looking for a clipping indicator schematic

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gusfinley

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I'm building a preamp for an Audio to Digital converter and am looking for a schematic for a clipping indicator. I want the "clip" light to turn on just before I hit the 5V peak to peak threshold. Anybody know where I might stumble across such a circuit diagram?
 
You can get an IC comparator, many are dual, quad, or more which you might not need. You can bang together a single comparator with an opamp if you have some extras, here is a page that gives some schemos:

http://home.cogeco.ca/~rpaisley4/Comparators.html

Just add a LED at the point labeled "output".

I tend to like indicators that glow a little before they get full on, that is even easier to implement with a single transistor driving a LED off the signal, you just need to select the LED forward voltage close to what you want for level, or attenuate the signal accordingly. A cap can smooth things out as far as the LED flickering.
 
You could take it a little closer to metering by using a tri-color green/yellow/red led, hooked up to a quad comparitor with the references set at three different signal levels.
 
Hmmmm....

I've been messing around with these comparator circuits and I'm having a but of trouble getting them to work right...

Let me be a little more specific, I have half of an NE5532 opamp remaining after building my preamp, so I am hoping to use this as the comparator. I want my "clip" led to turn on just before I reach the 5V peak to peak limit of the Analog-to-digital convertor. The supply rails on the opamp are +12V and -12V.

Am I comparing my voltages wrong? I am comparing a DC signal with an AC signal, and perhaps that is causing some trouble. Perhaps the +12V and -12V rails are causing trouble? I'm not sure... but something is a little screwy!!
 
gusfinley said:
I've been messing around with these comparator circuits and I'm having a but of trouble getting them to work right...

Let me be a little more specific, I have half of an NE5532 opamp remaining after building my preamp, so I am hoping to use this as the comparator. I want my "clip" led to turn on just before I reach the 5V peak to peak limit of the Analog-to-digital convertor. The supply rails on the opamp are +12V and -12V.

Am I comparing my voltages wrong? I am comparing a DC signal with an AC signal, and perhaps that is causing some trouble. Perhaps the +12V and -12V rails are causing trouble? I'm not sure... but something is a little screwy!!
Click to expand...

Did you see the schematics I linked? You need to divide the +12V supply to create a +5V reference for the opamp. Then when the signal hits +5V, the LED will light. It doesn't matter that it lights in a half-rectified manner, you can use a cap to smooth out the LED's blinking.
 
mshilarious said:
Did you see the schematics I linked? You need to divide the +12V supply to create a +5V reference for the opamp. Then when the signal hits +5V, the LED will light. It doesn't matter that it lights in a half-rectified manner, you can use a cap to smooth out the LED's blinking.
Click to expand...

yeah, I've created a voltage divider to give it a reference of 2.4V (max for half of the wave) but as soon as I plug it into the opamp terminal the voltage is no longer 2.4V. Wierd stuff like this keeps happening when I wire up the circuit. I works just fine in simulation, but when I wire it up its a different beast.. perhaps I'll go back to the transistor clipping indicator, but I wouldn't really like something that is non-linear....
 
gusfinley said:
yeah, I've created a voltage divider to give it a reference of 2.4V (max for half of the wave) but as soon as I plug it into the opamp terminal the voltage is no longer 2.4V. Wierd stuff like this keeps happening when I wire up the circuit. I works just fine in simulation, but when I wire it up its a different beast.. perhaps I'll go back to the transistor clipping indicator, but I wouldn't really like something that is non-linear....
Click to expand...

How much current to you have in the divider?
 
mshilarious said:
How much current to you have in the divider?
Click to expand...

not much. (.2mA or so) I used a 50K pot to set the reference voltage level.
 
gusfinley said:
not much. (.2mA or so) I used a 50K pot to set the reference voltage level.
Click to expand...


Hmm. OK, how about the LED, could its current be dropping your power rail :confused:
 
I brought this up with my instructors and they were baffeled as well... It didn't work for a simple DC comparator!! Looks like I'll look into different comparator circuits or perhaps a different type of clipping idicator circuit!!

Thank you very much for your help, though!! It would have been nice if it worked like it simulated in Spice!!
 
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