Free Stomp Boxes

freestompboxes.orgBAJA LA2A Style Optical Limiter25 Nov 2007, 10:52 bajaman

Hello my f riends I am part icularly proud and pleased with this new project - I have justcompleted the working prototype - pictures to follow I started this project by t rying to reverse engineer the Demeter Compulatorf rom pictures posted here by some of you folks, but I could not see the solderside of the board and despite numerous requests, nobody posted it So, I quiet ly shelved this project and did some work on other projects, butyesterday a f riend kindly provided me his unit to open up, and the rest as theysay is history. I got my t rusty digital camera out and got some lovely pictures f rom all angles- I will post these soon, so do not panic. Then I t raced the schemat ic and was a lit t le disappointed, because it did notseem to funct ion like the LA2A limiter that I believed it was modelled af ter

Hmmmmmm, I thought - i can do bet ter than this, i t hought to myself , so I setto work and this is what I came up with. Although it shares some similarfeatures and parts with the Demeter Compulator it funct ions completelydif ferent ly - in fact it funct ions just like the Telet ronix LA2A Limiter THIS IS NOT A COMPRESSOR like the Demeter it is a LIMITER The Demeter Compulator derives it 's cont rol signal f rom the OUTPUT of theunit . My Opt ical Limiter derives it 's cont rol signal f rom the INPUT of the unitand therein lies the major operat ing dif ference. I have played some guitar through the Demeter Compul;atorand although it isa very nicely made unit I was less than impressed by - no indicator to showhow much compression and a tendency to release errat ically on highcompression set t ings - a bit like an underdamped swing door Nevertheless, Pete Townshend and Dave Gilmour both use one in their PeteCornish rigs, so it cannot be that bad then can it Anyway - I have a board layout and parts placement overlay all done for thecompulator - I will t idy up the schemat ic and post it in the next few days, but Ithink you will like my Limiter bet ter. Anyway I will post them both as projectsand let you folks decide which one to build, or you can build them both if youare keen Enough t lk - here is the f irst instalment in this project - the Baja Opt ical Limiterschemat ic - board layout and PCB will f ollow very soon , but as it is myBirthday tomorrow, I may be a wee bit incapacitated enjoy bajaman BAJA Opt ical LA2A Style LIMITER25 Nov 2007, 16:13 Aharon

Happy birthday Baja!!!! Hey,your generosit y is limit less...another great project ,always original ,alwaysuseful................ I don't even look at the Boot ique boxes disected sect ion!! YOU RULE!!. Thanks Aharon

25 Nov 2007, 19:16 Stephengiles

Happy birthday indeed. I was discussing with my wife only this morning thedownside of a heavy drinking session - that is to say, how your head feels thenext morning!! Anyway as it is already tomorrow for you in NZ (I'm in England) It rust your head is not feeling too bad.

The worst ever for me was New Years Day around 1980, af ter a night of muchwhiskey, cards and rich food, I was faced with a drive home of some 40 mileswhilst hoplessly over the drink/drive limit .

I have some thoughts on your wonderful circuit which I'll commit to wordsanon........but now to the Italian Restaurant !25 Nov 2007, 20:48 goaltoday

Happy Birthday!![smilie=a_partyguy.gif ]

What Light /Dark Resistance would you recommend for the ldr? Thanks.25 Nov 2007, 20:58 DWBH

What 's does a limiter do?25 Nov 2007, 21:40 bajaman

What Light /Dark Resistance would you recommend for the ldr?

I used one of the small ones available f rom the local elect ronics store - I thinkit is a Philips, but not sure. I will t ry and get some specs for it for you - feelf ree to experiment OR you could just use a Vactec VTL5C9 or VTL5C10device - should work okay.

What 's does a limiter do?

f rom wikipediaLimit ing: Any process by which a specif ied characterist ic(usually amplitude) of the output of a device is prevented f rom exceeding apredetermined value.

Limit ing can refer to non-linear clipping, in which a signal is passed throughnormally but "sheared of f " when it would normally exceed a certain threshold.It can also refer to a t ype of variable-gain audio level compression, in whichthe gain of an amplif ier is changed very quickly to prevent the signal f romgoing over a certain amplitude.

Hard limit ing (not to confuse with "clipping") is a limit ing act ion in which there is(a) over the permit ted dynamic range, negligible variat ion in the expectedcharacterist ic of the output signal, and (b) a steady-state signal, at the maximum permit ted level, for the durat ion ofeach period when the output would otherwise be required to exceed thepermit ted dynamic range in order to correspond to the t ransfer funct ion ofthe device. Sof t limit ing is limit ing in which the t ransfer funct ion of a device is a funct ion ofit s instantaneous or integrated output level. The output waveform istherefore distorted, but not clipped

cheers bajaman25 Nov 2007, 22:09 goaltoday

Thanks bajaman.26 Nov 2007, 20:47 bajaman

Here is the complete project hope you enjoy it as much as I do bajaman PCB LAYOUT SCHEMATIC27 Nov 2007, 01:05 bajaman

I just modif ied a customers BOSS DD2 (DD3) to give the TES sound (tapeecho simulator) - the echo is less high t reble and the repeats areprogressively less bass, and a couple of small mods to increase the numberof repeats available etc. I will post details soon for those who wish to improvetheir BOSS pedal sound. ANYWAY - I connected my BAJA Opt ical Limiter AFTER the BOSS moddedDD2 and was very pleasnt ly surprised at how it fat tened and warmed thesterile digital sound - now it sounds much more like a tape echo. SO - build this project - you will not regret it , I promise you bajaman27 Nov 2007, 11:19 bajaman

