Hi!
Building a power supply for my audio preamp. The build is based on Rod Elliots ”Power Supply for Preamplifiers” using LM317 and LM337 but get noice/oscillaitons - 100kHz, 4.5mVpp and intermittent ~30Mhz, 2mVpp
How can I remove these 100kHz and 30 MHz oscillations?
/Anton
Building a power supply for my audio preamp. The build is based on Rod Elliots ”Power Supply for Preamplifiers” using LM317 and LM337 but get noice/oscillaitons - 100kHz, 4.5mVpp and intermittent ~30Mhz, 2mVpp
How can I remove these 100kHz and 30 MHz oscillations?
/Anton
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Hi that should work OK without too much noise and certainly without oscillation when built as pictured in the schematic.
Did you perhaps use ceramic caps at the outputs of the regulators?
Did you perhaps use ceramic caps at the outputs of the regulators?
Perhaps you are using fake parts that are unstable.
Try 10uF electrolytic capacitors that have significant ESR at the output of the regulators.
Try 10uF electrolytic capacitors that have significant ESR at the output of the regulators.
I do have 10uF electrolytic capacitors at the output of the regulators. About its ESR, 1060 mOhms, - is that big enough?
So there are also in parallell 10nF MKP polypropylen and these 10uF electrolytic as mentioned above.
So there are also in parallell 10nF MKP polypropylen and these 10uF electrolytic as mentioned above.
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Ok, then is the regulator from an authorized distributor, and not fake?
Is the circuit built on a pcb, or point to point?
Is the circuit built on a pcb, or point to point?
Maybe keep to the schematic with recommended parts as that is a proven concept? And what about a picture?
All parts from from Mouser, Digikey etc. The same result without the MKP. Built point to point.
Separated diode bridge and caps (2200u +10R+2200u) from the regulator circuit - measured at the last 2200u cap. 100kHz spikes are there. Please see added screen dump …. Weird.
Have included pictures from my circuit with still separated caps 2200u and regulator circuit.
I have net-filter Schaffer FN9222-3-06. Using a toroidal made by Toroid International.
Separated diode bridge and caps (2200u +10R+2200u) from the regulator circuit - measured at the last 2200u cap. 100kHz spikes are there. Please see added screen dump …. Weird.
Have included pictures from my circuit with still separated caps 2200u and regulator circuit.
I have net-filter Schaffer FN9222-3-06. Using a toroidal made by Toroid International.
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Just one thing to check, I have a magnifier lamp that contains a round cfl bulb. If I measure anything with that lamp on, I get way more noise than I was expecting, so I have to remember to turn it off for any measurements.
It may be worth checking that you don’t have a noise source close by.
I use Rod’s P5 PSU boards and have had no problems.
Looking at the data sheet, output noise is rated at 0.003%/V, so output noise of a few mV is expected.
A few mV on the opamp rails shouldn’t cause noise on the preamp output as the opamp PSRR is usually high enough to eliminate it.
Check that your preamp isn’t oscillating at 100khz, as that would probably modulate the psu rails.
Those are some causes I have experienced. Hope that helps.
It may be worth checking that you don’t have a noise source close by.
I use Rod’s P5 PSU boards and have had no problems.
Looking at the data sheet, output noise is rated at 0.003%/V, so output noise of a few mV is expected.
A few mV on the opamp rails shouldn’t cause noise on the preamp output as the opamp PSRR is usually high enough to eliminate it.
Check that your preamp isn’t oscillating at 100khz, as that would probably modulate the psu rails.
Those are some causes I have experienced. Hope that helps.
