Build The $5 Microphone Preamp

A little while back(2 years) the guys at record-producer decided to do another equipment test; this time with mic pre-amps. They chose three different ones ranging from $5 to over $1500. They recorded samples and allowed people to have a listen. Here is the link:
http://www.record-producer.com/learn.cfm?a=3062

Today I will be writing an Instructable on how to build the $5 pre-amp.

Mine cost a bit more then $5 but not that much since the majority of it was samples :D

Step 1 Prepare the Encloure

This time, I was able to borrow a drill for long enough so I could take picture of the project. Since the XLR jacks were not perfectly circular, i found i used my dremel a carve out most of it after a hole had been made.

Since the enclosure is made of plastic, I was able to use my wood drill bits. These bits are sharper and cut faster through the plastic.

Comments

[zerocool924]

Do you have access to the original schematic? The website took it down and it cant be found.

[jonboytang]

Should still be on the website: http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=sbos247b&fileType=pdf
It's on page 7

[zerocool924]

ahhh i got it. thanks!

[pigeonpants]

I was wondering, any chance you could just add a quick parts list?

[tigerdog330]

 what chip is that that you use for the power supply?

[jonboytang]

The documentation for the chip is here: focus.ti.com/lit/ds/symlink/ina217.pdf
This shows the two chips ina 217 and the OPA137.
The last chip TLE2426 is the ground splitter

[PuddleOfMudd25]

I am trying to make a microphone amplifier, and I'm short on cash and parts. I don't think I'll find all of these parts in my town anyways. I do however have two broken (not really broken, just old) computer amps lying around. Could it be possible to use one as a preamp (scavenging parts from it) and the second as the main amp? What will need to be done?

[derkoettner]

Hello, i saw your project. I would like to build my own one. But the probleme is i don`t know how to build a balanced output stage for it. Do you know how to do that? Thanks

[jonboytang]

pin 5 is negative (ground) while pin 6 is positive. ground is just connected to the plug casing.

[Kyosho]

What voltage was your power supply? Also, what exact resistors did you use to between pins 1 and 8 of the the INA217? I'm building a really simplified version of this amp and the datasheet has so many options that I'm totally confused. So, your answers to those questions would really be a help.

[jonboytang]

i just used a laptop power supply which was 18 volts it then gave me +9 and -9 volts by using the TLE2426. What you can actually do is cut out the four diodes, cut out the phantom power resistor (47k) and the cap(47uF), connect pin 5 to ground and just have pin 6 as out and cut out the 0.1 diodes.

[Kyosho]

I should mention that the simplified version I'm making leaves out pretty much everything else.

[Allemd15]

does this have phantom power

[djfrosty214]

hello I am a noob to all this stuff but can you but a list to all this stuff since i want to try to build it since i messed up my pre amp

[jeandeau]

Have you posted the power supply for the preamp? I searched the instructables site and didn't find it. thanks

[Darwins_Deathcat]

hey bro, I took a look at your schem, and if you are not using phantom power, then you do not need to use those large (polarized) electrolytic caps on your differential inputs. Large value caps like that are needed only to filter the power supply (and to act as power "resevoirs" to prevent sag), which, in a phantom powered arrangement is coming in on the same wire(s) as your signal. If you are not phantom powering it, you can (and probably should) use standard, non-polarised film or even ceramic capacitors on the inputs instead. These will probably sound a little better, but more importantly, you won;t have to worry about them ever leaking or blowing up if you accidentally cross wires or have a power spike. Any moderate value will do: 0.047 is fairly standard, 0.1 uf will let more bass through. I wouldn;t really go much higher than 1uf or too much lower than 0.022.

[jonboytang]

alright sweet thanks buddy, i wasn't really sure about the electrolytic caps in the first place because they can colour sounds. i was thinking for the next project i would build one for dynamic mics and this seems very useful. thanks again

[gnargnar]

i really need a friend who can teach me to make this stuff, because i would love to do so. great project btw, i like the look of it even

[jonboytang]

thanks, funny thing, I was originally planning to use another case until I realized the XLR jacks wouldn't it, so I randomly found another. I learned almost everything from google as well as other people's projects. Just make sure that you double check more then one website, But if you have questions about stuff, I can try my best to give you answers.