Does impedance mismatch cause hum/noise?

[aussievintage]

3 minutes ago, pulinap said:

So why are most Hifi manufacturer's still stick with RCA?

It's cheap,  what most consumers are used to,  and most of the time causes no problems.

[stereo coffee]

41 minutes ago, Spider27 said:

I checked my other DVD & BlueRay players and both use 2 Pin power plug. Powercord is fixed into chassis so cannot be used 3rd party IEC cable. They are AU model selling here in AU from retailers. Does this mean these are not really safe to use or these are internally grounded somehow so okay to use here in AU?

 

They are safe to use, if they comply with double insulation standards.

 

I would suggest you take up question to their manufacturers if you need evidence, other than the double insulation label-  of their compliance to that standard. 

 

Your post raises the question that internal grounding somehow assures safety. No it is rather the products Insulation that should assure safety in this case, where chassis safety earth grounding is not provided. And more so it is a connection from the chassis to safety earth in other equipment that is NOT double insulated, exiting via the mains lead that assures safety.  

 

Which is not to say that the chassis cannot be externally earthed on all panels  to comply with Class 01 requirements as well. https://en.wikipedia.org/wiki/Appliance_classes#Class_0I            examples where this might be needed are in areas subject to lightning strike, or as I alerted to before where a rogue piece of equipment fails double insulation standards and is also not Class 1 compliant by providing a mains cord earth connection typified by the IEC fixture, and is resident in your audio system.  

 

However the manufacturer has met their obligations to safety for the product to be sold to you if it is double insulated and actually complies with that standard . 

 

Whilst we have discussed earthing, another requirement is equipment have suitably rated fuses or circuit breakers to disconnect mains voltages where minor or major faults occur.    

 

 

Edited October 7, 2019 by stereo coffee

[stereo coffee]

44 minutes ago, pulinap said:

@March Audio thanks for the very simple explanation and superb diagram.

 

So why are most Hifi manufacturer's still stick with RCA?

 

Also if one component has RCA input and the other has balanced (and RCA) out put, can I use the balance out to RCA in?

 

@aussievintage  and @stereo coffee thanks for the very insightful input.

 

Cheers

Good question. The RCA is a poor connector for audio for a number of reasons ,

1.  Because it makes connection to positive before ground, which can lead to end users being confronted with connection disconnection noise

2. It lacks a tightening mechanism  - although seen and offered in the more expensive types via the earthing collar  

3. its widespread acceptance, has led to incorrect use with digital cables - where a BNC is the better choice.  a RCA is not compliant as a 75 ohm      connector, although some manufacturers will try to convince you otherwise.  

 

Regarding mismatching RCA and XLR,   XLR is a balanced standard plug, vs a RCA which is unbalanced. Your equipment should offer instead XLR out to XLR in. If you invite using XLR to RCA be aware it cannot transfer balanced audio properly and is a no benefit solution for creating a mismatch of those interfaces:    

http://www.aviom.com/blog/balanced-vs-unbalanced/

 

 

 

 

Edited October 7, 2019 by stereo coffee

[Spider27]

13 hours ago, stereo coffee said:

Suggest the OP makes a few diagrams, and lets us know of how his audio gear is presently connected, as it suggests a error there that should hopefully easily reveal itself. Certainly a isolation transformer is a grand solution if all else fails.... but I just do not like band aid solutions.   

 

Here is my quick humble diagram. 

 

Edited October 7, 2019 by Spider27

[March Audio]

1 hour ago, stereo coffee said:

You sadly are only partially quoting me,  What actually happens  with lower current carrying capacity equipment which is NOT to excuse it  ,which is why I used the wording ( the part you did not quote )  that they "pretend to use double insulation " is shown in the attached images. 

 

Can you see how this one fails in the images, despite the double insulation symbol ? 

"The requirements are:  https://en.wikipedia.org/wiki/Appliance_classes#Class_II

A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (ground).

 

The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having at least two layers of insulating material between live parts and the user, or by using reinforced insulation. "

 

It also lacks any label referring to not to open chassis -no user serviceable parts inside. 

