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In Reply to: RE: Grado RA-1 Battery -to- PSU Mod. Issues posted by Roastaman on January 10, 2016 at 11:51:03
The 9V batteries are connected in series, so you get +/- 9V (DC). If you got AC adapters, you're out of luck. If you got 9V adapters that have -VE tied to the ground lug of the adapter, then you're also out of luck.
Follow Ups:
I have two 9V DC adapters. They both have two prongs no third gnd. plug.
I did check the polarity of both psu's and both were correct.
I did try using one psu with tandem 9volt connectors to the RA-1, thinking it may work because there is a common ground. I was under the impression that the batteries were in parallel not a series.
If the DC converter's ground isn't tied to the -VE prong where would it be tied to?
It's funny cause Grado themselves rec. a Radio Shack 9 volt DC "battery eliminator" and recently, something similar. They look like nothing more than standard 2-prong 9v. DC adapters. I'm wondering if they have the ground connected differently.
See the schematic posted below. The two 9V batteries give you +/- 9V. If the adapters are 2 prong devices, then the DC supply should float, and two separate supplies should work just fine.
Yeah, that's kind of how I figured it but that's not what's happening for whatever reason. I've tried 3 different DC units, swapping out one of the pair for another and always get the same result. Short of chopping into them I can only guess that the grounding scheme is at odds with the RA-1.'
On another note, I'm find direct measurement of the DC output of the 3 to be wildly different; 8.6V, 11.5V, 13.5V. Even another 7V unit I have reads 9-10V. Why so much variation? I just assume when the output is listed as 9V it should be fairly close.
I think I'll just have to stick to batteries.
No cheap wall warts suck and are almost always unregulated. Usually they'll read 10-11 volts unloaded then they'll drop closer to nine with a load on them.
ET
An unloaded power supply may not be that tightly regulated. Your RA-1 draws so little current that you might be better off with a 7V DC supply that says "Class 2 Transformer" on the case.
The wall warts you tried likely aren't regulated. That means their DC output will vary based on AC voltage at the wall outlet, the impedance and current draw of the device they're powering.
My first thought was, "Wouldn't that give you +18VDC?", but a quick search for the schematic turned up the answer.
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