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Building an OPTO compressor, help ?!
Old 14th January 2010
  #1
Gear Head
 
🎧 10 years
Building an OPTO compressor, help ?!

Basically.. for my university dissertation i am to design and build an opto compressor BUT it must be "musical".
I assume most people here know what i mean by that so i wont go into to much detail, but .. like a joe meek sort of sound.

Has anyone attempted this before, or have any information that would help me along the way? id like to turn this thread into a step by step to help future projects. I'll upload pictures and information on the compressor as it happens
Old 14th January 2010
  #2
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studiostuff's Avatar
 
🎧 10 years
Here's a linky to the Meta page at Prodigy-pro. Much more info and reliable DIY advice there.

Meta-Meta: Look here for overview..
Old 14th January 2010
  #3
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DrFrankencopter's Avatar
 
🎧 15 years
The one you want to search on is the Forssell Opto compressor/limiter.

META - Forssell Opto Comp/Limiter help

DIY Factory - ffosc

This is a long one with tons of info in it:

Official Forssell Limiter Build thread

Cheers

Kris
Old 14th January 2010 | Show parent
  #4
Gear Guru
 
1 Review written
🎧 15 years
Joe Meek

The Joe Meek compressor consisted of the following:-
A little say 5W amplifier driving a 6V flashlight bulb.
This is light coupled with an LDR which directly attenuates the signal.
It has slow attack and decay, zero distortion.

When used on kit, the bass drum causes a huge gain reduction, the decay then makes cymbals appear to swell, almost backwards.
I did construct a version many years ago. I included a pair of back to back hi intensity green LED's to cause a fast attack. This was then followed by the bulb's slower actions.
I used it a lot for live work. It created great articulation on vocals and squashed bass in a most rock n roll manner.
Good luck with the project.
DD
Old 15th January 2010
  #5
Moderator
 
Tim Farrant's Avatar
 
🎧 15 years
There are some designs here too..

Silonex Inc.: Technical Reference: Compressor Applications for Resistive Optocouplers

Cheers
Old 15th January 2010 | Show parent
  #6
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mexicola's Avatar
 
🎧 10 years
Quote:
Originally Posted by DanDan ➑️
The Joe Meek compressor consisted of the following:-
A little say 5W amplifier driving a 6V flashlight bulb.
A flashlight bulb as the light source??!!!
That's so bonehead it's brilliant!

But what happens when the bulb burns out, haha!

It makes me want to open up my tfpro to see if it's the same...
Old 15th January 2010 | Show parent
  #7
Gear Guru
 
1 Review written
🎧 15 years
Brilliant indeed

The bulb's resistance increases with temperature, self limiting!
Another classic from the same era was the Grampian Ambiophonic 666 Spring Reverb.
I kid you not. This had a bulb in series with the spring drive coil. An overload indicator but also an organic limiter. Those Brits must have been on a different type of acid!
DD
Old 15th January 2010 | Show parent
  #8
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2N1305's Avatar
 
🎧 10 years
Huh... Simplistic elegance, elegant simplicity. Had to think of it though!

However I guess it wasn't used for long before more sophisticated models became available, models on which you could adjust attack, compression level, threshold, etc.

I think the only drawback (sonic) on a photoresistor is that it will bleed high-frequency to ground, but that will only affect the sound if it is on the "low-side" of the voltage divider. If it's on the top side (as I think it should be), then there's no problem.

Have FUN with your project!

2N
Old 3rd February 2010 | Show parent
  #9
Gear Head
 
🎧 10 years
Thanks so much guys ! i didn't think id get this much attention tbh haha. I'll check out your links now
Old 3rd February 2010 | Show parent
  #10
Lives for gear
 
🎧 15 years
Hi
I don't know where the 'bleeding high frequency' stuff is coming from that is not really true it works as a resistive divider pretty much flat over audio bandwidth.
Try different bulbs, bulbs and LEDS, more than one opto resistor.
You would usually have the opto resistor in the leg going to ground but how about one in series as well but biassed 'on' by a bulb which is then turned off by signal.
any or all of the 'control amplifiers' (driving the bulb or LED) could have 'EQ' applies to make them respond more to HF or LF.
Opto resistors are NOT zero distortion but can be pretty low when the light source is 'DC' (not fluctuating in any way).
You can of course use a BULB as a compressor, using a very low wattage say 12 Volt type, fed through a resistor from an amplifier with a bit of 'welly' (say 1 watt max needed).
Plenty of fun to be had and... it's cheap!
Matt S
Old 3rd February 2010 | Show parent
  #11
Gear Addict
 
monomono's Avatar
 
🎧 10 years
OK, this is really low end, but...