 

Yes it should have a cover over the live connections board AND a second cover over the entire power supply board, and the fixture to chassis keeping the board in place should be be insulated itself, rather than relying on the pcb as one of the insulation layers. 

 

Whilst I am here, another area where manufacturers (even the best) get earthing compliance short changed, is to no have the bottom plate of a chassis correctly earthed, but the metal above at the front or on the sides is painted and therefore parts of the chassis, are not at the same electrical potential as the earthed metal.  ASR ( Audio Science Review ) always picks this up.   

 

 

Is there a 6mm gap from any live part to the case? Then further insulation is not required. 

[stereo coffee]

1 minute ago, March Audio said:

 

Is there a 6mm gap from any live part to the case? Then further insulation is not required. 

You are missing that it lacks a "Do not open chassis no user serviceable parts inside label on its rear panel" hence it is NOT compliant as a double insulated identified product.   

[stereo coffee]

7 minutes ago, Spider27 said:

Here is my quick diagram.  

What is label LPS ? 

[Spider27]

12 minutes ago, stereo coffee said:

What is label LPS ? 

Linear Power supply output 5v.

[March Audio]

11 minutes ago, stereo coffee said:

You are missing that it lacks a "Do not open chassis no user serviceable parts inside label on its rear panel" hence it is NOT compliant as a double insulated identified product.   

Yeah sure, I couldn't see all the labelling on the case 

 

27 minutes ago, stereo coffee said:

Good question. The RCA is a poor connector for audio for a number of reasons ,

1.  Because it makes connection to positive before ground, which can lead to end users being confronted with connection disconnection noise

2. It lacks a tightening mechanism  - although seen and offered in the more expensive types via the earthing collar  

3. its widespread acceptance, has led to incorrect use with digital cables - where a BNC is the better choice.  a RCA is not compliant as a 75 ohm      connector, although some manufacturers will try to convince you otherwise.  

 

Regarding mismatching RCA and XLR,   XLR is a balanced standard plug, vs a RCA which is unbalanced. Your equipment should offer instead XLR out to XLR in. If you invite using XLR to RCA be aware it cannot transfer balanced audio properly and is a no benefit solution for creating a mismatch of those interfaces:    

http://www.aviom.com/blog/balanced-vs-unbalanced/

 

 

 

 

 

Agree with all of this except one thing.  You can retain most of the benefits of a balanced input if you have a single ended source so long as you use a correctly wired cable. 

 

 

The balanced input measures the voltage difference at the far RCA end and the problematic ground currents flow in the shield and not the low audio conductor. 

[Spider27]

just unplugged LPS to see if it makes any difference but NIL. So it is between amp and CDP. 

 

I can hear this low level hum when I am within 50~60cm from speaker. Further than that, very hard to hear. Since i am listening near-field, I am more sensitive than others.

 

I opened up the lid of CDP last night and took a few shots how ground is connected inside. It looks like toroidal transformer ground wire is soldered to circuit board then wire to ground socket of IEC plug at the back of the unit.

 

 

[stereo coffee]

11 minutes ago, Spider27 said:

Linear Power supply output 5v.

Does the Linear power Supply have a IEC cord 3 pin connection to the power board ? , do you have an image ? 

[aussievintage]

2 minutes ago, Spider27 said:

It looks like toroidal transformer ground wire is soldered to circuit board then wire to ground socket of IEC plug at the back of the unit.

No, I think that ground wire will purely go from the IEC socket to the circuit board, and I expect that circuit board screw connection will be ground to the case, if it is metal, probably a metal post underneath.

[Spider27]

2 minutes ago, stereo coffee said:

Does the Linear power Supply have a IEC cord 3 pin connection to the power board ? , do you have an image ? 

Yes, 3pin and I unplugged it completely and it does not make any difference. Only CDP is connected to power then it makes low level hum.

[stereo coffee]

3 minutes ago, aussievintage said:

No, I think that ground wire will purely go from the IEC socket to the circuit board, and I expect that circuit board screw connection will be ground to the case, if it is metal, probably a metal post underneath.

