TUTORIAL Measuring Pedal Current Draw

finebyfine

Well-known member
I recently had a commission that I was worried would draw more than the typical wall wart 100mA and was kind of surprised I had never measured a pedal's current draw before! I couldn't find a tutorial on this forum - apologies if I just missed it, so here's a short guide.

All we need to do is break one of either the ground or +9v(18, etc) power connection to the circuit, and recreate that connection through a multimeter set to measure current. Basically this:
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With PS being our pedal power supply, A being our ammeter, and RL representing our circuit / pedal.

There's a lot of ways to do this physically with varying degrees of having to finagle multimeter leads and circuit wiring, but we can also wire up two DC connectors together, leaving one path broken that we'll measure from. Conceptually, but starting to get less abstract, we can imagine it as this:

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I wired one up using a male DC connector on one end - to go into my pedal - and a female DC connector on the other - to connect to a power supply. For ease of use I added test clips on the broken path.

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For something a bit more skeletal, this would do the job too (imagining the contacts on the mat soldered). My male DC plugs are pretty flimsy and I thought this would break with one use if I made it.

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The test clips also make it easy to make sure everything's in working order before measuring.

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And once we're all connected and we have a reading, turn the pedal off and on to make sure you see a difference, fiddle with the knobs and play into it so we know the reading is representative of using the pedal. (Output cable was disconnected just for a neater picture but made no impact on the current)

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8.75mA is in the reasonable range for most fuzz pedals so we're looking good! The original Boss pedal's current draw is about double this, but also has relay switching and buffered bypass. The actual pedal I got this all setup for ended up staying pretty consistent at 70mA so a regular wall wart does the job :)
 

finebyfine

Well-known member
I'm really digging how others are starting to contribute to the Test Kitchen! The more we share/teach others the better we get as builders.

I’m really glad to hear that, I wasn’t exactly sure if this was the right spot for it and didn’t want to step on your toes if it wasn’t. Had a lot of fun writing it up :)
 
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BuddytheReow

Breadboard Baker
I wasn’t exactly sure if this was the right spot for it and didn’t want to step on your toes if it wasn’t.
Who said the Test Kitchen is mine? I enjoy doing all the write ups here. It's a way passing on what little knowledge I have to those that want it and to save countless hours searching google. My hope is that others follow suit such as yourself.
 

PedalPCB

Admin (Robert)
Staff member
Great tutorial sir! My PSU reports current draw but knowing how to diy is much more useful. :)

Is your PSU accurate at low mA? I tried a couple last year and they didn't give very accurate readings at single digit mA ranges.

If so... which one do you have?
 
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fig

Village Idiot
Good point. I've got a Siglent SPD3033X-E. It claims current accuracy readback .5% of reading +2 digits.
 

PedalPCB

Admin (Robert)
Staff member
That one is significantly nicer than the one I had. I might have to give one of those a shot and see if it's any better.
 
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