I have bought a Chinese Audiophile Linear Power supply and a lead for my MOFI phono stage. Checked the voltage before connecting it to the MOFI and is 24 volts. Plugged it into the MOFI and got whistling noise when playing a record and it sounded awful.
The lead is wired correctly to the special plug needed for the MOFI.
What could the problem be?
The company has given me my money back .
The lead is wired correctly to the special plug needed for the MOFI.
What could the problem be?
The company has given me my money back .
Could be oscillation of the linear regulators e.g. LT1083. Show is a schematic or a picture of the completed module to see if it has the reccomended 150uF electrolytic output capacitor.
Cheers,
V4lve
Cheers,
V4lve
Ah I see, its a TL431+LM317 Regulator with PNP pass transistor. That takes over from the LM317 at higher currents.
I supect its a design error on the part of the chinese designer, I think that red wima cap near the mounting hole bypasses the adjust pin of the LM317. and causes the TL431 to go unstable because its not in the stable region of anode-kathode capacitance on the TL431.
I suspect that if you remove the red wima cap (100n?) it will become stable. You either need to replace it with a electrolytic capacitor of a higher value, and add a 1n4001 between adjust and output of the LM317. Or leave it out completely.
Heres a quick sketch i made of how i think the circuit looks.
I supect its a design error on the part of the chinese designer, I think that red wima cap near the mounting hole bypasses the adjust pin of the LM317. and causes the TL431 to go unstable because its not in the stable region of anode-kathode capacitance on the TL431.
I suspect that if you remove the red wima cap (100n?) it will become stable. You either need to replace it with a electrolytic capacitor of a higher value, and add a 1n4001 between adjust and output of the LM317. Or leave it out completely.
Heres a quick sketch i made of how i think the circuit looks.
its likely that if you remove the wima 0.1uF next to the output set pot that the supply will behave. its likely that the TL431 becomes unstable with 100nF parallel to it.
Cheers,
V4lve
Cheers,
V4lve
Also please cut the excess lead wires of the pass transistor and check if PE is connected (at all). If the PE pin is soldered to a PCB track then follow the track as it often just ends with a … PCB pad. PE should be connected to the casing but not directly to the secondary GND.
There are at least 2 design errors in each of the cheap linear PSUs.
There are at least 2 design errors in each of the cheap linear PSUs.
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My two cents .TL431 is unstable with capacitor in parallel, even in simulation. This effect is present at best when TL431 loading resistor is high value , or current itself is low ,very close to minimal 1ma . As test you can remove that capacitor in parallel, or add small capacitor between pins 1 and 3 , something like 150pf , to prevent oscillation, when regulating element is slow, or output capacity high.
I don’t have a scope but connected it up to the piece of audio equipment and there was just silence now
Do you have dmm with ac millivolts meaurement function ? There maybe still present small oscillation, but at much higher frequency , lower amplitude , than before .