Ne5534 Mic Preamp Circuit  - Page 1
Forum section: electronics / beginners

author: Jbliss
author_rank: Regular Contributor
timestamp: January 13, 2016, 06:50:27 am
content: Does any one have a known working Simple Mic Preamp circut using the NE5534+- 15v PS

author: Lightages
author_rank: Unknown
timestamp: January 13, 2016, 06:59:12 am
content: Do you want balanced or unbalanced. Do you need phantom power or not? What type of microphone are you using, dynamic of condenser?

author: Jbliss
author_rank: Regular Contributor
timestamp: January 13, 2016, 07:07:05 am
content: would preferBalancedDynamic Mic / No PhantomSm58

author: Lightages
author_rank: Unknown
timestamp: January 13, 2016, 07:13:00 am
content: This should work well and is as simple as they get for a balanced input. Found it rapidly with googlehttp://www.circuitlib.com/index.php/schematics/product/29-balanced-microphone-preamplifier/category_pathway-28

author: Jbliss
author_rank: Regular Contributor
timestamp: January 13, 2016, 09:15:27 am
content: https://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwifovvvuKbKAhUKn5QKHfBWA-QQjRwIBw&url=http%3A%2F%2Fwww.eeweb.com%2Fblog%2Fextreme_circuits%2Fbalanced-microphone-preamplifier&psig=AFQjCNHwDFrZE7TLYPJoX0Im6kfNenIREw&ust=1452762683545810Thanks however after further research I have most of the components for this design i just found. how ever what does the black square mean is that 0v and the two outputs which is the hot and cold

author: Jbliss
author_rank: Regular Contributor
timestamp: January 13, 2016, 10:30:18 am
content: ?

author: AndreasF
author_rank: Frequent Contributor
timestamp: January 13, 2016, 10:40:31 am
content: The image (of the power supply) below the main circuit should answer your question. There the "black square" (it's not a square btw) is connected to the middle of the positive and negative power rails and marked as "0". It is simply another "ground" symbol, it's different to distinguish it from the "earth" ground symbol of the microphone shield.

author: Jbliss
author_rank: Regular Contributor
timestamp: January 14, 2016, 05:35:48 am
content: Ok so the shield of the XLR connector is the only thing technically "Grounded"Thanks !!

author: Jbliss
author_rank: Regular Contributor
timestamp: January 15, 2016, 03:09:51 am
content: ?

author: Jbliss
author_rank: Regular Contributor
timestamp: January 16, 2016, 11:04:06 am
content: Ok so i have made the circut and its working great. However P 1 is meant to set and optimum resistance for the common mode rejection however when I change it i don't hear anything different. Should I ? would someone mind explaining to me.thank you.

author: Keicar
author_rank: Regular Contributor
timestamp: January 19, 2016, 11:28:34 pm
content: So you're basically tweaking the circuit's ability to reject interference - and since it's not practical to use a really long mic cable and just hope it picks up something nasty, you'll want to apply your own common mode test signal. If you connect a signal generator to both pins 2 and 3 together, relative to pin 1, you'll have an equal amplitude on both the positive and negative inputs, then you can adjust your trimpot for minimum output, and that should give you the best possible common mode rejection.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 19, 2016, 11:40:24 pm
content: Quote from: Jbliss on January 16, 2016, 11:04:06 amYou didn't describe what noise you are trying to eliminate.IF the noise is being picked up on the input wiring (the mic cable), then adjusting P1 will optimize the COMMON MODE noise rejection.But if the noise is coming from the power supply, then adjusting P1 will have no effect.And if the noise is being picked up by a circuit on a breadboard, unshelded from the harsh environment, then adjusting P1 will have no effect.And if the noise is being picked up by the microphone (because it has a broken ground connection to the shell, etc. etc.), then adjusting P1 will have no effect.There are several different kinds of noise, and several different places it can come from. P1 only affects ONE of those.And if you don't have XLR pin 1 wired properly (to the ground of the circuit), then adjusting P1 won't help, either.The diagram shows the the outside shell of the XLR connector is bonded to the metal box around the circuit.But XLR pin1 is connected to circuit ground. And then circuit ground, and the outside shell and enclosure are inter-connected to circuit ground at some point. That point may be at the XLR connector by joining pin 1 to the XLR outside shell and the circuit enclosure.

author: macboy
author_rank: Super Contributor
timestamp: January 20, 2016, 07:34:31 pm
content: A gain of 316 using one op-amp stage is not a good design. There is not enough open-loop gain left to provide low distortion. It would be better to split this up into two stages of 17 or 18 each. You will get lower distortion and probably lower noise too, because of lower resistor values.Also check out TI LME49710 which may improve noise and distortion even more. The NE5534 is good, but it is a >35 year old design now.