you must add in the trace/wire routes at the PCB to complete each circuit.
Take just the Power Amp.
Look at the source @ P9 & P10.
That must be a circuit.
Remember, circuit is effectively shorthand for circular route. Electricity must flow around that route (from beginning right back to end) if it is to flow at all.
Take just the Power Amp.
Look at the source @ P9 & P10.
That must be a circuit.
Remember, circuit is effectively shorthand for circular route. Electricity must flow around that route (from beginning right back to end) if it is to flow at all.
Including the PSU as batteries in that diagram hides the very thing we want to see! Is the preamp PSU grounded via the preamp PCB or via the PSU PCB to the star (or both?).
You have two grounds coming off the star: chassis via 10 ohms and the 'ground' symbol. If the 'ground' symbol is meant to be external ground (e.g. via third pin of supply) then this should go to the chassis, not the star.
Is there a ground connection at the signal input socket? You haven't marked one, and there should not be one, but people sometimes forget and use non-insulated sockets so creating a hum loop.
You have two grounds coming off the star: chassis via 10 ohms and the 'ground' symbol. If the 'ground' symbol is meant to be external ground (e.g. via third pin of supply) then this should go to the chassis, not the star.
Is there a ground connection at the signal input socket? You haven't marked one, and there should not be one, but people sometimes forget and use non-insulated sockets so creating a hum loop.
Kz,
your job, if you want to get to the bottom of your hum enquiry, is to trace out the three circuits as I described and from there identify which if any of the routes share a trace or wire between two or more of those circuits.
I cannot and will not do that for you.
I cannot because I do not have the PCB in front of me, nor do I have the Power Amplifier with all it's cable routes open in front of me.
your job, if you want to get to the bottom of your hum enquiry, is to trace out the three circuits as I described and from there identify which if any of the routes share a trace or wire between two or more of those circuits.
I cannot and will not do that for you.
I cannot because I do not have the PCB in front of me, nor do I have the Power Amplifier with all it's cable routes open in front of me.
OK. The ground symbol is usually used to indicate an actual connection, typically to chassis.
Your diagram show one channel. How are the two channels wired? There should be one and only one ground connection between them. Possibly not even that, if the source joins the two channels together.
Your diagram show one channel. How are the two channels wired? There should be one and only one ground connection between them. Possibly not even that, if the source joins the two channels together.
Andrew df96 thanks for the responces so far. By all means I do not anyone to do anything for me. I done that Andrew pointed out I found two areas where the signal ground is shared by other parts of the circuit. One in the preamp and one and one in power amp. I quicly seperated them temporarely and it is true that the noise reduced a bit. This means that this is the problem and I will try to fix the other also. I will report as soon as I will do it. Thanks a lot Andrew for your help.
I stayed late yesterday and I made the changes I mention in my previous post. I tested the noise with with scope and some small earphones and is really less. Andrew you made a point. The area that was shared was about 3 and half centimeters, so I bypassed this one and it is better. Late in the afternoon, I will test it also in my very sensitive (103 db) speakers and I will also report. But so far it seems solved. Thanks
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