Measuring an UCD 180 I was just testing if my crosstalk was still ok and I was bit suprised to see that touching the wire tree made the crosstalk differ from 90db to 60db(@15khz). So I made a different input cable.
I think this only applies to people using 1 transformer with 2 power supplies and using single pole inputs.
I think this only applies to people using 1 transformer with 2 power supplies and using single pole inputs.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
trying to:
explain that in such a setup, 1 transformer 2 bridge rectifiers, 1 for each channel, 4 caps, 2 for each channel the original Hypex input cable says you have to connect the - input wire to shielding of the input cable at the input device which is on the back of the housing. This not a sym. input device but a standard cinch device. In that case with the Hypex recommendation you can expect microphonic cable sensitivity. It means it is very susceptable for EMI(electr.magn. interf.) hence your crosstalk will only depend how you position your cabling. What I did was to put the - input on the ground pin with a 10 ohm resistor in series. Also the input cable screening is connected to the 10 ohm resistor.
This makes the input cable almost insensitive for EMI hence your crosstalk goes from -60 to -90Db@15khz.
BTW case earthpoint is just at the 0V position in the middle of the Caps.
Bert
An externally hosted image should be here but it was not working when we last tested it.
explain that in such a setup, 1 transformer 2 bridge rectifiers, 1 for each channel, 4 caps, 2 for each channel the original Hypex input cable says you have to connect the - input wire to shielding of the input cable at the input device which is on the back of the housing. This not a sym. input device but a standard cinch device. In that case with the Hypex recommendation you can expect microphonic cable sensitivity. It means it is very susceptable for EMI(electr.magn. interf.) hence your crosstalk will only depend how you position your cabling. What I did was to put the - input on the ground pin with a 10 ohm resistor in series. Also the input cable screening is connected to the 10 ohm resistor.
This makes the input cable almost insensitive for EMI hence your crosstalk goes from -60 to -90Db@15khz.
BTW case earthpoint is just at the 0V position in the middle of the Caps.
Bert
sorry, mod. one
Twisted the output and +and- psu cables also. Quite difficult, they are thick ones. 4mm
It does sound different now but I don't know if its the twisting or the cable mod? It sounds more friendly now..........softer...ah well, different.
An externally hosted image should be here but it was not working when we last tested it.
Twisted the output and +and- psu cables also. Quite difficult, they are thick ones. 4mm
It does sound different now but I don't know if its the twisting or the cable mod? It sounds more friendly now..........softer...ah well, different.
here is a scope picture, noise level is about 10mv, than crosstalk is about 10mv while the active channels pumps out 100V at 15khz on 8 ohms. LF filter is 50khz. Input is loaded with 2k5(my passive pre).
When I did a long listening test the soundstage is much better, even the radio sounds better.
20mv/div.
15khz crosstalk
noise level
When I did a long listening test the soundstage is much better, even the radio sounds better.
20mv/div.
15khz crosstalk
An externally hosted image should be here but it was not working when we last tested it.
noise level
An externally hosted image should be here but it was not working when we last tested it.
Could you explain just how you originally connected the input cable to the RCA chassis parts? (i.e. before you made this mod). Please do not reply "As recommended by Hypex" but draw your own diagram and explain in your own words how the original configuration was.
It seems to me there must have been a problem there to begin with. Opening the shield connection increases RFI sensitivity because whatever happens to the shield efficiently couples into the signal conductors. Likewise, preventing the flow of HF current through the shield effectively allows external magnetic fields to create a voltage differential between the shield and the signal wire.
The mention of microphony in the discussion is indicative of a certain degree of confusion, one which I'd like to clear up.
It seems to me there must have been a problem there to begin with. Opening the shield connection increases RFI sensitivity because whatever happens to the shield efficiently couples into the signal conductors. Likewise, preventing the flow of HF current through the shield effectively allows external magnetic fields to create a voltage differential between the shield and the signal wire.
The mention of microphony in the discussion is indicative of a certain degree of confusion, one which I'd like to clear up.
Bruno Putzeys said:
Original was the standard Hypex cable on the UCD end and on the cinch part I've put the red cable end in the middle of the cinch bus, black one to the the cinch part housing(ground side) and the cable shielding went here also in series with a 10 ohms resistor.
If I would connect the shield to the cinch parts housing directly I had a humm.
this is the old situation
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m.parigi said:Situation Normal All F....d Up
The only reason I can think of in the old situation(input cable grounding) is that because of the changed gain resitor from standard 560 to 180 ohms to increase input sensitivity the opamp(AD8620) becomes prone to capative coupling. After having the input cable changed and listened to since yesterday I can only say it sounds much better. So whatever the reason may be.........it is an absolute improvement.
Bqt,
May I suggest you would get better crosstalk results if you eliminated the "rats nest" of closely coupled power supply,signal and loudspeaker cables!
You would need to rearrange your layout though;transformer centre back,caps centre front, left and right input and output sockets separated extreme ends of back panel.This would keep the various cables well separated with none of them crossing each other.
