JDS Synapse & Neutron V1 USB Isolators Review

[dmitrykos]

@dmitrykos Why is lower pF value better? Do you know what it is for the HS01?

I believe the lower the value the less voltage is induced due to parasitic/isolation capacitance on output of isolator. The effect of it is a kind of high pass filter when higher value allows more DC component on output side. I have no experience regarding this parameter and its affect on audio performance of the connected device, maybe it matters more the measurement equipment. This discussion gives practical example:

Do high impedance nodes have higher noise due to inductive coupling as well?

This link clearly explains how high impedance nodes are susceptible to capacitive coupling noise. Is the same true for inductive coupling? As per my understanding, inductive coupling would induce...

electronics.stackexchange.com

Have no idea about HS01.

 

[Ein]

Ok, and now blind test. With and without. For sure, no change. Too small to be hear.

 

[staticV3]

Ok, and now blind test. With and without. For sure, no change. Too small to be hear.

Indeed, isolators won't do anything if there's no underlying issue, like in Amir's measurement setup.

They're an effective solution to a particular, very real and quite audible problem.

 

[Ein]

Indeed, isolators won't do anything if there's no underlying issue, like in Amir's measurement setup.

They're an effective solution to a particular, very real and quite audible problem.

...a band-aid for the previously broken one. Ok. But, next please.

 

[bachatero]

...a band-aid for the previously broken one. Ok. But, next please.

Why does it have to be broken? Some bigger, more expensive things like lab equipment and guitar amps are sensitive to power noise but nobody considers them broken.

 

[dmitrykos]

...a band-aid for the previously broken one. Ok. But, next please.

I can hear ground loop induced noise very easily with any connected USB DAC, including Apple USB-C dongle. Just at normal volume with my external speakers. Ground loop is not about broken USB devices including DACs, it affects anything unless ground is physically disconnected.

 

[Oldson]

following this review i have ordered a V1.
thanks Amirm

unfortunately the V1 made no difference to the noise i was getting from my pc.
have gone back to using my isomax rca isolator instead.

 

[dmitrykos]

unfortunately the V1 made no difference to the noise i was getting from my pc.
have gone back to using my isomax rca isolator instead.

Most likely you have ground loop between DAC and amplifier which is fed from the DAC via RCA connection (I guess). And this ground loop induces most audible noise in your setup. If PC is AC powered and USB DAC AC-powered too then using USB isolator between PC and USB DAC would still be beneficial (as per discussion in the thread), unless PC or DAC have isolated power source (one of them, for example as we learned here Apple MacBooks have isolated power adapter).

Probably between PC and DAC you either do not have ground loop due to one of them having isolated power source, or the induced noise level is low. You could try improving power source of receiver (destination of RCA connection) to avoid using RCA isolator which affects audio quality (also discussed on ASR). If you have AC-powered USB DAC and RCA isolator solved the noise for you then using USB isolator could help only in case ground loop was formed via PC -> DAC -> Amp (so you break it over USB connection) and most likely it was not the case in your system or induced ground loop noise between PC and DAC is low (it can be confirmed by measurements, if you record output from RCA with another PC with/without Isolator and then compare noise floor of the spectrum).

 

[dmitrykos]

@Oldson I thought a little more. You could try getting isolated power supply for your USB DAC device and keep using Isolator V1 to have isolated USB path. With this approach RCA isolator will not be needed as DAC will be completely isolated from AC and PC (DAC will only share ground with amplifier on another end of RCA connector) and as a result audio quality will be improved due to absence of RCA isolator on the analog audio path.

 

[Oldson]

@Oldson I thought a little more. You could try getting isolated power supply for your USB DAC device and keep using Isolator V1 to have isolated USB path. With this approach RCA isolator will not be needed as DAC will be completely isolated from AC and PC (DAC will only share ground with amplifier on another end of RCA connector) and as a result audio quality will be improved due to absence of RCA isolator on the analog audio path.

have been playing around with my system for the last few hours, since my last post and have made some progress.

my setup is a bit over complicated atm as i have 3 headphone amps temporarily.
so the output from dac (rca not xlr) is taken to an input on my integrated amp.
tape out from there to Schitt Lokius.
output from Lokius to Isomax isolator.
output from Isomax using Y splitter to Midgard and Icon HP8.
loop out from HP8 feeds my 3rd headphone amp , NJC ref amp.

