TC Electronic TonePrint Pedals - DC Jack power filtering circuit?

[karis12]

I didn't know which section this would be appropriate for, so I decided to put it here.

I own a cheap 9V DC adapter for use with my Zoom G1on (IMHO a good-sounding, practical unit for "copying" analog pedal sounds onto BTW) which I found introduces a very strong high-pitched whining/whistling sound into my DIY pedals with little to no filtering circuit inside.

Not surprising to be sure, but what did shock me was the first time I tried to power via daisy-chain a Flashback delay together with my DIY builds. Even with the Flashback out of the actual signal path, it seems to filter out/regulate the dirty output of said adapter, bringing down the noise to near silence. Adding a similar pedal (a TonePrint chorus) to the daisy chain very slightly raises the noise floor, but is still quiet compared to not having the pedals connected at all.

Does anyone know what TC Electronic did to these pedals that they have this property? Has anyone had any similar experience with theirs?

[anotherjim]

A large capacitor directly on the DC input would be my guess. Many designs have little or nothing in the way of capacitance on the supply input.

That said, some may have a capacitor after a low value resistor, which will help that pedal filter out its own supply noise, but the location of the resistor means the filtering won't much benefit any other pedals on the same supply. I think an RC power filter should present in every pedal that can run off external DC, but if you look at various schematics, it isn't shown, especially of designs that date back to when they only ran off battery. Battery power don't need a supply filter of course.