Official Forssell Limiter Build thread

[DrFrankencopter]

Allright I'm moving onto the meter now....I have it wired up, but I'm not getting the right resolution out of it. I get maybe 5-6 dB across the full range (all 10 LED's). It's definitely measuring proportional to gain reduction, but way too sensitive, and I don't think it's repeatable across the various ratios.

Anyone have any tips on setting up the meter. What kind of range should I expect? 1 dB per segment would be nice as I rarely go beyond 10 dB compression, but I doubt if the opto is that repeatable (or match-able).

Cheers,

Kris

 

[soundguy]

after fiddling with both trimmer pots for a while I was able to get it to about 1 dB ish per segment. Its somewhat consistent over the range of ratios, but the resolution seems to be 1dB accurate for the first 6 or 7 led's and then increases to about 2dB. Works for me.

dave

 

[JustinS]

Hey guys,

I'm ordering parts for a chip in/out version of this project at the moment. I've got a bunch of 1/4 watt resistors for most values, are there any I should watch out for and get in 1/2 watt?

Justin.

 

[DrFrankencopter]

Keep the resitors in the regulator section at 1/2 watt or more. Particularly on the positive rail...those LEDs draw a fair amount of current (50 ma for all lights on).

Oh, and note my post a couple pages back about the incorrect values around the PS regulators...you'll end up with 27V if you use the values from the parts list.

Cheers,

K

 

[soundguy]

just in case anyone has forgotten about this one, let a friend listen to this limiter tonight and it basically exploded his head. Look at the equipment list on my website, this was his favorite limiter out of everything...

this box is truly awesome. The design is SO clean, its ripe for your own personal color with choice of opamps and/or transformers to really get the sound you want, I dont think the sidechain has a really overbearing tone to it. Attention to component selection can yield really different sounding boxes.

Fred, if you are reading, thanks for contributing such an awesome original idea.

It's a real shame more folks havent tried this one out, I think it's one of if not the best project talked about on this board.

dave

 

[Greg]

I need to finish mine !!!

 

[matthias]

@soundguy: can you compare the sound of the opto to some of the other compressors around..?

it would be great if someone could make a soundsample...

 

[soundguy]

it doesnt sound like anything else around, thats the whole point...

dave

 

[nrgrecording]

ahem... has anyone successfully finished the forsell with tommys pcb? :?:
Iam not sure i'd done all changes to the original layout, is there a list of all changes which has to be made?
From the thread "...DIY projects sitting in the closet..." the following guys haven't finished it right now? : orson whitfield, Svart, scenaria, omeiko, fum, JustinS, Zee1usa

I tried to finish it, but it doesn't work how it should work (as far as i remember... :roll: ) Ok, the circuit isn't much complicated but I don't want to trace the double sided pcb... so it would be nice to know if the project is working or not. I can't even find kev's forsell website... :?: If i can remember correctly you build it on a breadboard, dave?

Frank.

 

[soundguy]

i built it on tommy's boards, they work fine and you dont hav to make any changes to them. take a close look at them, tracing them is simple. Im a total idiot when it comes to tracing pcb's and if I can figure it out Im pretty sure anyone here could as well. If you stuff the boards right following everythign in this thread, the limiter should work, mine do.

I didnt use the on board power supply, so you guys are on your own with that.

dave

 

[nrgrecording]

Thanks Dave.
I have to give it a try. PSU is working fine, i think i had changed two resistors because the output voltage was a bit too high or so... we'll see.

Frank.

 

[Nele]

I finished my first of 4 units.. as I made the cheapo-version with 5534 in- and output I'll have to adjust the onboard power supply, make some small adjustments as described elsewhere and still need to add the output-transformer (I already hooked up a LL5402 with test-cords and it sounded very nice).

But even now it sounds great!

Corneel

 

[nrgrecording]

Ah... It works!
I'd done a little mistake.... don't wonna talk about it...

:green:

-changed R15,R16 to 4K7 (was 6K19)
-changed R35 to 35K
-added 100k pot for makeup gain
-added defeat makeup gain
-changed 2N5457 to BF245A

a little drawing...
http://www.nrgrecording.de/tempfolder/forsell_opto_rev1.pdf

Many thanks Mr. Forssell, Tommytones, kev, Soundguy and groupdiy!

Frank. :thumb:

 

[toffifee]

[quote author="nrgrecording"]
I'd done a little mistake.... don't wonna talk about it...

:green:
[/quote]

What did you do? :green: :twisted: :guinness:
Toff

 

[nrgrecording]

What did you do? :green: :twisted: :guinness:
Toff

ceramic in the sidechain aren't working good - wrong type, wrong value... interesting sound :wink: (330nF C6 in schematic, C26 on pcb)

http://www.nrgrecording.de/tempfolder/200-0029_MVI.AVI

 

[nrgrecording]

Regarding the stereo link switch...
Both channels were summed together after the non inverting opa2604 (after the 1k resistor) and the sidechain signal is linked to the opamp before the ratio potentiometer... is this correct?
Wouldn't it be better just after the ratio potentiometer?
And in link modus... one channel (mostly the first one) should control the other channel. So in link modus - one channels bypass mode must be switched on, right?

the old optolink schematic:
http://www.nrgrecording.de/tempfolder/OptoLink1.pdf

I found an old thread where ChuckD told about weird behaviors when pressing the link button... ChuckD... any news?
http://www.groupdiy.com/index.php?topic=5339&highlight=forssell+link

Frank.

 

[DrFrankencopter]

Not sure about the link, but regarding the tommytones PCB it is fine. The only caveats that I've noticed so far are:
1. The FET pinout needs to be checked if you're using the Bendo output driver option
2. The PCB resistors on the stuffing guide are not right...make the rails to high a voltage.
3. If you're using the discrete output amp (990 style) you neeed to cut traces to add in a makeup gain control.

Cheers,

Kris

 

[cstella]

Hi all so I finally got one of my Forssell's up and running. I built the discrete version with a DLR on the input and a 992 on the output. Very nice so far!

A couple things. The SC realy seems to have too much gain for me. I changed R22 to 10K (6dB in the SC as opposed to 24dB). I like this better for louder material. Also the Ratio behaves better too. I will probably adjust it to something more in between or maybe a High/Low switch between the 2 resistors for different program material.

I have the meter working well from 1db to 10dB GR. Has anyone done the Opto calibration or know where on the forum it is dealt with? I can't seem to find anything.

I cut the trace going to the + input of the output opamp and wired a 100k pot for output gain. With a 1k resistor to ground I get a nice +/- 20dB with zero at center.

I also cut the trace to R43 to wire a bypass. The differential amp is still in the chain when bypassed but that is ok by me.

This is just a temporary panel with periscope meter!

http://www.charlesstella.net/opto.htm

Thanks , Charles. [/img]

 

[cstella]

Also planning to bring the SC out to the panel and maybe experiment with the GSSL Highpass board I have here.

 

[Nora]

I've read the threads a few times and I came across this issue but it wasn't very clear:

I'm gonna use a discrete in and out buffer.

Can I use different opamps like the Tl072 or NE5534 in the sidechain ?

Will there be any sonical differences ??

And will they work with these voltage rails ??

thanks,
Arno