Best type of Preamp for guitar/mic FX

Thread Starter

lofiboy

Joined Dec 26, 2010
15
I need to boost a guitar signal to a minimum 4.5v for a project involving a 555 timer. What would be an effective, single stage, discrete transistor amp to utilize for this?
 

marshallf3

Joined Jul 26, 2010
2,358
Let's see, a guitar pickup jack output is usually around 10K - 47K and the output is between 100 mV to upwards of a volt - all specific to the type of pickup(s), player, type of strings used etc. No real standard on this.

An op amp would be the ideal solution but if you can put up with a bit of distortion I'm sure our resident expert on audio gear can suggest something using a single transistor with a gain of 400. He'll be along soon enough sometime in the morning.
 

Thread Starter

lofiboy

Joined Dec 26, 2010
15
A bit of distortion could possibly be a good thing in this project. If an op amp would offer better fidelity, then I think I could use one at the output stage instead.
 

Thread Starter

lofiboy

Joined Dec 26, 2010
15
Well, I don't really have one but I can try my best to describe it; it's basically an astable oscillator using a 555 timer. The amplified guitar/mic would be fed into pin 5 to modulate the oscillation, and a variable capacitor would control the effective sample rate, hopefully attaining a decimator kind of effect.
 

Thread Starter

lofiboy

Joined Dec 26, 2010
15
Pulse width modulation, as of right now. I didn't know about pulse position modulation. Thanks!

As the purpose of this circuit is to imitate low resolution digital sampling, I think I best keep the PWM scheme, though PPM seems like it could be used to make a cleaner amp out of the 555.

What is, if any, the original purpose of the 555's PWM and PPM abilities? I'm sure it wasn't intended to be used in audio fx processing!
 

bertus

Joined Apr 5, 2008
22,270
Hello,

The pin 5 was intended to create a for example an FSK (frequency shift keying), a modulation technique used in the old days to transmit a telex signal.

The pin 5 can also be usd for a low frequency FM modulation.

Bertus
 

Audioguru

Joined Dec 20, 2007
11,248
A guitar magnetic pickup needs a preamp with an input impedance of at least 1M ohms which is much too high for an ordinary transistor.
Here is a recommended preamp for a guitar magnetic pickup that has low gain that can be increased by reducing the value of R2.
 

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