new type of dc protection

[audiofan]

Since almost all power amp work as a giant OP-AMP if you feed only AC signal to the speaker you should not have a DC signal in the power supply, but you will get DC signal in the ceter tap of the power transformer if the amp feed DC signal to the speaker. Detecting DC signal in the center tap and using this to cut power supply output should be possible.
I have started a desing ( uncomplete ).

T1, T2 & R1 can detect DC signal in groud path.

A pair of low saturation voltage FET can be used as " missing device "

There is still some desing to be made ........................

With this configuration you no component ( relay ) in signal path.

[h_a]

Hi,

interesting idea, but it is certainly not universally applicable. Any single ended stage (common source) between ground and + rail will send current into the center tap.

While I know many don't like a protection in their signal path, cutting the psu this way will allow the secondary filter caps of one polarity (to the right) to discharge into your speaker. Better to cut the line to the speaker first IMHO.

Hannes

[audiofan]

I had some spare time so I made a quick test today

I simply add a 100 ohms resistor in the center tap of the transformer in a power amp.

The amplifier is a simple killer and I use it in a resitive load of 7.5 ohms and drive it up to 25 or 30 watts peak with music ( FM tuner )

Using an analog voltmeter acros the resistor readings did not go over 10 Mv (DC) using a digital voltmeter reading remain same average value.

Using an oscilloscope we can see a pulsating signal up to 0.6 volt , synchronised with rectifiers current pulse.

Across the resistor there was also a lot of noise ( i think it was rectifier noise )

[AndrewT]

I wonder if this is similar to what Sage describes in his literature?

[triplej]

Originally Posted by AndrewT

I wonder if this is similar to what Sage describes in his literature?

Yes he had a mysterious (small) black box that lived on the centre tap for DC protection. Never tested its behaviour.