on supercaps with the supply unplugged. Soundnews 40:35
2023-03-03Watts doubts an unspecified product would sell in volume and says it would cannibalize Mojo 2 and Qutest, since Mojo 2 only works commercially in large volumes. needs context Head-Fi, Mar 2023
2023-03-12Watts says some amps are overloaded by a 3V input, raising distortion and sounding harder without clipping, which is why Qutest has three output voltage settings. Head-Fi, Mar 2023
2023-03-26Watts says he aims for supplies that sound like a car battery; around 2016 he was shocked how much better 2Qute sounded on one, and addressed this with Qutest. Eric's Hi-Fi 18:34
2023-03-26Watts says Qutest and TT2 sound the same on a car battery as on the supplied switch mode supply, except TT2 with an M Scaler; better supplies would add RF. Eric's Hi-Fi 19:18
2023-09-24Watts says output level changes are made digitally, not with analog resistors and switches, without changing amplitude or phase (0.001dB, 0.001 deg) for his -301dB test signal. Head-Fi, Sep 2023
2023-09-24Watts says the 3v setting also has some attenuation, tuned for best dynamic range and lowest output distortion, while 2v and 1v add a bit more. Head-Fi, Sep 2023
2023-10-20Watts says Qutest is UAC2 compliant. Head-Fi, Oct 2023
2023-12-16Watts says Qutest's sample rate display is accurate because the WTA filter must know the incoming rate, so a 96k file shown as red was sample rate converted by the source. Head-Fi, Dec 2023
2023-12-16Watts says Qutest needs 5v +/-0.25v, a USB power bank is safe, and over 5v would blow an easily replaced protection diode, with no such failures reported. Head-Fi, Dec 2023
2024-01-14Watts says Chord's 3 V standard dates from 1990s passive pre-amps, Qutest added 1/2/3 V options, and a Mojo 2 line-level output was dropped to keep controls simple. Head-Fi, Jan 2024
2025-01-28Watts says WTA1's 98,304 taps are unaffected by filter options, red and orange switch out WTA2, and white and green only adjust the 256FS to 2048FS filter time constants. Head-Fi, Jan 2025
2026-10-02Watts says 2Qute sounded dramatically better on the car battery, so Qutest got better regulation and RF filtering, after which he heard no difference from the battery. HiFi Buys 2:22:57

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