Heat, thermal protection and stacking

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Answers on this topic

• Can Hugo, Hugo 2, Mojo, TT2 or DAVE drive loudspeakers directly from the headphone output, and what load is too low?
• Can I stack TT2 and an M Scaler, and how hot is too hot?

Everything he said on this topic (65)

One-line summaries in our words, oldest first. Each link opens the original.

• 2014-06-19Watts gives Hugo battery temperature ratings (45 deg C charging, 60 discharging), 2W dissipation and 3.2 deg C per W, and advises charging with nothing on top. Head-Fi, Jun 2014
• 2015-12-02Watts says Dave runs warm with large thermal margins, XLR headphone drive would distort, AES is poor for high rates, and Blu dual BNC works with proper RF cables. Head-Fi, Dec 2015
• 2016-06-28Watts says blocking some of DAVE's holes is fine, but covering them with something not thermally conducting reduces its heat dissipation. Head-Fi, Jun 2016
• 2017-06-18Watts says the problem is power: Mojo is so small that any more power dissipation would cause problems. needs context Head-Fi, Jun 2017
• 2017-07-10Watts says top-up charging is normal and Hugo 2 has three thermal trips; an FPGA trip forces 1A cyan charging, and charging at blue reduces heat. Head-Fi, Jul 2017
• 2018-02-15Watts says the unit still draws just over 2W when on without USB and not playing, so it should be warm. needs context Head-Fi, Feb 2018
• 2018-03-15Watts says the turn-off charging behavior assumes next use is mobile, and battery temperature in desktop mode is barely above ambient, with batteries rated for high temperature. Head-Fi, Mar 2018
• 2018-03-29Watts says active electronics add RF noise so sources should be simple and battery powered, Hugo 2 cuts out at 60 deg C, and thermal cycling, not warmth, harms reliability. Head-Fi, Mar 2018
• 2018-03-29Watts says nothing in DAVE exceeds 75 deg C and Blu 2's die reaches only 60 deg C, as the die mounts to the thick aluminum chassis. Head-Fi, Mar 2018
• 2018-04-24Watts says heat leaves via the PCB ground plane to the case through six M2 screws, and dissipation peaks when on and charging from flashing red. Head-Fi, Apr 2018
• 2018-06-09Watts explains desktop mode keeps Hugo 2's battery near 80% for about 10 years of use, a charger fault means under 1A, and thermal shutdown when charging at red. Head-Fi, Jun 2018
• 2018-06-22Watts says playing while charging from flat is the worst case for battery temperature, though thermal trips protect it; on long flights he recharges Hugo 2 at blue. Head-Fi, Jun 2018
• 2018-08-12Watts says the M scaler makes compression losses audible, audiophile BNC cables sound same or worse, TT2 measures identically in Class B, and the units stack. Head-Fi, Aug 2018
• 2018-11-11Watts says shorting unused amplifier inputs is insane, risking damage and ground currents; Hugo 2 survives a short via thermal trips but must not run into one constantly. Head-Fi, Nov 2018
• 2018-12-13Watts describes his flight rig: M Scaler, a Hugo, phone source and MrSpeakers headphones; in economy a battery runs it two hours, reaching about 45 degrees C. Pursuit Perfect System 18:35
• 2019-01-08Watts says the M Scaler's FPGA die runs only a few degrees above the chassis, about 45 C when stacked, far below its 125 C rating, so reliability is unaffected. Head-Fi, Jan 2019
• 2019-01-09Watts gives TT2 distortion figures, 0.042 ohm output impedance and low-gain voltages, notes no distortion above 3 kHz at 12 W, and says the FPGA sits die-down on the chassis. Head-Fi, Jan 2019
• 2019-04-30Watts confirms the FPGA's exposed die is clamped directly to the bottom plate, so the bottom chassis temperature equals the die temperature. needs context Head-Fi, Apr 2019
• 2019-05-02Watts gives the M scaler's 65 C thermal trip, says it recovers transient timing to 16-bit accuracy rather than adding information, and attributes optical's darker sound to RF, not jitter. Head-Fi, May 2019
• 2019-05-06Watts says it cannot overheat and lists reset, battery-check and overnight-charge steps, with service if it will not recharge. Head-Fi, May 2019
• 2019-05-12Watts says the M scaler's size keeps its case from reaching 90 C, measures radiative and convective cooling at about 50% each, and finds nearly all CDs now musically enjoyable. Head-Fi, May 2019
