BAJA Optical Limiter revisited - rev2

bajaman · Post by **bajaman** » 25 Nov 2008, 20:05

i was wondering about whether this would be a good project to rack up and use in my live sound duties. maybe running at a higher voltage via a charge pump? burr brown op amps? would it be possible to do balanced in/outs? or would it even be worth it at all?

I would use a dedicated bipolar +15 and-15 volt supply if making a rack unit - also i would consider two limiting paths for stereo perhaps with a combine or separate process switch. Balanced ins and outs are easy to achieve - either with op amps or transformers on the input and output.
Check out the Jensen transformer application notes on their website for more info on the latter.
However this is no longer a stompbox

bajaman

bajaman · Post by **bajaman** » 25 Nov 2008, 20:10

just got mine working except the indicator LED

First - the limiter indicator only flickers when the limiting action occurs. If you want a status indicator you will need to hardwire an LED and series resitor to an unused pole of the footswitch between +9v and ground etc.
Second - it is critical that the same LED as used in the optocoupler is used for the limit indicator light.
Third - is it oriented the correct way around??
I have built a few of these limiters - they all work VERY well - check your build for errors!!!
bajaman

MPUMarko · Post by **MPUMarko** » 25 Nov 2008, 21:00

Thank bajaman,
looks like I have my limiter working. I thought the led was status indicator, my mistake. As I said earlier, total newbie on electronics:). I have a VTL5C10 optocoupler. What kind of a led works with it?
Marko

bajaman · Post by **bajaman** » 25 Nov 2008, 21:49

have a VTL5C10 optocoupler. What kind of a led works with it?

As I said it needs to be the same type of LED for it to work properly - you will have to experiment with all the LED colours - try yellow first .

Otherwise make your own Optocoupler with an LED and LDR inside a black plastic tube with the ends sealed off etc.
cheers
bajaman

MPUMarko · Post by **MPUMarko** » 26 Nov 2008, 14:38

It's working now. The led flickers when limiting the level. It's not very bright, I guess I'll have to try other leds. I've tried yellow and green 5mm leds and they both are not very bright when on.
I have to etch the enclosure and start finding settings for bass. So far I've got some very nice limiting that'll suit my use fine.
Marko

bajaman · Post by **bajaman** » 26 Nov 2008, 18:31

It's not very bright

That's okay - it is only there to give a visual indication when the onset of limiting occurs.
Glad you got it working - how do you like it soundwise??
cheers
bajaman

MPUMarko · Post by **MPUMarko** » 26 Nov 2008, 19:54

I haven't tried it very much yet. I get a nice limiting when setting the limit to limit out just the loudest peaks. If I set too much limit I think it takes a bit too much out of the sound of the bass. When only the loudest peaks are limited the pedal has no effect on sound or just maybe it makes the notes sound a bit more sustained. I have to test it with the whole band hopefully next week. I think it will work great for limiting out the inaccuracy of my right hand finger technique just as I hoped it to do.
Marko

bajaman · Post by **bajaman** » 26 Nov 2008, 20:03

It is a very subtle but very useful effect - when set right it can make your bass sound slightly fatter.

MPUMarko · Post by **MPUMarko** » 26 Nov 2008, 20:16

I agree on making the sound somehow fatter. I think it will be a lot easier to set it after I have it inside the box and knobs on.
Marko

bajaman · Post by **bajaman** » 27 Nov 2008, 06:15

great on vocals too - at least that is what my friends tell me.

bajaman

chicago_mike · Post by **chicago_mike** » 28 Nov 2008, 14:02

Silly Question...

What do I resize the pcb to?

When I printed it, test rint, it was full page. Im a big parts guy myself..but....

Thanks.