(i do plan to sell one of the SS amps, just trying to decide which one)

anyway, without the isomax, i get a fairly loud hum and hiss. (admittedly at higher vol)
earlier today i read that the isomax "could" cause a loss in sound quality in the lower frequencies.
this is not what i was led to believe when i bought it.

so anyway, earlier i stripped down the complete setup and started again, listening for issues when adding any item.
to my surprise i found the culprit to be a set of chord chrimson interconnects that ive had donkeys years.
basically with just any single amp connected to the dac, i would get an incredible hum as soon as dac was turned off!
tried all my other interconnects in same way and all totally silent.

have set everything back up to enable all 3 amps and lokius and i only get minor noise at very high volumes on the HP8 now.
no isomax in chain now.
i have left the V1 connected for now, may try removing it later to see if anything changes.

i am looking to get a new pc next year and will try to get a fanless one.
will keep the V1 and Isomax in a draw, just in case.

cheers for the advice, btw

 

[dmitrykos]

culprit to be a set of chord chrimson interconnects that ive had donkeys years

Great that you managed to nail the bug in the system!

i am looking to get a new pc next year and will try to get a fanless one.
will keep the V1 and Isomax in a draw, just in case.

In this case USB isolator in the connection chain (PC -> USB DAC) will relax the requirement for an isolated power source of the new PC.

 

[HaveMeterWillTravel]

This is a review and detailed measurements of the JDS Labs Synapse and Neutron Hifi V1 USB isolators. They were both sends to me by the respected companies. Synapse costs US $69, and Neutron US $118.
View attachment 412507

USB isolation test? My first thought would be to perform IEC 60747-17 and 607475-5 with a relatively easy test level of 2.5 kVrms injected to the input signal while monitoring zero effect on the connected device.

 

[HaveMeterWillTravel]

I have used on multiple occasions (including NQA-1 applications) the following reference/development board from Analog Devices for USB isolation.

https://www.analog.com/en/resources/evaluation-hardware-and-software/evaluation-boards-kits/dc2438a.html

I have tested it well in excess of it's rated transient conducted immunity of 50 kV/uSec and in a magnetic field in excess of 30A/m.
The only limitation is if data rate of greater than USB 2.0 high speed is required. ( Not likely for audio signals )

 

[HaveMeterWillTravel]

They provide no isolation. And the filtering they do is only effective at much higher frequencies, hundreds of Kilohertz whereas these products are operating in audio band.

Sorry Amir, but I have to correct you. The lowest and original speed USB 1.0 operates at 1.5 Mbps. So, inline ferrite beads (not circumferential) can certainly have an effect. Is it necessary from an audible viewpoint? I haven't the slightest clue.

 

[dmitrykos]

USB isolation test? My first thought would be to perform IEC 60747-17 and 607475-5 with a relatively easy test level of 2.5 kVrms injected to the input signal while monitoring zero effect on the connected device.

The review was testing the effect of USB isolator on USB DAC's audio performance, so it was practical test towards application of USB isolator on specific problem domain - elimination of ground loop induced noise and how it affects cleanness of analog audio output.

The only limitation is if data rate of greater than USB 2.0 high speed is required. ( Not likely for audio signals )

LTM2894 supports max Full Speed USB, therefore it is not really useful for hi-res USB DACs which are High Speed USB devices if support PCM frequency >= 192 kHz. Full speed USB allows max 96 kHz PCM.

The lowest and original speed USB 1.0 operates at 1.5 Mbps. So, inline ferrite beads (not circumferential) can certainly have an effect.

They do not affect audible range (generally: 1-22000 Hz), therefore Amir's statement is correct actually. Excessive usage of ferrite beads could corrupt USB signal integrity though and we shall not forget that audio data is sent to USB DACs using Isochronous USB transfer which does not have error correction, therefore it is always better to use specialized isolating solutions instead of inventing the wheel and causing issues in other areas.

 

[HaveMeterWillTravel]

The review was testing the effect of USB isolator on USB DAC's audio performance, so it was practical test towards application of USB isolator on specific problem domain - elimination of ground loop induced noise and how it affects cleanness of analog audio output.



