I'm working on a Aleph 5 clone which is having hum issue, even without input cables connected. Upon tracing, I found the following waveform on the Gate of the lower half MOSFET, Is this normal or just due to poor power supply filtering? By the way, Purple trace is the Gate of the lower half MOSFET while Yellow is the Drain pin, aka the Output.
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Here are the pictures of the actual unit and also the re-designed pcb in 3D view. Note that this was originally a ZeroZone A5 unit, which now serve as a platform (by using the trafo and the chassis) to run on my experiment on the Aleph 5.
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if you are testing just one channel and it's having hum with inputs shorted, that's construction error
being dual mono, judging from pictures, best to have audio GND of each channel isolated from chassis through NTC or diode bridge-NTC combo, input connectors isolated from chassis
if that's done, and hum is present and if you can measure its frequency being double your mains - no other way than to re-check for possible schm error ( because we know that original/concept is proper) and - routing of energy paths
signal takeout point (from PSU to signal part of circuit) must be at cleanest area possible, where no pulsating currents are present
being dual mono, judging from pictures, best to have audio GND of each channel isolated from chassis through NTC or diode bridge-NTC combo, input connectors isolated from chassis
if that's done, and hum is present and if you can measure its frequency being double your mains - no other way than to re-check for possible schm error ( because we know that original/concept is proper) and - routing of energy paths
signal takeout point (from PSU to signal part of circuit) must be at cleanest area possible, where no pulsating currents are present
1)Input shorted test - does the balanced input also need to be shorted, or just leave it and work on the single ended input only?
2)If I get your point correctly, which mean the setup should be : L ch audio GND -- Lch NTC -- Chassis -- Rch NTC -- R ch audio GND, right?
Anyway, the input RCAs are isolated from chassis on the mounting side from day one, as per normal practice.
2)If I get your point correctly, which mean the setup should be : L ch audio GND -- Lch NTC -- Chassis -- Rch NTC -- R ch audio GND, right?
Anyway, the input RCAs are isolated from chassis on the mounting side from day one, as per normal practice.
Looking at the PCB, it seems to me that the power supply grounding mixes the clean and dirty ground, with a star ground at the input of the filter capacitors. At least that is what it appears to me. I have only marked up one half of the power supply filter ground but I assume the same issue exists in the other half.
If the layout is as I assumed, then that could be the source of the hum. I suggest rerouting the ground as marked.
If the layout is as I assumed, then that could be the source of the hum. I suggest rerouting the ground as marked.
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1.plural
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everything else - as Ben said; I'm not of practical use analyzing other people pcbs, have slight mental block, doing that for decades on the bench
I took my best guess. It's not easy with no schematic or information on PCB.
