BAJA LA2A Style Optical Limiter [documentation]
- swt
- Breadboard Brother
i've been playing some funk lately, and realised that jamiroquai's and red hot's guitarrists use dynacomps, and a lot of funk guitarrists as well, so i built one to get the sound. But being a fusion/jazz/blues musician didn't like it for anything but that. So i'm giving this compressor a try. The design looks terrific. Just one question...i don't get that fet...i'll use Bf245A, do you think it's better to use a 22k or 10k resistor at the source of the buffer?. Or the 68k is just fine?. What changes sonic and electronic speaking using a 10k or a 68k?. Thanks a lot for your help and design!.
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
should work okay as a bufferi'll use Bf245A
not a lot - maybe slightly better top end response with 10k and greater current drain, that is all - not critical - try anything between these extremes - should work okay for youWhat changes sonic and electronic speaking using a 10k or a 68k?.
cheers
bajaman
ps: let us know how it sounds when you finish building it - pictures, and comments always welcome
Information
So use a TLE2642 - its a dedicated rail splitter in a TO92 case. Its alsobriggs wrote:I'm trying to get it down to one op-amp in the gain section - so I can use the other op-amp for the regulation of the 1/2v supply.
on the TI samples program for developers.
Following my recent enquiries, Steve is now going to stock them. He thinks that they wil hit his web site mid March or so.bajaman wrote: ps: Steve Daniels at Small Bear has many VTL devices in his store - He can get the VTL5C10 devices too - I think he may put them in his inventory if enough folks request them
Ah, the power of the consumer!
m7th
Thanks, Vanessa. Unfortunately the minimum shipping costs to Australia that the larger firms charge makes it a rather expensive Vactrol.vanessa wrote:Newark has them in stock all the time:
http://www.newark.com/43F885/optoelectr ... stid=39514
Thanks for the info!
m7
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
Steve Daniels at Smallbear electronic's postal charges to Australia and New Zealand are very reasonable - fast service too.
bajaman
bajaman
- swt
- Breadboard Brother
Hey Steve!. i've just build the demeter comp clone and it's amazing. Have the la2style ready but, if i have the comp pot to min position, the fxs works, clean signal, but when i up that pot, the led works but a distorted signal appears riding on top of the clean signal, like a misbiased transistor or opamp. i tried flashing the ldr with a lantern, and it works fine, so i think it's the rectifier and led driver. is that 1k5 supposed to go to vr as well as the comp pot?, because that forms a network to vbias(vr), and might be making the bias of the second opamp behave strangely.
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, the pcb has a 100n.
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, the pcb has a 100n.
- analogguru
- Old Solderhand
Information
It´s nice to read your enthusiasm, but is it possible that you post your questions in the concerning thread and not start a new topic ?
analogguru
analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
Hi swt
The schematic is correct for the 10n and the 1k5 comp pot connection to v1/2 (bias half volts).
After measuring several Vactec devices and experimenting with different colour LEDs and different suppliers LDRs, I have come up with some improvements.
First change the 56 ohm resistor on the output of the LEDs driver op amp stage 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 that when held up to the light (Sun or whatever), measures about 90 ohms across the terminals - NOT the ones that measure 300 ohms or higher, when similarly tested in daylight.
Try these suggestions and I think you will get good results.
cheers
bajaman
The schematic is correct for the 10n and the 1k5 comp pot connection to v1/2 (bias half volts).
After measuring several Vactec devices and experimenting with different colour LEDs and different suppliers LDRs, I have come up with some improvements.
First change the 56 ohm resistor on the output of the LEDs driver op amp stage 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 that when held up to the light (Sun or whatever), measures about 90 ohms across the terminals - NOT the ones that measure 300 ohms or higher, when similarly tested in daylight.
Try these suggestions and I think you will get good results.
cheers
bajaman
be kind to all animals - especially human beings
- floris
- Cap Cooler
I had the same with a Flatline optical compressor using a fast vactrol or a homebuild LED/LDR. The distortion is due to the LDR being too fast in its attack and release responses. This superimposes the rectified signal back on the signal that is being compressed which we percieve as distortion. The opto compressor only works nicely without this distortion if the LDR has a slow enough response time so that it smooths the rectified signal.swt wrote:... but when i up that pot, the led works but a distorted signal appears riding on top of the clean signal, like a misbiased transistor or opamp.
I ended up using a VTL5C2 which has a 500ms decay time and sounded good without distortion:
http://optoelectronics.perkinelmer.com/ ... l5c1c2.pdf
The VTL5C1 gave me distortion, it has a 35ms decay time:
http://optoelectronics.perkinelmer.com/ ... l5c3c4.pdf
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
I have built a couple of these - never had any problems with distortion
bajaman
bajaman
be kind to all animals - especially human beings
- swt
- Breadboard Brother
ups! sorry for the double post, and didn't know the rules about having new post, just thought this one was a little old for getting responses. Apologise. I'll try disconnecting the ldr, if i still get the misbias sound, will check everything again, if i don't, will try a different model. I've used a 10mm for the demeter clone, and it works fine. Also gets really down on the values, compared to the smaller ones. Will report back. Thanks again for the replies!
- floris
- Cap Cooler
Lucky man!bajaman wrote:I have built a couple of these - never had any problems with distortion
Can you confirm that the LDRs that you have used were "slow": Decay time > 100ms or something?
What I got with a fast LDR, was a sort of soft fizzy sound on top of the clean compressed guitar sound which was noticable in the the release phase. This "fizz" was louder if the frequency of the played note was lower. This was completely gone when using a slow LDR.
Btw (not trying to hijack this thread...): If the LDR is really fast, this modulation (if not suppressed) would actually lead to multiplication and thus an octave-up kind of effect, right?
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
Honestly, where I live, there are four retail component suppliers - Dick Smith, Jaycar, Global PC, and South Island Component Centre. They all sell 5 mm oblong LDRs but only Global PC has the ones that go down to 90 ohms when held up to the light. These are the ones that I use I believe they are sourced from a company in Perth Australia called ALTRONICS - not sure if they have an online presence, but they would be worth Googling.
As for the delay response times - 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 5mm standard yellow LED.
By the way - check out my rev 2 design - in a separate thread but here in DIY projects section, for more info etc.
happy limiting
bajaman
As for the delay response times - 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 5mm standard yellow LED.
By the way - check out my rev 2 design - in a separate thread but here in DIY projects section, for more info etc.
happy limiting
bajaman
be kind to all animals - especially human beings
- swt
- Breadboard Brother
ok. Changed the led for a 5mm and the ldr for a 10mm and guess what...it works. guess i learn something new each day....now...i'll go and enjoy a usefull limiter. It does enhance the tone in a good way. Thanks Steve!