LTM2894 supports max Full Speed USB, therefore it is not really useful for hi-res USB DACs which are High Speed USB devices if support PCM frequency >= 192 kHz. Full speed USB allows max 96 kHz PCM.



They do not affect audible range (generally: 1-22000 Hz), therefore Amir's statement is correct actually. Excessive usage of ferrite beads could corrupt USB signal integrity though and we shall not forget that audio data is sent to USB DACs using Isochronous USB transfer which does not have error correction, therefore it is always better to use specialized isolating solutions instead of inventing the wheel and causing issues in other areas.

Note: I did not make a statement that adding ferrites was the appropriate post hoc solution (I'm of the opinion they generally should be the last resort of mitigation components.) Only that they can have an affect in the bandwidth range that USB signals operate at.

There often is little correlation between an EMI source's frequency and the resultant induced anomalous behavior.
For example, some years ago I was brought in to help resolve conducted susceptibility failures for analog isolators during compliance testing. The designers did not understand how test stimuli in the 10 MHz range could cause anomalous DC behavior despite there being 10 Hz low pass filters. The actual issue was RFI rectification of the initial instrumentation amplifier stage. Chip beads on the input traces were part of the solution.

My point being that the frequency range of EMI mitigation techniques (such as ferrites) are not constrained by the bandwidth of the analog signal. The USB signals are operating at a much higher frequency/bandwidth than the 1-22000 Hz of the audio signal. Several ferrite materials cover the 100 kHz to low MHz range.


Point taken on the higher frequency PCM now available in audio. There are other USB higher speed isolators with the testing pedigree out there, I just picked a quick example i'm used to using.

 

[dmitrykos]

The actual issue was RFI rectification of the initial instrumentation amplifier stage. Chip beads on the input traces were part of the solution.

In case of Isolator V1 input/output USB connections are protected with general-purpose EMI and Radio-Frequency Interference (RFI) filter + ESD. The same approach is used for Neutron HiFi DAC V1.

Several ferrite materials cover the 100 kHz to low MHz range.

Yes, and thus they do not directly affect the range of analog audio frequencies which we can hear. Some indirect effect may still exist (the case you mentioned) if for example suppressed EMI was inducing some noise/circuit misbehavior which could leak noise into lower audio frequency band but that it is a matter of coincidence than guaranteed effect.

 

[JasonC331]

I'll just ask this here: I don't see on the website which way the device goes in the chain. The device has 1 port on one side and 2 on the other. What flow direction should it be going? Maybe I am overlooking something straightforward.

The device took a while to get here, boy it is small, and no USB C cables of any kind. The topping device came with some basic short cables

 

[HaveMeterWillTravel]

In case of Isolator V1 input/output USB connections are protected with general-purpose EMI and Radio-Frequency Interference (RFI) filter + ESD. The same approach is used for Neutron HiFi DAC V1.



Yes, and thus they do not directly affect the range of analog audio frequencies which we can hear. Some indirect effect may still exist (the case you mentioned) if for example suppressed EMI was inducing some noise/circuit misbehavior which could leak noise into lower audio frequency band but that it is a matter of coincidence than guaranteed effect.

Having EMC tested hundreds of different analog systems, outside of power line related frequencies; there is very poor correlation between the frequency of the disturbance frequency and the manifested anomaly in the EUT.
If there is a significant correlation; it is more probable to be an issue of cross talk in the device itself or other such effects.

 

[dmitrykos]

I'll just ask this here: I don't see on the website which way the device goes in the chain. The device has 1 port on one side and 2 on the other. What flow direction should it be going? Maybe I am overlooking something straightforward.

The device took a while to get here, boy it is small, and no USB C cables of any kind. The topping device came with some basic short cables

There is User Manual in Details page of the web site. Details page also lists the package contents which is just the device unit. Many users use own cables, therefore instead of bundling some basic cable which would create additional trash in the World there are more advanced USB cables offered at additional cost.

The side wit 2 ports is the one to which you connect your USB device (USB DAC, ...), and the side with one port is connected to USB host (PC, TV, Streamer, ...). 2-nd Micro-B port is only for additional isolated power delivery, in case USB DAC requires >400 mA. It is explained in User Manual.