No damage done but had a Blonde moment

[62vauxhall]

I was listening for turntable hum between two of them plugged into the preamp's single phono input via a (cheap) turntable switcher. The hum was low level so I had the preamp's volume quite high. Not thinking (or not thinking quickly enough) I hit the switcher to go to the second table without backing down the volume. This produced a very loud transient that affected the WOPL'd 700B. After this incident, it was only producing a very small amount of sound which was extremely distorted. I figured I cooked something for sure but even though there was still noise coming from the amplifier, I thought I might as well check the fuses anyway. Turned out the bottom pair of 5A were blown. Put new ones in and the amp is fine. So now this is making me wonder why there was any output at all with those blown fuses? I assumed, obviously wrongly, that the amp would be completely dead signalwise with those fuses out of commission.

 

[laatsch55]

There are two separate power supplies, one fused and one unfused. When a rail fuse goes that still leaves the control board functioning, so what you were hearing was the predrivers doing their thing...I think, Joe will have to confirm that...

 

[laatsch55]

It cpuld also be just the positive part of the waveform coming through.

 

[Gepetto]

There are two separate power supplies, one fused and one unfused. When a rail fuse goes that still leaves the control board functioning, so what you were hearing was the predrivers doing their thing...I think, Joe will have to confirm that...

Lee is correct, the main output fuses blew on the bottom side but the top fuses were still in place and the control board was still active. The small signal transistors on the control board were trying to drive the load on the negative half of the signal.

 

[orange]

If it was a blonde moment, was she worth it?