1. Connect a 12v bulb to the speaker output of a old hifi amp, and keep volume low
2. Connect LDR directly in audio path
3. Place LDR beside bulb

Would this work?
Old 3rd February 2010 | Show parent
  #12
Lives for gear
 
🎧 15 years
Quote:
Originally Posted by monomono ➑️
OK, this is really low end, but...

1. Connect a 12v bulb to the speaker output of a old hifi amp, and keep volume low
2. Connect LDR directly in audio path
3. Place LDR beside bulb

Would this work?
Is this what you mean?

Ultra Simple Bass Guitar Compressor
Old 3rd February 2010 | Show parent
  #13
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monomono's Avatar
 
🎧 10 years
Yes! Thanks. I'm going to try it.
Old 3rd February 2010 | Show parent
  #14
Lives for gear
 
🎧 15 years
Hi.
Yes it will work.
Experiment with different bulb ratings (small 'rice grain' types will light up fast, larger ones won't).
The LDR and lamp must be in a light proof enclosure, a piece of pipe with 'putty' or plasticine to bung up the ends.
Try using a pot and a smaller fixed resistor (so you don't short it out completely) to vary the 'ratio'.
Search the schematic of the LA2A it is basically the same thing but the 'light' element is a luminescent display, chosen as it will light up almost immediately (similar to a a LED) but is large enough to illuminate 3 photocells (one is used to drive the meter in this instance).
You will discover that if you buy a handful of opto resistors that the 'law' and actual resistances at given illumination levels vary widely making production of well defined gear pretty tricky (much matching of devices needed).
Matt S
Old 5th February 2010 | Show parent
  #15
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monomono's Avatar
 
🎧 10 years
Wow, went out yesterday and bought a LDR and 5w resistor (total: $3) and now I have a working compressor! Doesn't sound too ****ty either!

For now I'm using a 3v flashlight bulb which is evidently too slow, at least on the drum machine I'm testing with - it has a kind of intertia whereby if there are 2 beats, they'll get moderately compressed, but if there's 3 in a row, the bulb goes really bright on the 3rd one and the sound gets completely smashed.

On the other had I don't think I want the instant response of an LED either, so I'll get one of these 'rice grain' bulbs. I'm thinking there is a world of possibilities with different bulbs, even combining an LED and incandescent.

My only question at this point is, if this is so simple, why do compressors have all the extra circuitry?
Old 5th February 2010 | Show parent
  #16
Gear Guru
 
1 Review written
🎧 15 years
Bulbs etc.

The lower voltage bulbs may have higher current ratings, thicker, slower.
The attack is very slow, I would not expect a drum beat to light the bulb, unless it is a fat kick with lots of tone. Try a bass guitar or vocal. I had good results enhancing the speed of my bulb with a pair of green hi intensity LEDs back to back.
DD
Old 5th February 2010 | Show parent
  #17
Lives for gear
 
🎧 15 years
Hi
Quote:
[My only question at this point is, if this is so simple, why do compressors have all the extra circuitry].
Very difficult to change things like attack, release and ratio in a repeatable manner.
Yes you can make a funky compressor that suits you and a handful of applications (instruments or whatever) but as such it is a 'one trick pony'.
Fun though!
Matt S
Old 7th February 2010 | Show parent
  #18
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monomono's Avatar
 
🎧 10 years
Having tried (and blown) a variety of bulbs I'm giving up on incandescents. Only LEDs have the speed and consistency required. However with LEDs I get heavy distortion on low frequencies. It reminds me of the MGMT sound...

I thought maybe I could "smooth" the light by putting a 47uf in parallel with the LED but that just decreased the intensity. Can anyone tell me why it distorts and any way to fix it?
Old 7th February 2010 | Show parent
  #19
Lives for gear
 
🎧 15 years
Hi
You need to feed the LED with 'precision rectified' DC with a suitable size capacitor to 'average' the light level, this brings in the compromises of attack and decay. Time to really start reading and learning!
Matt S
Old 7th February 2010 | Show parent
  #20
Gear Guru
 
1 Review written
🎧 15 years
Another Way

mono, the flashlight bulb compressor is a classic sound, very very twisted.
On kit on 60's records a boomy kick drum would make it eventually duck sometime after the event , then the release would swell up making the cymbals seem backwards. It is not an everyday compressor.
There are many modern opto designs. Look up Fred Forsell's one.
There are brilliant VCA designs, look up the Pico designs.
If you wish to get the ultimate optical experience though, look up the LA2A.
This uses a luminescent panel, like a kids nightlight. Takes over 100V AC to light it up, little or no current. There are of course transformers which step between normal low speaker impedances and 100V line systems. If you can buy or construct an opto using these ingredients I think you will find it has a very useful attack and decay behaviour.
It is actually very sophisticated and takes account of longer term elements in the music.
DD
Old 7th February 2010 | Show parent
  #21
Lives for gear
 
