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Old 16th March 2014, 08:59 PM   #1
teleman is offline teleman  Norway
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Default Mic Preamp limitor/Automatic level controller



I am trying to include either a limiter or an automatic volume control section to my INA217 based mic preamp. However, I'm not quite sure if the circuit shown below would be as good to use as the Phil Allison Fast Limiter circuit published in the Rod Elliot's site! However, I'd change the opamps TL071/2
to OPA123/2132.

AVC Automatic Volume Control Circuit

Fast Audio Peak Limiter

I like the circuit below for it's apparent simplicity, design wise!

All comments or suggestions would be greatly appreciated!

Cheers!
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File Type: gif automatic-volume-control-schematic.gif (66.9 KB, 114 views)

Last edited by teleman; 16th March 2014 at 09:08 PM.
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Old 17th March 2014, 02:22 AM   #2
Zero D is offline Zero D  United Kingdom
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Hi, well neither are HiFi as distortion < 0.5% typical for both. But i'd say that Phil Allison's would most likely be better, as for one thing, it has a Full wave rectifier. Also the SNR appears better too.
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Old 17th March 2014, 06:05 AM   #3
teleman is offline teleman  Norway
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Thanks Zero D,
Yes, I 2nd that. Is there anyway I can improve the distortion on either of these? If only I can find a near studio quality compressor/limiter circuit, then I'd just use the limiter section of it!

Last edited by teleman; 17th March 2014 at 06:18 AM.
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Old 17th March 2014, 11:12 AM   #4
teleman is offline teleman  Norway
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Here's another limiter schematic I found! Is this any better?
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File Type: jpg LIMITER-Seek IC-2.jpg (108.2 KB, 94 views)

Last edited by teleman; 17th March 2014 at 11:36 AM.
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Old 17th March 2014, 01:55 PM   #5
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Have a look at the THAT4301 and design note 125. E
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Old 17th March 2014, 03:47 PM   #6
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Quote:
Originally Posted by teleman View Post
Here's another limiter schematic I found! Is this any better?
Where did you find that? That is a simple and interesting circuit. It could be especially useful just ahead of a subwoofer amplifier.
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Old 17th March 2014, 05:07 PM   #7
teleman is offline teleman  Norway
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Quote:
Originally Posted by Carl_Huff View Post
Where did you find that? That is a simple and interesting circuit. It could be especially useful just ahead of a subwoofer amplifier.
Thanks Mickeymoose,...I'll have a look.

I found it here;
http://www.seekic.com/circuit_diagram/Audio_Circuit/Low_distortion_audio_gain_limiter.html


If the above link doesn't work then just write: Limiter circuits/seekic.com

Do you think this schematic could be used/modified in the input or output stage of a mic preamp?

Cheers

Last edited by teleman; 17th March 2014 at 05:12 PM.
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Old 17th March 2014, 05:33 PM   #8
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Quote:
Originally Posted by teleman View Post
... Do you think this schematic could be used/modified in the input or output stage of a mic preamp?
Yes but it would not have a lot of finesse. The 'One Knob Squeezer' that has already been mentioned is a much better choice for what you are looking to do.
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Old 17th March 2014, 08:36 PM   #9
AuroraB is offline AuroraB  Norway
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A 'studio quality' limiter is most probably not a simple, 2-opamp job.... some resources may be found here:
Classic Schematics
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Old 17th March 2014, 08:43 PM   #10
teleman is offline teleman  Norway
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Quote:
Originally Posted by Carl_Huff View Post
Yes but it would not have a lot of finesse. The 'One Knob Squeezer' that has already been mentioned is a much better choice for what you are looking to do.
Yes, you're absolutely right! I will prototype it & see how it works. My only reservations are the cost of 4301s for 8 channels & some of the component values, which are akin to figures found on bottles for medcines!Lol!

Thank you indeed Mickey Moose for pointing me in the right direction.

Deviating a little, I lifted this very interesting circuit from another forum. This schematic was originally published in the Swedish magazine called "MusikerMagazine" in 2006. Unfortunately, I couldn't locate the article, yet luckily, the circuit is still available!

This circuit is supposed to be wired at the mic ch. input before the mic preamp input buffer!


Fig.1: INGÅNG=input , UTGÅNG= output

Fig.2;
Green line = Dynamic Mic alone
Blue ine = Condenser Mic alone
Red line = Condenser + limiter in

Fig.3
Red signal = DPA 4011 Direct
Green signal DPA4011 with the Limiter
Attached Images
File Type: jpg xlr_limiter_schematic.jpg (65.6 KB, 61 views)
File Type: jpg Limiter Graph.jpg (81.5 KB, 59 views)
File Type: jpg dpa_transientresponse.jpg (40.1 KB, 58 views)

Last edited by teleman; 17th March 2014 at 09:09 PM.
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