I have an LM3886 amp that I'm having a ground loop problem with. If I connect my phone or another battery powered source it works perfectly, but if I try something running off AC - computer, TV, laptop plugged in etc. I get the loud hum.
It's based off of the schematics here:
Synergy - a LM3875 Gainclone Amplifier (Chip Amp)
What I find confusing is that it uses different marks for the ground in the same schematic - should those not be connected, and if not, where?
In my build all the ground wires meet at the ground pin of the AC connector, so the wall earth/ground, transformer output middle, signal connector shield are all connected.
From reading the other forums and sites I'm coming to the conclusion that I need to add a ground loop breaker.
But I understand that doesn't remove the problem, it just attenuates it. Is there a better solution? How does a store-bought amp get around the ground loop problem?
Also, if I do use the ground loop breaker, should the chassis be connected before it - eg. to wall ground directly, or it doesn't matter?
Pictures of my build:
http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-239.html#post3444353
It's based off of the schematics here:
Synergy - a LM3875 Gainclone Amplifier (Chip Amp)
What I find confusing is that it uses different marks for the ground in the same schematic - should those not be connected, and if not, where?
In my build all the ground wires meet at the ground pin of the AC connector, so the wall earth/ground, transformer output middle, signal connector shield are all connected.
From reading the other forums and sites I'm coming to the conclusion that I need to add a ground loop breaker.
But I understand that doesn't remove the problem, it just attenuates it. Is there a better solution? How does a store-bought amp get around the ground loop problem?
Also, if I do use the ground loop breaker, should the chassis be connected before it - eg. to wall ground directly, or it doesn't matter?
Pictures of my build:
http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-239.html#post3444353
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It'll usually be a Class II appliance that does not even have a protective earth connection since construction ensures that it's adequately safe without one. Consumer hi-fi assumes that there is no more than exactly one ground spot in any setup.
Your best bet when using unbalanced interconnects is learning how to (safely) build your stuff like that.
Currently your amp is a Class I appliance. Using unbalanced interconnection between two or more devices like that is a sure-fire recipe for a ground loop. Studio gear uses balanced interconnects, and there it really is the best thing to do. Unsurprisingly, connecting consumer and studio gear is good for all kinds of trouble.
That makes good sense. Different job/location equals different connection
This sounds completely wrong. All those different locations/connections taken to the biggest interfence source in your house !!!!
Audio Component Grounding and Interconnection - diyAudio
Few have the skills and/or knowledge to build an actual Class II device. In my opinion differential/balanced signalling is the way to go. Differential signalling moves the ground loop out of the main signal path and voila! the hum is gone.
Tom
The center tap of the transformer carries quite a high current, mostly a mix of AC and DC and is modulated by the signal output.
I would not refer any kind of audio ground to that point. A loop breaker will not help here.
Chassis MUST be connected directly to mains earth. The connection must not be defeatable. So the breaker, if used, must connect to mains earth/chassis at one end and to the power/signal ground at the other end.
Ideally the signal, power and mains ground must be all connected together. The loop breaker alleviates hum when other equipment (usually DIY) is connected to main earth as well, forming a loop between the RCA barrel/shield and the chassis which picks up interference currents. The 'breaker' introduces a high resistance in the signal connection, forcing the currents to travel along the mains earth lead instead of the interconnect shield.
In principle it's sound and it works provided nothing else is problematic in the system. I usually prefer to refer the output/power ground to mains earth and introduce a small resistance in the signal line instead (the same network is used, just located differently). This does increase THD slightly but in a system ridden with hum it helps more than hurts.
Wouldn't that be the case even when playing from a battery powered source? I get not hum in that case.
Ground loop breakers may solve your problem. If you go that route, you should install one in every system component, not just the power amp. Also, be certain that ground loop breakers do not constitute an electrical code violation in your country. Even at that, you may still have the noise circulating across one of the signal interfaces. The surest general solution is to block the noise at the inter-component signal interfaces. For single-ended signal interfaces this means either transformers, or common-mode signal chokes.
Here is a transformer coupled signal interface designed for single-ended interconnection: CI-2RR | Jensen Transformers
Here is a transformer coupled signal interface designed for single-ended interconnection: CI-2RR | Jensen Transformers
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