Simple Pre-amp

[danrogers]

Thanks, what is a peak detector then, I guess that is external circuitry before the the input on the signal pin?

I was hoping it would be simple but its looking more complicated by the minute

 

[audioguru]

I made a few LM3915 bar graph displays. I always include a peak detector circuit.

 

[danrogers]

anything like the peak detectors in the datasheet Guru?

 

[Dragon Tamer]

Yes, the peak detectors in the data sheet do work, but the average detector gives the best results in my opinion. Trying to make the circuit without a peak detector will give you a horible disorgonised mess.

 

[danrogers]

Thanks, so you recommend using the "Precision Full-Wave Average Detector" instead of the others? On the data sheet, some of the capacitor vaules do not display which decimal they are in, for example.. C1 0.2, or 0.47. Are these in farads?

 

[audioguru]

you recommend using the "Precision Full-Wave Average Detector" instead of the others?

The simple transistor peak detector needs a fairly high max input of about 10V peak.
The full-wave peak detector is too complicated and the LEDs will look like the much simpler half-wave peak detector anyway.
The simple half-wave peak detector with an opamp uses an opamp that needs a dual-polarity supply. My circuit uses an MC33171 single or MC33172 dual single supply opamp that does not need a negative supply and works from a supply as low as 3V.
I use a transistor instead of a rectifier diode because it can charge the filter capacitor very quickly. I am attaching my half-wave peak detector schematic.

On the data sheet, some of the capacitor vaules do not display which decimal they are in, for example.. C1 0.2, or 0.47. Are these in farads?

The capacitor values are in micro-farads.

 

[danrogers]

Thanks Guru as always! I think I will try out your circuit