Which Chord inputs are galvanically isolated, and which setups short the isolation out?

Which inputs he says are isolated

USB on the desktop DACs and M Scaler. In September 2014 he said Chord's new QBD "has galvanic isolation built in" Head-Fi, Sep 2014. In April 2015 he named USB galvanic isolation as one of the Hugo TT's changes over Hugo and said "That is a big, big benefit" article, Apr 2015. In October 2015 he said DAVE, Hugo TT and 2Qute "are galvanically isolated", and in August 2016 that "2 Qute, Hugo TT and Dave have the same USB decoder and galvanic isolation" Head-Fi, Oct 2015Head-Fi, Aug 2016. In November 2020 he checked the schematics and said the TT1 HD USB "does have galvanic isolation - same circuit as TT2 and Dave" Head-Fi, Nov 2020. He has said TT2 and the M Scaler are "galvanically isolated on the USB" (February 2019) and that Qutest is isolated (March 2019) Head-Fi, Feb 2019Head-Fi, Mar 2019. By April 2021 his summary was: "All the desktop DACs have galvanic isolation on the USB inputs" Head-Fi, Apr 2021. In June 2022 he dated this to "all the desktop DACs since the launch of Dave" Head-Fi, Jun 2022.

How it is built. Across 2015 to 2020 he described the isolation as sitting after the USB decoder chip, so the decoder runs on the source side, powered from the USB 5 V VBUS line, and the FPGA receives I2S-type data with its clock supplied from the DAC side article, Apr 2015Head-Fi, Feb 2019Head-Fi, Mar 2019Head-Fi, Aug 2020. For that reason he says USB 5 V must be on for the desktop DACs and the M Scaler (April 2020) Head-Fi, Apr 2020. He said in March 2019 that Qutest's isolation uses "high speed RF digital isolators", not transformers, with 2 pF of coupling capacitance, plus chip ferrites and capacitors for GHz isolation Head-Fi, Mar 2019. In June 2022 he said he used to use opto-isolators but now uses isolators with an RF carrier Head-Fi, Jun 2022.

Optical. He calls optical the perfect isolation, "as the coupling capacitance is almost zero" (July 2018), and treats it as the reference input Head-Fi, Jul 2018Head-Fi, Mar 2022AVstore 42:56.

Coax/BNC inputs. In July 2018, in the Qutest thread, he said "Coax has no galvanic isolation", and in August 2020 that "the BNC inputs don't have galvanic isolation for all the DACs" Head-Fi, Jul 2018Head-Fi, Aug 2020. In August 2024, in the Mojo 2 thread, he said "coax is the most sensitive input to common mode RF noise currents", because ferrites on coax stop the SPDIF from being decoded reliably, and that this is why he put high speed galvanic isolation on the Hugo M Scaler Head-Fi, Aug 2024.

M Scaler, Blu 2 and Quartet outputs. He has said Blu 2's BNC connection to DAVE is galvanically isolated (a slide talk at Chord's Pump House, in a clip published by Hifistatement in October 2017 with the recording date not stated; and February 2018) Hifistatement 0Head-Fi, Feb 2018. In December 2018 he described Blu 2's BNC output as galvanically isolated with the grounds "not connected - except by 5pF of capacitance", and said that on the Hugo M Scaler he improved that isolation with 2 GHz chip ferrites in the BNC driver Head-Fi, Dec 2018. In November 2018 he said the M Scaler's "dual BNC outputs are completely isolated from the other outputs" Head-Fi, Nov 2018. In 2020 he put the capacitance across the M Scaler's output isolation at 2 pF, and in an interview published in August 2022 (recording date not stated) said "two picofarads worth of I think it's three" (check the recording) Head-Fi, Apr 2020AVstore 42:06. In March 2021 he said "The single BNC OP on the M scaler is not galvanically isolated" Head-Fi, Mar 2021. In 2024 he said Quartet has three stages of isolation where the M Scaler had one (check the recording) ConvinceMeAudio 11:00.

