Author Topic: Is it okay to have a small resistance between 9v and ground?  (Read 429 times)

Esppse

Is it okay to have a small resistance between 9v and ground?
« on: January 13, 2019, 12:11:21 AM »
Hello,

I'm building a project where 15 distortions and modulation fx are daisy chained.

I have not powered up yet. Just doing continuity tests. There is zero continuity between audio in/out and ground. Good.

There is 577 ohms between 9v and ground when every thing is unpowered. Is that ok? Is this how transistors/ICs/components are supposed to display resistance when no voltage is applied? I was very careful and tested each circuit individually for sound and functionality before daisy chaining. All grounds are star grounded. Just concerned a bit before powerup.

Thanks

anotherjim

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #1 on: January 13, 2019, 04:31:47 AM »
If all of that looked like it was only going to draw 15mA (9/600) I would be pleased. However, the test meter is not going to drive the circuits into their fully biased working condition. It is a good indication that there is unlikely to be anything nasty going on and reduced likelihood of hearing that "Pffft" sound and wisp of smoke when you power it up.
But you always need to be ready to turn it off quickly ;)

"Designing with PLLs in production circuits is reserved to those with the courage of the thoroughly uninformed."
Nuts & Volts
"Turtles have the short legs, not for the walking."
-Kenji "Damo" Suzuki

Esppse

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #2 on: January 13, 2019, 10:12:55 AM »
OK thanks a lot, I'll be sure to take quick precautions!

antonis

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #3 on: January 15, 2019, 05:52:00 AM »
Don't get me wrong but if you measure with your tester set on "continuity" with reversed probes, you might get 577mV(not Ohms) reading in case of reverse polarity protection diode between +9 & GND ..  :icon_wink:
Can't follow your signature changes, Stephen..!!
but I like what follows:
"put the coffee down, Antonis, and nobody will get hurt."
"Arggg, Jim ...."

Esppse

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #4 on: January 16, 2019, 02:58:04 AM »
Ooomph, it was on continuity. Yikes. OK I switched it to 2000 ohms setting, it says 1277 ohms, does that raise alarms or is that still cool?

antonis

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #5 on: January 16, 2019, 05:18:29 AM »
Can't say for sure without any schematic but 7mA current draw (without semiconductors activated) should be considered cool enough..

A rough estimation of expected resistance could be made by any obvious resistors set between +9V & GND..
(e.g. Vref voltage dividers, transistors bias networks, etc..)
Can't follow your signature changes, Stephen..!!
but I like what follows:
"put the coffee down, Antonis, and nobody will get hurt."
"Arggg, Jim ...."

Esppse

Re: Is it okay to have a small resistance between 9v and ground?
« Reply #6 on: January 16, 2019, 06:34:55 AM »
Yeah most are distortions that draw about 5 to 15 ma. All together every effect should sum up to about 300ma maybe since there are a couple digital fx too.