Good spot, I was on to that too, it appears that there is a label either side of the screw. What brand model is the CDP  ? - time to look at a schematic I think. 

[Spider27]

2 minutes ago, aussievintage said:

No, I think that ground wire will purely go from the IEC socket to the circuit board, and I expect that circuit board screw connection will be ground to the case, if it is metal, probably a metal post underneath.

Yes, it is metal chassis and bottom plate too. Very solidly built unit that sounds great. 

 

Here is a quick summary so far.

 

+ Low level hum is definitely grounding issue

+ Grounding issue is happening between AMP and CDP.

+ 2 Pin powercord eliminate hum (not safe option I guess)

 

Possible solutions discussed so far (If I missed anything please add);

 

+ Use 2 pin powercord (Not Safe... Not Recommended but kill hum) 

+ Use one end ungrounded RCA cable (possible simple option but not sure if this is ok for long term use?)

+ Use isolating transformer (possible frequency alteration)

+ Do surgery by adding capacitors (least attractive option for me)

 

i think that RCA cable with ground signal wire disconnected should work because when I unplugged RCA cable but leave the power cable on then hum disappears. And this also happens when I unplug the power cable but leave RCA cable connected, too. 

 

But, the best way would be finding the cause of this hum and eliminate it after all.

[Spider27]

10 minutes ago, stereo coffee said:

Good spot, I was on to that too, it appears that there is a label either side of the screw. What brand model is the CDP  ? - time to look at a schematic I think. 

 

 

This is exact model. http://opera-consonance.com/products/digital/CD120.html

Not sure if we can find schematics.. 

[pulinap]

48 minutes ago, March Audio said:

Yeah sure, I couldn't see all the labelling on the case 

 

 

Agree with all of this except one thing.  You can retain most of the benefits of a balanced input if you have a single ended source so long as you use a correctly wired cable. 

 

 

The balanced input measures the voltage difference at the far RCA end and the problematic ground currents flow in the shield and not the low audio conductor. 

@March Audio - what does most of the benefit mean...? most importantly what are the benefits left out?

 

Furthermore, would this reduce the chance of ground loop occurrence?

 

Thanks

[March Audio]

55 minutes ago, pulinap said:

@March Audio - what does most of the benefit mean...? most importantly what are the benefits left out?

 

Furthermore, would this reduce the chance of ground loop occurrence?

 

Thanks

I will copy something I wrote elsewhere to save time

 

Contrary to popular audiophile belief, ground (as in a connection to the physical earth and mains electrical safety earth) is not a sink for noise. Noise does not go into it and disappear. A ground connection is not required for any audio or noise reason. If you dont believe that then explain how electronics works quite successfully in portable devices, aircraft or space 

The only reason any audio kit has a ground connection is for electrical safety. Even then Class II devices (have a double square symbol on them) have no earth connection because they are double insulated or have at least a 6mm gap between any live component and the chassis. No single electrical failure inside can cause their chassis to become live.

Physical ground is just used as another conductor. At your local mains transformer (or at your fusebox) the neutral conductor is connected to physical earth. This just provides a fault path to make high currents flow if live connects to ground (equipment chassis) to blow fuses, or these days to make RCDs work.

For domestic audio ground connections are actually *only* a potential source of problems. The ubiquitous RCA interconnect system is fundamentally flawed. You have probably heard of the infamous "ground loop" problem. (see previous posts)

 

 

First audiophile myth to bust is that balanced sounds worse because it has more components and is more complex etc. This is simply not true. All things being equal, with good design balanced or single ended does not sound any worse or better than the other. If you do not believe that then consider the fact that *ALL* professional applications use balanced equipment, including music recording studios. So the music you are listening to at home has been in a balanced system from the microphone through to the  balanced input on the A to D converter. Also most DAC chips have a balanced output that gets converted to single ended RCA for you to use!

 

Balanced (differential amplifiers have a property call common mode rejection.  If we look at a simple balanced input circuit you will see that the Op Amp (the triangle) has 2 inputs, one marked plus and one marked minus. In simple terms the op amp amplifies the difference in voltage between these two connections. The plus keeps the signal in the same phase (non-inverting) whilst the the minus inverts the phase.

