Author Topic: Strange amperage reading on my power supply -.001  (Read 1588 times)

blearyeyes

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Strange amperage reading on my power supply -.001
« on: February 02, 2018, 08:05:17 PM »
When powering a circuit I usually see the amperage at a normal draw say for a distortion it might be .005 or 5ma. But while powering my Ultrastoner build it shows up @ -.001 or -1ma.

Iím trying to diagnose why the Ultrastoner doesnít sound right.. maybe DC leaking into the ground plane?

Can anyone give me a reason this might be?

davent

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Re: Strange amperage reading on my power supply -.001
« Reply #1 on: February 03, 2018, 02:48:01 PM »
Total shot in the dark... too big a resistor in series with the power supply?
dave
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blearyeyes

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Re: Strange amperage reading on my power supply -.001
« Reply #2 on: February 03, 2018, 03:06:53 PM »
Well it's a cheap $50 linear power supply, I figured after 10 9v batteries it pays for itself. I just put a (pinhical) clone on it and it is reading -002 so I'll just have to chalk it up to another unanswered question of the universe.

somnif

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Re: Strange amperage reading on my power supply -.001
« Reply #3 on: February 03, 2018, 03:35:41 PM »
Well, lets see. The 9V rail juices 4 transistors and an LED. Depending on the version you went with, each tranny pulls between 0.4 and 0.9 milamps. So a total current draw of 2mA is.... not outside the realm of possibility.

As for why its negative.... cheap DMM or leads plugged in the wrong sockets? Dunno.

blearyeyes

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Re: Strange amperage reading on my power supply -.001
« Reply #4 on: February 03, 2018, 03:51:43 PM »
Well, lets see. The 9V rail juices 4 transistors and an LED. Depending on the version you went with, each tranny pulls between 0.4 and 0.9 milamps. So a total current draw of 2mA is.... not outside the realm of possibility.

As for why its negative.... cheap DMM or leads plugged in the wrong sockets? Dunno.

It's showing up on my linear power supply that I use on my
"bench”which is of course a folding table. I'm suspecting my cavalier grounding practices. BUT I'll check if I reversed the leads.

Dumber things have happened here....

Nope red is red and black is black.
« Last Edit: February 05, 2018, 06:02:34 PM by blearyeyes »

reddesert

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Re: Strange amperage reading on my power supply -.001
« Reply #5 on: February 03, 2018, 10:17:16 PM »
Sometimes at the limit of precision/accuracy of a meter, you get funny or unreliable readings.  I can get readings of a few millivolts by waving my DMM probes around in the air, due to induced currents, CFLs, or the Ghost of Pedals Past floating around the room - who knows? If your current draw is below a couple of mA, maybe the minus sign is insignificant. I would follow the usual debugging advice for the project (voltages, check continuity, audio probe the signal path, etc).

blearyeyes

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Re: Strange amperage reading on my power supply -.001
« Reply #6 on: February 04, 2018, 03:37:42 AM »
Yea, it's the amperage readout on my cheap power supply.
My cheap meter acts the same as yours.

I guess the operative word is "Cheap"
« Last Edit: February 05, 2018, 06:03:38 PM by blearyeyes »