• 2019-08-05Watts says TT2's SE outputs dissipate fine driving his B&W 803 D3 at +6 dB or +12 dB, but balanced quadruples internal loss, risking thermal trips at 8 ohms or less. Head-Fi, Aug 2019
• 2020-03-25Watts says a cable with a left-right short would explain it; Hugo 2 drives a short for about 15 minutes before the thermal trip, heard as mono. Head-Fi, Mar 2020
• 2020-06-09Watts says the M scaler's thermal trip protects hands, its case bottom reflects FPGA die temperature rated to 85 C, and hours in a bag stayed below the trip. Head-Fi, Jun 2020
• 2020-06-25Watts names 1 million taps and the M Scaler, though a thumb-sized battery running 12 watts for eight hours would make a tiny device very hot. Part-Time Audiophile 30:56
• 2020-06-25Watts says that would then raise the issue of fans. needs context Part-Time Audiophile 31:18
• 2020-06-25Watts says Mojo's small size limits dissipation: 1.7 watts raises temperature about 15 degrees C from memory, charging is more like 3 or 4 watts, and about 3 watts is comfortable. Part-Time Audiophile 31:24
• 2020-06-25Watts says a 12 watt device that small would burn your flesh without a fan, so thermal efficiency and removing waste heat matter as much as the battery. Part-Time Audiophile 32:06
• 2020-08-17Watts says it should run warm to the touch at 20 deg C, warmer when charging while playing, and shut down after 15 minutes into a short. Head-Fi, Aug 2020
• 2020-11-23Watts says TT2's balanced output into 4 ohms may thermally trip, restarting once cool, single-ended into 4 ohms won't trip, and Dave would have no problem with the Voxativ. Head-Fi, Nov 2020
• 2020-12-04Watts used crossfeed on Hugo only for hard-panned 60s recordings but runs it at max on Hugo 2 for depth; shrinking dimensions by a third would more than double temperature. Head-Fi, Dec 2020
• 2021-01-08Watts says TT2 drives efficient speakers single-ended, but XLRs thermally trip into 8 ohms or less; 16 ohms is fine, and amps shorting pins 1 and 3 risk damage. Head-Fi, Jan 2021
• 2021-03-25Watts says TT2's XLR used single-ended into a high-impedance input is fine, but some XLR inputs short pins 1 and 3; avoid balanced loads at or below 10 ohms. Head-Fi, Mar 2021
• 2021-04-30Watts says 1 ohm below 3kHz trips thermals, the Aeon 2 closed gives the best depth, MQA's -40dB aliasing is unacceptable, and FPGA timing closure rules out 112.896 MHz clocks. Head-Fi, Apr 2021
• 2022-02-17Watts says TT2 should not use balanced outputs into speakers or loads under 16 ohms as it will thermally trip; single-ended drives his B&W 803 D3 loud enough. Head-Fi, Feb 2022
• 2022-03-19Watts says Mojo's case can dissipate about 1.8 watts; he saved about 300 milliwatts in the analog section, spent 250 more on the FPGA, and battery capacity rose 9%. MFG Audio Reviews 25:11
• 2022-04-12Watts says TT2 will thermally shut down driving 8 ohm loads or less in balanced mode, and anyone not seeing shutdowns does not need the extra power. Head-Fi, Apr 2022
• 2022-04-25Watts says TT2 and M Scaler can be stacked, but are better apart with Wave or solid-ferrite BNC cables; use high gain unless IEMs hiss; avoid wireless subwoofer links. Head-Fi, Apr 2022
• 2022-04-25Watts says TT2 need only be separated if it thermally shuts down, explains how Blumlein encodes lateral and depth information, and says conventional SRC has severe sound-quality problems. Head-Fi, Apr 2022
• 2022-04-26Watts advises high gain into a power amp, keeping units on Wave cables apart to avoid capacitive coupling and cable ends touching, and says TT2 tolerates running warm continuously. Head-Fi, Apr 2022
• 2022-04-26Watts says Mojo's limits were size, not technology: its package can dissipate only about 2.5 watts, so the original Mojo got too hot when used while charging. Audio Force 2:44
• 2022-04-26Watts says the original Mojo was limited to about 1.8 watts, so he used only a third of its FPGA; for Mojo 2 he reworked the analog section's efficiency. Audio Force 3:29
• 2022-04-26Watts says he designed an FPGA-driven charging circuit for Mojo 2 so it can be charged while listening without getting hot, bringing Hugo 2 technology into it. Audio Force 4:58
