Preamp

hey, does anyone know of a cheap and very simple mic preamp I can build? I want to install it in my mini amp I built so i can plug my guitar right in to it. I also want it to have a rather hot output so I can have distortion.

I have a few transistors, dont know what kind tho. I'd like to be able to find whatever I need at radio shack. Also, I have a 12au6 and 12be6 tubes, can either be used as a preamp for guitar?
 
From the questions you ask I think you may not know the basics in electronics. Please forgive me if I am wrong.

Doing DIY audio is alright if you know how to deal with voltages and currents, and you should start with basic stuff as you learn your way up. Going straight to a chip may be problematic too.

It can also be very dangerous, not to speak of being very expensive, both in the things you build and destroy as on the others your interface your projecs with and may get burnt.

It may be better to get a ready made module, where you can plug your guitar and get along.

Chip amplifier projects are easier to get running, but you still have to know quite a bit. But this chips have also contributed to man prices going down, so you will still be benefitted from them.


Carlos
 
well I already have a power supply for my guitar amp thats suitable, I'm sorry, this was a little off topic, the transformer question was about my portable audio amp that I built , not for guitar. By the way, every chip amp I've built sofar is still working ( with the exception of the 12 watt one I fried before I understood operating a chip AT its maximum supply voltage was bad...very bad..) Anyways , about the transformer, I know I need a regulation circuit. I was simply asking what amperage my amp needs and how to find out/calculate it.
 
I found a design online for a simple preamp, hooked it up on a breadboard and it sounded great! although the distortion goes up as voltage goesdown.

has a slight background hum thats just noticable. Anything I can do to help this? heres the schem.

Magnetic_mic_to_amp.gif
 
ThSpeakerDude88 said:
I found a design online for a simple preamp, hooked it up on a breadboard and it sounded great! although the distortion goes up as voltage goesdown.

has a slight background hum thats just noticable. Anything I can do to help this? heres the schem.

This one might be a better, more stable option:

http://www.redcircuits.com/Page49.htm

As this is a mic preamp and you intend to amplify a guitar, there might have to be some attenuation at the input so as not to overload it.


Carlos
 
The ideal thing would be to first put a multiturn-pot at the input with no pot at the output. It's not a good thing that a source (the guitar) "sees" a variable resistance at the preamp input. So you try different positions and then replace the pot for a series/parallel resistor combination. But this might be problematic without a scope to see where the transistor is clipping.

Let's do a different approach to your problem.

Why not try a proper guitar preamp instead? Something like this might do the job:

http://www.till.com/articles/GuitarPreamp/

This will probably work fine.


Carlos
 
well, I tryed it, but it didnt work. Just a nice low power hum. What could I have done wrong?I cant seem to find anything to make the mpf102 work. I did build the tube screamer with some success, and am currently messing with the gain stage for different sounds. Theres a lot of oscilation in it though with some different values, and the diodes I found out make its output a little on the low side. Remove the diodes and you have a nice CLEAN hot output. Raise the gain and you get a bit of a tube sound, sort of a hot guitar sound. Anything else I can do on this circuit? O yeah, didnt have a 47 pf cap so I used 2 22pf caps in paralell, remove one and it gives you some cool distortion.