sismofyt

Forssell Opto Compressor
« on: June 12, 2004, 11:43:18 AM »
I did some experiements, don't remember anything specific though. Didn't take any notes either  :roll: I've tried many kinds of opto sidechain/circuits, but I've settled on using the 'build in' attack/decay times of the LDRs. Sounds much better to me  :grin: Optos and high ratio sound like piss to me  :evil:

Why don't you ask Fred  :green:  Isn't he a member here  :green:  :?:


Forssell Opto Compressor
« Reply #1 on: June 12, 2004, 12:34:23 PM »
...
Note to self:  Don't let c**ts wind you up

Jonathan Hayward

Forssell Opto Compressor
« Reply #2 on: June 12, 2004, 01:10:01 PM »
Any idea what the main parts are supposed to be - PRs and buffers etc?

sismofyt

Forssell Opto Compressor
« Reply #3 on: June 12, 2004, 01:18:56 PM »
PRs are Vactrols, you can use a dual one. Can't remember the part# right now, I'll look it up.

Buffers could be anything.. NE5532/34s, BBs etc.. U4 needs to be able to put some current though..

Fred is mojo. I just prefer the build in characteristcs of LDR'n'lamps/LEDs..

[email protected]

Re: Forssell Opto Compressor
« Reply #4 on: June 12, 2004, 01:24:39 PM »
Quote from: "buttachunk"
hey all,

i think we should figure out c & r values as this would be a GREAT project.

anyone want to start it off ?  

 :guinness:  :sam:  :guinness:  :sam:  :guinness:


I have been thinking about this.
For a mock-up rig the RC values are not that crucial.

This is just an example and it has not been tested yet:

VR1=500k
VR2=1M
VR3=500k
VR4=500k

C1=1.5u
C2=0.47u

PR1=PR2=NSL-32R3

Attack:
VR3*C2=250ms max

Release:
VR2*C1=1.5s max

R3=10k (unsure how much gain one needs here)
R4=1k
R8=1.5k

I hope we can get Fred's attention...

Tamas

sismofyt

Forssell Opto Compressor
« Reply #5 on: June 12, 2004, 02:38:39 PM »
But then it wouldb't be an opto compressor  :grin:  :grin:  :grin: Nice schematic though..

sismofyt

Forssell Opto Compressor
« Reply #6 on: June 12, 2004, 02:42:12 PM »
Actually, that FET comp would be dead easy to make. Someone make a PCB..  :wink:

FredForssell

Forssell Opto Compressor
« Reply #7 on: June 12, 2004, 03:58:16 PM »
Hello eveyone...

OK, you got my attention (fwiw)....

An aside... I built my first version of this circuit back in 1978.  I had been working with a band called "Loggins and Messina" and after they broke up I did some work with each of them individually.  At the time I designed an preamp for Jimmy's electric guitar rig and I wanted to have a compressor in it.  This is how this side-chain circuit got started.  Over the years I messed around with it in various configurations until I arrived at the one shown on my website.  The part that took the longest to get correct was the gain reduction metering... specifically getting it to accurately indicate GR as the ratio is varied.  If you doubt that this was difficult to do, go out and measure actual GR vs meter indication on almost all of the currently available opto based compressor that have variable ratios. You'll find that darn few of them track the ratio control very well, if at all.

Originally I had the ratio pot connected in series with LDR and tried various dual pot techniques to have the meter sensitivity track the ratio control.  Basically it all sucked.  When I hit on the idea for making the ratio control vary the current to the LED the whole thing clicked into place.  

So, if you plan on using a variable ratio control (highly recommended, imo) you should use a 5k rev log (who groaned out there?) pot in this position (VR4).  The current limiting resistor should be set for the max current rating of the LED, typically 100-200 ohm.   I personally do not like using VU type meters for GR reduction, finding them too slow for attack indication.  I typically use a LM3916 type IC with a 1k resistor to ground on the input (usually a pot).  This shows GR from the Lowest to the highest LED, not from "zero" down like a VU meter, so you do not need VR5.  And it's fast.

Also a 500 ohm trim pot (wiper to the output of R7) and a cell's LED connected to each end of the pot will allow you to trim the balance of the cells.  Typically I drive the circuit into a measured 5 dB of GR and use the 500 ohm trim pot to get 5 dB GR on the meter. I hope that make sense.

Other than the ratio control (VR4) Tamas values are very close to what I ended up using with this design.  I used...

VR1= 100k log
VR2= 500k linear
VR3= 500k linear
VR4= 5k Rev Log

R6= 49.9k
R5= 2M

Gain of U1 set so that threshold is reached when pot is set at 2 o'clock position with +4 dBu feeding side chain.  

Now, having said all of that, I recommend that anyone building this circuit pay very careful attention to the connection of the side chain and LDR to the audio signal path.  The schematic shows a series R, then the LDR in shunt to ground.  That's cool, but where to pick off the feed to the side-chain?  There are two choices (three actually)... feed forward (side chain picked off in front of the series R) and feedback (side chain after the series R).  For use as a compressor, I do NOT recommend a feed forward approach.  It is far better to have the pick off point after the series R.  The only down side to this approach is that you will be asking your side chain amplifiers to put out lots of voltage if you want to have very high amounts of GR.  So the third approach is to use two series connected resistors, pick off the side-chain input at the junction of the two Rs and place the LDR in shunt at output of the second R.  You've seen this in the LA-2a circuit and in other places.  It is, imo, the best of both worlds.  If you only want small amount of compression ratios you can opt for the single resistor approach.

