Audio Mixer project - 6 -> 1

[Moegoe]

Hi guys (girl or two possibly),

I'm needing a little help with a small project.
6 into 1 mixer - mono channels.

I need to record the drums (rough recording, but still fairly clear) for a band and I would rather build a simple mixer for the purpose as opposed to buying one.
I'd rate my electronic skills / knowledge on a scale of 1 - 10 as a firm 2... highly dangerous!

At first, i thought that a severely simple circuit of inputs -> pot -> output would work, but my research shows otherwise.

I've pulled a simple schematic for a 2 into 1 mixer that is simple enough. The problem arises when you add more inputs. Apparently i'll pick up a lot of unwanted noise and the attenuation will drop.
**broken link removed**
while this is for RCA's it's easy enough to modify for 1/4" jacks.

I then found a 6 line mixer schem and this is where i got scared...
**broken link removed**

I don't understand the majority of the symbols and reasoning behind the use thereof.

So i ask you, with tears in my baby blues:
1. What components are needed to complete this project?
2. Is there an easier way?
3. Would i be able to modify the simple 2into1 by adding another 4 inputs into the equation?

Sorry about the absolute Noob Q's...

(For those wondering, Moegoe is Afrikaans for 'idiot'... )

 

[Moegoe]

OK, that was a little vague...

To make lives a little easier i understand the following: (if i am wrong, please correct me)

I'll be needing: 10khm: logarithmic pots.
1k, 100k and 47khm: resistors.
as well as the 1/4" jacks.

What are the 1 and 10u (or should that be :mu components? Capacitors?
and what are the large yellow triangles representing?

Why do they run three simple channels and three complex ones? Attenuation? Amplification?

 

[Nigel Goodwin]

The 'triangles' are operational amplifiers (IC's), the 'complex' inputs are microphone ones, and the simple ones line inputs. And yes, ''u is used for the greek letter 'mu' (micro).

You can add as many channels as you like.

 

[Moegoe]

Ok! makes more sense now, Thanks Nigel.

Would an 741 opamp work for this purpose? Any recommendations?

I think i'll modify to run 6 mic inputs, then it should act as a full mixer / preamp. (?)

 

[Nigel Goodwin]

Ok! makes more sense now, Thanks Nigel.

Would an 741 opamp work for this purpose? Any recommendations?

I think i'll modify to run 6 mic inputs, then it should act as a full mixer / preamp. (?)

Don't use 741's, they are antiques and of the lowest possible quality - try the Texas TL07x or TL08x series.

 

[audioguru]

You have a mixer circuit that is designed to amplify the very low level from microphones. The high level from drums might overload your microphones and your mixer circuit.

The input of the circuit must match the type of microphone.
What type of microphones are you using for the drums? Dynamic (coil and magnet) or electret?

 

[Moegoe]

I'm actually not sure what I'll be using.

What's the difference between the two and which one will work with this mixer?
Just so that i know what to look for / build.

 

[Nigel Goodwin]

Usually to mike drums you use a combination of dynamic and condensor (not electret) microphones, with the condensors requiring phantom power.

But basically all such mikes are low impedance (600 ohm) and balanced.

I would seriously suggest you buy a mixer, Behringer make excellent quality ones at very decent prices.

I made a mixer for a band from scratch back in the 70's (using 741's), but to buy a mixer back then was a LOT of money - now you can buy a Behringer mixer for less than the cost of buying all the knobs you need!.

 

[MrDEB]

polerizer capacitors?

In the mixer circuit I plan on using same for the EQ unit I have been working on.
Question = WHY electrolytic capacitors instead of poly caps (less noise) ??

 

[audioguru]

Electrolytic caps used for audio coupling create distortion at low frequencies. But they have high values cheaply when impedances are low. Poly caps create no distortion but have a limit on value before they get huge and expensive. They are used at fairly high impedances.

Very high quality speakers use very high value huge poly capacitors in their crossover network. Cheap speakers use non-polar electrolytic capacitors.

 

[MrDEB]

capacitor values

In the mixer sch. it shows a 10uf elec. cap.
a 1uf poly is around $1 per. is 1uf to small or ??
a 10uf poly = $80

 

[audioguru]

The 10uF input capacitor causes a -3dB rolloff at 16Hz. 4.7uF will rolloff at 34Hz.
Use a 10uF non-polarized electrolytic capacitor and frequencies below 16Hz won't exist and you won't know that they are distorted.