9vdc into 16vac circuit. Possible damage?

[digi2t]

Hey folks. Quick Q...

I have someone that just wrote me saying that they plugged a 9vdc adapter into the Frostwave Funk-a-Duck, which is designed to use a 16vac power supply. The AC is taken down and split into +/-15 by 7815/7915 combo of regulators.

I'm wondering if any possible damage may occur in this case? I know the actual voltage is much lower, but I'm not sure if introducing DC into a power section designed for AC could maybe damage the regulators regardless.

No reported damage yet (builder doesn't have a 16vac PS at the moment), but just want to brace them for the possibility.

Schematic;

[EBK]

Given that at least one manufacturer (ST) was willing to put the phrase "essentially indestructible" on their 78xx spec sheet, I cannot imagine that one of these regulators has failed under these circumstances.

[R.G.]

That's a definite maybe.
Applying DC to that circuit forward biases one of the two power input diodes, reverse biases the other. Depending on the polarity of the connector feeding it into the circuit, either the 7815 or 7915, but not both, will be activated. The other is held off by that input diode not letting any current through. There's not enough DC voltage there for the "on" regulator to work properly, so the output of the regulator will be about a couple of diode drops lower than the input DC. The active regulator will put out about 8.something volts.

So, no damage to the regulators. Whether anything else in the pedal will be damaged depends on whether the circuit has some components/connections that are damaged by one power supply being there at a lower DC voltage than intended. I have not dredged through the circuit to find out everything about what might happen.

If it seems to have survived, it probably did. Most likely.

[digi2t]

Muchos gracias for the info. Looking at the min/max values of the 3080 and TL07*, I don't believe that anything is toasted either, but I'm not high enough on the knowledge totem to know better, so that's why I thought it best to throw this out here.

Final determination will be when they plug in the right adapter.

Thanks everyone.