Also, if you use the feed forward connection and place the LDR in series with the main audio path with a shunt resistor to ground, you can use this thing for a gate.  Making the shunt resistor variable will allow you to control the amount of "off" attenuation.

Good luck fellow DIY'ers.  Let me know if I can answer any other questions about this circuit.

Fred


Quote

This is just an example and it has not been tested yet:

VR1=500k
VR2=1M
VR3=500k
VR4=500k

C1=1.5u
C2=0.47u

PR1=PR2=NSL-32R3

Attack:
VR3*C2=250ms max

Release:
VR2*C1=1.5s max

R3=10k (unsure how much gain one needs here)
R4=1k
R8=1.5k

Fred Forssell

Flatpicker

Forssell Opto Compressor
« Reply #8 on: June 12, 2004, 04:17:15 PM »
:thumb: Thanks Fred!!  :thumb:

Kev

Forssell Opto Compressor
« Reply #9 on: June 12, 2004, 04:24:23 PM »
thanks fred

yes , you people are very lucky   :cool:
Kev
DIY Factory


Forssell Opto Compressor
« Reply #10 on: June 12, 2004, 06:20:57 PM »
...
Note to self:  Don't let c**ts wind you up

Forssell Opto Compressor
« Reply #11 on: June 12, 2004, 11:02:08 PM »
...
Note to self:  Don't let c**ts wind you up

Forssell Opto Compressor
« Reply #12 on: June 13, 2004, 01:21:46 AM »
...
Note to self:  Don't let c**ts wind you up

soundguy

Forssell Opto Compressor
« Reply #13 on: June 13, 2004, 02:11:35 AM »
they exchanged cash.

beer out the nose, all over my keyboard...

f**ker.

dave

chips are good with dip...

sismofyt

Forssell Opto Compressor
« Reply #14 on: June 13, 2004, 06:58:41 AM »
UA can just roll over and fukkin' die. 'Let's bring out the dead and make some serious cash' is just the lamest concept. While the LA2A & 1176 are fine, okay comps, they're not worth the UA money..

sh*theadz..  :twisted:  :twisted:  :twisted:  :twisted:  :twisted:

Erno Borbely on the other hand is one of my heroes. I've buld several of his (J)FET projetcs over the years. I still have the MC amp I build like uhmm.. 13 years ago when I was 16. Now _there's_ a designer  :thumb:

I'm sorry to hear that crap you've been going through John. Screw 'em. 'The Lab' is behind you 100%  :grin:  :thumb:

Nothing wrong with being an ex-junkie though. I've been clean for five years now  :razz:

Ohh, and if Erno feels like dropping by I'm sure the door is WIIIIIIIDDDDEEE open..  :thumb:  :thumb:  :cool:  :green:  :grin:

Now back to that optocomp...

sismofyt

Forssell Opto Compressor
« Reply #15 on: June 13, 2004, 07:00:53 AM »
TEC awards and MIX mag is a goddamn disgrace to this industry.. oh wait, they are the industry  :roll:

Would love to check out your design Winston!  :thumb:

[email protected]

Forssell Opto Compressor
« Reply #16 on: June 13, 2004, 01:09:28 PM »
Quote from: "Winston O'Boogie"

and was then asked to sign the aforementioned document that was basically restricting my income as I was being asked not to design for any other company before giving UA first refusal on any design I did for the next year or so and to disclose all designs I'd done during the last few years,  including all my pre UA ones if I wished to prove they were indeed my intellectual property at some unforeseen :wink: , but more than likely to happen, time in the future.  I declined to add my signature and that was pretty much the end of that.  


This is standard in the hi-tech industry. If you don't sign it you cannot get a job. It has become nearly meaningless and most people go along with it. Still the principle is wrong, IMHO.

Quote

originated from the Putnam camp that I was/am a Heroin and/or Crack addict.  This is a complete and utter fabrication and a damn lie and I was very upset when I heard it, to say the least.  


Rumors are just that, nothing more.

Cheers,
Tamas
PS.: I wear high heels.

Forssell Opto Compressor
« Reply #17 on: June 13, 2004, 01:11:04 PM »
...
Note to self:  Don't let c**ts wind you up

soundguy

Forssell Opto Compressor
« Reply #18 on: June 13, 2004, 02:10:55 PM »
Quote from: "buttachunk"

Everyone---
is there a consensus that this comp should be tx balenced... ?



Isnt it just safe to assume that 'round here EVERYTHING should be transfoemer balanced?

chips are good with dip...

dave

chips are good with dip...

gyraf

Forssell Opto Compressor
« Reply #19 on: June 13, 2004, 02:15:48 PM »
Quote from: "soundguy"

chips are good with dip...


..that makes a good signature..
..note to self: don't let Harman run your company..


 

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