Further to the above try the following:remove your 10ohm resistor mod. and wire the input cable as suggested by Hypex and then remove the centre tap to chassis ground connections and fit 100ohm ground lift resistors at the input sockets,I.E. signal ground to chassis.
Although centre tap of power supply caps to chassis ground connection is widely accepted as being correct it is in fact anything but ideal.It can and in my experience did result in unnecessary hum,instability and distortion and no doubt increase crosstalk as well.
Bob Lewis
May I suggest you would get better crosstalk results if you eliminated the "rats nest" of closely coupled power supply,signal and loudspeaker cables!
You would need to rearrange your layout though;transformer centre back,caps centre front, left and right input and output sockets separated extreme ends of back panel.This would keep the various cables well separated with none of them crossing each other.
Further to the above try the following:remove your 10ohm resistor mod. and wire the input cable as suggested by Hypex and then remove the centre tap to chassis ground connections and fit 100ohm ground lift resistors at the input sockets,I.E. signal ground to chassis.
Although centre tap of power supply caps to chassis ground connection is widely accepted as being correct it is in fact anything but ideal.It can and in my experience did result in unnecessary hum,instability and distortion and no doubt increase crosstalk as well.
Bob Lewis
Will try it in my next amp. which I am busy with. With the input wire mod. I am quite happy as it is now. Channel separation is just great, either way around.BOB LEWIS said:
Sound stage is superb. Lady singer is out of the box. No humm.
If I move the wires now in the wire tree it makes no difference as where in the old situation it would.
Our recommendation is as follows;
Use a balanced XLR chassis connector, a good version would be from Neutrik which automatically connect pin#1 to chassis. Don't connect the ground of the power supply to the chassis.
In this way you have no hum!
When you would connect an asymmetrical signal to the amplifier, create a symmetrical cable with a XLR and a Cinch connector. Whereby you connect the shield and the ground together at the side of the cinch connector.
In this way you still have all benefits of a symmetrical connection.
Jan-Peter
Use a balanced XLR chassis connector, a good version would be from Neutrik which automatically connect pin#1 to chassis. Don't connect the ground of the power supply to the chassis.
In this way you have no hum!
When you would connect an asymmetrical signal to the amplifier, create a symmetrical cable with a XLR and a Cinch connector. Whereby you connect the shield and the ground together at the side of the cinch connector.
In this way you still have all benefits of a symmetrical connection.
Jan-Peter
The difficulty is obviously that there is never a truly "correct" way of wiring an unbalanced system, or certainly not a surefire recipe to get it right every time in all circumstances. Otherwise put, for every recipe there will always be someone who manages to set up a system that defeats it. Unbalanced audio should be banned by law... coax cables are for RF, not audio. The aim of using balanced connections is to relieve the ground connection of its secondary job of providing a signal reference and allowing it to do what it's intended for i.e. to roughly equalise the ground potentials either side of the connection. A correctly designed balanced connection is immune to ground loops. In fact, correctly designed balanced connections (see AES48) are almost guaranteed to produce ground loops but they do so without incurring any performance loss.
The problem in Bgt's setup is that part of the ground return current to the power supply circulates round the shield of his RCA cables, through his preamp. In an unbalanced system this is annoying for two reasons. One - this current creates a voltage drop on the audio cable shield which unfortunately is also the signal reference. Two - depending on the design of the preamp this current may well start flowing inside the preamp as well...
A trick which might be used in this situation is to short the two RCA grounds together. In this way, any ground current will be restricted to the shields of the input cables inside the cabinet. However, the input cables are *differential* which means that the inputs will cancel any common mode voltage appearing on the inputs as a result of this current.
Ideally this would be done by using uninsulated RCA connectors screwed on the back panel. Of course, the unbalanced demon pops up again there because this allows only one box in your audio system to be connected to mains earth and requires that all others be connected to ground only through their RCA connections. This is why consumer gear typically has no earth prong (and those that do often have hum problems) - in order to allow direct chassis connection of all RCA's via the chassis. This is the closest anyone can get to a surefire unbalanced recipe (I will add this note somewhere in the documentation) but keep in mind that it too is easily defeated by having two earthed boxes in one system of by using a power supply with excessive primary-to-secondary capacitance. Only balanced connections per AES48 are always guaranteed to work (caveat: only if both ends of the connection are per AES48 is the connection guaranteed to work).
As an aside (OT for those who abhor XLR but very relevant otherwise) I'd like to recap what AES48 prescribes: connect pin 1 and the outer part of XLR inputs and outputs straight to the chassis and only then to the PCB. This requires the use of silver-coloured XLR chassis parts (not the black kind) that will make positive electrical contact with the chassis. Connect pin 1 to the chassis lug on the XLR part (parts with pin 1 directly connected to chassis are also available) and connect the internal cable shield there (if at all).
This insures that:
*Your box cannot induce currents from one pin-1 to the other.
*No amount of current externally fed from one pin-1 to another can cause interference, including severe RFI.
The problem in Bgt's setup is that part of the ground return current to the power supply circulates round the shield of his RCA cables, through his preamp. In an unbalanced system this is annoying for two reasons. One - this current creates a voltage drop on the audio cable shield which unfortunately is also the signal reference. Two - depending on the design of the preamp this current may well start flowing inside the preamp as well...