Portables. In January 2017 he said Hugo 2 would not get USB isolation because the USB chip would drain a portable source's battery, and that he had instead improved RF filtering and isolation on the USB power and ground Head-Fi, Jan 2017. At CanJam NYC 2022 (late February; the video was published in March 2022) he said "Mojo and Hugo 2 does not have galvanic isolation" MFG Audio Reviews 56:58. In 2020 he wrote that Hugo 2 "does not have ioslation on USB" and that it "is not galvanically isolated" Head-Fi, Apr 2020Head-Fi, May 2020. The 2022 transcript says "Mojo", not "Mojo 2", although the seminar was about Mojo 2.

Where he says it matters

He said in 2017 that with Hugo 2 on headphones and a mains-powered laptop he could not hear a difference between USB and optical, and he concluded "don't bother with galvanic isolation when using headphones and modern lap-tops" Head-Fi, Feb 2017. In June 2017 he put the reduction in benefit from Hugo 1 to Hugo 2 at "at least an order of magnitude", saying it is a non-issue on headphones and a small improvement when feeding power amps Head-Fi, Jun 2017. In January 2018 he said "You only need galvanic isolation when driving amplifiers that are mains powered" Head-Fi, Jan 2018. In June 2022 he said battery-powered Mojo 2 or Hugo 2 into headphones "won't need it" Head-Fi, Jun 2022.

Setups he says short out or weaken the isolation

Powering the source and DAC together. In August 2018, in the Qutest thread, he said a proposed setup would be "shorting the galvanic isolation on the USB inputs" and advised: "don't power the DAC and lap-top together" Head-Fi, Aug 2018.

Other connected sources during optical use. In November 2018 he said that for optical on the M Scaler the other sources must be disconnected, "otherwise the isolation is being shorted out via the BNC ground", adding that BNC directly couples the grounds Head-Fi, Nov 2018Head-Fi, Nov 2018. In 2019 he said a CD player on optical can still cause trouble when it is also electrically connected to a PC that connects to the DAC, because "the optical path is being electrically connected as well" Head-Fi, Feb 2019.

Grounding at the wrong point. In August 2021 he said grounding an M Scaler via DAVE "will not be the best from a SQ POV, as the galvanic isolation on the OP's will be shorted out", and suggested another ground far from DAVE or a battery Head-Fi, Aug 2021. In 2020 he said a TT2 with hum through IEMs cannot be grounded via USB "as it is galvanically isolated", and named the XLR pin 1, phono ground, BNC inputs or a chassis screw instead Head-Fi, Apr 2020Head-Fi, Jun 2020.

Intersecting mains loops. In March 2019 he said Qutest's isolation is "almost perfect" from DC to GHz "but it's easy to short circuit the isolation externally", for example with a mains-powered source and a mains-powered USB reclocker whose ground/mains loop intersects the loop through Qutest and a mains-powered amplifier Head-Fi, Mar 2019. In the same month he said one earthed component on each side does short the isolation but causes no problem, because current needs a loop: "We need a current flow to happen for problems to occur" Head-Fi, Mar 2019.

The isolator's own capacitance. Since 2016 he has said the isolation is not perfect because of about 2 pF of coupling capacitance, which at GHz frequencies becomes tens of ohms; at 2 GHz he gives 40 ohms, reduced to about 200 ohms with ferrites on TT2 (June 2020) Head-Fi, Jun 2016Head-Fi, Jul 2016Head-Fi, Apr 2020Head-Fi, Jun 2020. In May 2022 he said it "works perfectly at low frequencies but does not work effectively above 1 GHz" Head-Fi, May 2022. In March 2023 he said chaining USB into the M Scaler and its BNC outputs into DAVE leaves two 2 pF paths, about 80 ohms at 2 GHz, "so current could still flow into Dave's ground plane" Head-Fi, Mar 2023. He also said in 2016 that adding another isolator at the source would only halve the capacitance and "will probably make things worse" Head-Fi, Jun 2016Head-Fi, Jul 2016. In 2014 he said two USB cables would not help because "you are still connecting the grounds together" Head-Fi, Sep 2014. In April 2022, in the TT2 thread, he said Wave cables "effectively isolate the two units" and that stacking them risks spoiling this by capacitive coupling Head-Fi, Apr 2022.

