Topping E70 Stereo DAC Review

[ICIETDIYEUR]

In fact, there is a very simple solution that can be achieved by modifying your existing cables ->

Thus we find ourselves in 'floating ground' in the audio circuit of the device that receives the end where pin 1 is not connected

 

[glicioto]

Almost certainly a ground loop issue (a system problem, not a component problem).

What is your source into the DAC? If A PC connected via USB, try connecting it via toslink. Use a USB to toslink converter if you don't have toslink out of the PC.

the source is a beelink mini-pc with daphile and USB connection. Unfortunately the problem exists and it is hearable even just connecting the E70 to the power amplifier with USB disconnected and without any other connections (just DAC + power amplifier)

 

[glicioto]

Hello.

anticollinet has pointed out exactly the defect you notice with your source (DAC) by talking about a 'ground loop'.

I will try to explain.

In my opinion, as a general rule, a well-designed 'source' is a source that has its 'floating' audio mass.

This is because the ground of an audio circuit should normally be completely isolated from the ground of the chassis.

In the case of joint use with a 'class I' 'receiver' (amplifier), i.e. with a 'ground' conductor for its power supply, you will necessarily create a 'ground loop' if the source does not have its audio ground separated from the ground of the device.

Even when used in conjunction with a 'Class II' 'receiver' (amplifier), i.e. without a 'ground' conductor for its power supply, the link cable(s) can carry unwanted 'interfering' signals through their ground conductor. This is why in the 'professional world', equipment is often equipped with switches called 'ground lifts' that eliminate this problem if it occurs.

In your case, you need to check if the ground of the RCAs, the ground of the XLR or TRS (external metal part) and the ground of the USB socket (also external part) is not in direct contact with the ground of the chassis of the device OR if the latter is 'conveyed' through the conductors present in the link cables.

That's why anticollinet suggests that you first use an optical connection (TOSLINK) to be sure from the start if it doesn't come from the PC via its USB cable, for example.

After this first check, the same procedure should be followed for each link between the devices and the receiver (amplifier).

PS: if you look closely at your MARANTZ PM 7001 amplifier, it is 'class II' (without a ground conductor for the AC socket). I think that's why you don't have a 'ground loop' with this one and the TOPPING E70 DAC which has a ground driver for its mains socket.

Thanks for the comprehensive explanation and for the time spent writing it. The fact is that it is the first time I have such problem. So it is new to me. Power Amplifier has the AC ground connected to the RCA negative (the outer side of the connector). The premamplifier instead has the AC ground disconnected from the RCA (I saw different pictures and they correspond to mine: the AC ground pin is not connected to RCA and chassis). The noise appears also when the DAC is connected (no USB, no Coax, no inputs) to the power amplifier. Should I deduct that the loop originates between the DAC and the power amplifier?

 

[KSTR]

Even in a balanced connection, you should have pin 1 the XLR jack to the audio ground but not to the chassis ground: which is achieved with the 'ground lift' switch on professional equipment and that I also saw on a recent DAC but I don't remember which one...

Sorry, but that's completely the wrong way, creating the dreaded "pin1 problem" (google it, please).

Balancing mains current must never flow through any audio GND.

XLR pin 1 must go directly to the chassis (earth-grounded or not), for all devices. Circuit GND is connected to chassis GND at on single point (for DC and low frequencies), either directly or with some isolation resistance.

 

[KSTR]

In fact, there is a very simple solution that can be achieved by modifying your existing cables ->

View attachment 425389

Thus we find ourselves in 'floating ground' in the audio circuit of the device that receives the end where pin 1 is not connected

That's a very bad workaround (as is any "GND lift" strategy). You are now relying on the CMRR of the receiver instead of trying to bond both pin1 potentials together as much as possible.
It might help a bit in scenarios where pin1 is connected wrongly to the audio GND (see above post).

 

[ICIETDIYEUR]

Yes.

You must therefore use a cable such as I described in my little diagram: the problem will disappear

Once you have noticed this, you will just have to leave this type of cable at the output of your DAC and reconnect your configuration as you described it at the beginning

KSTR will write to KLOTZ to tell them that they have been marketing a (bad) cable to professionals for years that is out of stock at distributors...

Another and better solution because it allows you to use different types of connectors is this one ->

Amazon.com

 

[KSTR]

KSTR will write to KLOTZ to tell them that they have been marketing a (bad) cable to professionals for years that is out of stock at distributors...

Haha! Actually, it wouldn't be the first time I've been consulting professional companies to fix some basic long standing misunderstandings about signal integrity, and pin 1 issues have been very common in the past, almost everybody got that wrong ;-)

Here's some reading on the pin 1 problem, by a true expert, Bruno Putzeys

 

[glicioto]

Ok, made the final test. I disconnected the ground cable from the DAC: basically opened the plug and disconnected the cable. Bum, problem solved. Everything quiet....so what? why only DAC E70 shows this behaviour while the SMSL does not? IS it a DAC issue or I just need to live with it?

 

[ICIETDIYEUR]

Thank you, but personally, I am well aware of Bruno's thoughts on this subject.

He wrote: "Correct shielding practice requires that pin 1 connects to chassis and nowhere else"

That's why I suggested using this type of cable because on old equipment such as the McIntosch amplifier or the SONIC FRONTIERS preamplifier we are talking about here, we are exactly in the case where pin 1 is connected to the audio ground and the chassis when it should only be connected to the chassis.

All you have to do is open these devices to definitively remedy the problem, but this seems, perhaps, to be beyond glicioto's skills.

I was just trying to find a solution that was more within his reach.