A trick which might be used in this situation is to short the two RCA grounds together. In this way, any ground current will be restricted to the shields of the input cables inside the cabinet. However, the input cables are *differential* which means that the inputs will cancel any common mode voltage appearing on the inputs as a result of this current.
Ideally this would be done by using uninsulated RCA connectors screwed on the back panel. Of course, the unbalanced demon pops up again there because this allows only one box in your audio system to be connected to mains earth and requires that all others be connected to ground only through their RCA connections. This is why consumer gear typically has no earth prong (and those that do often have hum problems) - in order to allow direct chassis connection of all RCA's via the chassis. This is the closest anyone can get to a surefire unbalanced recipe (I will add this note somewhere in the documentation) but keep in mind that it too is easily defeated by having two earthed boxes in one system of by using a power supply with excessive primary-to-secondary capacitance. Only balanced connections per AES48 are always guaranteed to work (caveat: only if both ends of the connection are per AES48 is the connection guaranteed to work).
As an aside (OT for those who abhor XLR but very relevant otherwise) I'd like to recap what AES48 prescribes: connect pin 1 and the outer part of XLR inputs and outputs straight to the chassis and only then to the PCB. This requires the use of silver-coloured XLR chassis parts (not the black kind) that will make positive electrical contact with the chassis. Connect pin 1 to the chassis lug on the XLR part (parts with pin 1 directly connected to chassis are also available) and connect the internal cable shield there (if at all).
This insures that:
*Your box cannot induce currents from one pin-1 to the other.
*No amount of current externally fed from one pin-1 to another can cause interference, including severe RFI.
did some measurements yesterday with my PC using NCH tone generator version 2.01, SPDIff out to DAC to passive preamp to UCD's. 1 channel 0hz, other 15khz all on 0Db, measured crosstalk.....90Db Tried 20khz...still 90Db.
This weekend testing the different input configurations as suggested by Bob Lewis and JP(I hope).
Tried 20khz...still 90Db.This weekend testing the different input configurations as suggested by Bob Lewis and JP(I hope).
Modified 1 poweramp with JP's suggested wiring scheme. So no 10 ohm resistors but the original balanced cable going to the rear of the poweramp, grounding the shield of the input cable there(no other grounding) and than go balanced out to the preamp where you, at the cinch plug connect the shield to the - wire.
Listening, in an AB test, to Katie Melua's "Piece by Piece"album, Andreas Vollenweiders "Book Of Roses"and Dire Straits "On Every Street" shows in both ways of wiring the crystal clear voice with rasor blade sharp ssssss's of Katie Melua and Andreas Vollenweiders superb harp and Dire Straits guitar play. The biggest difference really is the depth/soundstage my modded input cable shows here. It is like there is more echo. Walking in the room does not change the clarity of the voice. Even going round a corner(L shaped room) keeps the clarity of the voice intact. This is less with JP's recommended wiring scheme.
But still the biggest surprise comes from listening to the tuner, a Sony ST361, suddenly it is fun to listen to the radio. Here JP's wiring scheme drops the most points. Why.....I am really puzzled. Did not know radio could give such a wide soundstage.
It is a bit like switching in a Dolby system. The music is not fixed to a speaker anymore.
Either way...there is no humm.
Bob Lewis's recommendation is a bit the same as JP's except even less depth. Sound is superb mind you, no doubt about it. But in an AB comparison where you switch the power amps so you have a direct comparison it is obvious.
BTW, the way the cable tree/"rats nest" is done, is again more sensitive for layout.
So for me there is no doubt anymore. I will keep using the single wiring arrangement.
This test is done with the intention to share information, not to prove anything or to say this is the best way to do the input wiring.
Listening, in an AB test, to Katie Melua's "Piece by Piece"album, Andreas Vollenweiders "Book Of Roses"and Dire Straits "On Every Street" shows in both ways of wiring the crystal clear voice with rasor blade sharp ssssss's of Katie Melua and Andreas Vollenweiders superb harp and Dire Straits guitar play. The biggest difference really is the depth/soundstage my modded input cable shows here. It is like there is more echo. Walking in the room does not change the clarity of the voice. Even going round a corner(L shaped room) keeps the clarity of the voice intact. This is less with JP's recommended wiring scheme.
But still the biggest surprise comes from listening to the tuner, a Sony ST361, suddenly it is fun to listen to the radio. Here JP's wiring scheme drops the most points. Why.....I am really puzzled. Did not know radio could give such a wide soundstage.
It is a bit like switching in a Dolby system. The music is not fixed to a speaker anymore.
Either way...there is no humm.
Bob Lewis's recommendation is a bit the same as JP's except even less depth. Sound is superb mind you, no doubt about it. But in an AB comparison where you switch the power amps so you have a direct comparison it is obvious.
BTW, the way the cable tree/"rats nest" is done, is again more sensitive for layout.
So for me there is no doubt anymore. I will keep using the single wiring arrangement.
This test is done with the intention to share information, not to prove anything or to say this is the best way to do the input wiring.
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