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Old 17th July 2017, 05:13 PM   #31
vzaichenko is offline vzaichenko  Russian Federation
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Input Resistor
At the same time - this is not the only solution possible - there are other good ways to arrange grounding the right way.
BTW, in CFA designs, normally having low-impedance feedback networks, this resistor (if used) must be rather low-value (like 2.2R or so).
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Old 17th July 2017, 05:45 PM   #32
Bonsai is offline Bonsai  Europe
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Nice post Valery - you can get 20dB Hum reduction using this technique because of the attenuator action of the HBR.

Using good quality low resistance interconnects also helps to improve things.
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Old 17th July 2017, 05:52 PM   #33
Bonsai is offline Bonsai  Europe
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"A loop must have the shape of a loop. Two shielded cables for a stereo connection (with their shields connected both at the ouput of the source and at the input of the receiver) kept well parallel as already mentionned have not the shape of a loop. "

No - this is not correct.

Any circuit is a loop. Any magnetic field impinging on any part of the circuit - be it between the shield and the central conductor or within the circuit inside either the transmitter or the receiving equipment will generate an EMF that will cause current to flow around the circuit.

The key issues is to keep the LOOP AREA as small as possible and this is the main reason for using interconnect cables that have the signal and return closely coupled in unbalanced connections. Shields have virtually no effect at audio frequencies (different story at RF) - its the fact that the loop area is minimized that reduces hum.
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Old 17th July 2017, 06:05 PM   #34
ctrlx is offline ctrlx  United Kingdom
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can someone post a clear schematic for the grounding in a dual mono psu
(showing amp connections, input conections etc)
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Old 17th July 2017, 06:24 PM   #35
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Bonsai View Post
The key issues is to keep the LOOP AREA as small as possible and this is the main reason for using interconnect cables that have the signal and return closely coupled in unbalanced connections. Shields have virtually no effect at audio frequencies (different story at RF) - its the fact that the loop area is minimized that reduces hum.
I picture the ground loop like a loop aerial and so the larger the area the more interference it can pick up. But you are talking about the send and return loop?
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Old 17th July 2017, 06:39 PM   #36
Bonsai is offline Bonsai  Europe
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The whole thing is a loop. It happens to be constricted through the shielded cable part but it is still a loop but with two lobes - one lobe inside the transmitting side (the source component) and the other on the receiver side (the amplifier).
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Old 17th July 2017, 08:37 PM   #37
forr is offline forr  France
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Hi,
I spent a bit of time reading DiyAudio posts on the subject of ground connections especially those of members Speedskater and Marce because they much refer to experts who have experience not limited to audio. Views are often radically different from those wich are the most popular in audio

Quote:
Originally Posted by Bonsai View Post
Most commercial amps do not connect the RCA shield to ground where they enter the chassis.
So interferences enter the chassis (ref. Keith Armstrong).
Measurements apparatus have their sockets not isolated from the chassis.

Quote:
The shield connection is usually tied to the chassis through a low value cap (~1nF) at the point of entry which at RF makes the shield and the metal housing one conductor - very effective.
More effective is the shield connected to the chassis (many refs)

Quote:
Forr > A loop must have the shape of a loop. Two shielded cables for a stereo connection (with their shields connected both at the ouput of the source and at the input of the receiver) kept well parallel as already mentionned have not the shape of a loop.

No - this is not correct.

Any circuit is a loop. Any magnetic field impinging on any part of the circuit - be it between the shield and the central conductor or within the circuit inside either the transmitter or the receiving equipment will generate an EMF that will cause current to flow around the circuit.

The key issues is to keep the LOOP AREA as small as possible and this is the main reason for using interconnect cables that have the signal and return closely coupled in unbalanced connections. Shields have virtually no effect at audio frequencies (different story at RF) - its the fact that the loop area is minimized that reduces hum.
For the same resistance and connections at both ends, will the current be the same for
- a pair of long wires very close to each other
- and for a pair of shorter wires but separated by a distance such as the loop area is equal to the first pair
?

What would give a stereo unbalanced cable made of two shielded cables as usual but with the shields in electrical contact all the way
?
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Old 17th July 2017, 08:40 PM   #38
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by forr View Post

What would give a stereo unbalanced cable made of two shielded cables as usual but with the shields in electrical contact all the way
?
This would be very good, do you know of such a cable?
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Old 17th July 2017, 08:56 PM   #39
forr is offline forr  France
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Quote:
Originally Posted by vzaichenko View Post
Attached are some input stage fragments from
well-known manufacturers - all of them use this technique[...]

If you assume RCA shield is not connected to the chassis - you will see the ground wires inside the amplifier + two shields of the cable form a pretty evil loop (the longer the cable is - the longer the loop is). This is not the case in case of dual-mono setup with separate grounds - that's why some manufacturers use this configuration. Monoblocks - radical solution of the problem
I do not deny that the Hum Breaking Resistor is used by quite many manufacturers. Are they the majority ?

Many stereo amps with only one power supply do not have it and they are absolutely hum free (my Self Blameless for example).

I hope dual monoblocks builders have better reasons than hum suppression to build them

Quote:
At the same time - this is not the only solution possible - there are other good ways to arrange grounding the right way.
I am interested by all schemes and by comparisons between them.
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Old 17th July 2017, 10:26 PM   #40
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by forr View Post
Hi,
I spent a bit of time reading DiyAudio posts on the subject of ground connections especially those of members Speedskater and Marce because they much refer to experts who have experience not limited to audio. Views are often radically different from those wich are the most popular in audio


So interferences enter the chassis (ref. Keith Armstrong).
Measurements apparatus have their sockets not isolated from the chassis.

More effective is the shield connected to the chassis (many refs)

For the same resistance and connections at both ends, will the current be the same for
- a pair of long wires very close to each other
- and for a pair of shorter wires but separated by a distance such as the loop area is equal to the first pair
?

What would give a stereo unbalanced cable made of two shielded cables as usual but with the shields in electrical contact all the way
?
There are many fine amplifiers out there that use the techniques described that do not have noise problems (hum or RF). They have minimized loop areas, used sound RF filtering techniques, and used HBR (see Valery's list).

I have two signal generators on my bench (ITT and BK) that are in plastic boxes. They have no problems.

I do not understand your last question

You need to separate ground loop noise (hum) and RF noise in the discussion. It may help clarify the subject.
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