Here is a label - it f it s a standard Hammond 1590B case. The cont rols and the led pilot light indicator will f it t o the pcb perfect ly. I used Alpha 16mm spline shaf t pots with 30 amp fuse wire to extend the legs.The pots are mounted on the solder side of the circuit board and a 3mm selfadhesive bumper is at tached to the rear of the pot case to prevent it short ingagainst the solder side of the board. Once the pots are at tached to the casethey hold the circuit board and pilot indicator light f irmly in place too. cheers bajaman

Baja Opt ical limiter label27 Nov 2007, 18:13 MoreCowbell

Cool project Baja...I'm gonna take a "building break" for a bit , but I might f indt ime to make this one in the next couple months. Anyway, HappyBirthday...and Happy Holidays !27 Nov 2007, 20:31 Skreddy

Wow; looks great ! Nice project . Bajaman!27 Nov 2007, 21:17 bajaman

I might f ind t ime to make this one in the next couple months

Don't wait that long Andrew This sounds really really nice af ter any fuzz or

distort ion pedal - fat tens the sound, warms it up, and generally makes itsound more tube amp like. cheers bajaman27 Nov 2007, 21:21 bajaman

Designing (with some help f rom the Demeter Compulator - do a search on thissite) this ef fect has completely changed my out look on compressors / limiters.i used to think they sucked tone big t ime - Boss CS2 for example, but af terbuilding this project I am a t rue believer in their real worth (opt ical baseddevices - NOT VCA) bajaman27 Nov 2007, 22:16 analogguru

i used to think they sucked tone big t ime - Boss CS2 for example,but af ter building this project I am a true believer in their realworth (opt ical based devices - NOT VCA) bajaman

bajaman.... I can understand your enthusiasm, but you are technician enough toexplain me what an opto based compressor should be able to do, what aVCA-based cant ....?

The CS-2 is "dynacomp based" the same concept most of the compressors(including keeley) use.... but only in the "guitar world".

Sorry, but the "guitar world" is not ident ical with the whole compressor world.And even in the "guitar world" are except ions: for example the DOD 280 or the Boss CS-1 are opto-based... so opto isnothing new - but guitarist only ask for Dynacomp-clones.

This doesnt mean that the Demeter concept is the last wisdom of the world...it sounds maybe bet ter than the well-known dynacomp-world... but IMHO it s acheap and poor concept which doesnt produce any result what cannot beachieved also with VCAs.

If you dont believe it , have a look to f ind such a unit for comparision:

It s VCA based (CEM 3381) and should deliver at least the same result s.

analogguru28 Nov 2007, 01:11 bajaman

but IMHO it s a cheap and poor concept which doesnt produceany result what cannot be achieved also with VCAs.

Tell that to Dave Gilmour and Pete Townshend They pulled their VCA based compressors f rom their boards and areCURRENTLY using the Demeter Compulator in their touring Pete Cornish builtpedal boards. Seriously though, I was t rying to build a 9v pedal to mimic the sound andresponse characterist ics of the famous Telet ronix LA2A broadcast limiter,and it uses optocouplers and senses the input signal BEFORE the voltagegain recovery amplif ier - in this respect it operates far dif ferent ly than anyVCA feedback AGC based design that I am aware of on today's market . Compare a 1khz square wave fed into a VCA based device such as the BOSSCS2 and you will be horrif ied at what comes out of the output socket . Nowbuild my pedal - it should not take you very long - and compare the response,and you will see why I am so enthusiast ic about this project . bajaman28 Nov 2007, 01:24 modman

analogguru wrote:i used to think they sucked tone big t ime - Boss CS2for example, but af ter building this project I am a truebeliever in their real worth (opt ical based devices -NOT VCA) bajaman

bajaman.... I can understand your enthusiasm, but you aretechnician enough to explain me what an opto based compressorshould be able to do, what a VCA-based cant ....?

The CS-2 is "dynacomp based" the same concept most of thecompressors (including keeley) use.... but only in the "guitar world".

Sorry, but the "guitar world" is not ident ical with the wholecompressor world. And even in the "guitar world" are except ions:for example the DOD 280 or the Boss CS-1 are opto-based... soopto is nothing new - but guitarist only ask for Dynacomp-clones.

This doesnt mean that the Demeter concept is the last wisdomof the world... it sounds maybe bet ter than the well-knowndynacomp-world... but IMHO it s a cheap and poor concept whichdoesnt produce any result what cannot be achieved also withVCAs.

If you dont believe it , have a look to f ind such a unit forcomparision:

It s VCA based (CEM 3381) and should deliver at least the sameresult s.

analogguru

If it would be revolut ionary he wouldn't be post ing it , I know him, he's anintelligent guy. I'm sure he's got much more convoluted stuf f up his sleeve.

If you can provide schemat ic and layoout we could put it in a dif ferent folderand then the challenge is on. We can never have enough 'f resh' answers on old quest ions...

Where's that Tubezipper schemat ic? PT has escape all t racing here...28 Nov 2007, 02:59 bajaman

anyway - mine only has two knobs bananaman 28 Nov 2007, 04:27 paulc

Bajaman,

that looks pret t y cool. I've got something close to that myself , and I've gotsome t ricks for it that you might want to t ry if you're into it .

The main one is I use two LDRs instead of one. The LED's are wired back toback like a diode clipping pair, and the resist ive elements are paralled in thesame place you have them. I add some series resistance to one of theresist ive elements, and a parallel resistor across both. This lets me putzaround with the "taper". You can spend a lot of t ime there get t ing thingsperfect to your ears.

