Will sensitive IEMs hiss on a Chord DAC?

Practical answer. Watts says extremely sensitive IEMs can reveal a faint hiss from a Chord DAC, while normal-efficiency headphones will not Head-Fi, Mar 2016Head-Fi, Mar 2017. He describes the hiss as fixed residual noise, and of Dave in April 2016 he said "if you can't hear the hiss, then it has no bearing whatsoever" Head-Fi, Apr 2016. The product remedy he describes is Hugo TT 2's low gain mode Head-Fi, Apr 2022. For the original Hugo with the Shure SE846 he suggested the IEM's own attenuator, with a caveat about sound quality Head-Fi, Sep 2014.

By product

Hugo (2014 to 2015). In July 2014 he said the SE846's sensitivity is "extremely high (114dB 1mW 9 ohms), so you will hear some hiss from Hugo" Head-Fi, Jul 2014. In August 2014 he gave Hugo's no-source noise as 5uV A-weighted and said this is true on all units passing production Head-Fi, Aug 2014. In September 2014 he called the SE846 "the most sensitive I have seen" and said Hugo's residual noise "would be just audible" Head-Fi, Sep 2014. He repeated this in April 2015 Head-Fi, Apr 2015. With his own Noble K10, music muted, he said "I can just hear Hugo's noise - but only when I switch Hugo off is it noticeable, it is smaller than background noise" Head-Fi, Aug 2014.

Dave (2016). In March 2016 he gave Dave's residual noise as 2.6uV and said it "might be just audible with ultra sensitive IEM's as a hiss". With normal-efficiency headphones you "will never be able to hear Dave's residual noise" Head-Fi, Mar 2016.

Hugo 2 (2017 to 2021). In April 2017 he said Hugo 2 has half Hugo's residual voltage noise, 2.6 uV, so the hiss is 6 dB quieter, and that dead silence depends on your hearing and the IEM Head-Fi, Apr 2017. In the Hugo 2 thread in March 2021 he again gave the residual noise as 2.6uV A-weighted Head-Fi, Mar 2021. In March 2017 he said lower noise is not needed, since "unless you have hyper sensitive IEM's you will never hear it - but the real reason is distortion" Head-Fi, Mar 2017.

Hugo TT 2 (2018 to 2022). Of the products here, TT 2 is the one where he describes a gain switch for this purpose, lowering residual noise for sensitive IEMs Head-Fi, Sep 2018. He gave the low-gain residual noise as 1.6uV in one 2018 post Head-Fi, May 2018 and 1.7 uV in others Head-Fi, May 2018Head-Fi, Sep 2018, calling it the lowest of any DAC he had designed Head-Fi, May 2018Head-Fi, May 2018.

His advice on which mode to use, by date: in late 2018, "use low gain when you need the lower noise" Head-Fi, Nov 2018; in February 2020, low gain "is intended for IEMs where the residual noise could be an issue"; in low gain, stay at or below -3L, as distortion and clipping rise above it Head-Fi, Feb 2020. In April 2022 he said "Sure you can use sensitive IEMs - but use the low gain setting as this will limit the power and reduce background static noise" Head-Fi, Apr 2022, and that TT2 should be in high gain unless you hear its hiss with sensitive IEMs Head-Fi, Apr 2022. In September 2020 he warned that a pop or click when TT2 is not last on, first off "might cause damage problems with ultra sensitive IEMs on high gain mode" Head-Fi, Sep 2020.

Mojo 2 (2022 to 2023). In December 2022 he said Mojo 2 has no analog gain changes, only a digital volume control, and that he extended its low-volume range after an owner wanted to run very efficient IEMs lower Head-Fi, Dec 2022. In June 2023 he said overall gain sets noise ("Double the gain, you double the noise"), and that Mojo 2's 5.2 V RMS capability increases background noise Head-Fi, Jun 2023.

Attenuators

For Hugo in July 2014 he said an in-line attenuator "will eliminate the hiss, but I can't say whether it will affect the SQ" Head-Fi, Jul 2014, and in September 2014 that it "may upset SQ" Head-Fi, Sep 2014. In June 2023, in the Mojo 2 thread, he said output attenuators reduce noise but add output impedance, so "will make the IEM or HP sound softer and warmer", and that they degrade transparency and "create dynamic SQ problems" Head-Fi, Jun 2023.

Hum is a different problem

For a buzz or hum, he blamed earth leakage current flowing through the IEM via your body, and advised grounding the unit: on Hugo 2 in February 2020 Head-Fi, Feb 2020 and on TT 2 in 2020 Head-Fi, Apr 2020Head-Fi, Jun 2020. For Mojo 2 in February 2022 he said mobile-phone (2G) buzz cannot be fully eliminated because some pick-up is via the IEM itself Head-Fi, Feb 2022.

What he has not said. For Mojo 2 he gave a dynamic range figure (125 dB A-weighted) Head-Fi, Feb 2022 but, no microvolt residual-noise figure and no statement on whether particular IEMs hiss on it Head-Fi, Jun 2023. This archive gives no microvolt figure for the original Mojo or for TT 2 in high gain, and no list of which IEMs hiss on which model Head-Fi, Feb 2022.

Quotes

“The Shure SE846 is very sensitive, the most sensitive I have seen, and Hugo's residual noise at 5uV A wt. would be just audible.”2014-09-02 Head-Fi, Sep 2014

“Sure you can use sensitive IEMs - but use the low gain setting as this will limit the power and reduce background static noise.”2022-04-09 Head-Fi, Apr 2022

“unless you have hyper sensitive IEM's you will never hear it - but the real reason is distortion”2017-03-15 Head-Fi, Mar 2017

“Life would be an awful lot easier if IEM manufacturers did not have such crazy sensitivity.”2023-06-21 Head-Fi, Jun 2023

Dated positions

Caveats and open points

• Several Hugo TT 2 forum dates are estimated from post IDs.
• His TT 2 low-gain figures vary between posts: 1.6 or 1.7 uV residual noise Head-Fi, May 2018Head-Fi, Sep 2018, and 2.5 V Head-Fi, Jun 2018 or about 3 V RMS Head-Fi, May 2018Head-Fi, Apr 2019 maximum output.
• Hugo, Hugo 2, Dave and TT 2 noise figures come from his forum posts; none of the cited items gives a hiss threshold for a named IEM other than the Shure SE846 on Hugo.
• This archive has no microvolt residual-noise figure for Mojo or Mojo 2 and no list of IEMs that hiss.

Topics: Driving headphones and IEMs, Headphone, IEM and speaker pairing