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PostPosted: 09 Aug 2017, 16:10 
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Joined: 02 Jun 2016, 03:28
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Location: India
laurie54 wrote:
HI Ravi. Sorry for the delay. I don't believe a ground loop would cause the amp to hiss. A ground loop will cause a hum. When you make a ground loop in a cir. The signal going down the line which is normally being shielded by the outside ground shield, no longer is because of the physical loop created by the connection making the loop. Normally the signal goes in one end of the wire, travels down it and comes out the other end. Any magnetic fields the wire passes which would get into the signal wire, is stopped (and bled to ground) by the outer shield. However if the shield is part of a loop, the magnetic induction will induce into the shield and travel round and round the loop in an endless circle. While it is doing this it also gets into the signal wire and is passed on to the amplifying stages as part of the signal and thus is "heard". The loop is a hum because most injection of outside magnetic interference is produced by transformers and house wiring carrying current to something at it's end. These sources are operating at 50 or 60 cycles (Hz). So they are heard as a HUMMMMM. Higher frequencies also get in but we hear the harmonic of them and thus again humm.

It is said over and over threw a hugh percentage of the threads that ALL GROUNDING should be done as a "STAR GROUND SYSTEM". This means all wires which are ground wires will be brought to ONE common point. Thus avoiding the possibility of loops being created.

A hiss usually comes from transistors and resistors which are in the cir's power or signal path. It is the micro amount of heat coming off the device (res, trans, etc) which occurs when current is passed threw them. Remember all devices have a resistance. This means a resistance to the current flowing threw it. This resistance causes a buildup of excess of energy which is expelled as heat. Even if it is such a small amount of heat one could not ever detect it, IT still exists and is happening.

Your source of hiss could be the fact that you have built the cir on breadboards plugging in each part in it's entirety. Each part is connected by way of the metal clips in the breadboard. Not nearly as good as solder connections. Also a biggy is,, the parts on the breadboards are not shielded AT ALL. Especially when building an amplifier which by it's very nature is designed to amplify any signal connected to it, having no shield around the cir will cause a worst case scenario to be present.

Printed Circuit Boards are desirable for their ease of construction but also,,,,, a wire is "round". So any emissions from it in or out are on a 360 deg plan. But a PCB does not use wires it has copper foil on the surface making the connections. If you picture a PCB cut down the middle and you look at the cut edge you will see the foil lines are varying widths (depending on the amount of current it is to handle), but more importantly the foil is very thin (top to bottom). So any emissions coming off or getting into the foil track are much LESS side by side as the majority of the emissions field is from the wide surface so away from the board and not into/from neighboring components on the board.

Really building up and working with any electronics and understanding it and what is going on just takes time and the experience gained by doing so. Don't get discouraged just keep plugging away at it.


Thank you very much for clearing things up for me. I also thought it was issue with the bread board. I tried 2 times, disassembled and again created the same circuit. But the output was same. Thank you very much for boosting my confidence. I will surely try the circuit in new bread boards now. :)

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Regards,
Ravi


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