LM833 OpAmp pre amp

LowQCab

Joined Nov 6, 2012
4,023
There's only 2 sources of noise,
the Chip, and, to a far lesser extent, the Resistors.

Use one of these for each channel ........ LT1630IN8#PBF-ND ~$10.oo each.

Here are some useful Filter-Circuits that You can "Mix-n-Match" to get the Frequency-Response You need.
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BandPass 3-Order Sub Bass .png
BandPass 3-Order Mid-Bass .png
BandPass 3-Order Tweeter .png
 

Ian0

Joined Aug 7, 2020
9,668
What sort of a preamp is it meant to be?
It looks to be a 39kHz 2nd order low-pass filter to me followed by a gain of ten (and I would have reached that conclusion far more quickly if you had drawn an op-amp as an op-amp).
The LM833 is a particularly quiet op-amp, so if it's noisy then the op-amp is most likely not the problem.
Why don't you look at the circuits in the LM833 datasheet?
 

AnalogKid

Joined Aug 1, 2013
10,986
When someone says audio preamp, three things come to mind: microphone, phono cartridge, and tape head. What is it that you are trying to achieve? Gain, frequency response, noise floor?

Please post a link to the source of your schematic. Without that, we cannot evaluate it in context.

What is the source for your LM833 components? There are a lot of bogus chips out there . . .

ak
 

k1ng 1337

Joined Sep 11, 2020
940
There's only 2 sources of noise,
the Chip, and, to a far lesser extent, the Resistors.

Use one of these for each channel ........ LT1630IN8#PBF-ND ~$10.oo each.

Here are some useful Filter-Circuits that You can "Mix-n-Match" to get the Frequency-Response You need.
.
.
.
View attachment 268579
View attachment 268580
View attachment 268581
Missed a resistor label on the first schematic. What software are you using? Your colour scheme is nice to look at.
 

Audioguru again

Joined Oct 21, 2019
6,673
The circuit is probably built with a tangle of wires all over the place on a solderless breadboard causing it to oscillate.
Its voltage gain is only 10 times then it should be very quiet.
I agree that there are many cheap fake opamps from the Orient. They are very noisy.
 

Attachments

ag-123

Joined Apr 28, 2017
276
some (cheap) mics are 'horrible', well they are *cheap* (from the online flea markets) they work (kind of)
this is what to expect for those cheap mics
https://forum.allaboutcircuits.com/...nded-electret-microphone.184747/#post-1705927
https://forum.allaboutcircuits.com/threads/lm358-electret-mic-amp.184812/post-1709481

there are good mics, I think those mems mics that are special designed for mobile phones (e.g. iphones) are likely good.
costly, and some of them simply give you the digital output, zero noise, in the wires between the mic and the mcu.
the op amp can be anything, 'cheap' ones, or even a transistor for that matter. more often, it isn't the source of the problem.
the mic is itself the problem.
 

Thread Starter

nt2ds

Joined Jun 2, 2022
17
What sort of a preamp is it meant to be?
It looks to be a 39kHz 2nd order low-pass filter to me followed by a gain of ten (and I would have reached that conclusion far more quickly if you had drawn an op-amp as an op-amp).
The LM833 is a particularly quiet op-amp, so if it's noisy then the op-amp is most likely not the problem.
Why don't you look at the circuits in the LM833 datasheet?
as i said i did not draw the circuit
its from the official LM833N Datasheet
You can check it out here
https://www.ti.com/lit/ds/symlink/lm833.pdf?ts=1654238192729&ref_url=https%3A%2F%2Fwww.google.com%2F
it is shown in the first page
 
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Thread Starter

nt2ds

Joined Jun 2, 2022
17
But what is it meant to do?
Or what were you hoping it would do?
what im trying to do is control the gain of an input signal (most likely RCA Connector ,since the circuit is not designed for balanced inputs) and then feed the signal into an amplifier
 

Audioguru again

Joined Oct 21, 2019
6,673
The schematic shows no supply voltage and no part number (rated voltage) for the zener diodes.
The first opamp is a second-order lowpass filter with a voltage gain of only 1. The second opamp has a voltage gain of only 10.
The first opamp should be fed from the low output impedance of an opamp, not from a microphone.

With such a low gain it should be VERY quiet.
Usually, a mic preamp has a fixed gain of 150 to 200 times then it feeds a volume control. The volume control is at the line-level input of a recorder or power amplifier.
 

Thread Starter

nt2ds

Joined Jun 2, 2022
17
The schematic shows no supply voltage and no part number (rated voltage) for the zener diodes.
The first opamp is a second-order lowpass filter with a voltage gain of only 1. The second opamp has a voltage gain of only 10.
The first opamp should be fed from the low output impedance of an opamp, not from a microphone.

With such a low gain it should be VERY quiet.
Usually, a mic preamp has a fixed gain of 150 to 200 times then it feeds a volume control. The volume control is at the line-level input of a recorder or power amplifier.
i dont want to control a mic
i want an RCA input signal (probably from a computer or a phone) and being able to control the gain for that signal and then feed the signal to an amplifier
 

Ian0

Joined Aug 7, 2020
9,668
The output from a computer of a telephone is usually meant to drive headphones, so is likely to need attenuation rather than gain; unless it's an Apple computer then it will be line-level suitable for connection straight to an amplifier.
 
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