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Old 14th October 2011, 08:41 PM   #31
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Another thing I noticed is that when in romove the resistance from RC filter in the positive rail (only caps) nothing different is happening, but when I do this in the negative rail then an excessive ripple noise is heard. TGhis is the case for both channels. Why this difference between rails is happening I do not know. Any ideas?
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Old 14th October 2011, 08:57 PM   #32
DF96 is offline DF96  England
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Yes. PSRR often varies considerably between rails. Can you confirm that C4 in the JLH circuit goes to ground, not the negative rail? Clearly the circuit is picking up hum from the negative rail. A little normally, but a lot when the PSU smoothing is reduced.
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Old 14th October 2011, 09:09 PM   #33
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As you can spot I have a commoon ground that is the connection of the regulated and non regulated supplies. The feedback capacitor defenitely goes to this common ground. The unregulated -V goes in to the emmiter resistor of the output transistor. What can I do to make better PSRR? Thanx for the help DF96!
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Old 18th October 2011, 06:58 AM   #34
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Another fact is that I measured yesterday the voltage between the chassis and the signal ground to be about 14mV ac. I would like to mention here that the chassis is connected to power ground via a 10 ohm resistor and a cap in parallel. Is that normal? Is maybe the cause of the hum. Also as it is obvious the chassis is connected to the outlet ground of the house.
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Old 18th October 2011, 10:49 AM   #35
DF96 is offline DF96  England
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14mV across 10 ohms is 1.4mA which seems rather high, unless you have several items of modern equipment connected each contributing some leakage current from their mains filter capacitors. However, this may not be the source of the hum as everything ought to be referred to the signal ground.

Having confirmed that your circuit has poor PSRR on the negative rail, you really need advice from someone who has successfully built the JLH class A circuit. You probably have a grounding problem.
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Old 18th October 2011, 10:50 AM   #36
AndrewT is offline AndrewT  Scotland
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14mVac between Signal Ground and Chassis indicates an earth leakage current of ~ 0.014/10 ~ 1.4mAac
This is not excessive but more than normal. Usually one cannot measure (<0.1mVac narrow band on a DMM) the AC voltage across the Disconnecting Network between Signal Ground and Power Ground.

However, have you connected Power Ground to Signal Ground.
The leakage current from Power Ground to Chassis could be contaminating the Signal Ground connection route. The amplifier then multiplies this up to appear as hum at the speakers.
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Old 18th October 2011, 11:16 AM   #37
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The common power ground comming from the PSU is the ground of jlh circuit hence the signal ground. Can be done differently???????
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Old 18th October 2011, 11:50 AM   #38
DF96 is offline DF96  England
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It all depends on how they are connected together. It is surprisingly easy to inject hum or noise into a ground. Remember, a piece of wire (however thick) is only an equipotential when no current is flowing.
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Old 18th October 2011, 12:06 PM   #39
AndrewT is offline AndrewT  Scotland
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Identify the signal circuit route. All the way from the Source Hot pin back to the Source Cold pin. Find this route in the actual amplifier. Draw it out as it is actually assembled in the amplifier. Mark this route in Red

Now identify the Power circuit route. Go through the same steps as for the Signal route. Mark this route in Black

Finally identify the speaker circuit route do the same again and mark this route in Green.

Are there any traces or wires that share their length, or just part of their length between any two of these circuits? If there is, you must separate them, particularly the Signal Route.
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Old 18th October 2011, 02:04 PM   #40
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Attached is the cable network showing the actual ground routes paths
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