Mic Preamp limitor/Automatic level controller

[teleman]

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!

 

[Zero D]

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.

 

[teleman]

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!

 

[teleman]

Here's another limiter schematic I found! Is this any better?

 

[mickeymoose]

Have a look at the THAT4301 and design note 125. E

 

[Carl_Huff]

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.

 

[teleman]

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

 

[Carl_Huff]

... 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.

 

[AuroraB]

A 'studio quality' limiter is most probably not a simple, 2-opamp job.... some resources may be found here:
Classic Schematics

 

[teleman]

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

 

[teleman]

Correction;

Fig:2

Green Line =Condenser Mic alone
Blue Line = Dynamic Mic alone
Red line Condenser Mic with Limiter

 

[AuroraB]

That is not really a limiter, although somehow it is.... it is called a soft clipper, - and will sound like one.......

 

[teleman]

A 'studio quality' limiter is most probably not a simple, 2-opamp job.... some resources may be found here:
Classic Schematics

Agreed, yet I've found many compressor/limiter circuits a hinderance than much help due to the (ADSR type?) circuits employed, let alone being quite noisy!

 

[teleman]

I have now spent the best part over a week reading & researching on compressors & limiters & have decided that a limiter only implementation in the mic pre would be the best way to go. I hope you guys would bear with me & read on.

My prime concern is to physically prevent spurious peak signals destroying my pc sound card & maintain constant signal levels at the same time.

I also feel that the full blown compressor/limiter in the mic-pre will be an overkill, since I already have a few excellent VST plugins of both modern & vintage compressors in my DAW! Many of these sound exceptionally good & are very effective as their respective hardware counterpart units i.m.h.o!

Using the THAT 4301 just for the "One Knob Squeezer" would be rather expensive for me, since these cost $8-$10/ piece. According to the THAT 4301 data, to obtain those low distortion & noise figures one has to use the trimmed circuit component values or else it would only give an average performance, both noise & distortion wise.

I came across these 2 limiter circuits which look promising for my exact need for a limiter. However, I am not good at "disiphering" circuits, so really would appreciate any help if you guys could give your opinion on these two & any possible mods which to improve these even further.

Thanks

Audio limiter

Was ist ein OTA? (Dynamiklimiter mit OTA LM13700, LM13600, CA3080, transconductance-amplifier, agc-amplifier)