XLR input to amp module connections?

[Racheski]

The highlighted portion in yellow is nonsense, right?

 

[March Audio]

Though in my opinion when we are on here chasing the last 0.00001 % THD we should just bin the 1940's technology of single ended RCA as it offers nothing other than nostalgia.

I binned it years ago. When I saw vendors claiming that some carbon/unicorn loaded RCA cable could work magic for only £ 300/Metre while the musicians/studios were using Van Damme star quad for less than £ 2 /Metre.

RCA/phono was cutting edge in the days of the gramophone.
The live pin makes contact first, if someone designed that today we would all roll around the floor laughing.


Don's tin hat awaiting incoming.

Those who still swear by cross ply tyres will be along to swear that RCA is 'good enough'.

Not really, it depends on circumstance. It can cause overt problems if done incorrectly.

However I entirely agree about RCA. You keep hearing arguments that RCA is better and that xlr balanced is more complex and expensive to implement but this is all rubbish. RCA is fundamentally flawed using a signal conductor as the screen. We should bin it.

 

[March Audio]

The highlighted portion in yellow is nonsense, right?
View attachment 79930

I think the whole thing is nonsense. I don't see any real benefit from using Quad cable in RCA.

The screen should be connected at both ends. If you have a ground loop (you will to a degree even it's not an overt hum) the current flowing between the two components in the RCA low outer shell and in this case the blue quad cable generates a voltage. This voltage is proportional to the current and the resistance (impedance). This voltage is noise that is in your signal conductor. It will usually be the mains frequency. So to minimise this noise voltage you need to make the resistance as low as possible. The screen is much lower resistance than the quad signal conductors. It should be used and connected both ends

Basically I wouldn't use this cable. Just a normal coaxial design with heavy guage screen will work better.

 

[Racheski]

I think the whole thing is nonsense. I don't see any real benefit from using Quad cable in RCA.

The screen should be connected at both ends. If you have a ground loop (you will to a degree even it's not an overt hum) the current flowing between the two components in the RCA low outer shell and in this case the blue quad cable generates a voltage. This voltage is proportional to the current and the resistance (impedance). This voltage is noise that is in your signal conductor. It will usually be the mains frequency. So to minimise this noise voltage you need to make the resistance as low as possible. The screen is much lower resistance than the quad signal conductors. It should be used and connected both ends

Basically I wouldn't use this cable. Just a normal coaxial design with heavy gage screen will work better.

This is an image from World's Best Cables on Amazon, btw. They are probably using quad cables because they bought them in bulk, but yeah it doesn't make sense. When you say "screen", this is the same as "shield", right?

 

[March Audio]

That, then, seems to nail the correct connections pretty succinctly. .The shield on the cable from the amp module to the input XLR should be connected directly to the chassis at the nearest practical point -- definitely not to Pin 1.

Not quite, it means the shield from the incoming cable (which is connected to the socket pin1) should be connected to chassis at the nearest point. The xlr sockets I use on our amps actually have sharp pins connected to pin1 built in which pierce the chassis.

The screen from the amp module cable should be connected to chassis elsewhere (non specific) but definitely not pin 1 on the xlr socket.

 

[March Audio]

This is an image from World's Best Cables on Amazon, btw. They are probably using quad cables because they bought them in bulk, but yeah it doesn't make sense. When you say "screen", this is the same as "shield", right?

Yes screen/shield same thing

Quad cable has benefits in balanced systems when you need the absolute lowest noise such as long runs of microphone cable where signals levels are much much lower than the line level component interconnections use. Also in extremely harsh electrical environments. In a domestic environment and short lengths it won't be of any practical benefit.

In the above example the noise created by the ground loop will exceed any benefits of the Quad cable, especially in that configuration.

 

[misterdog]

In a domestic environment and short lengths it won't be of any practical benefit.
/QUOTE]

Though for the £ 1.20/ Metre additional cost of Van Damme quad core, I am happy to pay that premium.

 

[March Audio]

The problem is that Johns test in the above video is not actually representative of a domestic hifi system. He has tested at microphone signal levels which are much, much lower than the line level signals in your system and put that through a mic preamp to demonstrate a point. As I mentioned above use of starquad certainly has benefits in that scenario. However at line level the external noise picked up by normal balanced cables (generally-im sure you can find an exception if you try hard enough) falls below the system noise floor. As such it becomes irrelevant and no practical benefit to use starquad.