What he says completes the isolation. For DAVE in 2016 to 2017 he said a battery-powered laptop with nothing else connected gives "effectively perfect isolation", better than optical from a mains-powered source Head-Fi, Jun 2016Head-Fi, Jul 2016Head-Fi, Oct 2017. For the M Scaler feeding a DAC he said in January 2023 that "the only way currently to guarantee 100% noise free operation is to have optical source and battery on the M scaler" Head-Fi, Jan 2023. He also said an Opto-DX isolates completely only if both sides are battery powered (August 2021) Head-Fi, Aug 2021.

How his framing changed

In 2014 and 2015 he described USB isolation as a large improvement for Hugo and Hugo TT, saying that before it he was "hearing huge differences between laptops as a source" Head-Fi, Sep 2014article, Apr 2015; in 2017 he recalled "an absolutely enormous difference" when isolating Hugo 1 from his Dell PC Head-Fi, Mar 2017. From 2016 he described what remained with DAVE's isolation as small, audible only on careful AB tests Head-Fi, Jul 2016Head-Fi, Aug 2016.

On USB versus optical his account changed in steps. In July 2016 he said optical was not as good as USB on DAVE because USB's clock comes from DAVE Head-Fi, Jul 2016, and in March 2022 he recalled that "In 2016 with Dave I did indeed prefer the brightness of USB" Head-Fi, Mar 2022. In January 2018 he wrote "I was wrong about that", saying the brightness was worse RF noise pick-up, not better timing Head-Fi, Jan 2018. From June 2017 to May 2020 he repeatedly said USB can sound the same as optical, depending on the source and setup Head-Fi, Jun 2017Head-Fi, Jan 2018Head-Fi, May 2020. In February 2019 he wrote "Technically USB is better from the clock POV; but in practice I have had optical sound identical to USB" Head-Fi, Feb 2019. In 2022 he restated optical as the reference input, saying USB is identical or worse depending on the source and that not all USB sources match optical because the isolation is not perfect Head-Fi, Mar 2022Head-Fi, Mar 2022MFG Audio Reviews 56:58. In October 2022 he opened a reply with "I too used to prefer USB than optical" and said there is no technical benefit to USB over optical with his DACs Head-Fi, Oct 2022. That differs from his February 2019 remark, and this page does not choose between them.

What he has not said: beyond his general remarks that portable DACs do not need USB isolation with a battery-powered source and that the DACs' BNC inputs are not isolated Head-Fi, Apr 2021Head-Fi, Aug 2020, this archive holds no product-specific statement from him about isolation on Hugo 2Go, Alto or Anni, and whether his 2022 remark about "Mojo" means the original Mojo or Mojo 2 is not clear from the transcript.

Quotes

“Yes isolating the USB really helps; its smoother (lower RF noise) and with much better sound stage depth”2014-09-13 Head-Fi, Sep 2014

“So my conclusions are - don't bother with galvanic isolation when using headphones and modern lap-tops.”2017-02-28 Head-Fi, Feb 2017

“You only need galvanic isolation when driving amplifiers that are mains powered”2018-01-10 Head-Fi, Jan 2018

“Qutest provides almost perfect isolation from DC to GHz - but it's easy to short circuit the isolation externally.”2019-03-12 Head-Fi, Mar 2019

Dated positions

Caveats and open points

• In an October 2026 interview transcript he says DAVE was the first product with galvanic isolation, which conflicts with his 2014 to 2015 statements about the QBD and Hugo TT; the transcript may be garbled.
• His capacitance figures vary by item and date: 2 pF for USB isolators, 5 pF for Blu 2's BNC output (2018), and 2 pF (2020) or 2 to 3 pF (2022 transcript) for the M Scaler's BNC outputs.
• Effects on sound are from his own listening, often qualified YMMV; he calls the residual effects small.
• A January 2019 post says "both have galvanic isolation on the BNC outputs" but the question it answers is not preserved, so it is not used here Head-Fi, Jan 2019.

Topics: Ground loops, galvanic isolation, earthing and mains