I plan on using an LM3914/LM3915 circuit as a LED vu meter for my PC and it will be connected to the "line out" from sound card. Can anyone suggest a good a transistorized or IC preamp that will suite my needs? Thanks
EDIT: I'd like to build something along the lines of this velleman kit... **broken link removed**
Use the LM3915 for a VU meter because its response is logarithmic like your hearing. The LM3914 is linear and so loud sounds will have the LEDs jammed together at the top and soft sounds will have the LEDs spread out too much at the bottom. The LM3915 also has a wider range of loudness indication.
The Velleman kit instructions are in your attachement and has the schematic of its "half-wave peak detector" and preamp which is similar to the circuit in the datasheet for the LM3915. Why don't you make it?
I like the LM3915 better than the LM3916 because the volume spacing steps are equal. The LM3916 has a range of only 23dB with the bottom space huge, and the LM3915 has a range of 30dB with equal steps.
The circuit is the same for both.
Thanks again for your help, im hoping to get these parts soon to get this started... oh, and i reinstalled adobe acrobat, i can now view all the schematics/pdf files for all the velleman kits.
Most simple FM transmitter circuits on the web have a transistor preamp.
Simple transistor preamps produce very high distortion if the gain and output level are high. An opamp circuit using a modern opamp is much better.
An audio preamp amplifies a low level signal like from a microphone, up to line level. You already have line level.
If you want to replace the opamp circuit in the Velleman kit with a transistorized version then forget it. It amplifies and it is a fairly complicated half-wave peak detector circuit.
Sorry for the bump, quick question out of curiosity... this is still going in a PC using the "line out" from the sound card, will this circuit shown work as well? thanks
The simple peak detector circuit will replace the opamp peak detector circuit in the Velleman kit but it has no voltage gain. Many parts must be changed in the kit to use the simple peak detector circuit.