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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  Lm386 mic preamp? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Lm386 mic preamp?  (Read 7244 times)
TimWaldvogel
Posts: 524


Tim W.


Lm386 mic preamp?
« on: May 23, 2010, 09:28:51 PM »

Someone in a thread  I was looking at said the built a clean mic preamp with a lm386. Can you cascade these op amps in anyway? I want clean 1/4" in/out mic pre and since I bought a few Lm386 for a smash drive I figured icould find out
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PRR
Posts: 5720


Paul R. - Maine USA


Re: Lm386 mic preamp?
« Reply #1 on: May 23, 2010, 11:13:13 PM »

Yes.
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TimWaldvogel
Posts: 524


Tim W.


Re: Lm386 mic preamp?
« Reply #2 on: May 23, 2010, 11:31:54 PM »

To which question. And how? :-)
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TimWaldvogel
Posts: 524


Tim W.


Re: Lm386 mic preamp?
« Reply #3 on: May 24, 2010, 12:33:45 AM »

i guess my other question would be. if not the lm386. how can i use a dual op amp to create a quiet yet loudly effective mic preamp?

what would be quieter making a two channel preamp with each half? or using both with a small boost hooked up to a dual gang pot ? like would that help keep the noise from entering the signal and amplify the signal quite a bit? i want to use this as a mic preamp and a preamp for my acoustic electric
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petemoore
Posts: 18719


As Yet Unrated


Re: Lm386 mic preamp?
« Reply #4 on: May 24, 2010, 04:55:42 AM »

 http://sound.westhost.com/project66.htm
 Will you like the 386 is where I'd try to finish the questions, beginning with a 386 configured on BB or board, using a datasheet circuit, or other.
 The power supply...near maxV should give a strong boost, and minimize the ''386 sound''.
« Last Edit: May 24, 2010, 05:03:25 AM by petemoore » Logged

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Minion
Posts: 354


Re: Lm386 mic preamp?
« Reply #5 on: May 24, 2010, 10:54:14 AM »

The LM386 is way to noisy to use as a Mic preamp , plus you need between 1000x and 10,000x Gain for a Mic preamp ...... Look into the INA217 ...... Cheap , easy and sounds great .....
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TimWaldvogel
Posts: 524


Tim W.


Re: Lm386 mic preamp?
« Reply #6 on: May 24, 2010, 01:28:03 PM »

Ok thanks guys. You know how it is, I am an intermediate electronic nut so I wanna try everything out as if I might actually come up with a revelutionary design for something
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PRR
Posts: 5720


Paul R. - Maine USA


Re: Lm386 mic preamp?
« Reply #7 on: May 24, 2010, 08:38:02 PM »

Note that Tim said 'I want clean 1/4" in/out mic pre'.

I didn't know anybody still used non-XLR mikes.

> LM386 is way to noisy to use as a Mic preamp

Is it?

No noise is specified. But the 50K input and particularly the internal currents are a lot like the preamps we used when 1/4" was still a common mike input, on tape-decks and non-Pro mixers.

I bet a good '386 has input noise voltage across the audio band near 1uV-2uV, a hair lower than most all-purpose opamps.

> need between 1000x and 10,000x Gain

A low-Z ribbon on a harpsichord into a might need 80dB gain. Using dynamics on live performers (often not loud) I was always fine with 2mV-5mV input sensitivity for peak level. Most "line" inputs are fine with 500mV-1,000mV. Gain of 200 (46dB) is often ample.

An awful lot of good music was recorded with preamps not as snazzy as the '386.

It IS about 1,000 times the "grunt" you need to swing 10K line inputs. But with '386 prices what they are, it isn't like it costs too much.

> I figured icould find out

Right. Just do it.
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Minion
Posts: 354


Re: Lm386 mic preamp?
« Reply #8 on: May 25, 2010, 04:19:42 PM »

Come on PRR , you know your electronics and you know very well that the Lm386 is a Noisy piece of Crap chip especially for a Mic preamp , compare 0.2% at 1khz THD for the LM386 and 0.004% THD for the Ina217,... And while you might need 10000x gain for a Ribbon mic , you will still need at least 50-60db for many dynamics or 2000x gain .....