MPUMarko · Post by **MPUMarko** » 28 Nov 2008, 16:06

I opened the PCB file in Paint and then printed it. I got it correct size that way.
Marko

Barcode · Post by **Barcode** » 28 Nov 2008, 16:14

bajaman wrote:
i was wondering about whether this would be a good project to rack up and use in my live sound duties. maybe running at a higher voltage via a charge pump? burr brown op amps? would it be possible to do balanced in/outs? or would it even be worth it at all?
I would use a dedicated bipolar +15 and-15 volt supply if making a rack unit - also i would consider two limiting paths for stereo perhaps with a combine or separate process switch. Balanced ins and outs are easy to achieve - either with op amps or transformers on the input and output.
Check out the Jensen transformer application notes on their website for more info on the latter.
However this is no longer a stompbox
bajaman

This interests me baja. I have limited/no experience with balanced signal, but I would like to. I think this would be a great limiter for vocals and I'd like to whip one up with a balanced in and out. I have a couple of 42TM013 transformers around, how exactly would one wire these to acheive balanced signal. I know that is kind of a noob question considering how long I've been building now, but I'm a little dense anyway and I've never messed with balanced signal before.

briggs · Post by **briggs** » 28 Nov 2008, 16:41

Here's a question - How do ya slow the decay of the follower circuit? I'm liking it's attack speed but could just do with adjusting it for a slightly longer decay?

MPUMarko · Post by **MPUMarko** » 02 Dec 2008, 17:37

Just came from rehearsals. The limiter worked out great! I couldn't hear it at all but the red clipping lights from the mixing table were gone. We use in-ear monitoring and I play direct to table via ART Tube pre as DI. Limiter also made my sound a bit fatter. Well spent 50€!
Thanks Bajaman!
Marko

scaai · Post by **scaai** » 11 Dec 2008, 13:04

@bajaman:
Made an OR, but it doesn't really satisfy me (for bassguitar), so I want to try your Limiter next.
Is it possible to insert a pot for "Threshold" anywhere like the Sandwich of Fran got one?

JesseKlaasse · Post by **JesseKlaasse** » 04 Jan 2009, 13:57

This project sounds really interesting! On the virtual effects side (VST), I own a Universal Audio UAD1 card with the LA2A compressor/limiter, which I totally love. I am planning to build this thing for guitar first, in stomp box form. After that, I would like to try to build a 2-channel rack version. From time to time I do live front-of-house mixing, and I would really like to have my hands on (the ease of use of) a LA2A style limiter.

However, I'm not very experienced building effects yet (I have built only four stomp boxes so far, a Box of Rock, OCD and two Klon Centaurs). So far, I have only used vero/stripboard. I'm kind of hesitant to etch PCB's, since I don't trust myself with chemicals. At least with electronics I kind of know what I'm doing, which is not the case at all with chemicals.

I am currently in the process of trying to translate the schematic to a vero layout, however I'm kind of having problems with it (never done it before, and my theoretical knowledge of electronics is kind of basic). Has someone already created very layouts of this project? That would save me lots of sleepless nights

Furthermore, are there things which need to be changed when placing two units in a rack using a bipolar +15V and -15V power supply, as Baja suggested? Or would the layout stay as it is?

Thank you very much in advance.

Post by **modman** » 05 Jan 2009, 09:18

You could use simple household chemicals like HCL (commonly used a pool detergent) and H2O2 (as used by BJF to dye his hair):

For 1L of etchant you need:

750ml H2O water
200ml HCL hydrochloric acid http://en.wikipedia.org/wiki/Hydrochloric_acid
50ml H2O2 hydrogen peroxide http://en.wikipedia.org/wiki/H2O2

Put some of this mixture in a plastic container that you put in another plastic container containing hot water. This hot water will accelerate the process of etching. Stirring the etchant CAREFULLY also helps. Don't breath the fumes, stand away if you're not stirring or checking how it goes.
It takes some time, dependent on the size of the board. Be patient and watch.

Contrary to Ferric Chloride use can dispose this after dilluting with plenty water.

DIY Layout Creator is the solution for making layouts without losing time. You can always go back and correct stuff instead of having to do an entire redraw.

Fuzzer · Post by **Fuzzer** » 06 Jan 2009, 00:41

How much water is needed Modamn?, to get rid of a L of that etchant?,

RLBJR65 · Post by **RLBJR65** » 07 Jan 2009, 02:11

Contrary to Ferric Chloride use can dispose this after dilluting with plenty water.

A little known but easily verifiable fact is that the majority of Ferric Chloride (AKA Iron Chloride) is used in drinking water and waste water treatment.
http://www.americanchemistry.com/s_chlo ... TYPEID=113

Its the copper thats the real issue. The EPA's action level for copper in drinking water is 1.3 parts per million. Below that level it is considered safe for consumption so you be the judge.

BAJA Optical Limiter revisited - rev2 [documentation]