diode clipping circuit or passive limiter

[rosa]

Hello,

 

Can anyone suggest a circuit for a passive limiter, using diodes and resistors. I would like to know if it is possible to suppress audio signal peaks  higher than +18dbu. (6.16v?). I am using a mic preamp, with line level out, into a recorder and constantly get digital distortion when there are fast transients like hand claps or even laughter.  The recorder has a digital limiter but it does not help. There is a product available in the form of an xlr barrel, but I would like to know if it is a circuit I can put in a small box with ta3f in and out, or something I can add to the preamp out, internally. 

 

 

Thanks,

Rodrigo

[Rick Reineke]

Digital limiters do not limit the analog input stage.

What mic pre amp and what recorder are you using? Connectors? Balanced, unbalanced?

You can buy or make some attenuation pads. Just five resisters in an balanced audio H-pad and less for an L-pad. They can easily fit inside an XLR  or 1/4" plug. Tight fit for a TA-3, but it's been done.

 

[rosa]

thank you,

 

you are referring to this http://realoldiesradio.com/?p=212 , however I am searching for a circuit that will attenuate the signal once it reaches a certain voltage, depending on which diodes are used. https://www.quora.com/How-do-protection-diodes-work

 

I using the 633 with a 3 channel preamp made by vark audio.  

[Rick Reineke]

According to specs, the 633 can handle maximum input peaks of +40dBu in line level mode, which should be more than sufficient. If that ain't enough, something's not set right.

 If your just looking for something to build for fun, that's another story.

[rosa]

+40dBu is for XLR inputs set to line level. ta3 inputs don't have the analog limiter xlr inputs do.

[Rick Reineke]

I assumed the TA3 line inputs would have the same +40dBu max. There are post fader limiters on all the 633 inputs.

[al mcguire]

Is it the Vark pre amp part of this problematic signal flow ?

 

[rosa]

No. I have had similar issues using other preamps, including a mixpre-d, and MP1, both with very effective  limiters, which did help but occasionally I would still get distorted pops.  I haven't had issues with radio mics, which makes me wonder if the lower frequencies of a boom microphone might cause the distortion. in all cases the audio levels were within safe range. 

 

I will build a simple zener diode clamper and see what happens.

 

thanks 

[al mcguire]

If the signal is distorted in the mixer how will an outboard limiter help ?

You are monitoring  the peak metering ?

I would try a pad in front of the mixer before I started soldering.

Al

[Jim Feeley]

What source and what boom mics generate this problem for you?

[rosa]

What Ive tried now: Schoeps->preamp->Inputs4-6 of 633

 

=Digital distorted pops

 

What I want to try: Schoeps ->preamp->diode limiter->inputs4-6 of 633

[Johnny Karlsson]

Assuming you have tried:

- turning down the pre amp gain,

- adjusting the input level trim in 633 ch 4-6,

- engaged the hi-pass filter (70Hz?) in the 633 ch 4-6,

- different cables....

 

- maybe this 633 needs to go in for a checkup...?

[al mcguire]

It seems you want to build your limiter, let us know how it turns out.

 

I would suggest a 10db pad on the Schoeps would be more effective.

 

https://www.bhphotovideo.com/c/product/1132547-REG/schoeps_pad_10ni_10_db.html/

 

 

[John Blankenship]

Do you have the same issue if you go directly into a mic pre on the 633?

 

[rosa]

5 hours ago, al mcguire said:

It seems you want to build your limiter, let us know how it turns out.

 

I would suggest a 10db pad on the Schoeps would be more effective.

 

https://www.bhphotovideo.com/c/product/1132547-REG/schoeps_pad_10ni_10_db.html/

 

 

That pad, as I understand it, would prevent distortion in the cmc or the preamp input. it isn't the the cmc or the mic preamp that is distorting.  

 

This seems to work well for many in a studio setting, but too bulky for a bag after converting to ta3, and they are calibrated to +18dbu, which would not allow me to adjust gain within the 633. 

 http://www.prismsound.com/music_recording/products_subs/overkiller.php

 

 

4 hours ago, John Blankenship said:

Do you have the same issue if you go directly into a mic pre on the 633?

 

no issues on inputs 1-3

 

 

[tourtelot]

Have you talked to Sound Devices?

 

D.

[rosa]

Yes I have. Along with some of the tips also suggested in this thread, the person helping me wrote: Certain transients can cause the crackling/distortion rather easily depending on the source.

 

 

 

 

[The other Chuck Cooperman]

A bit late, but I just came across this discussion. The signal clips whenever the current in R1 exceeds the current through either R2 or R3. You can easily trim the clipping level by adjusting R1. Values aren't critical but they all affect the clipping level. Higher current levels will have less distortion but will load the source more. coopecb1@gmail.com