Lightbulb compressor

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Keala

Active member
Joined
Aug 22, 2017
Messages
42
Hello guys!
I've recently found this cool little channel on youtube called "Look Mum No Computer"

He made this video where he wire a lightbulb to a an old jack cable and plays his guitar through, and claims that this works as a compressor.

https://www.youtube.com/watch?v=TMGqWFdby1A

What do you guys think about this idea?
If this thing actually works, it would be fun to put in a rack.


- Andreas
 
The resistance of the light bulb is low when it is cold. As it begins to glow its  resistance increases. So, if you use it in the top arm of a pot divider it will compress. Very old idea. I first saw it in the 50s I think.

Cheers

Ian
 
Keala said:
What do you guys think about this idea?
Using a light bulb for speaker protection (and incidentally compressing the signal) is a trick that has been outrageously  copied by our elders about 80 years ago.


  If this thing actually works, it would be fun to put in a rack.
Remember it needs to be inserted between a power amp (head) and a speaker (cab); many loadboxes incorporate a lightbulb limiter.
 
There's at least one 500 module that's just a lightbulb.

The Gates 17/18/27/28 broadcast limiters from 1938-1947 use a bridge circuit with two 6V bulbs as arms of the bridge. 

 
MagnetoSound said:
Peavey used this technique to good effect in many of their PA cabs to protect their tweeters from overload.

12v car bulbs IIRC.
The technique predates Peavey using it for speaker protection.

Peavey did come up with an improvement where the light bulb was shorted by a PTC fuse, until it heated up and allowed the bulb to start protecting the HF section. Lamps in series are known sources of distortion from their on resistance changing as they heat up and cool back down. Keeping the bulb out of the circuit until actually working was the improvement. 

Lamps were classically used in AGC loops of old signal generators.  A 100W light bulb in series with the mains cord can limit surge current when troubleshooting a broken amp for repair.

Ancients stealing our ideas again?

JR
 
There's also this patent for using a light bulb for amplitude stabilization of an oscillator:
https://patents.google.com/patent/US2268872
 
Also used in the HF section of the UREI 813B monitor, I assume in place of a fuse

Some wag once said that a tweeter is the ideal thing to protect a fuse

Nick Froome
 
Didn't the Studer C37 have a lamp in series with the spool motor, shorted out with a relay, that opened shortly after play  was pressed, and gave a lovely smooth reduction of torque in the supply reel ( Osram 120V lamp IIRC)
 
Martin Griffith said:
Didn't the Studer C37 have a lamp in series with the spool motor, shorted out with a relay, that opened shortly after play  was pressed, and gave a lovely smooth reduction of torque in the supply reel ( Osram 120V lamp IIRC)

Correct! I calibrated one of those once, what a fantastic machine to work on.

And the sound! ...  (gasp)

 
Martin Griffith said:
And the sound! ...  (gasp)

LR56 ?, a bit like a reel of cardboard, cover with magnetic mud, hand painted by Elves, while facing North. PEM 468 as well

Good for relapping though. Nah, this was 2010, it was 911 I think.

 
I built the Rod Elliot light bulb compressor about 10 years ago and tried it with my bass guitar rig.
It surely compressed but as with any other effect / stompbox I've had I tried it only once or twice.  I guess I don't like my bass sound being compressed by thingamagadgets  8) Best sound yet: pots at 12 o'clock, curly cord and fender with flats  ::)
 
Lamp-type compressors were often used for video levelers, as you can easily get the needed very-wide bandwidth..

Jakob E.
 

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I build a spring reverb unit based on Rod Elliot's schematic which includes a small 6V bulb in the drive amp, acting as a limiter to prevent overdriving the tank's coil. Seems to work well, also neat because you can (I think...) vary the bulb's current rating for different compression characteristics.
 
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