I will post a similar video to above to demonstrate later.

 

[March Audio]

Video as promised

 

[misterdog]

Compared to a single conductor or an untwisted balanced pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference. It was invented by Alexander Graham Bell.

For the extra £ 1.20/Metre I'll stick.
Benchmark advocate the use of quad core speaker cable for the same reason.
I've just invested in a DAC with THD+N of 0.00007 % I value the silence.

I feed my signal to monoblock amplifiers and electrostatic loudspeakers, necessitating that the signal cable runs parallel to 2 mains cables, so my system is not your average set up, though not unique.

I have some 20M of signal cable so the additional cost of using starquad cable was £ 24.

 

[waynel]

For the extra £ 1.20/Metre I'll stick.
Benchmark advocate the use of quad core speaker cable for the same reason.
I've just invested in a DAC with THD+N of 0.00007 % I value the silence.

I feed my signal to monoblock amplifiers and electrostatic loudspeakers, necessitating that the signal cable runs parallel to 2 mains cables, so my system is not your average set up, though not unique.

I have some 20M of signal cable so the additional cost of using starquad cable was £ 24.

Canare starquad only $0.59 per foot in the USA in small quantities and less by the roll. It does roll off highs faster than non starquad if you are using 100’s of feet as the capacitance per meter is roughly 50% higher than non starquad cables.

 

[misterdog]

AHB2 in the US is £ 2250, in the Uk it is .........£ 3500.

which is why I don't yet have one.

Canare starquad only $0.59 per foot in the USA

That's nuts, I may have to move. Though our 'free' healthcare needs to be paid for somehow..

 

[March Audio]

For the extra £ 1.20/Metre I'll stick.
Benchmark advocate the use of quad core speaker cable for the same reason.
I've just invested in a DAC with THD+N of 0.00007 % I value the silence.

I feed my signal to monoblock amplifiers and electrostatic loudspeakers, necessitating that the signal cable runs parallel to 2 mains cables, so my system is not your average set up, though not unique.

I have some 20M of signal cable so the additional cost of using starquad cable was £ 24.

Yes agreed there is nothing wrong with using it, no disadvantage, but equally quad is very unlikely give you any practical advantage. I just wanted to point out that the Benchmark video could be a little misleading if you dont appreciate technically what they are doing there. It gives the impression that star quad is going to make significant improvements. Their video is absolutely correct in the context they have configured it, but thats not what goes on in a domestic line level system.

Remember in the video I put a transformer right on top of the cable, its radiated magnetic field is much higher than that of a mains cable.

0.00007% is -123dB. We saw pick up levels of -145dB ( 0.000005% - yes an extra zero!) in the video. So normal balanced cable is performing way better than the noise floor in your system.

I also advocate the use of Canares 4S11 quad speaker cable, less about noise more about low inductance. Its what we sell.

 

[bigguyca]

Yes agreed there is nothing wrong with using it, no disadvantage, but equally quad wont give you any practical advantage. I just wanted to point out that the Benchmark video could be a little misleading if you dont appreciate technically what they are doing there. It gives the impression that star quad is going to make significant improvements. Their video is absolutely correct in the context they have configured it, but thats not what goes on in a domestic line level system.

Remember in the video I put a transformer right on top of the cable, its radiated magnetic field is much higher than that of a mains cable.

0.00007% is -123dB. We saw pick up levels of -145dB ( 0.000005% - yes an extra zero!) in the video. So normal balanced cable is performing way better than the noise floor in your system.

I also advocate the use of Canares 4S11 quad speaker cable, less about noise more about low inductance. Its what we sell.

Towards the end of the video John lays a power cord on top of the two different cables. Have you ever noticed that there are power cords in domestic environments? Do you understand that there are electric and magnetic fields around those power cords; think Maxwell's equations, basic stuff? Do you realize that these fields can be quite intense close to the power cords?

Have you ever noticed that at the back of a set of shelves with electronics there are often power cords close to signal cords? Have you ever noticed that on the floor around a set of domestic electronics there are often signal cables close to power cords?

Why do you believe these power cords in domestic environments will not have the same effect on signal cables as John demonstrated in the video. This is, power cords that are very close to signal cables?