I've found that running the driver at a higher voltage can help. Once you hit therails you wont be able to get the LEDs brighter. This can limit the range, so byincreasing the headroom you can hit the LED's harder making the resistorsdrop more. If you can get them to drop low enough (having the two in parallelhelps right of f the bat ) then you can make the ef fect st ronger without havinga large series resistor on top reducing level at quiescence. Less recovery gainwill be needed keeping the noise down.

Also adding a tone cont rol t ype circuit around the driver can make the compreact to dif ferent f reqs. This can be cool to keep bass f rom being boomy, or ifyou crank the highs you can get it to act like a deEsser comp'ing the highs

more to keep things f rom get t ing shrill. But before it get 's said I know that 's anold t rick... st ill cool though.

I love these type of opto comps much bet ter than the VCA's. The nice thingabout the optos is in your audio path the whole comp element is nothing morethan a resistor. This allows you to use your fav buf fers/gain stages and whatnot . It 's sort of like making discreet ops. you can get in there and go to towninstead of being stuck with what 's in the "package".

One of the things I regret most is in a house move I tossed some old Ureioptos I'd been saving for a LA2A build. I was bummed when I unpacked andcouldn't f ind 'em.

Later, PaulC HEritage amps/ T im & t immy pedals28 Nov 2007, 04:52 seniorLoco

I've found that running the driver at a higher voltage can help

Pf f f t t t ...done before !

Roland Sustainer AS-1 .... (gut shots coming soon)

Get t ing all 'surgical precision' with either a compressor or limiter for guitar useis a bloody waste of t ime .... imo. more for studio use maybe!

We tend to drif t f rom the fact with these kinda of ef fects, it 's the "feel" thatmat ters, not much of the "hear Ye" how it s squishes or sustaines!

Opto rule since they sluggish just like we humans ...aye mate !?28 Nov 2007, 05:05 paulc

seniorLoco wrote:I've found that running the driver at a higher voltagecan help

Pf f f t t t ...done before !

Roland Sustainer AS-1 ....

(gut shots coming soon)

Get t ing all 'surgical precision' with either a compressor or limiterfor guitar use is a bloody waste of t ime .... imo. more for studio usemaybe!

We tend to drif t f rom the fact with these kinda of ef fects, it 's the"feel" that mat ters, not much of the "hear Ye" how it s squishes orsustaines!

Opto rule since they sluggish just like we humans ...aye mate !?

Ummmm O.K... Need to spend more t ime get t ing to know the guys here Iguess - I can't tell if t his was a pro/con/cool/shut up etc responce! Just t ryingto join the gang ya know?

Later, PaulC Heritage amps/t im & t immy pedals28 Nov 2007, 05:12 seniorLoco

Hey Paul nothing like that ya ....

Sorry if i was rude ..... 28 Nov 2007, 06:07 analogguru

bajaman wrote:but IMHO it s a cheap and poor concept which doesntproduce any result what cannot be achieved also withVCAs.

Tell that to Dave Gilmour and Pete Townshend They pulled their VCA based compressors f rom their boards andare CURRENTLY using the Demeter Compulator in their touringPete Cornish built pedal boards.

Sorry, but I dont intend to teach lemmings not to follow his neighbour, and itdoesnt mat ter if ones name is David or Pete.But why I should be so stubid to do it for myself .

Seriously though, I was t rying to build a 9v pedal to mimic thesound and response characterist ics of the famous Telet ronixLA2A broadcast limiter,

Seriously... the Demeter Compulator and your concept have the same amountin common with a LA2A like a FuzzFace with a Tubescreamer - both of thelast distort and both "compress".

One of the "secret recipes" of the LA-2A is the use of an elect roluminescentlight device with a special characterist ic (and not the LDR).... without includingthat behaviour you are far away f rom an LA-2A.

So please let s talk about a "feed-forward opto-compressor-concept " andnot the LA-2A... that would be blasphemy in the ears of hardcore-studio-guys.

and it uses optocouplers and senses the input signal BEFORE thevoltage gain recovery amplif ier

This concept is called "feed-forward" compressor and also made with VCAs:ht tp://rupertneve.com/products/port ico-5043/and very well knon since the mid-70s:ht tp://www.aes.org/e-lib/browse.cfm?elib=2252

I for myself designed one with 2 OTAs in parallel as variable resistors in thefeedback loop of an op-amp in 1981.

- in this respect it operates far dif ferent ly than any VCA feedbackAGC based design that I am aware of on today's market .

If you are not aware of it , doesnt mean that it doesnt exist since more than30 years.

Compare a 1khz square wave fed into a VCA based device suchas the BOSS CS2 and you will be horrif ied at what comes out ofthe output socket .

As I wrote above:The sh*t t y "Dynacomp & Clones" concept is not all and everything in the VCA-compressor-world.... And I dont intend to discuss about the behaviour of theworst example. Noone is using this sh*t - and paying horror prices for it -except of guitarists.

If the At tack and Release t imes are correct ly adjusted on a (non-dynacomp)(feedback)VCA-based compressor/limiter we can compare itwithout any problems.

Now build my pedal - it should not take you very long - andcompare the response, and you will see why I am so enthusiast icabout this project . bajaman

Yes, it will sound new and good.... (espacially for the guys who only knowdynacomp-(clones).... and it s ok to be enthusiast ic - but please stay on thetechnical f loor...

As you can read in long discussions about lamps/ldrs for the univibe theresponse of both have an inf luence on the tone.... Did you ever have a look onthe response curves of an LDR ? they have a very long recovery-t ime.....

