Mic Preamp, hoping to get feedback.

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Leek

Well-known member
Joined
Jul 11, 2016
Messages
105
I've been working on a mic preamp for a little over a month now. It consists of a NE5532 differential input stage, followed by a BC547 emitter follower output stage. I'm still working out all the bugs though. I am fairly new to Electrical Engineering. So, all feedback is very welcome. I have breadboarded the whole thing, but I have yet to apply voltage. I want confirmation that everything looks ok before I do so I don't blow anything up. I have provided two emitter follower output stages, but, I am leaning towards the top/first one. Simply because the voltage divider step was needed for the op amp as it set up in a single supply confirmation. So, using the existing divider in my circuit would be beneficial.

Here is my schematic, and all parts values are provided as well. I also am having issues of what to exactly do with the 2nd amp in the NE5532. I for now have the output of the 2nd amp feeding the inverting input, and the non-inverting input being feed by a voltage divider (9v) the divider then connects to pin 4 of the op amp itself. 

https://postimg.org/image/9h3b2wznt/

Any feedback would be great, and again thank you guys so much for all the help you have already provided. I'm learning tons and I feel I'm getting better at implementing ideas and design techniques.
 
https://postimg.org/image/9h3b2wznt/

You need to earth the bottom of R3 or the circuit won't work.  Actually even if you do this, the circuit will still have very poor 'balance' and poor noise.

The bottom emitter follower won't work as it has nothing connected to the base to bias it.

You actually have a 3rd and MUCH better 'emitter follower' in your schematic.  It is the other half of the 5532.  Just connect C4 to the junction of R7, 8 & p5.
 
Ok, fixing to post better, more updated schematic. If all looks good will breadboard it, power it and see how testing goes. It's now for better noise input, transistor based on the front end, and has a NE5532 output stage. I am still learning and trying to find my best application here. Will post schematic in just a second Ricardo.
 
https://s10.postimg.org/yhueefcbd/1477458082091_1899588157.jpg

Here is also a cheat sheet :

R1 = 100 Ohms
R2 = 1K
R3 = 100 Ohm
R4 = 100 Ohms
R5 = 1k
R6 = 100 Ohms
R7 = 3k3
R8 = 10K
R9 = 10K
R10 = 10K
R11 = 100K
R12 = 10K
R13 = 10K
R14 = 100K
R15 = 1K
R16 = 1K

C1 = 1000uf 25v Electrolytic
C2 = 0.1uf 63v FIlm Cap
C3 = 0.1uf 63v Film Cap
C4 = 1000uf 25v Electrolytic
C5 = 0.1uf Film Cap
Power Supply decoupling = 0.1uf Film

VR1 = Bourns 10k Audio Potentiometer
IC = TI NE5532 or equivalent
Pin 7 of NE5532 Amp #2 is the output
Output is connected to an Amphenol 1/4" connector
Pin 3 is the + signal and pin 1 ground

Supply voltage is 18v+, a voltage divider is used (creating a virtual ground)
to bias the amp (NE5532) with 18v+ and 9v+ at input. 
 
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