I have an AC to 18v DC, 25MA, power supply (wall wart) that is used for a guitar flanger pedal. The supply generates some ripple noise into the pedal's audio (it is not there when using batteries). The supply has a transformer, two diodes, and a 1000uf 25v capacitor. I changed the cap, but the hum is still there. The diodes seem OK. Would changing the cap to 2200uf help or should I try something else? Thank you.
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3\$\begingroup\$ You could measure the ripple and then calculate some filter to know what components to put where. \$\endgroup\$– PlasmaHHCommented Apr 15, 2016 at 14:25
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1\$\begingroup\$ What does "ripple noise" sound like? \$\endgroup\$– Andy akaCommented Apr 15, 2016 at 14:31
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\$\begingroup\$ @Andyaka Probably 50/60hz hum \$\endgroup\$– Brendan SimpsonCommented Apr 15, 2016 at 14:32
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\$\begingroup\$ Question aimed at the OP \$\endgroup\$– Andy akaCommented Apr 15, 2016 at 14:46
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1\$\begingroup\$ It sounds like a very basic half wave rectifier adapter. I could give a lesson in DC regulation. But adapters are so cheap these days. For audio applications I would recommend a Linear regulated DC supply. There are plenty of options out there. Avoid switching adapters for audio. \$\endgroup\$– crowieCommented Apr 15, 2016 at 17:03
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In your job the current is low and the DC voltage does not have to be at all accurate .Batteries themselves however do not make ripple which means that the ripple rejection of your preamp may be poor .Single ended discrete component circuits can have poor ripple rejection but they sound good .So keep the adapter and the preamp and place some RC filtering in the DC rail between the adapter and the preamp .You could start with say 47ohms and 2200microfarad 25V.This will reduce the power supply hum much better than capacitance alone.