 

[March Audio]

Towards the end of the video John lays a power cord on top of the two different cables. Have you ever noticed that there are power cords in domestic environments? Do you understand that there are electric and magnetic fields around those power cords; think Maxwell's equations, basic stuff? Do you realize that these fields can be quite intense close to the power cords?

Have you ever noticed that at the back of a set of shelves with electronics there are often power cords close to signal cords? Have you ever noticed that on the floor around a set of domestic electronics there are often signal cables close to power cords?

Why do you believe these power cords in domestic environments will not have the same effect on signal cables as John demonstrated in the video. This is, power cords that are very close to signal cables?

With respect Big you have missed the fundamental point.

Johns video was testing at MICROPHONE signal levels. These are MUCH MUCH MUCH LOWER than the levels found in component to component line level connections. Therefore very small levels of noise have more of an impact on the small microphone signals than on the line level signals.

The effects are absolutely still there, they will still have the same effect, its just that they are insignificant in level compared to the high signal levels involved.

Please read my comments and watch the video again.

Just for reference my background is instrumentation and data acquisition at Rolls Royce Aero engines. I have been dealing with acquiring, recording and analysing very low level audio frequency signals (strain guage, thermocouple, accelerometer etc etc) out of extremely harsh mechanical and electrical environments using very long cables for decades.

Johns video is excellent and correct at showing what star quad cable does, however it is not correct to interpret that the dramatic effect shown is relevant to what happens in a high signal level system.

 

[tmtomh]

Not quite, it means the shield from the incoming cable (which is connected to the socket pin1) should be connected to chassis at the nearest point. The xlr sockets I use on our amps actually have sharp pins connected to pin1 built in which pierce the chassis.

The screen from the amp module cable should be connected to chassis elsewhere (non specific) but definitely not pin 1 on the xlr socket.

So for those of us who are really thick, is this correct:

1. The XLR jack's pin 1 should be connected to the chassis, so that the incoming XLR interconnect cable's shield, which connects to pin 1, proceeds to also connect to the chassis.
2. The cable going from the amp module to the XLR jack should have its shield connected to the chassis, but its shield should NOT be connected to pin 1 of the XLR jack.

Yes? If so, then is the idea to ground both cables to the chassis but to avoid their shields being connected directly to each other via pin 1 of the XLR jack? To put it differently, if both are connected to the chassis AND to pin 1, is that double connection what potentially can cause a ground loop?

 

[littlejoe]

Their video is absolutely correct in the context they have configured it, but thats not what goes on in a domestic line level system.

Johns video was testing at MICROPHONE signal levels. These are MUCH MUCH MUCH LOWER than the levels found in component to component line level connections. Therefore very small levels of noise have more of an impact on the small microphone signals than on the line level signals.

The effects are absolutely still there, they will still have the same effect, its just that they are insignificant in level compared to the high signal levels involved.

Thanks for the video and the good points. Doesn't what you are saying here also show that the current dust up going that I have been reading about the Pin 1 issue is also much to do about nothing? A few extra CM of wire in an amp going to ground will not make any difference in line level connections.

 

[March Audio]

Thanks for the video and the good points. Doesn't what you are saying here also show that the current dust up going that I have been reading about the Pin 1 issue is also much to do about nothing? A few extra CM of wire in an amp going to ground will not make any difference in line level connections.

Good question, but no it's a different issue. Tied up at the moment, I will try and expand on it later, but suffice to say that it has been considered a significant enough (and misunderstood) problem for the AES to issue a standard which describes correct wiring practice; AES48.

 

[misterdog]

Great article by Bruno Putzeys here. Even has some audio humour thrown in.
https://www.edn.com/the-g-word-how-to-get-your-audio-off-the-ground/

When you get to section 4 there is a preamp to build which costs peanuts. Clever engineering by Bruno allows the use of a £6 car stereo potentiometer to produce results you would pay £ 00000 for.

As I see it the shield of the balanced cable is connected to metal shield around your audio components but not to the ground of the PCB where your delicate audio signals are.

 

[boXem]

Clever engineering by Bruno allows the use of a £6 car stereo potentiometer to produce results you would pay £ 00000 for.

Although I tend to define myself as a Bruno fanboy, this design has a huge weakness: if the pot track breaks open, the op-amp will be open loop, which could have catastrophic consequences.
As a side note the DC removal circuit from this preamp is the same as the one used in the NAD M22.