• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Microphone Amp/Mixer

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Hey Everyone, this is my first time posing here and I really need some help with a project I want to do. I need a way to amplify some mics, probablly three or four. I'd like to not pay 100 bucks for a cheap mixer and then another 3-400 for an amp and speakers, but rather bild my own amp, power supply, and mixer. I dont know tons about electronics, but i know the basics and my dad can help me out. Umm lets see.. i dotn even know how many watts i want for the amp- i just know the mics are going to be used with drums and a few guitars.. so loud enough to be able to hear the voices over those things. Nothing has to be real fancy, this is just goin in my basement to practice, so i dont need 10 controlls for each mic, just volume:) Another question is: do you need a mic pre-amp when amplifying mics or can they go right into the mixer and the amp? Well i'd really appreciate it if any of you with info/schematics/help would post! By the way, i dont even know what kind of amp would be best for this (chip, tube, solid state..) whatever is easy and will get me by! Thanks.
 
I'll give you some hard won advice after having built, maintained and modified desks; buy a decent quality second hand mixer. You don't know enough at the moment to pull it off, esp with tubes, which you're not going to be able to do for a couple of hundred dollars.
 
Re: lots of quetions (need more info)

MIKET said:
a. what kind of microphones?
b. what kind of speakers?
c. are any line inputs involved?

Here are a few links to get you started.
http://www-s.ti.com/sc/ds/ina103.pdf
http://members.ozemail.com.au/~lisaras/
http://www.jensen-transformers.com/as/as054.pdf
http://homepages.ihug.co.nz/~rwillis/alex/

Good luck with your project.

It's be a dynamic microphone, probablly one like this:
http://www.musiciansfriend.com/srs7...w i just wantto plug in around 3 micrpphones.
 
How to design the box for your speaker

You can model a box for your driver using WinISD
availible for free at:
http://www.linearteam.dk/
Here is an example of the output you get:
Driver : Eminence Beta 12LT
Project by : Michael Talbot
Project for : you
--
Number of drivers : 1
Box type : Vented
Box size : 142.1 l
Tuning frequency : 50.72 Hz
Vent : 1 vent(s)
-0.009 m length for each
0.102 m round


Relative
Freq Gain SPL
[Hz] [dB] [dB]
20.00 -32.79 66.21
25.00 -24.89 74.11
30.00 -18.39 80.61
35.00 -12.92 86.08
40.00 -8.39 90.61
45.00 -4.90 94.10
50.00 -2.56 96.44
55.00 -1.24 97.76
60.00 -0.59 98.41
65.00 -0.30 98.70
70.00 -0.16 98.84
75.00 -0.11 98.89
80.00 -0.08 98.92
85.00 -0.07 98.93
90.00 -0.06 98.94
95.00 -0.06 98.94
100.00 -0.06 98.94

The driver rolls off at about 10KHz so for PA use a tweeter isn't really needed.
 
Thanks everyone, i appreciate the replies. Well, i set off to build my first tube amp a couple of days ago and went and got some parts. (caps, resistors, my first breadboard:) ) I'm building one of sc3m@t1c's amps, shown here: http://webpages.charter.net/dawill/tmoranwms/Elec_Revision3.html . I think he said bout 5w or so.. not huge but all i want to do for now. Well, I'm hoping to be able to use this so amplify a microphone, but i'm pretty sure i need a mic pre-amp of some sort. (i'm using a dynamin mic BTW).. Am i correct with thinking this? If so, anyone got a schem for a simple one? There's also simple, really cheap resistance mixers like: http://www.musiciansfriend.com/srs7...0032849574/g=live/search/detail/base_id/42048 that you cam plug mics into.. doesnt seem like this would have preams in it, and i think it's designed to go right into am amp... well any advice will be appreciated!
 
mixer and preamp will be required for amplifier

There are quite a few simple microphone preamp circuits available, some for low impedance (balanced) [Burr-Brown INA103], and some for high impedance (unbalanced) [Burr-Brown OPA37].

From the mic preamp you can go to a passive mixer as you indicated or an active one.

If you are on a budget, solid state microphone preamp may be your 1st choice (low noise and no input transformer needed).
 
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