If they wouldnt , Demeter and your circuit would be a ringmoduator instead ofa compressor due to the lack of a smoothing-cap in the side-chain. For thisreason you only have two knobs instead of three... : You cant adjust the recovery (release) t ime....

analogguru

--------------------------------- Every (bootweak)-pedal has a purpose.... ...it might be a door stop or a hammer, but every (bootweak)-pedal has apurpose.28 Nov 2007, 06:57 bajaman

Thanks for your comments and suggest ions for improving this design Paul In pract ice - yes, I have built a fully operat ional unit , - this is not a designconcept , but a fully working 9v stompbox limiter. it most certainly is not aRupert Neve studio designed compressor, it is a guitarist 's stompbox on thef loor. If I was set t ing out to design a studio qualit y processor with a gazillion knobs,conmpression rat ios, at tack and release t imes etc., then i most certainlywould not be post ing the design on this forum - OK Sorry - i digressed a lit t le In pract ice - i have found that by using a standard 3mm red led, that I can getmore than enough limit ing act ion with the 9v bat tery supply.

Noone is using this sh*t - and paying horror prices for it - except ofguitarists

And this is exact ly why I designed (with some help f rom the DemeterCompulator) this opt ical limiter - so guitarist 's, including myself , could enjoy afar bet ter sounding pedal than all those hopeless Dynacomp clones

I certainly didn't design it for studio geeks OK

Did you ever have a look on the response curves of an LDR ? theyhave a very long recovery-t ime..... Yes - just like our ears do too, and look ma no pumping.

Yes - just like our ears do too, and look ma no pumping.

You cant adjust the recovery (release) t ime....I do not want to - i am perfect ly happy with it as it is - just like theLA2A

Opto rule since they sluggish just like we humans ...aye mate !?Agreed

Also adding a tone cont rol t ype circuit around the driver can make the compreact to dif ferent f reqs

I thought about doing this but wanted to keep the design simplewith just two cont rols - I did think about put t ing a similar f ilt er asthe LA2A uses in the side chain, but in pract ice the f lat responseseems to do exact ly what i want soundwise. Good thinking though

The nice thing about the optos is in your audio path the whole comp elementis nothing more than a resistor. This allows you to use your fav buf fers/gainstages

Yes - agree 100% here too.

Thanks for all the feedback - now go ahead and build it like I did bajaman

28 Nov 2007, 08:57 analogguru

I certainly didn't design it for studio geeks OK

But the LA-2A was designed for and/or used in studios ?

And this is exact ly why I designed (with some help f rom theDemeter Compulator) this opt ical limiter - so guitarist 's, includingmyself , could enjoy a far bet ter sounding pedal than all thosehopeless Dynacomp clones

That s f ine and good.... and maybe you will f ind your concept in the near futurein a bootweakers pedal..... but is it really necessary to make a comparision with a LA-2A..... ?

BTW, what should be so ingenious on the "rect if ier"/sidechain part of theDemeter Compulator to borrow it ?

analogguru28 Nov 2007, 10:24 bajaman

BTW, what should be so ingenious on the "rect if ier"/sidechain partof the Demeter Compulator to borrow it ?

Hey AG - you are the expert here - you tell me All I know is it works in this applicat ion, but I must admit my confusionregarding the two 1N4148 diodes and the 4k7 resistor in the addit ional bias tothe led driver stage - I think the circuit will work without these addit ionalcomponents - i may remove them and see - any thoughts f rom you on whatthey actually do??? If a booteeker wants to use this design, that is f ine by me - I have some otherstuf f up my sleeve for a rainy day - stay tuned cheers bajaman28 Nov 2007, 10:36 jakerandall

the real quest ion how does it sound?28 Nov 2007, 16:10 paulc

bajaman wrote:BTW, what should be so ingenious on the"rect if ier"/sidechain part of the Demeter Compulatorto borrow it ?

Hey AG - you are the expert here - you tell me All I know is it works in this applicat ion, but I must admit myconfusion regarding the two 1N4148 diodes and the 4k7 resistor inthe addit ional bias to the led driver stage - I think the circuit willwork without these addit ional components - i may remove themand see - any thoughts f rom you on what they actually do???If a booteeker wants to use this design, that is f ine by me - I havesome other stuf f up my sleeve for a rainy day - stay tuned cheersbajaman

Put t ing a DC of fset in will allow the LED to have a lit t le "sof t glow" atquiescence. This will get them started early so you don't have a dead spot inthe curve while you're wait ing for enough signal to get the leds to start light ingup. Gets everything in a nice working range at the start .

Later, PaulC "bootweaker"28 Nov 2007, 16:48 PurplePeopleEater

analogguru wrote:One of the "secret recipes" of the LA-2A is theuse of an elect roluminescent light device with a specialcharacterist ic (and not the LDR).... without including that behaviour

you are far away f rom an LA-2A.

A very important part of the sound of the LA2A is the t ransformer. It 's onereason that the older unit s, even if refurbished completely (other than the x-former) sound bet ter to most people than the reissues. The older unit s, IIRC,had a heavy duty UTC HA100X x-former that used materials that are current lynot legal to use (you can thank the EPA for that ). The Fairchild 660/670 aresimilar in that the clones being made are not t rue clones, because thematerials of the original unit s are no longer legally available.

I understand that the goal of this project is to mimic some of the LA2A'sdist inct characterist ics, but IMHO that cannot be done in stompbox form, sothe name is a bit misleading. St ill, it looks like a fun and easy to build projectthat could be especially useful to tweak and build into a bass d.i. / preamp.28 Nov 2007, 21:38 bajaman

Put t ing a DC of fset in will allow the LED to have a lit t le "sof t glow"at quiescence

Thanks for the clarif icat ion here Paul Jakerandall - how does it sound?? Well Jake, it doesn't sound!! It limit s the signal fed into it and is veryt ransparent in operat ion - play some single note lines quiet ly and it sounds thesam eon or of f , but play a aggressive full chord and you will hear what it does.

