![]() The strength of the induced return current depends on a number of factors. As the signal rises to full strength and moves through the board, the signal and return traces create a current loop. In a PCB layout, signals are routed around the board using signal and nearby return traces. If you remember your Electronics 101 class, you know that all electric currents move around closed loops. Read on to find out about preventing PCB ground loops. Ringing or humming sounds in some audio systems are just one manifestation of PCB ground ring. Large currents can exist in ground planes, and a voltage differential between ground connections causes the formation of a ground loop. Ground loop PCBs generate noise in electric circuits, sometimes called a ground ring. In reality, PCB ground loops that form due to shoddy design are the source of the problem. What components are to be considered a problem? The decoupling capacitor or ground wire? How about the bypass capacitor or PCB ground loop design interference? The stereo manufacturer will blame the component manufacturer and the component manufacturer can’t blame anyone. When you take it back to the store the clerk blames the manufacturer. You buy that awesome stereo system only to hear that familiar humming sound in the background. An isolation transformer is also useful but they are expensive and will become dead weight once you've got the hang of working with high voltages.I think we’ve all been there. Just some advice from an old timer: If you enjoy working with valves and other high B+ devices, invest in a good RCCB your room. Once you have verified that the circuit is properly wired, power up and check if the hum remains use an incandescent bulb in series. Ideally, all interconnect wires in point-to-point systems should be the same thickness, which will allow you to subtract wire-resistance from your measurement. With an ohmmeter, check all connections to ground, i.e., check that every node in the circuit that should be at ground potential is connected-you should see near identical resistances very close to zero when you measure from one leg of a component to another. Disconnect everything from the chassis and test the circuit, without power, on an insulated surface. In its present configuration, your chassis is part of the signal chain which it not ideal. ![]() When implementing a star ground, we used to connect all grounds to a single nut by means of a crimped ring-terminal the nut was then connected to the chassis (a ground lifter might be useful in some situations) along with the earth wire from mains-you are using a three-pin plug I hope? Do not attempt a double-isolated build with triodes in a metal case! Check if the hum remains after you have moved the filament supply as far away from the outputs as possible.ģ) Now, on to minor tweaks. If you must shield the input connector, use a shielded RCA wire and connect the shield to the ground and not the sleeve.Ģ) It looks as if the wires that supply the filament current are not twisted together. Nice to see triodes.Thought they had, gracefully, accepted their obsolescence like many other things from my generation! Anyway, here's a checklist that might help:ġ) Are the input grounds connected to the chassis? Disconnect the RCA inputs from the chassis and check. I can also provide pictures of the amplifier internals, but really what I am looking for is an expert who can "read" the schematic, take some measurements and suggest changes to the grounding scheme. I am trying to source those locally but it's hard during these times. Hari has suggested replacing the paralleled 100uf electrolytic caps for the cathode resistor with MPP or MKP capacitors. I lifted this and the hum disappeared but it also stopped playing music. ![]() The PS capacitor leads have all been grounded to the chassis at a single point. It's loud enough that I can hear it in the next room 20 feet away. It's loud and independent of position of potentiometers. When I say inputs it's the RCA, Volume potentiometer and cathode resistor ground leads. The amp was initially implemented with Star ground but this is not recommended by the designer so have now implemented sectional grounding atleast for the inputs. I have to confess this is way beyond my pay grade. I need help from an expert in Bangalore who can troubleshoot and fix the ground loop hum. This design has been implemented countless times with inaudible hum. Amp is making music but there is a really loud 50Hz hum that is simply unacceptable. Just completed putting together a JE Labs design 2A3 SET with help from HFV member Radium.
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