Are you just playing the devils advocate ?? it doesn"t suit you especially when you know Im right .... You can do way better even with a Lowly TL072 ....

And snazzy and the LM386 should never be used in the same sentence ..... icon_mrgreen
« Last Edit: May 25, 2010, 04:21:37 PM by Minion » Logged

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TELEFUNKON
Posts: 596



Re: Lm386 mic preamp?
« Reply #9 on: May 26, 2010, 12:16:42 AM »

Minion: are you talking noise or distortion?
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Minion
Posts: 354


Re: Lm386 mic preamp?
« Reply #10 on: May 26, 2010, 05:20:14 PM »

It doesn"t matter which , Low Noise and low THD are needed for a good mic preamp , pluss the Lm386 datasheet doesn"t even have a spec for Noise (not a good sign) but its THD goes up to 10% when at max output .... It just simply isn"t suitable for a Mic pre unless you just want a Noise maker or a Toy, which is cool if that is what you want buy it wouldn"t be anything that you would use in a studio .....

For the Same price of a LM386 you can get a TL072 or a NE5532 which could be made into a useable mic preamp .....
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Top Top
Posts: 1068



WWW
Re: Lm386 mic preamp?
« Reply #11 on: May 26, 2010, 05:34:44 PM »

It doesn"t matter which , Low Noise and low THD are needed for a good mic preamp , pluss the Lm386 datasheet doesn"t even have a spec for Noise (not a good sign) but its THD goes up to 10% when at max output .... It just simply isn"t suitable for a Mic pre unless you just want a Noise maker or a Toy, which is cool if that is what you want buy it wouldn"t be anything that you would use in a studio .....

For the Same price of a LM386 you can get a TL072 or a NE5532 which could be made into a useable mic preamp .....

The dude is talking about a 1/4" mic input - obviously not balanced. I am just going to venture a guess here and say this obviously isn't for a super hi-fi studio situation, unless you know of any professional studios that use unbalanced 1/4" mics.

I don't want to speak for the guy, but he may not need the cleanest most pristine thing ever for this project, but maybe just something that will get the job done simply and quickly... for that 386 excels.
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TimWaldvogel
Posts: 524


Tim W.


Re: Lm386 mic preamp?
« Reply #12 on: May 26, 2010, 07:06:07 PM »

Seriously plenty of studios still do. Especially with vintage mics. It's balanced up til the last 6 inches where the adapter is. Ad I kinda wanted a mic pre that gives that old school light saturation kinda of sound. I have nice mic preamps tht I have bought including a U.I.
Just wanted to experiment for cheap, if not it would make a great bass preamp.
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Top Top
Posts: 1068



WWW
Re: Lm386 mic preamp?
« Reply #13 on: May 28, 2010, 05:56:39 PM »

I use those kinds of mics in my studio, but generally any professional studio is wired for balanced xlr throughout and the use of a 1/4" mic is for effect/special occasions. High fidelity preamps are generally not designed with 1/4" unbalanced in mind.

The point stands. If you are using 1/4" mics, it isn't for super pristine high fidelity sound.

If you want to experiment for cheap, then do it, 386 is just the thing!
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Derringer
Posts: 929



Re: Lm386 mic preamp?
« Reply #14 on: May 28, 2010, 06:08:52 PM »

funny, I was just thinking today about trying to design a vocal distortion that uses a lm386

I know I know ... beware the feedback ... I figure with enough clipping and the output volume at unity I should be OK ... whether it sounds good or not is another question

think I could make it sound like to vox in "21st Century Schizoid Man?"

http://www.youtube.com/watch?v=g8Yo3FJDrbc
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Derringer
Posts: 929



Re: Lm386 mic preamp?
« Reply #15 on: May 30, 2010, 09:11:36 AM »

I know you wanted a clean lm386 ... but here's a distorted one

I basically took the "Grace" design from ROG, stripped the input buffer and made the input cap 4700pf

here's me singing through it with and without a backing track

http://www.4shared.com/audio/KdsUYjly/21st_Century_Schizoid_Man_vox_.html

http://www.4shared.com/audio/7wOJxFyX/Vox_distortion.html


I sang through my mic, into the effect, into the mixer, poweramp, then PA speakers
recorded with a pair of condenser mic's into an m-audio box into the computer via usb
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