I suppose you could say it evens out the sound levels and adds a subject ivefatness to the sound - t ry it af ter a chorus, delay, f langer, distort ion etc., andyou will see why I like it - did you read about the Clay Jones overdrivepedal??? Just some food for thought cheers bajaman29 Nov 2007, 21:53 Skreddy

I just designed a minimal version, omit t ing the buf fer and output stage and 1/29v opamp, just to use as an add-on daughter board for adding limit ing to anygain stage. I'm planning to experiment with it in a delay project that I want tosound more "tubey."

I've added a parallel and a series resistor (both opt ional) for tailoring the LDRto your part icular applicat ion.30 Nov 2007, 04:12 celadine

On the optoisolator based VCA vs. t ransistor based VCA thing:

- Cont rol voltage bleedthrough is not a problem with LDRs, simplif iying VCAdesign. - Optoisolators have a natural nonlinear response to cont rol voltage whichalso simplif ies VCA designs used for musical applicat ions. This is adisadvantage if you want a linear responce. - Some LDRs are f ine in vacuum tube designs, with the high voltages involved.T ransistor VCAs can't handle this high voltage. (yes, I'm looking at you

Transistor VCAs can't handle this high voltage. (yes, I'm looking at youlm13600.) - LDR based VCAs can be designed to have except ional DC performance (CVcont rol, etc.).

I'm not an absolute optoisolator fan, just wanted to point out these things.T ransistor-based VCAs have their uses too. (i.e., the THATco. 4320ht tp://www.thatcorp.com/4320desc.html is pret t y sexy, despite being QSOP)

Here's a PDF with more than you wanted to know about LDRs: ht tp://optoelect ronics.perkinelmer.com/ ... olator.pdf

And more LDR stuf f ; check out the 'Technical Reference' sect ion: ht tp://www1.silonex.com/audiohm/principles.html

On the diode-CV thing - could be the diodes are used as voltage-cont rolledresistors like in this LPF: ht tp://f iles.muziq.be/schemat ics/paia_2720-3l.gif05 Dec 2007, 13:03 briggs

How does the "precision 1/2v supply" af fect the overall design? Is it requiredfor correct operat ion or can it be lef t of f? I was thinking of using that op ampas the buf fer sect ion 05 Dec 2007, 16:00 briggs

One more quest ion - can you reduce the gain in the recovery stage to around3 - 4 without it impact ing on the limit ing amount?05 Dec 2007, 20:48 bajaman

Is it required for correct operat ion

yes can you reduce the gain in the recovery stage to around 3 - 4without it impact ing on the limit ing amount

yes - but why - on full limit , you will not have a high enough output level cheers bajaman05 Dec 2007, 21:02 bajaman

I have been doing some extensive research into led and ldr home made optocouplers. Red, Yellow, Blue, white, standard, hi brite - dif ferent ldrs etc. The best combinat ion I have come up with so far, that most easily mimics theVTL5C10 type is a 5mm 16000Cds Hi brite White Led and a 0.5 megohm darkresistance small ldr.

VTL5C10 with 9.4v dc bat tery series resistor - measured resistance 1k5 - 70 15k - 186 150k - 900 1M5 - 8k5

Home made opto coupler 1k5 - 90 15k - 330 150k - 1k8 1M5 - 15k

cheers bajaman

ps: Steve Daniels at Small Bear has many VTL devices in his store - He canget the VTL5C10 devices too - I think he may put them in his inventory ifenough folks request them 06 Dec 2007, 00:44 goaltoday

Thanks for the research baja!

Last week I ordered the VTL5C10 f rom banzai.But I'm going to t ry someled+photocell to compare and decide what I like.06 Dec 2007, 09:16 briggs

bajaman wrote:Is it required for correct operat ion

yes

Why is the buf fered 1/2 v required? Is there a specif ic reason?

Thanks for the project baja, looks like a great ef fect ! There's just some thingsthat I don't quite understand there!06 Dec 2007, 12:23 bajaman

Why is the buf fered 1/2 v required? Is there a specif ic reason

The buf fered or regulated 1/2 volt supply rail is necessary because of the waythat the led opto coupler works - you will not ice that the led is connectedbetween the output of the op amp (1/2 rail volt s) to the 1/2 rail voltage andnot to ground. i am sure AG can explain this bet ter than I can though.

One small problem I have encountered with this pedal - when I t ried to use a 9volt regulated switch mode power pack, i got a very loud white noise. Theremedy was to add a decoupling capacitor f rom the anode of the power inputdiode to ground - I used a 470uf 16v type elect rolyt ic (posit ive to the anode). Itis now dead quite - no problem with the bat tery operat ion though - hmmmm.

bajaman07 Dec 2007, 14:49 briggs

Interest ing! I'm having a play with the envelope sect ion of the compulatormyself . It may be useful in one of my on-going designs

I'm t rying to get it down to one op-amp in the gain sect ion - so I can use theother op-amp for the regulat ion of the 1/2v supply.

