Help with schematic.

nenad88

Member
2016-11-06 11:28 am
Is this tl081 acting as servo in this amplifier output?

$_57.JPG
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
:cop: Moved to 'Everything Else'.

The opamp is configured as a simple inverting amplifier/mixer with a gain of 100k divided by 33k on each input (L and R). The input impedance is 33k.

The two diodes (which I assume were to be some kind of limiter) serve no purpose because there is never any measurable signal at that point... its a virtual earth mixer.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
Of course it is not any sort of "servo". What does the sales-page call it?

It senses sustained DC from a Power amp and cuts-out a relay. Opamp gain is about 3. The inputs could be swinging 40V peak. Above 4V peak the "summing node" will be overwhelmed. While the TL0 input can take some abuse, the diodes are wise.

Q1 Q2 are a full-wave rectifier. Either + or - input here, over 0.6V (0.2V at amp) will turn-off Q3, open the relay.

C58 deemphasizes stuff over 2Hz (audio). C59 with 470k sets a 2+ second delay before cut-out to reduce false triggering.
 
Of course it is not any sort of "servo". What does the sales-page call it?

It senses sustained DC from a Power amp and cuts-out a relay. Opamp gain is about 3. The inputs could be swinging 40V peak. Above 4V peak the "summing node" will be overwhelmed. While the TL0 input can take some abuse, the diodes are wise.

Q1 Q2 are a full-wave rectifier. Either + or - input here, over 0.6V (0.2V at amp) will turn-off Q3, open the relay.

C58 deemphasizes stuff over 2Hz (audio). C59 with 470k sets a 2+ second delay before cut-out to reduce false triggering.

I agree. It looks for DC and protects speaker by disconnecting power.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
> to eliminate dc component.

It disconnects the speaker when it sees "too much" DC.

"Too much" is roughly 0.2V for (I was *wrong* before) more than 0.2 seconds. (The 470k+100uFd is a turn-ON delay.)

0.1V of DC can happen forever.

A very strange condition: +1V on L and -1V on R will never be detected.