Forssell Opto Compressor

[Kev]

but chips are a great way to get started
and
they give an excellent starting point to compare your later, trafo and tube based units of the future.

... this is of course after you have been bitten by the DIY bug.

 

[mnats]

[quote author="buttachunk"]Tamas' values are posted-- which opto can we all agree on for this project ?

once breadboarded, do we have a volunteer to layout the boards ?[/quote]

Silonex NSL-32R3 looks good. Agreed - chip opamp to start. I'll take a crack at the PCB layout once a design is finalized.

 

[tk@halmi]

[quote author="buttachunk"]"chip opamp to start"

agreed. V1 should be opamp to evaluate and tweak this project.
Project final will be discrete make up plus iron.

Who will host the associated files for this project ?[/quote]

Buttachunk,

I was laying hardwood floor for my in-laws all weekend so I did not have a lot of time for fun. I have started to draw up the schematics last night and might finish it tonight. Not wanting to duplicate efforts or take anyone's fun please let me know if someone else wants to post what we have pieced together so far.

Tamas
PS.: Fred Forssell ROCKS!

 

[Plexibreath]

This looks like a promising project as a solution to my thread on adding a limiter to my API 312 project. I might breadboard it to see.
Kelley

 

[mnats]

[quote author="buttachunk"]
Several of us will breadboard the design (probably with ICs for makeup), and share feedback.

Then the boards will be laid out and revised as neccessary.[/quote]

Assuming the sidechain will use general opamp ICs as well I might just start laying out that part of the circuit for the PCB. I'm thinking two dualies might be the best choice instead of a quad - more options for opamp 'mods'.

If we use an LM3916 like Fred suggested for the gain reduction display should this just be another small board, or possibly on a board incorporating all the pots or would you rather see everything on a single pcb?

 

[FredForssell]

Hey everyone...

I have a simple PCB layout for this thing. Here is a link to a PDF of the top layer. http://forsselltech.com/optopcb1.pdf

If anyone wants to build these boards let me know and I'll send you the gerber files.

 

[tk@halmi]

Fred,

First, I want to say that this is more than what we dream here to have,
and we are greatful to you for offering it. I am absolutely interested in this board.
my address is: gfargone at yahoo dot com

Thank You,
Tamas
PS.: You should add on the JFET-992 to the board as the gain element to encourage its use. :wink:

 

[FredForssell]

Here are links to the Opto pcb gerbers (zipped)

http://forsselltech.com/gerbers/optopcb.ZIP

and to a pdf file containing the schematic used to lay out the PCB.

http://forsselltech.com/gerbers/optoSch1.pdf

Since I've never made and tested this pcb, I suggest that one might want to track it out against the schematic to make sure that it is correct. Let me know if you find any errors and I'll correct them and repost.

Have fun!

 

[Kev]

This pleases Kev greatly ... all say thanks to Fred. :grin:

 

[TomWaterman]

Thanks very much Fred! - very cool to have you here.

I'll be watching this project with keen eyes!

Tom

 

[peter purpose]

Weeeeee aaaaalllllll agreeeeeeee.....Fred Forssell is MAGIC ah..!!

 

[Svart]

what would the range of compression ratios be in this design? would this be a better overall sound than the WHAT?

 

[FredForssell]

what would the range of compression ratios be in this design?

The range of the ratio control is a function of two things... the total amount of series R against which the shunt LDR is working, and the size of the max current limit resistor in the LED drive circuit.

You can make the thing go flat-line (limiting) for about 20+ dB of input increase if you want. Typically, I don't in my designs because it's an opto and too slow for most limiting applications. I restrict my (typically) to about 8 or 10:1 ratio, but hey this is DIY land and you can do whatever you want.

I'll try to get around to posting some compression curve tomorrow or the next day... It's kind of busy around here.

would this be a better overall sound than the WHAT?

I don't know. Someone else will have to answer that. BUT, I will say this, it doesn't really sound like anything until you really drive it hard into compression. So, I'd have to say that it's a really, really transparent opto compressor. You can change the "sound" somewhat by your choice of gain make-up/buffer amp, adding a transformer (egads!) or doing whatever you might wish to do external to the gain control circuit, which by itself doesn't really sound like much of anything.

YMMV.

 

[sismofyt]

Fred, is there any reason why you didn't choose a dual Vactrol, instead of two singles? I've noticed that TubeTech does the same in the CL1B...

Cool that you're sharing this :thumb: :grin:

 

[FredForssell]

Fred, is there any reason why you didn't choose a dual Vactrol, instead of two singles? I've noticed that TubeTech does the same in the CL1B...

Well, let's see-- it's been a while since I choose the optos that I use (VTl5C1). But if I remember correctly the main reason for singles was that there was a huge unit to unit variation (its the cells) and the only way to deal with that was to either match individual cell/led by selecting them or by using the trim pot balance method that I use these days.

However, I've not revisited this issue in many, many years and today there may dual cells available that have good matching.

 

[sismofyt]

Thanx for the info, Fred. I've seen several opto comps using one for the compression and one for the meter. I think the Avalon 737 does this too.

 

[mnats]

[quote author="FredForssell"]Here are links to the Opto pcb gerbers (zipped)[/quote]

Looks like I work too slowly for this project.

I was in the middle of my sidechain layout when you posted and decided to be inspired rather than discouraged. I thought maybe some folks might want a single sided board to play around with anyway so I went ahead using your potentiometer placement as a guide.

Zipped PDF files here

Parts designations should correspond to Fred's schematic optoSch1.pdf. Optos are Silonex NSL-32R3, LED side on the board.

 

[mnats]

[quote author="buttachunk"]Alright--

now we have the boards, so we need to nail down the last of the component values.

D1 & D2
R5, R6, R7
R9 (depends on the meter...)


Is Silonex pretty cool about ordering ? I haven't dealt with them yet...

what about the VTl5C1s in this config. ? any other changes ?[/quote]

Fred's done it first again! Sorry, I had the schematic name wrong on my post - anyway, look at Fred's post for the link to his last schematic.

D1 & D2 - 1N4148
R5 - 2M
R6 - 49k9
R7 - "selected for each opto for max slope"

Silonex usually available from alliedelec.com:

Mfr.'s Part #: NSL-32SR3
Allied Stock #: 699-3012
Manufacturer: SILONEX INC.
Description: OPTOCOUPLER
Current Page #: 1200*
Previous Page #: NIPC

Qty. In Stk.: 0

U / M:
1 Ea.
Min. Order Qty.: 1

Request Lead Time

Notify Me When Stock Is Available

1-99 $1.860 Ea.
100-499 $1.810 Ea.
500-999 $1.770 Ea.
1000-1499 $1.740 Ea.
1500+ $1.670 Ea.

...Vactrols also available from Allied.

 

[Bauman]

Looks like Siliconex is cheaper than Vactrols?

 

[fum]

I think the forsselltech.com is havin some personal problems at the moment =)

ju