I have an earth loop which I'd prefer to leave in place and hoped wouldn't matter. Yes this problem is as old as the hills but not quite like mine. This is a long one. Perhaps you should visit the small room before proceding, and then only if you'd otherwise be bored.
No problem with line level signals but when the gain is very great - amplifying 5mV phono up to 20 Volts into speaker loads - I get low a frequency feedback howl which is so low as to be almost subsonic when the gain is turned up. This because RIAA gain is highest at low frequencies.
The situation is:
Two sets of speakers (electrostatic and dynamic) crossed switched from two amplifiers (valve and transistor). One amplifier is a stereo integrated amp and the other (valve) is a stereo power amp. Nice set-up.
Unfortunately I have to use the integrated amp's phono stage via its tape record outlets to drive the valve power amp. All signals except phono are attenuated and switched to either amp outside of both amps. Both amps are earthed to the house mains.
Here we go.... Both amplifiers' speaker minus outputs are connected to their respective mains earths - neither amp works in bridge-mode. I've commoned all speaker minus inputs and all amplifier minus outputs. That's 8 wires connected together. All live lines are switched with two DPDT switches.
[ Imagine two simple stereo two way speaker select switches mounted back to back with their commons connected together. One box switches the speakers conventionally, the other selects the amplifiers working backwards. They wouldn't need to be four pole switches because it wouldn't matter if both pairs of speakers got one of the phases provided the other phase is switched to either one of them. Maybe some good switcher boxes do it properly with a four pole double throw. Thinking abt it I reckon that would solve my problem just wouldn't be as neat as my purpose-built switch box]
Needless to say if one amp (the valve one) is simply unplugged from the mains the problem goes away.
Aside from the safety aspects, mitigated by bloody great labels saying "This device's earth is disconnected at the plug", Where do I put a (very high current) mains-earth path for star-earthing?
My guess, in my situation, would be to the 8 commoned heavy-wired speaker ground-lines, with a ninth connection to a dedicated mains plug with a single green and yellow conductor from its mains earth.
But OK, back to the real world, would it correctly go? To the deck/tuner, the control unit or the power amp? My guess would be to the power amp. But in any such case, you'd have signal lines carrying massive fault currents from the other components' failures.
Got it! Run everything from individual isolation transformers! Hang on, then how'd you know there was a fault......?
No problem with line level signals but when the gain is very great - amplifying 5mV phono up to 20 Volts into speaker loads - I get low a frequency feedback howl which is so low as to be almost subsonic when the gain is turned up. This because RIAA gain is highest at low frequencies.
The situation is:
Two sets of speakers (electrostatic and dynamic) crossed switched from two amplifiers (valve and transistor). One amplifier is a stereo integrated amp and the other (valve) is a stereo power amp. Nice set-up.
Unfortunately I have to use the integrated amp's phono stage via its tape record outlets to drive the valve power amp. All signals except phono are attenuated and switched to either amp outside of both amps. Both amps are earthed to the house mains.
Here we go.... Both amplifiers' speaker minus outputs are connected to their respective mains earths - neither amp works in bridge-mode. I've commoned all speaker minus inputs and all amplifier minus outputs. That's 8 wires connected together. All live lines are switched with two DPDT switches.
[ Imagine two simple stereo two way speaker select switches mounted back to back with their commons connected together. One box switches the speakers conventionally, the other selects the amplifiers working backwards. They wouldn't need to be four pole switches because it wouldn't matter if both pairs of speakers got one of the phases provided the other phase is switched to either one of them. Maybe some good switcher boxes do it properly with a four pole double throw. Thinking abt it I reckon that would solve my problem just wouldn't be as neat as my purpose-built switch box]
Needless to say if one amp (the valve one) is simply unplugged from the mains the problem goes away.
Aside from the safety aspects, mitigated by bloody great labels saying "This device's earth is disconnected at the plug", Where do I put a (very high current) mains-earth path for star-earthing?
My guess, in my situation, would be to the 8 commoned heavy-wired speaker ground-lines, with a ninth connection to a dedicated mains plug with a single green and yellow conductor from its mains earth.
But OK, back to the real world, would it correctly go? To the deck/tuner, the control unit or the power amp? My guess would be to the power amp. But in any such case, you'd have signal lines carrying massive fault currents from the other components' failures.
Got it! Run everything from individual isolation transformers! Hang on, then how'd you know there was a fault......?
Just run a heavy wire from the chassis of pre-amp/receiver along the same path as the interconnects to the chassis of the amplifier.
That's a very good suggestion and if I'd thought of it I'd have already done it, though it will create more of a delta-earth than a star (where have I heard that before?). Certainly two soldered eyelets via the shortest piece of thick wire will greatly lower the resistance between the two chasses, which are already connected by two longer parallel pairs of speaker ground wires and their banana plug connections with ascociated resistances.
It makes the problem considerably worse. Work that one out! I'm off for a beer or two.
It makes the problem considerably worse. Work that one out! I'm off for a beer or two.
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Could you draw a sketch of the setup and post it here?
With all the speaker and mains wires included.
The idea is to get the chassis of the interconnect source output and the chassis of the load input to nearly the same potential as possible.
Star Grounding/Earthing is often done incorrectly! The best keep the length of the Protective Earth/Safety Ground wires from audio component to audio component as short as possible.
Delta is 3 phase power system, mostly without a Ground/Earth connection.
