Coupling Capacitor

The attached circuit has two issues.
(1) When the B+ to the plate is applied, it produces an initial audible hum.
The hum indicates to me that a surge through C2 has taken place.
(2) When the circuit powers up, one of two things take place.
(A) The hum disappears and the circuit performs normally.
(B) The LM4562 is destroyed.
The coupling capacitor does not appear to be doing the job.
Is there another solution?

A and B are mutually exclusive, you can't say it behaves normally but it blows up!
My guess is you will be putting excess voltage on the opamp non inverting input at turn on until it discharges to ground through R6. Diodes are the most common way of preventing this, their placement and the resistors used to limit the diode current depend on the circuit configuration.
By the way, I don't believe you have the opamp configured correctly either, R7 serves no useful purpose,
Cheers,
Richard

Hi Richard,
I've learned that if I don't know what I'm talking about, I listen instead of pretending to know something. You should do the same. You do serve a purpose to this community though. You're an example of someone who should be ignored.
Thanks so much for your contribution...C

Hi,

Let's not make complications here. Can we try making this forum as productive and fun for all? If not, please leave this forum.

Thanks

You didn't indicate how the power is being switched in your schematic. Assuming that it is a switch on B+ and B+ is a low impedance voltage source you could get a very fast edge on power on. The capacitor would couple this fast edge and R6 is too large to damp the pulse (as Richard alluded to).

If this is the case, then a resistor (or series inductor) in series with the battery (to create a RC/LC low pass with C1 (which might need to be increased) will solve the problem. A pair of ESD diodes between the output the blocking cap and the V+/V- rails would also be a good addition as well as a series resistor on the input of the opamp. The series resistor will not affect the gain and will limit the current sinked by the opamp internal ESD diodes when the pulse arrives. You might use a pair of fast zeners (head to head) between the output of the cap and ground in combination with the series resistor instead.

I apologize Kevin.
But I stand by the comment about pretending to know something.
When I'm asked something and I don't know, I say so.
I don't try to dazzle them with brilliance, or Buffalo them with bull****.
From now on I'll keep my negative response to myself.
BTW... Dean Franks makes sense...C

Hi Dean,
Thanks for the response Dean.
Your assumption about switching
the B+ is correct. Your logic is
good, and I'll give those ideas
a try.
Bob Cordell was kind enough to
suggest a pair of anti-parallel
diodes at the + side of the IC
to ground.
Your thinking is similar to his.
Both of which I'll try.
Thanks So Much...C

Hi Charles Johnson,

See my attachment it is self explanatory.

Hi Sambath,
Thanks for the response.
I'm not able to download your illustration.
Can you send it to: netminer(_at_)juno.com?
Thanks...C

Hi CHARLES

using your mouse right click over the image now copy the image ,open word and paste it on that .now go to view and zoom the image to 200 or 150 .

Hi CHARLES,


You can down load the image as i told you . what happened pl reply.

Hi Sambath,
I was able to download the schematic.
It makes sense to me.
I haven't tried it yet, but will soon.
I had quite a few more projects ahead
of that one on the bench. I'll send the
results when I have them. Thanks...C