Re: Using Op-Amp to drive Amp Gauge with Audio Signal

On Feb 26, 8:22 pm, Tom <kuh...@xxxxxxxxx> wrote:
On Feb 26, 7:28 pm, John Popelish <jpopel...@xxxxxxxx> wrote:



Tom wrote:
Just to let you know it worked great!

Excellent. Now we can move on to making the scale read in
decibels. ;-)

I do have one concern that I
was wondering if I could get some advice on. I set up everything as
mentioned above. To get the +/-12V for the op-amp, I took my 24V
supply and split it with two resistors. The tap in the middle being
ground. I had to use that as ground for the audio ground and the final
output resistor. My concern is what problems could be encountered
having the audio ground hooked to this "floating ground" and at the
same time having the ground go to the main amp? Is there a way to
have the V- be ground without having to DC offset? Possibly the
bridge before the op-amp?

The only risk I can think of is if turning the volume way up
bounces the 24 volt supply around, feeding another,
unintendedsignalinto the circuit. But if the 24 volt
supply is stiff or regulated, that is not a problem. The
opamphas to be able to swing both ways to work with theAC
signal. So the simulated split supply is probably fine.

Tom

--
Regards,

John Popelish

Awesome,

Thanks for the help!

Tom
I finished up the circuit for the VU meter. It worked great when I
hooked the inputs to my iPod, so this morning I began installing it in
the amp(I was supposed to be painting the house, and there was hell to
pay) Well lo and behold, it does not work. I was wondering if any one
could help me out? Below is a simple diagram I made in SPICE.

Diagram at -> http://spilledwhine.com/pics/AmpCircuit.JPG

Please note that the values are correct and the bridge is actually a
chip, but I did not find one in the library, so I just drew 4 diodes.
My meter is the between the bridge and resistor.

The problem I am having is that when I connect the signal ground to
the amp, it seems to remove my floating ground, so that the input to
the op-amp is now 27V, where as when it is hooked to the iPod, the
power is properly split +13.5/-13.5. I am sure it has to do with using
a virtual ground in this setup. I think the virtual ground is getting
shorted out to system ground.

I have been looking into using something like a MAX4242 Op-amp that
does beyond-the-rail. From the literature, it can be used for AC
without any bias. I am hoping that it could be the solution.

Can anyone help me out?
.

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