>the DC converter puts out around 12v with no load and around 9v under load...
This is quite common. If you connect an LED (and associated resistor) to the output, you will have both a handy indicator that it is working, and likely enough load to keep the output close to 9V.
>For filtering try 22 Ohm and 470uF instead.
I would not expect a 1/4W resistor to last very long here with the current draw of a few pedals + some inefficiency in the DC-DC converter.
>typical switching frequencies of these 5v chargers ... 50kHz or more, 33kHz
Heterodyning between the charger and DC-DC converter might be the culprit. If your charger is whining at 50 kHz, this will beat agaist the 62 kHz DC-DC converter to give you noise at 12 kHz and 112 kHz (which will only bother the neighbourhood bats).
If you can get a low dropout 5(ish)V regulator between the charger and DC-DC converter, you may be able to filter out the 50 kHz and thus prevent the heterodyning. Alternatively, try another changer. At the price we (don't) pay for them, I would expect the quality to vary from crap to marginally ok. Also, a 33 kHz switching charger will have advantages in this application...
This is quite common. If you connect an LED (and associated resistor) to the output, you will have both a handy indicator that it is working, and likely enough load to keep the output close to 9V.
>For filtering try 22 Ohm and 470uF instead.
I would not expect a 1/4W resistor to last very long here with the current draw of a few pedals + some inefficiency in the DC-DC converter.
>typical switching frequencies of these 5v chargers ... 50kHz or more, 33kHz
Heterodyning between the charger and DC-DC converter might be the culprit. If your charger is whining at 50 kHz, this will beat agaist the 62 kHz DC-DC converter to give you noise at 12 kHz and 112 kHz (which will only bother the neighbourhood bats).
If you can get a low dropout 5(ish)V regulator between the charger and DC-DC converter, you may be able to filter out the 50 kHz and thus prevent the heterodyning. Alternatively, try another changer. At the price we (don't) pay for them, I would expect the quality to vary from crap to marginally ok. Also, a 33 kHz switching charger will have advantages in this application...