Skreddy - did you get your minimal version working?05 Jan 2008, 12:39 swt

i've been playing some funk lately, and realised that jamiroquai's and red hot 'sguitarrists use dynacomps, and a lot of funk guitarrists as well, so i built one toget the sound. But being a fusion/jazz/blues musician didn't like it for anythingbut that . So i'm giving this compressor a t ry. The design looks terrif ic. Just onequest ion...i don't get that fet ...i'll use Bf245A, do you think it 's bet ter to use a22k or 10k resistor at the source of the buf fer?. Or the 68k is just f ine?. Whatchanges sonic and elect ronic speaking using a 10k or a 68k?. Thanks a lot foryour help and design!.05 Jan 2008, 14:12 bajaman

i'll use Bf245A

should work okay as a buf fer What changes sonic and elect ronic speaking using a 10k or a 68k?.

not a lot - maybe slight ly bet ter top end response with 10k and greatercurrent drain, that is all - not crit ical - t ry anything between these ext remes -should work okay for you cheers bajaman

ps: let us know how it sounds when you f inish building it - pictures, andcomments always welcome 05 Jan 2008, 15:31 Anonymous

briggs wrote:I'm t rying to get it down to one op-amp in the gainsect ion - so I can use the other op-amp for the regulat ion of the1/2v supply.

So use a TLE2642 - it s a dedicated rail split ter in a TO92 case. It s also on the T I samples program for developers.05 Jan 2008, 15:46 swt

wow that was fast . thanks a lot for the answer. i have it ready to solder. willreport the buld and also send pictures if you want . thanks again.30 Jan 2008, 22:17 minor7th

bajaman wrote: ps: Steve Daniels at Small Bear has many VTLdevices in his store - He can get the VTL5C10 devices too - I think

he may put them in his inventory if enough folks request them

Following my recent enquiries, Steve is now going to stock them. He thinksthat they wil hit his web site mid March or so.

Ah, the power of the consumer!

m7th31 Jan 2008, 18:57 vanessa

Newark has them in stock all the t ime:

ht tp://www.newark.com/43F885/optoelect ronics-lamps-displays/product .us0?sku=EG-G-VACTEC-VTL5C1&_request id=3951410 Feb 2008, 14:18 minor7th

vanessa wrote:Newark has them in stock all the t ime:

ht tp://www.newark.com/43F885/optoelect ronics-lamps-displays/product .us0?sku=EG-G-VACTEC-VTL5C1&_request id=39514

Thanks, Vanessa. Unfortunately the minimum shipping costs to Aust ralia thatthe larger f irms charge makes it a rather expensive Vact rol.

Thanks for the info!10 Feb 2008, 21:22 bajaman

Steve Daniels at Smallbear elect ronic's postal charges to Aust ralia and NewZealand are very reasonable - fast service too. bajaman

calling baja...bajaman style opt comp br and qs21 Apr 2008, 17:55 swt

Hey Steve!. i've just build the demeter comp clone and it 's amazing. Have thela2style ready but , if i have the comp pot to min posit ion, the f xs works, cleansignal, but when i up that pot , the led works but a distorted signal appearsriding on top of the clean signal, like a misbiased t ransistor or opamp. i t riedf lashing the ldr with a lantern, and it works f ine, so i think it 's the rect if ier andled driver. is that 1k5 supposed to go to vr as well as the comp pot?, becausethat forms a network to vbias(vr), and might be making the bias of the secondopamp behave st rangely. i really want to have this one working properly. Thanks a lot for any help.PS: the input cap is incorrect on the pcb. i used the one at the schem, 10n, thepcb has a 100n.

Re: calling baja...bajaman style opt comp br and qs21 Apr 2008, 18:00 analogguru

It s nice to read your enthusiasm, but is it possible that you post yourquest ions in the concerning thread and not start a new topic ?

analogguru

Re:22 Apr 2008, 00:01 floris

Torchy wrote:So use a TLE2642 - it s a dedicated rail split ter in aTO92 case.

Did you perhaps mean the TLE2426? I can not f ind any info about theTLE2642.

Re: BAJA LA2A Style Optical Limiter22 Apr 2008, 01:03 Anonymous

Sorry, t ypo ...

ht tp://focus.t i.com/docs/prod/folders/p ... 26-q1.html

Re: BAJA LA2A Style Optical Limiter22 Apr 2008, 02:12 bajaman

Hi swtThe schemat ic is correct for the 10n and the 1k5 comp pot connect ion to v1/2(bias half volt s).Af ter measuring several Vactec devices and experiment ing with dif ferentcolour LEDs and dif ferent suppliers LDRs, I have come up with someimprovements.First change the 56 ohm resistor on the output of the LEDs driver op ampstage to 560 ohm.Second - use 5mm standard yellow LEDs - NOT the 3mm red ones!!!Third - select an appropriate 5mm LDR element - the one you want is one thatwhen held up to the light (Sun or whatever), measures about 90 ohms acrossthe terminals - NOT the ones that measure 300 ohms or higher, whensimilarly tested in daylight.

Try these suggest ions and I think you will get good result s. cheersbajaman

Re: calling baja...bajaman style opt comp br and qs22 Apr 2008, 11:39 floris

swt wrote:... but when i up that pot , the led works but a distortedsignal appears riding on top of the clean signal, like a misbiasedt ransistor or opamp.

I had the same with a Flat line opt ical compressor using a fast vact rol or ahomebuild LED/LDR. The distort ion is due to the LDR being too fast in it sat tack and release responses. This superimposes the rect if ied signal back onthe signal that is being compressed which we percieve as distort ion. The opto

compressor only works nicely without this distort ion if the LDR has a slowenough response t ime so that it smooths the rect if ied signal. I ended up using a VTL5C2 which has a 500ms decay t ime and sounded goodwithout distort ion: ht tp://optoelect ronics.perkinelmer.com/ ... l5c1c2.pdfThe VTL5C1 gave me distort ion, it has a 35ms decay t ime: ht tp://optoelect ronics.perkinelmer.com/ ... l5c3c4.pdf

Re: BAJA LA2A Style Optical Limiter22 Apr 2008, 11:41 floris

release t ime, response t ime, decay t ime... too many words for the samething... sorry...


