DC Servo question

[artquake]

I think a DC detection circuit is for fault conditions. Because in some case there may be very high DC offset levels on outputs. And if its a fault condition (like output transistors fail) you cannot control the DC offset with a DC servo..

Ok, but in my thoughts the insertion of a servo is to control the offset in a limited width and if the circuit has faults then a servo anyhow can't help and when the output transistors fail too. Is there a need for DC detection when you add that allready in the speaker protection ? It's the last component which could get damaged when transistors fail.
With my question I meant that dc - detection circuit would help in the servo circuit when the servo has faults (changing polarity or other deseases) ... because that will/can blow the chip accordingly ... not ?

artQuake

 

[Dxvideo]

Wait, wait...
As I understand, we were talking about just two circuits;
- One DC servo which will control a limited DC error,
- And one DC detector which will sense big offsets and OPENs the speaker line, so its a speaker protector.
And are you talking about a third circuit which detects big DC offsets and do what?

 

[ken.berg]

So where is the NFB return?
I can only see a speaker in and speaker out connections!

Look at the bottom of Greg's board in the thread posted above. The feedback control signals do not pass through connector blocks; they are hard soldered to the input stage.

- bkb

 

[artquake]

Dx, i meant that out of andrew's post ....

No, it's a DC servo with added DC detection and cut off when beyond the range that the servo can correct.

Maybe i missunderstand that but when the dc detection's cutting off beyond the range of the servo, than also cutoff will react when servo is defect ... isn't it ? On the other hand why servo then ? Would be interesting to know how such detection circuit looks like ...

Would it substitute/replace the functions of a speaker protection circuit ?

 

[AndrewT]

The DC servo is only capable of correcting a small offset and is usually incapable of fast correction of pulses.
The DC detection/cut off should limit the effect of pulses or offsets that get past the DC servo.

 

[Dxvideo]

As I mentioned in another topic;
That DC servo matter becoming a complex situation!
If we add a circuit that will compansates the DC offsets, add another circuit to protect the speakers from also DC offsets and our speakers are still not in safe !!!!
What other precautions should we take?

 

[AndrewT]

...... and our speakers are still not in safe !!!!
What other precautions should we take?

lock off the power at the distribution board and go to bed when it gets dark, to avoid the need for candles.

 

[Dxvideo]

I am happy with my non DC servo and "semi DC coupled" LM4780 amp... (~50mV offsets on each channel)
But I think somebody needs these three circuits together..