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Hum from σ25 w/wall wart

sigma25, sigma26, sigma24

Re: Hum from σ25 w/wall wart

Postby funch » April 23rd, 2018, 9:18 pm

Oops. My bad. Pin 1 to ground is 27.61VDC.
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Re: Hum from σ25 w/wall wart

Postby amb » April 23rd, 2018, 11:01 pm

OK, so the 7818 is getting a 27.6V - 17.9V = 9.7V of dropout, which is above the minimum of 2.5V to maintain regulation. Do you have another 18V DC supply that you could test with to see if there is hum? Maybe the amp itself is making the hum noise...
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Re: Hum from σ25 w/wall wart

Postby funch » April 24th, 2018, 9:14 am

I previously tried two 9V batteries to power the amp, and it was dead silent.

It's looking like the wall wart is the culprit. Time to look for another tranny I suppose.
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