 

 

This does an interesting thing, any signal or noise that is present and the same on both input wires (Common Mode) gets cancelled out! This is also why balanced cables have the signal wires tightly twisted together, it makes the noise signals as similar as possible on both wires so the amp will more effectively cancel out noise.

 

 

 

So whilst most of us, most of time get away without any overtly noticeable problems with single ended RCA connections, I guarantee there will be more noise and mains pick up with it compared to balanced. We worry about noise with dacs at ridiculously low numbers and then forget about it all being ruined by the way we connect the components together! So my advice is that if a balanced connection is available, use it.

 

The disadvantage with using a single ended output with a balanced input, as shown in the previous post, is that the effectiveness of the common mode rejection will be reduced.  This is because the two legs of the signal path are not absolutely identical and will have different levels and characteristics of noise on them meaning you wont get perfect cancellation.  However it is still of benefit. 

 

As mentioned, even with an RCA source it should help with those ground noise currents because they no longer flow in the low signal wire, which is whats causing the buzz you hear.
 

 

Edited October 8, 2019 by March Audio

[Guest Muon N']

Try having the Exposure amp plugged directly into a wall socket with the rest from the power board.

[pulinap]

31 minutes ago, March Audio said:

The disadvantage with using a single ended output with a balanced input as shown in the previous post is that the effectiveness of the common mode rejection will be reduced.  This is because the two legs of the signal path are not absolutely identical and will have different levels and characteristics of noise on them meaning you wont get perfect cancellation.  However it is still of benefit. 

 

As mentioned, even with an RCA source it should help with those ground noise currents because they no longer flow in the low signal wire, which is whats causing the buzz you hear.
 

 

@March Audio thanks again taking time to explain.

 

Does this mean it works the other way around - A balance output to single ended input?

 

Also, doe sit affect the sound quality?

 

Cheers

[March Audio]

21 minutes ago, pulinap said:

@March Audio thanks again taking time to explain.

 

Does this mean it works the other way around - A balance output to single ended input?

 

Also, doe sit affect the sound quality?

 

Cheers

If the amplifier has a single ended RCA input then there will be no common mode rejection, so that bit wont work.  In theory I suppose it should help to divert the noise currents away from the signal low.  Never actually tried this in this situation.  You could also try using the CDP balanced out and not connecting the shield wire at the RCA end at all so the high / low balanced just drives the RCA.  However it will work to connect the two units.

Edited October 8, 2019 by March Audio

[pulinap]

2 minutes ago, March Audio said:

If the amplifier has a single ended RCA input then there will be no common mode rejection, so that bit wont work.  In theory I suppose it should help to divert the noise currents away from the signal low.  Never actually tried this in this situation.  You could also try using the CDP balanced out and not connecting the shield wire at the RCA end at all so the high / low balanced just drives the RCA.

Thanks.

 

Actually it would be from Pre balanced out to power RCA in.

 

DAC to pre all balanced, Pre to Power  - balanced out to RCA in

 

 

[Spider27]

39 minutes ago, Muon N' said:

Try having the Exposure amp plugged directly into a wall socket with the rest from the power board.

That is a good idea but one issue. The other wall socket is too far 4m apart and it is already engaged with other electronic equipments.  

[March Audio]

5 minutes ago, pulinap said:

Thanks.

 

Actually it would be from Pre balanced out to power RCA in.

 

DAC to pre all balanced, Pre to Power  - balanced out to RCA in

 

 

 

Edited October 8, 2019 by March Audio

[Spider27]

7 minutes ago, March Audio said:

You could also try using the CDP balanced out and not connecting the shield wire at the RCA end at all so the high / low balanced just drives the RCA.

 

Thank you very much..  Do you mean connect between Consonance CDP with Balanced out (3Pin XLR) to Amp with RCA in but desolder ground wire in RCA socket?  If so, isn't it same as SE out from CDP to Amp with RCA In with ground wire/shield wire lift out?