I have built a couple of these - never had any problems with distort ion bajaman

Re: BAJA LA2A Style Optical Limiter22 Apr 2008, 13:46 swt

ups! sorry for the double post , and didn't know the rules about having newpost , just thought this one was a lit t le old for get t ing responses. Apologise. I'llt ry disconnect ing the ldr, if i st ill get the misbias sound, will check everythingagain, if i don't , will t ry a dif ferent model. I've used a 10mm for the demeterclone, and it works f ine. Also gets really down on the values, compared to thesmaller ones. Will report back. Thanks again for the replies!

Re: BAJA LA2A Style Optical Limiter22 Apr 2008, 15:20 floris

bajaman wrote:I have built a couple of these - never had anyproblems with distort ion

Lucky man! Can you conf irm that the LDRs that you have used were "slow": Decay t ime >100ms or something? What I got with a fast LDR, was a sort of sof t f izzy sound on top of the cleancompressed guitar sound which was not icable in the the release phase. This"f izz" was louder if the f requency of the played note was lower. This wascompletely gone when using a slow LDR. Btw (not t rying to hijack this thread...): If the LDR is really fast , this modulat ion(if not suppressed) would actually lead to mult iplicat ion and thus an octave-upkind of ef fect , right?


Honest ly, where I live, there are four retail component suppliers - Dick Smith,Jaycar, Global PC, and South Island Component Cent re. They all sell 5 mmoblong LDRs but only Global PC has the ones that go down to 90 ohms whenheld up to the light . These are the ones that I use I believe they are

sourced f rom a company in Perth Aust ralia called ALTRONICS - not sure ifthey have an online presence, but they would be worth Googling.As for the delay response t imes - sorry I have not got any info in that respect .all I know is they work great for my limiter design, when used with a 5mmstandard yellow LED. By the way - check out my rev 2 design - in a separate thread but here in DIYprojects sect ion, for more info etc. happy limit ingbajaman

Re: BAJA LA2A Style Optical Limiter25 Apr 2008, 17:23 swt

ok. Changed the led for a 5mm and the ldr for a 10mm and guess what ...itworks. guess i learn something new each day....now...i'll go and enjoy a usefulllimiter. It does enhance the tone in a good way. Thanks Steve!


As I ment ioned in the Opto limiter rev 2 thread, a suitable LDR can beobtained f rom ht tp://www.futurlec.com - PHOTOCELL 1 is how it is listed - 5klight resistance, 500k dark resistance.cheersbajaman

Re: BAJA LA2A Style Optical Limiter01 Dec 2009, 19:25 kierc

Sorry to bump this up - just f inished put t ing mine together but pret t y sure Iwired it wrong because it isn't working!

I used "Photocell 1" f rom Futurlec... not sure if it 's the same one Bajaman had,but it 's pret t y small (smaller than a 5mm Yellow LED anyway)

Well, I couldn't f igure out how to wire it so I just went with the way picturedbelow, and I'm guessing it 's wrong!!

Symptoms :

No signal passing in either switch posit ion, panel LED doesn't light up - notsure about internal one at the moment ...

If anyone could help with the wiring that 'd be great !!

Re: BAJA LA2A Style Optical Limiter02 Dec 2009, 09:39 Jarno

Have you seen these sites?Beavis, stompboxwiringGauss Markov, wiring 1590b


Hi Jarno,

Thanks for the links - I've seen them before and have wired up pedals usingthe Beavis way a couple of t imes, but this pedal has dif ferent connect ionswhich confuse me, such as having 2 Outputs f rom the board and 2 pads for aSwitch....

Somebody please enlighten me!!


Not sure what the two pads for the switch are for, but you don't really need touse the two outputs. If you want it to be t rue bypass, don't use the buf feredout . If you do want to use the buf fered out , you only need a DPDT footswitchand just switch the output f rom buf fered to ef fect out (and a LED on theremaining pole).

Edit :

Could the two switch pads be to both switch the indicator led AND the ef fecton/of f led?


Hmm... That 's what I thought I was doing when I wired it like my sketch

I thought with my sketch that to the right it would cut of f the Indicator LED andpass the Buf fered Output to the output jack, and to the lef t it would turn theLED on and pass the ef fected signal out ...

I've placed the Layout over the PCB to get a clearer look on everything :

Looks like the Switch breaks the circuit between the 2 LEDs which are inseries(?), so I think it would cut both the indicator and ef fect LEDs of f ...

I've been out of the ef fect world for a while now, and I just can't see how toget this running through my t ired eyes

Is the orientat ion of the 3PDT switch in my sketch the right way? with the pinshorizontal and the holes vert ical?


Just been playing with the wiring a bit ...

I de-soldered everything f rom the 3PDT, and soldered the two "Switch" wirestogether to close the connect ion and t ry and get some light f rom the LEDs...

Seems that no power is get t ing to them

I wired the bat tery 9v + direct ly to the board rather than f rom the DC jack justin case, but st ill no lights was hoping it was just the wiring or somethingsimple!

Anyways... could it be the LF353N's I got f rom Futurlec? the 2SK117? (this waslabelled just "K117" on the devise?)

