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Topic: Make a Preamp with 2N9304 Transistor/Arduino (Read 1 time) previous topic - next topic

dsese1234

Hello Guys,


I have wonder How i can build 1 Preamp using 2N9304 Transistor. and the output should be connected to the Analogs Pin. I am  trying to  very basic guitar effects. But i dont know how to build preamp.  :smiley-roll-sweat:



Dsese.





Be careful what you mean by "preamp".  A Mesa Boogie Tri-Axis is considered a preamp as is a Neve 1073.  (The Tri-Axis is a guitar preamp and the Neve 1073 is a mic preamp.)  These are very different gadgets even if their principal function is to boost the gain of a low-level signal. 

By mentioning guitar it's presumably you will want your circuit to overdrive or distort.  Is this correct?

Brandon

retrolefty

#3
Sep 03, 2012, 03:54 pm Last Edit: Sep 03, 2012, 03:56 pm by retrolefty Reason: 1

Hello Guys,


I have wonder How i can build 1 Preamp using 2N9304 Transistor. and the output should be connected to the Analogs Pin. I am  trying to  very basic guitar effects. But i dont know how to build preamp.  :smiley-roll-sweat:



Dsese.






Well first you have to deal with a hardware restriction, an arduino analog input pin (as well as digital pins) cannot safely handle AC voltages, which is what a audio signal is. The negative part of the waveform has to be biased such that the whole audio waveform is contained in a 0 to +5vdc voltage range that an arduino can handle electrically. A single transistor circuit is a rather limited way to amplify and bias a low level audio signal. A two stage op-amp in a 8 pin DIP package is probably the minimum way to go. Second, what do you want your program to be able to do with this analog audio signal? An arduino is pretty limited in what it can extract from such a signal and limited SRAM space makes storing such sampled information very difficult.

Lefty

DVDdoug

FYI - It's a LOT easier to build a preamp with an op-amp than with transistors.   You can make a preamp with an op-amp and two resistors.  You can make a buffer amplifier  (an amplifier with a gain of 1.0) with an op-amp and no other components (except for a couple of bypass capacitors, and of course a power supply).

What are you planning to do with the Arduino?   Are you trying to use the Arduino as an effect box/pedal, or are you making a lighting effect or something like that?

The signal from an electric guitar is somewhere around 1V, so you don't really need to amplify it.   However you do need to deal with the negative half of the signal, and it wouldn't hurt to use a buffer amplifier to isolate the guitar signal from the Arduino and the negative-voltage protection circuit.

MarkT

If you want a low-noise pre-amp you'll find many op-amps are noisy and you might need to chose carefully.  This will matter most for a microphone preamp rather than guitar though.

With audio preamps you first need to know your source's output level and impedance and look for a circuit that is designed for that.  Feeding a guitar signal to a microphone preamp for example might lead to over loading and distortion, and vice-versa might mean insufficient output or too much noise.

The generic class-A amp is pretty simple and can perform quite well - you'll need to find a tutorial that explains how to set the gain and input impedance and choosing the right bias point.
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