# Milliamps, please explain in great detail.

Discussion in 'Effects [BG]' started by Josh Ryan, Jul 19, 2002.

1. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
Hi all, I've recently been told that everything I know about mA, (which could fit in a fortune cookie, no problem) is wrong!!! Can someone give me the technical rundown? the definitive answer? the final word? the TRUTH with a capital TRUTH? I'm sort of confused about it again.

edit: pedal power is the reason, of course.

2. ### pudgefactor

Mar 28, 2002
Boston
mA in terms of what? A milli-amp is one-thoasandth of an amp. An Amp is a measure of the
flow of electrons. The good ole engineering formula is [ Voltage = Current * Resistance , V=IR ].

Impedance is basically Resistance in this formula. A 4 ohm cab sucking up 20V will be using 5 Amps, or 5000 mA.
(Impedance is resistance with a phase altering relation to sinusoidal signals and involve more complex formulas than V=IR)

An example might be: a signal from your bass is a +/- 1.0V 10Khz signal. This feeds into a filter with
a bad bypass that offers 50 ohms of resistance. Your amp is only getting a +/- 20mA 10Khz input signal (+/- 0.02A).

I'm a little rusty on this...........

3. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
In a nutshell, if I have a wall wart with a mA rating of say, 350, and a pedal that says 9v 100mA, can I use that wall wart for the pedal? And what makes that OK? My friend had his theremin repaired recently, and I went with him to pick it up. The technician who repaired it said that the high mA of the plug he was using cooked a resistor inside the theremin.

4. ### BigfeetRegistered

That's 1/1000th of an amp, very low resistance and voltage... like pudgefactor said.

5. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
OK, I'm not getting my point across for some reason. Maybe if I break it down. I have a wall wart that's for a 9 volt 500mA pedal. Can I use this for any pedal that is 9 volt, and LESS than 500mA?

6. ### BigfeetRegistered

pretty much... yeah

7. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
OK, the guy who fixed the theremin said that would burn out the pedal, that's where they confusion comes in. I'm wondering what the juice box or the Voodoo labs thing do to not destroy pedals.

8. ### BigfeetRegistered

If you're affraid it will burn it out why not just but a new power suply? They're pretty cheap already, and besides I would rather trust the guy who fixed the theremin than us.

9. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
Well, I wanted to use an all in one to minimize plugs, and you guys haven't steered me wrong yet. In general you all seem to know what your talking about here, so I thought I'd ask in the hopes of getting a response like, "the power brick things send only the mA needed" or something like that, if that is the case. I can't imagine Dunlop or Voodoo labs make a products that actually destroys pedals, but I was hoping for some confirmation.

10. ### Jeff MooteSupporting Member

Oct 11, 2001
I'm not sure I would, here's why: max current rating of the supply (500 mA in this case) is how much current any loads may draw from this. If a pedal draws 13mA, then that's what it draws. The power supply doesn't force electrons through the circuit. Where the opposite is true, is if you use, say a 12VDC adapter for your 9VDC pedal. This puts the full 12V through it, and can cook it, but current is drawn, not pushed.

Hope that helps

11. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
Yes ,that is EXACTLY what I was asking! Thanks MontyP!!!!

Oct 11, 2001
No problem

13. ### MunjibungaTotal Hyper-Elite MemberGold Supporting Member

May 6, 2000
San Diego (when not at Groom Lake)
Independent Contractor to Bass San Diego
The theremin repairemin is full of beans, and Monty is correct. I remember at least that much from when I used to teach electronics (back in the 60's, LOL).

14. ### Phat Ham

Feb 13, 2000
DC
We just studied power supplies last semester and MontyP is right on the money. The 500mA rating is just the maximum the wall wart can supply. Like Munji said the theremin repair dude doesn't know what he's talking about. just goes to show just because someone is a "professional" doesn't mean that person knows anything.

15. ### Paul A

Dec 13, 1999
Hertfordshire U.K!
I think they are 'bout 2 inches long with loadsa legs...

16. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
Thanks all, thats what I was looking for!

17. ### BigfeetRegistered

In the 60's, eh?

18. ### Mark Reccord

This is absolutely........correct. Time to get a new repair guy! If what he was saying was true, you wouldn't be able to plug, say, a TV that only draws 4A into a wall socket that can provide 15A. How inconvenient would that be?

19. ### Josh Ryan- that dog won't hunt, Monsignor.Supporting Member

Mar 24, 2001
True! It rung false to me, I'm glad you guys could clear it up.

Oct 11, 2001