Delta is 3 phase power system, mostly without a Ground/Earth connection.
Yes indeed on star/delta - start/run on 3-phase motors. My weak analogy was connecting earth points to two of three points which are themselves connected together.
Some food for thought from this thread, and yes I ought to make a big drawing of all of it including the earthing of the signal lines. My problem is to solve the feedback problem, probably with star-earthing while maintaining electrical safety.
Somewhere there's speaker current flowing through a wire, with its finite resistance, and enough of the in-phase voltage developped along it is arriving at and adding to the signal being amplified. Hence oscillation. It isn't enough to just stop the oscillation, if there's nearly enough loop-gain for oscillation there will be a peak in the system frequency response at the frequency which it's not quite oscillating at!
Some food for thought from this thread, and yes I ought to make a big drawing of all of it including the earthing of the signal lines. My problem is to solve the feedback problem, probably with star-earthing while maintaining electrical safety.
Somewhere there's speaker current flowing through a wire, with its finite resistance, and enough of the in-phase voltage developped along it is arriving at and adding to the signal being amplified. Hence oscillation. It isn't enough to just stop the oscillation, if there's nearly enough loop-gain for oscillation there will be a peak in the system frequency response at the frequency which it's not quite oscillating at!
It would be two new speaker switches and they would have to be fully isolating ones as mentioned in the op.
Sorted to my satisfaction now.
I went for the option in the op. The difference is that the mains wiring to all the components remains untouched. The single earth wire from the dedicated earth plug was tried in a number of places and the point which added no noise was indeed at the 8 commoned speaker and amplifier minus lines.
Isolation was achieved by getting medieval with a Dremel and isolating seven of the 8-gang mains extension lead's sockets which run all my audio and AV, from the house earth line and from each other. The eighth socket has kept its earth and carries the dedicated earth-wire-only plug. The 8-gang is clearly marked as to what state it's in.
So earth fault currents will have to be carried by the signal lines of the audio sources or by the heavy speaker minus lines coming from the amps.
In the UK all mains appliances' plugs carry fuses - that's partly why they are so big. These days we have a choice of a 13 amp or a 3 amp fuse to put in. None of the kit needs a 13 amp so they've all got 3 ampers fitted. The signal lines' grounds should be able to pass enough current to blow a 3 amp fuse before they are totally fried.
Sorted to my satisfaction now.
I went for the option in the op. The difference is that the mains wiring to all the components remains untouched. The single earth wire from the dedicated earth plug was tried in a number of places and the point which added no noise was indeed at the 8 commoned speaker and amplifier minus lines.
Isolation was achieved by getting medieval with a Dremel and isolating seven of the 8-gang mains extension lead's sockets which run all my audio and AV, from the house earth line and from each other. The eighth socket has kept its earth and carries the dedicated earth-wire-only plug. The 8-gang is clearly marked as to what state it's in.
So earth fault currents will have to be carried by the signal lines of the audio sources or by the heavy speaker minus lines coming from the amps.
In the UK all mains appliances' plugs carry fuses - that's partly why they are so big. These days we have a choice of a 13 amp or a 3 amp fuse to put in. None of the kit needs a 13 amp so they've all got 3 ampers fitted. The signal lines' grounds should be able to pass enough current to blow a 3 amp fuse before they are totally fried.
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But if the short to chassis happens with the components turned off and the interconnects not connected.
When you go to plug in the interconnects with one hand on the connector and the other hand on the chassis, you get electrocuted.
* * * * * * * * * * *
Is the circuit a 'ring' or a 'spur' ?
When you go to plug in the interconnects with one hand on the connector and the other hand on the chassis, you get electrocuted.
* * * * * * * * * * *
Is the circuit a 'ring' or a 'spur' ?
Perfectly true, but the kit was alright when it was switched off and nothing's been moved....
As a perfect example of what you describe, equipment exists which does exactly what you say .... and from the factory!!!!
It's my Quad AM2 tuner. Would you believe that by design it uses the signal lines as the DC HT minus supply! It would do exactly as you say unless you followed the usual practice of the day and connected everything up before applying power. Couldn't believe it until I saw it. Needless to say my tuner has a dedicated HT minus to its PSU.
Yes, what I've done with the switcher is a compromise.
Not sure what you mean by ring or spur, It's a spur going to a ring I suppose. No idea how the earth gets to the wall socket.
As a perfect example of what you describe, equipment exists which does exactly what you say .... and from the factory!!!!
It's my Quad AM2 tuner. Would you believe that by design it uses the signal lines as the DC HT minus supply! It would do exactly as you say unless you followed the usual practice of the day and connected everything up before applying power. Couldn't believe it until I saw it. Needless to say my tuner has a dedicated HT minus to its PSU.
Yes, what I've done with the switcher is a compromise.
Not sure what you mean by ring or spur, It's a spur going to a ring I suppose. No idea how the earth gets to the wall socket.
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Yay!!
@Antos': Sorry to burst your bubble but you will never get a perfect star ground. The best you can do is to use differential inputs (-> remove the ground connections from the signal path). Second best would be to ensure that the equipment grounds are connected via beefy wires so the error current flows in the beefy wire and not as much in the signal path.
Tom
safety earth wiring must not be tampered with.
you cannot move the job of safety earth wiring to other wiring.
there are other methods to deal with ground loops which have been discussed in many threads already.