Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Effects => Topic started by: smackoj on June 15, 2019, 06:10:01 pm

Title: Noisy power supply for stomp boxes
Post by: smackoj on June 15, 2019, 06:10:01 pm

Hello again gents; Like so many other guitar players, I seem to be plagued by noisy stomp pedals. I have done lots of switching around trying to quiet them down and what seems to be the biggest problem is noise from the wall wart 9vdc power supply. I have a couple bench type regulated PSs that have ample filtering but they are designed for loads that draw more current than a few stomp boxes. So I ask this question; will a stout regulated PS that can push 12vdc all day up to 10-12 amps damage a stomp box that is only drawing milliamps?


Thanks amigos   :icon_biggrin:

Title: Re: Noisy power supply for stomp boxes
Post by: sluckey on June 15, 2019, 09:17:07 pm

no

Title: Re: Noisy power supply for stomp boxes
Post by: smackoj on June 16, 2019, 07:40:35 am

thanks SL

Title: Re: Noisy power supply for stomp boxes
Post by: OrganicEffects on June 16, 2019, 10:11:45 am

You don't mention what you're using, but I've had fantastic experience with 1Spot's powering a couple dozen pedals at once, DIY and commercial, digital and analog. Very quiet.

Title: Re: Noisy power supply for stomp boxes
Post by: smackoj on June 16, 2019, 08:39:03 pm

I appreciate the tip Organic!

Title: Re: Noisy power supply for stomp boxes
Post by: jjasilli on June 19, 2019, 10:27:27 am

10 -12A is OK but overkill especially for portability.  There's lots of quiet expensive & inexpensive pedal supplies available today.


Maybe not OK for some 9V pedals to have a 12V supply. 


Over voltage causes excessive current draw, which may exceed the handling capacity of leads or components in the pedal's circuitry.  Let's say a 9V pedal draws 9mA, or .009A.  Per the Power Formula, the pedal is dissipating .081 W.


Per Ohm's Law the pedal is functioning as if it were a 1000 Ohm resistor.  If we increase the voltage to 12V, current draw increases to .012A.  Per the Power Formula, the pedal is now dissipating .144 W, a 56% increase in current, even though the voltage is only 33% more.

Wallwarts have very poor voltage regulation, which can be a problem for pedals.  A typical 9V wallwart may put out 14V unloaded.  If the wallwart is rated for 500mA but is feeding only a 9mA pedal, then the pedal may receive near the full 14V.  This can cause a harmful over-current condition as shown above.

Voltage regulation is good.  It prevents over-voltage; and I think that the process of voltage regulation also compresses noise in the DC power supply.