I have finally gotten round to listen to the AQ jitterbug, as a quest to understand where the RF noise problems from the source was coming from - via the mains or the USB.
Firstly - very much - YMWV as RF noise is a funny thing and source noise may affect other parts of the system, so the findings here may well be different in other circumstances.
So I did the tests with just a Win 10 lap-top (jRiver), Dave and pair of Nighthawks, in a hotel in Singapore. The idea was to try to evaluate whether the SQ improvements I heard when disconnecting the lap-top from mains and running off battery was from the USB connection or via the mains supply. Now Dave is galvanically isolated from LF and RF noise, and this makes a huge difference in SQ. But the galvanic isolation is not perfect as there exists a 2pF coupling capacitance. Now you may think 2pF is nothing to worry about; but at 1 GHz it is nearly 80 ohms impedance, so RF noise in the GHz will couple through - and I know that GHz noise is significant in causing noise floor modulation and hence changing the sound quality.
I used my design lap-top, an MSI Intel i7 machine, as it will be noisier than my music lap-top (HP Pavilion) which is very power efficient. This is so it would be easier to hear any changes.
So adding the Audioquest Jitter Bug did indeed improve SQ - it was fairly easy to hear it, with it sounding smoother, warmer, with less sibilance and glare. Instrument separation and focus was better. These are exactly the kind of change I hear with lower RF noise, so it was not unexpected.
Next was to do the listening test with the lap-top on batteries - and then it became impossible to reliably hear the effect of the jitter bug. Additionally, the improvements heard were much smaller with the jitter bug connected when you disconnect the lap-top power. Here is a
rough assessment of SQ performance with 100% for best, 0% for worst:
Lap-top battery power, no jitter bug 100%
- Best quality - no difference with the Jitterbug.
Lap-top battery power with jitter bug 100%.
- Best quality - no difference without the Jitterbug.
Lap-top mains power with jitter bug 75%.
- Good quality - Jitterbug does improve the SQ.
Lap-top mains power no jitter bug 0%.
- Relatively speaking, the worst quality.
So what does this tell us? Basically the most significant path of RF is residual coupling via the USB, not via the mains supply as the jitterbug alone gets you most of the way.
Use the jitter bug for mains powered USB sources - it is worth the small cost.
The best sound is still with a Win 10 lap-top on battery and for critical listening that is what I do. Battery operation and Dave's galvanic isolation means effectively perfect RF noise isolation from the source.
Note also Win 10 is technically better than iOS xx, Android or Linux as these driver less USB's do not guarantee bit perfect data at the DAC; but Chord's Win driver does resend faulty packets, so we can guarantee bit perfect data for Dave. It would be interesting to do a listening test of driver less against Win.
Rob