🎧 15 years
Hi
The 'step up transformer' approach is used in the transistor LA3A design which uses the T4b opto resistor/ luminescent panel as the LA2A.
Matt S
Old 13th April 2010 | Show parent
  #22
Gear Head
 
🎧 10 years
Thanks for all the replies guys it was alot of help, im now moving onto producing it in the next 10 days. I'm still very amateur though.. using a pcb.. you HAVE to make them yourself ? (i didnt know this) is it hard? is there a get a round?

and can somebody from the uk guide me towards a good place to buy components ? maybe suggest components ? sorry guys !
Old 13th April 2010 | Show parent
  #23
Gear Head
 
🎧 10 years
anybody? I'm not just being lazy, i really am an electrionics "n00b" :$
Old 14th April 2010 | Show parent
  #24
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gyraf's Avatar
 
🎧 15 years
Stick around the groupdiy.org - search and read other people's posts in that forum. Your questions has been answered hundreds of times.

Jakob E.
Old 14th April 2010 | Show parent
  #25
Gear Head
 
🎧 10 years
thankyou
Old 14th April 2010 | Show parent
  #26
Gear Head
 
🎧 10 years
I've been through so many threads but im in need of some more help. if someone has a few moments to help id be very thankful.


I have in my basket on Maplin Electronics

Β£50 worth of stuff i think i need to make an opto compressor. but.. im still unsure really

and i have no idea how you power the unit?

Ill be making my own freehand pcb (never done it ) using 1/4" jacks to input and output.

including an on/off switch

pots to use as a ratio control (not sure how to do this yet)

and a capacitor and resistor kit. as im sure ill need them.. lol

(i really am a n00b)

Ive ordered 3mm led's and a grain of rice bulb just to see which is best.

and the LDR's i ordered are 16k-33k is that ok?

last thing was obviously just a plastic housing to hold the unit. any comments, hints,tips, advice !! anything would be GREAT !! thankyou


EDIT:
Also someone helping me how to construct it would help, the links provided are too complicated for what i want, i originally said joe meek style. aslong is it can compress. slightly musically say in the style of a stomp box (as im using 2 1/4" jacks) is fine. Do i need to build an amplifier to run the bulb :S ?!?!

Last edited by no3chris; 14th April 2010 at 01:31 PM.. Reason: confused
Old 14th April 2010 | Show parent
  #27
Lives for gear
 
🎧 15 years
Show us your DESIGN. Then after Matt Syson fixes it for you, you'll know which parts to order. Order 4x the components you need.
One set for the breadboard you'll use to prove the design, one set for the PCB you'll make based on your revised prototype, two sets to turn into charcoal.

Power it with batteries or dc wall wart.

Don't wait until 10 days before the project is due.

How is it that you're doing your dissertation on a subject that you have no education in?
Old 14th April 2010 | Show parent
  #28
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studiostuff's Avatar
 
🎧 10 years
Quote:
Originally Posted by ripple_fx1 ➑️
How is it that you're doing your dissertation on a subject that you have no education in?
+1

And will this make all the slutz that help you partial doctors... or co-doctors...?

Take it over to the nearest fire department station the first time you plug it in. No need for those guys to have to risk their lives driving in traffic just to put out something like that.
Old 14th April 2010 | Show parent
  #29
Gear Head
 
🎧 10 years
I don't do electronics, i did basically, create an oscilattor with a breadboard and an opamp circuit.... (electronics odule was a joke) i do an audio & recording technology BSc

I thought id do something different than "im a robot and i'll record a band and get 40% for it" due to alot of work and my own fault its now ten days before.

matt has been alot of help so far i realise that and i thank him but the problem is im not gifted enough to design it completely alone, all im doing is asking for some guidance, not you to do my dissertation for me. no need for smarmy comments man. Just need some help, thought this was the place to seek it
Old 14th April 2010 | Show parent
  #30
Gear Head
 
🎧 10 years
Quote:
Originally Posted by studiostuff ➑️
+1

And will this make all the slutz that help you partial doctors... or co-doctors...?

Take it over to the nearest fire department station the first time you plug it in. No need for those guys to have to risk their lives driving in traffic just to put out something like that.
Luckilly, i live within 100ms of my towns fire station



thanks for the useful on topic helpful comment, considering i did question powering the unit admitting i have no knowledge on the matter.
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