Power supply hum - what to do?

[glesconz]

Hi, I completed two units, an Orange squeezer and a DOD 250, both worked well with batteries. But after casing them both together in one unit (from the Guitar Gadgets schematic)and powering from a multi-tap supply (which the 9V setting read 14V so I bought it down to the 6V setting for a 9V output) the Compressor had a loud hum that got louder when I turned the volume control up. Eventually I replaced the power supply back with a 9V batt as power source and hey presto, the hum had gone.
So, what are my options here? Can I put some sort of cap in somewhere to filter any hum? As Im in New Zealand we have a 50Hz supply.  Should I just get a new supply and what should I get - regulated or Unregulated?
Please explain in Real Noobie Speak, thanks!!!

P.S. The DOD had no problems at all, the compressor was first in the chain..

Thanks for your help,
Glenn

[glesconz]

After some googling, I see from the Muzique site that a 100 ohm resistor in series from the ac adaptors +ve to the PCB's +ve acts as a hum filter, and a 220 uF electro cap can be added from the PCB point to ground if needed. I'll try this tomorrow and see.
The Orange Squeezer does not have this in the circuit, but the DOD 250 does which may explain why one had hum and the other not...

Cheers
Glenn

[Wild E]

50Hz doesn't matter, it can happen with 60Hz too. The resistor and cap should do the trick. If it's still not enough you can add another cap around 47nF in parallel with the 220uF cap.

[anchovie]

(which the 9V setting read 14V so I bought it down to the 6V setting for a 9V output)

You have an unregulated supply. Get a good quality, regulated PSU. The voltage of your current unit will vary according to the load of your pedals.

[tubelectron]

Hi glesconz,

Everything just has been said here : or you buy a 9VDC filtered-regulated PSU (like BOSS or EH sells) or you add a filter in your stompbox.  To be ultimately hum quiet on my DIY stompboxes, I put a filter which usually is 1000µ 25V / 100ohms serial / 1000µ 16V + 47n + 1N4007 reverse polarity protection, if there is enough room for that...

Proco only puts 47ohms serial / 1N400x + 100µ 16V + 10n in its RAT distortion, and it already works very well.

I experimented an "Any-Adaptor" filter which allowed external PSU to be : DC any polarity / AC 50-60Hz / any voltage from 9 to 25V / regulated or non-regulated, but even if it works perfectly, it remains somewhat "Art for Art".

A+!

[Canis guitarus]

Hey glesconz,

Build yourself a power supply bro. Its really easy and you get to learn about filtering etc. I built one from an unregulated supply like yours and a few bits from Jaycar for about $40 NZ and its quiet as a mouse.

[darron]

i did a small write up on this problem specifically for pedal power supplies on my site. it's at the very bottom of this page:

http://www.dazatronyx.com/support/quality/


there are some diagrams to help visualise it too (: