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previous: Fj I'm getting a HUM using a "CONDOR" ... -- 8/19/1999 1:42 PM View Thread

Re: TS-808 hummmm...

8/19/1999 9:16 PM
Mark HammerRe: TS-808 hummmm...
Two things matter when using a wall wart:  
1) The polarity of the plug from the adapter matches the polarity required by the effect. Some adapters have shaft positive, some shaft-negative. If you have a meter or if there is information on the adapter and effect itself, check this.  
2) The level of filtering and regulation. To count as a 9VDC adapter, all it really needs to do is tack on a diode and a capacitor after the transformer. While this can be *called* +9VDC, there is still considerable ripple and that is what you hear as hum. The 9VDC you get from a battery is a steady voltage. The 9VDC you get from this kind of adapter is simply the positive half-cycle of 60hz AC with a wee bit of low-pass filtering - hum city. I'm not saying this is what you have, but I mention it to illustrate that not all DC adapters are created equal, even though the writing on the adaptor suggests otherwise.  
Obviously, the goal is to make the adapter *behave* as if it were a battery. One way is to start with a 12V or greater adaptor and stick a 9V 3-pin regulator after it (voltage regulators always want a few volts more than they turn out), along with the 1 or 2 caps that make regulators work nice. Another way is to stick a couple of capacitors from hot to ground (say, one 1000uf, a 10uf, and a .1uf, in parallel) to provide more of the "low pass filtering". I know it's hard to think of 60hz and 120hz as "treble", but essentially what you want to do is turn down the "treble" on your power supply line. The safest thing to do is to get a little plastic box, put the extra components in there, and then run the last leg of the adapter cord out from there.  
Finally, I might point out that many FX can operate very nicely with more than 9V (although there are always those fuzzes that become "magical" at less than 9V). I run my own pedal-board (home-brew and commercial FX) from a 12VDC regulated supply, and everything works just fine, some things work even better.