As a reminder, he does not experience this problem with a Class II DAC, so he can also strive to use only sources of this type so that the problem does not appear.

However, as you can see, my (very simple) solution seems to have worked well and glicioto seems satisfied so why look elsewhere...

glicioto: your SMSL DAC does not have a ground connector to your AC outlet, that's why.

NB: your DAC TOPPING E70 works perfectly and it has no problem with it, it is simply a combination of equipment that creates this defect and nothing else.

Now you have the right to put thumbs up everywhere (LOL)...
... I don't live for it, just so that people can enjoy listening to their system (as does O-NOORUS )

 

[glicioto]

Thanks

All you have to do is open these devices to definitively remedy the problem, but this seems, perhaps, to be beyond glicioto's skills.

I was just trying to find a solution that was more within his reach.

Thank you. Well open a box and disconnect the ground from the cabinet is actually within my skill. But is it safe? Am I misunderstanding something? The fact is that I am not understanding why you are referring to pin 1....I am using only RCA....Sonic Frontiers has only RCA

 

[ICIETDIYEUR]

I didn't want to talk about your manual skills but your technical skills.

You probably don't have enough of the latter, since I realize that you didn't understand my explanations or maybe I expressed myself badly.

By removing the ground wire from the power conductor that is connected to the chassis, you have the risk of electric shocks in the event of a short circuit in the DAC: this is not a thing to do!

If you only use RCA connections then it is better to buy the box I talked about on AMAZON.

 

[glicioto]

Dear ICIETDIYEUR You are probably referring to yourpost that starts with: In fact, there is a very simple solution that can be achieved by modifying your existing cables ->

I do understand, but I am not using XLR cable....Sonic frontiers only has RCA inputs and I have only RCA. Can I abuse your patience asking to develop a little bit what you mean with "All you have to do is open these devices to definitively remedy the problem, but this seems, perhaps, to be beyond glicioto's skills."....what would be the involved change?

Thanks

 

[antcollinet]

the source is a beelink mini-pc with daphile and USB connection. Unfortunately the problem exists and it is hearable even just connecting the E70 to the power amplifier with USB disconnected and without any other connections (just DAC + power amplifier)

What happens if you also turn off all other electrical gear in the room (especially the PC.) - In fact ideally any other gear connected to the same mains circuit as DAC and amp.

 

[ICIETDIYEUR]

Glicioto: you don't abuse my patience, it's with pleasure that I answer you

I am not going to dwell on a (complex) explanation of the circuits and transformations necessary for your devices but I will take into account your remarks about their use and propose the solution that seems to me to be the most 'rational' but also economical while being technically efficient.

Your two old appliances are reputed, sought-after brands that have a certain quality as well as a significant resale value.

It would rather be 'absurd' to modify them without keeping their original state, which would make them lose value and which will not be without possible risk regarding their respective qualities and performance.

As you only use the RCA connections, I would suggest you instead to use the following equipment which is economically affordable while being technically correct but would also guarantee you a good 'SQ' ->

Audio Isolation Transformer Ground Loop RCA - Audiophonics

This stereo RCA isolation transformer isolates the audio signal in order to considerably reduce interference and therefore noise. This allows a large transmission distance to be achieved without distortion.

www.audiophonics.fr

DYNAVOX Line Audio ground loop isolator Transformer - Audiophonics

This Dynavox GLI2.1 stereo line filter by professional galvanic isolator transformer

www.audiophonics.fr

There are other identical models distributed by other brands by other retailers, in my opinion this is only the most appropriate solution for your use

 

[glicioto]

That sounds very reasonable and available in Europe. Thanks!

 

[Ecaroh]

Ok, made the final test. I disconnected the ground cable from the DAC: basically opened the plug and disconnected the cable. Bum, problem solved. Everything quiet....so what? why only DAC E70 shows this behaviour while the SMSL does not? IS it a DAC issue or I just need to live with it?

You disconnected the ground (third, middle wire) from the DAC power cable, and that solved it? Or something else? If it was that, it means the Topping and the SMSL don’t use the third wire the same way. Entirely possible the third wire connects to nothing in the SMSL.

 

[ICIETDIYEUR]

Be careful because in your DAC it is quite possible that this ground feedback (GND) also exists on the XLR connectors via their pin 1 (that's the reason why I was talking about this one at the beginning).

In this case, you have to 'adjust' the technical detail on the RCA AND the XLR (or TRS when this is the case).

You will agree that it is much easier and less risky (for the device but above all FOR YOUR SAFETY) to use the 'box' I told you about (principle of 'galvanic' isolation by transformers)

 

[Labjr]

Bill Whitlock wrote a great paper on grounding.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.jensen-transformers.com/wp-content/uploads/2014/08/generic-seminar.pdf&ved=2ahUKEwidmKbb7KWLAxUsv4kEHUIiJnQQFnoECBQQAQ&usg=AOvVaw1ybPqvfiEiIwrxWciz1c1j

 

[Adaboy4z]

the source is a beelink mini-pc with daphile and USB connection. Unfortunately the problem exists and it is hearable even just connecting the E70 to the power amplifier with USB disconnected and without any other connections (just DAC + power amplifier)

Its the Beelink PC. I had one and sent it back as it caused/introduced noise into the system.

 

[glicioto]

That sounds very reasonable and available in Europe. Thanks!

Its the Beelink PC. I had one and sent it back as it caused/introduced noise into the system.

Not so sure...the noise appears even with the beelink disconnected. I am prone to agree with ICIETDIYEUR. Maybe in some weeks I'll buy the decouplers he suggested on Audiophonics, just to give a try.