Official Forssell Limiter Build thread

[ChuckD]

No it wasn't

Tom is working on a calibration technique right now. The value for that resistor I think is back in this tread somewhere. Just check Tom's posts in this thread and you will find it.

-ChuckD

 

[strangeandbouncy]

thanks, Chuck!

Can't find it at the mo! I'll leave it now, cos i'm already cross-eyed!

BTW - why use opa2604? is it just because it'll handle +/-24v? if I use +/-15v, can I use Ne5532 or TLO72?

All very exciting . . .

Andy p

 

[strangeandbouncy]

Got it!

Tommy used 100R for R28.

:idea:

Andy P

 

[strangeandbouncy]

hi All,


My first board is nearly finished. Just waiting for opto-couplers. i have a no. of surplus VU meters of various sizes, and have always prefered needles to leds. i have found a bit of schemo from early on showing a VU meter, but no resistor values. I was wondering what approximate values would be a good starting point for the resistor between the meter and ground, and the pre-set to adjust 0VU. I would hate to fry one of my beautiful meters!



Thanks,

Andy p

 

[strangeandbouncy]

Dear All,

i was pondering the lack of output adjustment if using the Discrete o/p. Is there any good reason why one shouldn't replace R6(100k) with a 100klog pot as a fader, with the wiper feeding +ve input of op-amp, and the opa-amp circuit configured to give say, 20dB(more than enough imo)?
Also, I have given up trying to get a revlog 5k pot. I still don't understand what it is v.v. a normal log pot. Is it anti-log, log backwards, or what? Seems to depend on who you ask. Some say lin pot with resistor strapped over pins 1 and 2, some say rear section of dual log pot, - Nuts! I say! I was thinking of using a pre-set to establish correct value for set ratio and using a switch, say, 2:1/3:1/5:1/8:1/lim? Any reason why not? Also considering doing the same for Attack/Release values. Makes for a much more accurate re-call . . . . . . maybe threshold too . . . .
Also, can i use TLO72 or NE5532 in this circuit instead of OPA2604 with reduced Voltage rails (+/- 15v)
Does anyone have any experience using an analogue vu meter in this circuit? I need help with the value of resistor between meter and ground, and value of trimpot to give 0dB if at all possible. . . .

Finally, has anyone plotted any resonse curves for one of these babies? i guess it would be helpful in finding the values for ratio switch and also for analogue gr meter . . . . .

eagerly awaiting my opto-isolators . . . .

Many, many thanks in advance, you wonderful, wonderful, people . .


Andy P .

 

[soundguy]

trying to make time this week to work on this one, thought Id kick this one alive again.

two questions for now-

anyone get anywhere with a VU meter?

second:

If I use a 5K lin instead of an antilog, it will work, but just backwards, right? A regular 5K lin pot can be used to dial in values for building a switch, for instance, yes?

dave

 

[cstella]

Hello all My name is Charles and I have recently obtained some Limiter boards to build. I am having trouble sourcing the 5k Rev log. Newark has a 80day lead time on the Bourns model. Are there any good substitutes or does any one have any Bourns spares they would be willing sell. Thanks! Charles.

 

[hitchhiker]

I'm still just using my bread board unit .I have a vu working just fine,
hooked up exactly as shown on Fred's original drawing.
I 've been too busy to do up the boards.I'm using Quad Eight ca-127 amps
for my buffer/make up and it works well.I think when I can afford them I'll
do my boards up with the Forssell opamps.

I 've not touched the rev 5k since it was set months ago, so I'm not sure why it would need to be reverse.

The one thing I find touchy is the threshold pot. It would be nice if it
dialed in slower.Is there a such thing as a 2 turn pot?

How is everyone liking this comp?

cheers,
Lance

 

[j.hall]

so, how many people have finished this unit?

anyone have any sonic opinions about it?

i'm probably going to start building mine soon. just curious what people with finished units think.

 

[StephenGiles]

With a general election coming up, this thread always reminds me of the Official Monster Raving Loony party - whose election manifesto includes a proposed issue of a 99p coin - to save on change!!!! Lord Sutch RIP!!
Stephen

 

[j.hall]

couple quick questions that i'm sure have been answered but i'm sitting in mouser/digikey/newakr/allied hell and haven't the patience to look

the PSU caps on parts list rev. #3, that are shown as a range of values. i take it those are filter caps and a higher value is prefered, however the lower values are exceptable. is this the case?

the .33uF/16v and the .68uF/16v i have some of those in 100v values. i'm pretty sure it doesn't matter, but i just want to check. can i use the 100v value, or should i order some 16v in both caps?

 

[soundguy]

has anyone completed one of these using discrete gain blocks on tommy's boards?

I finally got some pots that were on backorder and fired it up and have intense gating- if I yell into a mic, it'll open for a brief moment and sound all distorted. Boo.

dave

 

[soundguy]

a note:

perhaps silly on my part, but while building a mono version, I omitted U9 thinking it was only needed for the stereo link, not so... U9 needs to be installed in order for the unit to switch out of bypass. Sat for a half hour scratching my head until I realized that one...

So far, sounds really nice, quite a bit nicer than what I was expecting. Gonna try to work out a level control pot for the output driver and see about hooking up a VU meter.

Am I the first to finish this using discrete gain blocks?

who here besides tom has one totally done?

dave

 

[Infernal_Death]

Not totally done but i have a ic version working so far. It's just missing the output trannies and the stereo link.
And i don't have that much time to record right now so i can't really comment on the sound quality. I just put some test music through it and listened on some active pc speakers so i guess this doesn't count.

Flo

 

[soundguy]

what did you wind up doing for metering?

Im trying to figure a way to make a standard VU meter work for gain reduction metering.

dave

 

[Infernal_Death]

Nothing fancy, i used the included meter driver for LEDs (LM38something). Since my G1176 and GSSL both use VU Meters i think it's a nice thing to have something different.

Flo

 

[Nele]

Hi,

I've almost finished building my first of 4 Forsell-compressors and have two small questions.

1. Do I need to use the capacitors listed under 'Off Board PSU' in the parts list? This when also mounting C14 and C15.

2. Do I need to match the vactrols or is all the matching done by VR2.

Thanks!
Corneel

 

[hitchhiker]

hey Dave,

I'm using this circuit of Fred's that uses a second opto tied to GROUND (not
to plus 24v)and it works just fine . It is his first post of this comp I beleive.

http://www.forsselltech.com/SideChain.PDF

cheers,
Lance

 

[Jonathan Hayward]

Dave, I used a standard 1mA meter as gain reduction (only) meter.
Someone posted the circuit for doing 'backwards' gain reduction metering a la 1176 etc, I scribbled it down on an envelope it was so simple but can't now find the link (is it in this thread earlier on?). you just need a trimmer (I used 500k) off the + rail and a fixed resistor (20k) to ground at the other end to set the meter at 0 reduction the metering vactrol then brings the meter back towards ground during compression.
Haven't matched the vactrols, but they all behaved similarly as far as making the units compress and meter in a similar way, but have yet to measure the onset voltages etc between units.
Compression is very natural (if a little slow at times) and excellent for voice; the gate funtion works okay (though of course, controls are reversed) but might be too slow to be reeeeally useful - unless I've got a bug in all of them... I've built a 3 channel chip version with LL1517s on the outputs, all expediency rather than planning.

 

[soundguy]

I tried the meter in the original schem and couldnt get it to work right, maybe I'll try it again. I drilled the front panel last night for LED's, so at least onee of them will have LED metering. Im hoping to have that one completed totally today so hopefully I can post a piccture later.

dave