Strange problem with computer and home AM transmitter

As I have posted previously, I've had fine results using my home AM transmitter, the same type that "Bob" on YouTube discusses (although I found the circuit long before "Bob" made his video). It has worked for me beyond my best expectations, using as audio sources an FM receiver and a CD player. I get no hum, no buzz, no "FMing" (whatever that means), no heterodyne whistle or other interfering noise, and more than enough volume. Usual transmitting frequency is about 1300 kc and I cover my entire house plus an appreciable exterior distance.

However, twice now when I attempted to use the audio output from my computer I instantly tripped the house circuit breaker. I first used the headphones jack, then tried the audio output jack on the computer sound card.

I did some troubleshooting, thinking that a voltage leak or somesuch was causing the short but I found nothing out of the ordinary. I checked two transmitter units and both produced the same voltage measurements at the audio-in connection, about 0.5 vdc, 0 vac.

Why this problem occurs only with the computer as audio source is unknown to me. Can anyone help or offer suggestions? Thanks in advance.

Do you have a transformer on the audio input? If there isn't a transformer there, there may be some sort of difference in voltage potential causing the issue. I haven't tried using a computer as an audio source for my transmitter, but I have used sources using A/C power with no trouble at all. I'll try it with mine tomorrow.
Dave

I gave my transmitter a whirl with it connected to my computer and had no problems at all. If your transmitter design doesn't have a transformer on the audio input to isolate the source from the radio, add one. If it already has one, make sure that it's not shorted.
Dave

Problem solved! No one, apparently, took note of the 0.5 vdc (actually, closer to 0.6) measurement at the input that I had noted. The reason for the voltage is that I had neglected to make certain that the "hot" terminal of the volume control is free of all original connections. I snipped a side of a resistor that was still there, tried the unit at the computer audio output again, and--lo!--no circuit breaker tripping.

However, another simpler problem was present. The audio quality was poor--too much hum. A matching transformer took care of this right away. I've had the transformer, an antiquish 5:1 unit, in a hell box for almost 35 years. I simply connected the primary side to the computer audio output and the secondary side to the transmitter audio input. So, all in all, an interesting problem and a successful learning experience. But why the other audio sources (an AM-FM receiver and a CD player) did not also create a short and trip the house circuit breaker remains a mystery.