I'll t ry and get some voltages and post back


Got some voltages :

Top LF353N:1. 4.542. 4.493. 4.074. 05. 4.076. 4.467. 4.478. 8.88

Bot tom LF353N:1. 4.432. 4.423. 4.324. 05. 4.436. 4.437. 5.798. 8.79

2SK117 ( haven't got the pinout handy so I'll say lef t , middle, right as per PCBlayout )Lef t . 8.72Middle. 2.17Right . 4.69

Took these with a f resh 9v bat tery that read 9.46v at the board input ...

Don't know if anything looks of f or what , but I'm completely lost as it is!


I think those voltages are ok, but it would be really helpful if Baja would helpout , as I haven't built this thing (yet ). I am working on the compulator, which issurprisingly similar (although that 's a compressor and this is a limiter ????).


Bit of a good update I guess!!

Got it working to an extent - seems my 3PDT is fubarred (it 's been in a coupleof pedals now I think...) I'll f ind something else at some point ...

Have hard wired the "Switch" connect ions closed so the LED's are alwaysworking, and also hard wired the ef fected output to the output jack, so that it salways working

Now, the only thing is that when it "limit s" the signal is distorted - is this thephotocell? I used Photocell 1 f rom Futurlec paired with a standard 5mm YellowLED...

Cheers for your help so far Jarno - hope your Compulator build goes nice andsmoothly I'm tempted to build both and t ry to hear the dif ferent result s...


My f irst react ion was that it shouldn't be the LDR, but looking back in thisthread, apparent ly they can cause mayhem. Maybe add a cap on the input side of the LED driver opamp, to smoothen outsome of the ripple?

Have you measured the "light " and "dark" resistance of the LDR? Although,apparent ly, if it is causing problems it 's because of it react ing too fast , I don'tthink your going to catch that behaviour with your DMM.


Could anybody chime in on this clipping/distort ion/whatever it is?

I've changed the switch to a nice Alpha DPDT I stole f rom my Echo Base build (was noisy and haven't got round to f ixing that one yet !)

Through the buf fered output the signal also clips to an extent but not asdrast ic as when limited... I thought the buf fered signal wouldn't be passingthrough the LED/LDR combo to share the problem? If so - could it besomething else causing it?

@Jarno, could you explain adding the cap a bit bet ter for me? I'm not much ofa modder/t inkerer with circuit s, usually just build them stock!

I would t ry another LDR, but I'd have to order specially which is expensive -and the Vact rol VTL5C10 used in the Compulator is like 5?!?

I might have an LDR lef t over f rom my Neovibe build - doubt it would beuseable if I even have one though!

Anybody have a spare to sell?

Re: BAJA LA2A Style Optical Limiter04 Dec 2009, 23:39 bajaman

smallbear has VTL devices if I remember correct ly.bajaman


Cheers for the input Steve, but (to me anyway) that 's st ill a hell of a lot ofmoney for such a small part

From my symptoms (in my last post ), do you think the LDR is the culprit? asyou yourself said the Futurlec part is suitable, or were you just going f rom thelight /dark resistance on paper? as they state it has a fast response t ime...

I don't suppose you would have a suitable LDR spare that you could sell me doyou?

Re: BAJA LA2A Style Optical Limiter08 Dec 2009, 14:33 swt

hi guys. you can go with a standar ldr, the problem with the st range distort ionis the second opamp rail clipping. in the compulator, i solved this going higherwith the t rimpot , the 1k1 suggested just made the distort ion. In this case, the560 ohm resistor didn't work for me, can't remember the value i chose, but gohigher and the distort ion will disappear. But , it does change my guitar tonecompared to the bypass signal, it makes it a lit t le thinner, don't know why...


Got my VTL5C10 f rom Small Bear today (fast ! was shipping on Saturday Ithink?!), got it all wired in and I changed the LED to an Orange one as I think Isaw someone suggest it ... (couldn't be bothered to swap some out to t ry, justwent with it !!)

s'all working f ine now - will have to t ry it bet ter later as I could only play quietearlier, but it had lit t le to no distort ion, and did make it sound a bit fat ter!

Will have to t ry a Compulator next t ime!

Re: BAJA LA2A Style Optical Limiter20 Dec 2009, 14:12 roseblood11

Hi,

Bajaman, why did you chose a 1n4148 as polarit y protect ion diode? Wouldntthe voltage drop be lower with a Schot tky (1n5819 or similar)?

Re: BAJA LA2A Style Optical Limiter23 Feb 2010, 15:17 pablopearljam

Hi guys,

I have been t rying to build the Demeter Compulator, but it is impossible to getthe VTL5C10 here in Argent ina. I have been t rying to f ind an alternat ive, andthen I found this project .

I have a few quest ions: 1. Has anyone t ried this with a bass? Do you think it can sound similar/bet terto/than the compulator?2. Does anyone have the layout and PCB for this circuit?3. Are there any audio samples of this lit t le beast working?

I hope this is not much t rouble for you to reply to

Thanks in advance!Pablo

Re: BAJA LA2A Style Optical Limiter20 Dec 2010, 10:16 elz iel

Hi!

Im wondering Is it possible to add Va meter showing gain reduct ion?.

Re: BAJA LA2A Style Optical Limiter26 Jul 2013, 20:13 matt239

This seems very cool. There is some stuf f I don't get about it :

What makes it a limiter vs. compressor? Feed-forward doesn't automat icallymake it a limiter.. Is something happening to raise the threshold here so it onlyacts on peaks?How does the detector/envelope sect ion work; how do the two 1N4148 diodesfunct ion? (I saw what PaulC said about DC of fset , but it 's a bit over my headHOW it actually works..)

Could more cont rol be added: threshold? rat io? at tack? release?

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