• 2022-05-28Watts says a TT2 over-temperature (OT) error is most likely a shorted headphone cable or plug; if it recurs with nothing connected, the TT2 has a problem. Head-Fi, May 2022
• 2023-01-03Watts says TT2's XLR outputs trip thermally into 8 ohm speakers, leaving the 7W single-ended outputs, and Hugo 2's second-order noise-shaper amp eliminates crossover distortion. Head-Fi, Jan 2023
• 2023-02-05Watts says Hugo must keep power low: linearly regulating 8 volts to a 1 volt, one amp FPGA core dissipates 8 watts; a Mojo-style unit manages 3 watts at most. Soundnews 25:32
• 2023-02-05Watts says Hugo can dissipate about 4 watts without fans; a 95% efficient switch-mode regulator from 8 volts to 1 volt cuts dissipation to about one and a half watts. Soundnews 26:15
• 2023-03-01Watts says the M Scaler needs no warm-up, Hugo 2's in-flight change was ear pressure, describes flying with his battery rig and thermal trip, and says battery plus optical isolates. Head-Fi, Mar 2023
• 2023-03-03Watts says a Hugo M Scaler in a Mojo-size case would run at 100 deg C, and fanless operation needs a fivefold FPGA improvement without rising cost. Head-Fi, Mar 2023
• 2023-04-03Watts says it has exactly DAVE's form factor, causing heat dissipation headaches; he has heard the prototype for about two years and hopes to launch by year end. needs context Amplify Audio 1:02
• 2023-05-23Watts says all buttons flashing red indicates the over-temperature trip and asks whether the poster was playing and charging at once. Head-Fi, May 2023
• 2023-10-01Watts says heat sinking is a major issue: fanless Mojo 2 can dissipate about 2.5 W at 38 C, his preferred maximum, through convection and infrared radiation. The Source AV 45:19
• 2023-10-01Watts says a prototype heatsink performed poorly because it was not anodized; anodizing, whatever the color, doubles performance through radiative cooling, which he verifies by measuring thermal resistance. The Source AV 46:08
• 2023-10-01Watts says what matters is the heatsink's color at infrared, which should be bright, though we cannot see infrared. needs context The Source AV 46:53
• 2023-10-01Watts says a surface bright at infrared dissipates more, and that the new scaler he is working on had heat sinking and power dissipation problems from his own mistakes. The Source AV 46:59
• 2023-10-01Watts says his mistake was not calculating beforehand, assuming the big box would be fine. needs context The Source AV 47:19
• 2023-10-01Watts says output-stage bias must not drift with heat, notes he began as an analog designer, self-taught in digital, and says the DACs sound the same at switch-on and later. The Source AV 47:35
• 2023-10-01Watts says many parameters alter sound quality, and a sound that changes after switch-on signals something adrift, even if the temperature change happens to sound better. The Source AV 48:23
• 2023-10-05Watts says unanodized Hugo M Scaler prototypes showed anodizing doubles heat-sink performance, and Choral scaler heat issues led to a redesign of metalwork, PCB and FPGA code. Head-Fi, Oct 2023
• 2023-12-22Watts says that traveling with TT2 and Hugo M Scaler, he stacked or separated them by hotel layout and never noticed a sound-quality difference. Head-Fi, Dec 2023
• 2024-06-27Watts says a thermal trip turns all LEDs red and mutes, needing a hot unit; ventilate it, and if it trips while cool it needs service, likely more thermal paste. Head-Fi, Jun 2024
• 2024-07-19Watts says flashing red lights indicate a thermal trip from a short on the outputs, likely an amplifier shorting its inputs when powered down, so remove the cable. Head-Fi, Jul 2024
• 2024-07-24Watts says to wait for launch; he has only stacked the units, expects no difference given his screening and filtering design, but must prove it with PSU listening tests. needs context Head-Fi, Jul 2024
• 2025-03-27Watts says TT2's balanced outputs should not drive 8 ohm speakers, as above 7W it thermally trips; balanced is for low-sensitivity 32 ohm headphones or balanced amp inputs. Head-Fi, Mar 2025
• 2026-10-17Watts lists Quartet's hardware problems: heat removal, nine prototypes, over 2,000 components, BNC cables sounding the same, and a supply as good as battery power. article, Oct 2026