BAJA LA2A Style Optical Limiter

snaper · Post by **snaper** » 05 Mar 2015, 08:36

I can't see the 470R resistor in the schemo, but its on the PCB layout.
Is there an upadted schemo what I've missed?

johnk · Post by **johnk** » 16 Nov 2018, 00:15

how would i go about making the limit knob have a better sweep range?i used a 3mm diffused yellow LED and it works great, but the B10K limit knob has a very narrow range at the beginning of it's sweep. i tried it with both red and green opto leds but other than the amount of limiting, it still comes on too quickly.

johnk · Post by **johnk** » 16 Nov 2018, 03:46

nevermind. i just used an audio 10K pot for the limit control and it's perfect.

FeatureBug · Post by **FeatureBug** » 13 Feb 2019, 22:11

Just fyi for you diy'ers pot curves can be logified (i.e. audio tapered) by adding fixed resistors, as detailed in this excellent article by Rod Elliot at ESP: http://sound.whsites.net/project01.htm
I've done this when audio taper pots are difficult to find in the configurations I want, and with very good results. Cheers!

temol · Post by **temol** » 29 May 2019, 19:22

Hi Bajaman,

why did you use LF535 here?

T.

bool · Post by **bool** » 30 May 2019, 13:41

Its a "353" ... probably because that's what was used in the "inspiration" pedal. It's a a TL072-workalike.

temol · Post by **temol** » 30 May 2019, 16:31

You are absolutely right, a typo.. of course 353.

Thx.
T.

bajaman · Post by **bajaman** » 13 Sep 2019, 22:58

Because photfuckit (photobucket) changed their free viewer status, the original schematic, and layout views are now unreadable to most of us, SO - here is a readable version for you all!
cheers bajaman

: BAJA LAYOUT.png (8.73 KiB) Viewed 7091 times

: BAJA PCB.png (9.92 KiB) Viewed 7091 times

: BAJA OPTICAL LIMITER LABEL.png (7.12 KiB) Viewed 7091 times

bajaman · Post by **bajaman** » 13 Sep 2019, 23:01

In the above post schematic, I found it a good idea to reduce the 68k source to ground resistor on the input jfet buffer to 10k

cheers
bajaman

Jmpj48 · Post by **Jmpj48** » 14 Sep 2019, 06:39

Thanks Baja for the schematic.

Jmpj48 · Post by **Jmpj48** » 14 Sep 2019, 16:33

Baha do you use both led’s or just one with the ldr?

Jmpj48 · Post by **Jmpj48** » 14 Sep 2019, 16:36

Oops sorry I put my glasses on I see one led is the indicator lol. Would it be possible to lay this out on vero? I know the ldr and led need to be close together.

bajaman · Post by **bajaman** » 14 Sep 2019, 22:49

You should check this thread out: BAJA Optical Limiter revisited - rev2
cheers
bajaman

Dingleberry · Post by **Dingleberry** » 28 Nov 2019, 13:28

Anyone tried this with NSL-32 optoisolator?
At first glance it looks like the parameters would match well.

jmpj45 · Post by **jmpj45** » 22 Feb 2020, 03:42

Were is the best place to put this.Run your guitar through this to amp or would it be better through the effects loop.Just wondering I'm still building it.

jmpj45 · Post by **jmpj45** » 22 Feb 2020, 18:55

Finally got it built this thing is freaking awesome.I have never been into limiters or compressors or anything but what this limiter does to the sound is incredible.It makes the clean sound really come out thick and meaty thanks baha awesome design.

ranko0537 · Post by **ranko0537** » 12 Jun 2020, 07:16

I'm having problems with this - once it starts limiting, it also starts distorting the sound. Tried different optos, and NSL32 sounds the best, although it also distorts a little. What could be the cause? Which optocouplers did you, people, used?

I tested all the vactrols I have with this circuit and this is the conclusion:
- the best is NSL32, almost no distortion
- the second placed is LCR-0202
- the third is some VTL5C10, marked with those letters and PRC, so I'm not sure if it is the original Perkin Elmer one or some kind of a copy.

All the others (I tested 5 more) distort the sound a lot, and I actually don't like those "best" 2nd and 3rd either. Strange circuit.

bajaman · Post by **bajaman** » 12 Jun 2020, 10:23

you are doing something wrong if it distorts

Jmpj48 · Post by **Jmpj48** » 22 Jun 2020, 21:16

I used VTL5C10 works perfect

Frank_NH · Post by **Frank_NH** » 05 Apr 2021, 00:53

I built the LA-2A style limiter circuit recently on my breadboard and used the lcr-0202 opto coupler. The limiter works great as does the lcr-0202. I modified the circuit to use a split supply (+/- 9V) which didn't introduce any complications. I also used an op amp for the input buffer (didn't need the extra op amp for the reference voltage circuit), but will also try the jfet eventually. I plan to use the limiter at the end of a preamp, and my experiments so far indicate it should work fine, although one might want some additional make-up gain if the input signal is hot.

BAJA LA2A Style Optical Limiter [documentation]