Cheapskate limiter

[microx]

I have a mixer that gets used for live work and the idiots who use it are always driving it to clipping. Each channel has a clip LED so I wired the LED of a Vactrol in it's place and the LDR part across the signal in the preamp. It's not 100% but the clipping is much less and they say it sounds louder.
Limiting for 2 bucks a channel! thats mean,
Steve

 

[BYacey]

That's a great idea from one point of view; on the other hand the clip LED no longer means "clip".

 

[chrissugar]

If the clip LED is active the signal is already cliped so it would be a better idea to trim the cliping point a hair lower. Limiting would start before clipping.

chrissugar

 

[PRR]

> on the other hand the clip LED no longer means "clip".

Often they blink a few dB below clipping anyway. In which case the microx hack actually tends to avoid clipping.

If the CLIP really is clipping: still, there is 10% clipping ("edge") and 80%-99% clipping ("gross fuzz"). If the LED is bright enough to hold gain down when it is blinking only 10% of the time, then it tends to stabilize at about 10% clipping. That's obvious to the golden-ear, or even most tin-ears, but doesn't stink too bad and may even be the "sound" the band wants. Clipping percent will rise with input overdrive: depending on LED-LDR sensitivity and the input headroom, they may be able to drive it from 1% clipping (hardly audible) to 50% clipping (fuzz, but not totally-gross).

Depending how the clip-sense works, you may be able to wire the panel LED and the Vactrol LED in series, and have both working at once. LED brightness is a measure of how bad you are whacking-back gain: dim blinks is gentle, bright is major mash-down.

 

[aurt]

eeeeeeeexcellent!

 

[microx]

For these guys the clip LED just meant that the mixer was "on". In truth it does not sound that bad and if I played with the clip circuit a bit I could maybe get it better but it serves it's purpose well and no more blown PA- I hope!
Steve

 

[jhaible]

[quote author="microx"]I have a mixer that gets used for live work and the idiots who use it are always driving it to clipping. Each channel has a clip LED so I wired the LED of a Vactrol in it's place and the LDR part across the signal in the preamp. It's not 100% but the clipping is much less and they say it sounds louder.
Limiting for 2 bucks a channel! thats mean,
Steve[/quote]

I did the same thing to an analogue (BBD) delay, preventing it from gross overload with echo feedback factors >100%.

By happy accident, the remaining (slight) distortion is just what this application needs, and I got the most amazing "loop sounds" for my music with that device.

JH.

 

[Svart]

interesting! I have clip lights on mine too.. driven by a 5532. that's something to try.

 

[ciminosound]

Excellent idea! Most of the boards I've used the clip light comes on just before actual clipping. Now I'm thinking about how one might adjust the drive circuit for the clip light to allow adjustment for compression rather that jist limiting......

 

[microx]

Well I guess most clip circuits will be fast attack and decay. To get it to work as a comp you would need to introduce decay and ratio into the equation. LDR's have a degree of linger which you could extend with some capacitance, and a resistor in series or parallel with the LED would give some control. However I think the original idea was good, a cheap way to limit channel gain, and that it does.
Steve

 

[dale116dot7]

I did that exact thing on my Audiopro (Yorkville) 512 powered board about two years ago. I did add a capacitor somewhere in the circuitry that drives the LED to extend the decay time, but it works. I did this mostly for open mics where someone decides to just go to the mic and scream sometimes. Or they don't think the guitar is loud enough so they crank up their volume. It's obvious something's compressing but you can crank the gain up to maximum and not get clipping. (You can still get feedback, though.)

It's not quite like a LA4 or anything but it's certainly useable. It acts more like a limiter in that the ratio is typically very high, and the decay is fixed by whatever capacitor you put in there and by the LDR. Actually, the ratio moves around with the channel gain pot, but for this purpose it's ok.