LA-4 Help Thread!
- Thread starter Luny Tune
- Start date
Help Support GroupDIY Audio Forum:
Luny Tune
Well-known member
Now I've finally had the chance to really test our diy version against an original. (Serial # 0372 so it doesn't get much more "original" than that! 
)
It also dawned on me that when I tested the different optos in the circuit I hadn't found out that I was missing ground in the sidechain yet and apparently that has made some difference in the behaviour.
I noticed that the original sounded a little bit different. Difficult to explain but I've touched on it a bit before... I've mentioned earlier that there might be "something" with the attack time and as it turns out the original does behave slightly different. It's really not a lot when you listen to it and if you allow for the different margins and tolerances and thereby accept that you may have to set the threshold at 12:30 instead of on 12 o'clock on the original and little things like that then it's not too difficult to dial in a setting where you virtually hear no difference.
However, I did notice that the original seemed to be faster to dial in. I quickly found the right settings for the track I used it on whereas the DIY version seemed a bit more unforgiving. It sounds great, but a little too low threshold and you get punished with a slightly squeezed result... And I distinctively remember years ago I was working on a silverface LA-4 and I could just squash material and I still didn't think it killed the sound. It maintained good transient integrity and introduced no annoying pumping... The DIY version certainly has all the right character and I love it as it is but once you fall for certain details, it's hard at least for me to let it go until I've completely nailed it. Well, this is it...
Let me start by giving you the recipe I have found to give the sound of the original. Well, with one little difference. Our diy version is slightly brighter. Only in a good way and I'm not gonna do anything to change that. here's what I've found to be the perfect combination:
DIY optos: 2 x red LED + NSL 6910 LDR (EDIT: It seems the red LEDS is not so "standard" after all. Or rather: Many different types fall under the catagory of being "standard". The ones that work for me right now is 2V, 20mA, 150 mcd, 50 degree angle.)
Opamps: 2 x TL074 in the signal path + 1 x MC33079 in the sidechain
My explanation for the different opamps is that the TL074 has a bit of a "smiley curve" to it. I love the sound of it and I think it aids the overall sound so that we can live without a transformer even beefier than the OEP, Cinemag or even the cheapos I've mentioned earlier...BUT the smiley curve is not helping us in the sidechain because a smiley curve there actually makes the sidechain react to a slightly different signal than what we're hearing coming through the damn thing. Experimenting back and forth has proven me right...at least to myself. The more neutral MC33079 lets it work a bit more freely and there's a perfect coherence between the sound you hear and the effect you're putting on it.
And now to the optos. I must admit that they do mean more for the behaviour of the LA-4 than I have thought myself and led others to believe. I apologize if that has in any way messed up anybody's plans.
Here's what I experienced when comparing the original to my diy version:
The first clue was the meter actually. The needle returned to 0 veeeery slowly. I did see that the manual stated that somewhere but I was thinking that we just have a different view on what "slowly" is. I was thinking in the way that a VU meter reacts slowly compared to a peak LED meter... But it really DOES move sloooowly when it's releasing.
I then put two diy optos (Red LED and 6910) in there and voila!...there's the exact same needle movement.
I had of course made the first two test files at this point and this next test file was just right on the money straight away. Listen to the pauses between notes. You can hear the very slow release of it. And then listen to the NSL-32 version and the release whipping up right after the signal is gone.
So the NSL-32 does indeed sound good, but it doesn't quite sound exactly like the original. And this experiment shows us that it IS the opto that makes that difference. (And more difference that which opamps you use where.)
So how about the VTL5C4/2 from Vactec? That's the opto I believe JBL recommends as a direct replacement for the original optos. Obviously that one is very interesting to check out. Well, it sounds more like the NSL32 than like the original but I also think that it has a slightly weird distortion sound to it. BUT that could be due to inadequate adjustment!
I'm not able to tell the original and the diy opto apart in a blind test either so there you have my recommendation and the one that rank #1 in my opinion.
A close second is the NSL-32 and third is the VTL5C4/2. (Remember the Vactrol may sound better with adequate and accurate adjustment!)
Now give it a look and listen yourselves:
24 bit test files here in one zip file! (They're levelled by ear so you shouldn't have to compensate although they look different. That was my aim anyway.)
And the picture montage:
So, Insomniaclown! Don't give up on your plans just yet if you hear some interesting differences. I would though, after my test here, recommend the option to switch between the diy opto and the NSL 32. The NSL32 sound damn good in it's own right but there's something odd going on with the Vactrol as far as I can tell.
Maybe there are other Vactecs that'll give different flavours...(?)
EDIT: Just tested the Vactec VTL5C1. No good at all unless you like distortion a lot: LA- 4 with Vactec VTL5C1 opto
)It also dawned on me that when I tested the different optos in the circuit I hadn't found out that I was missing ground in the sidechain yet and apparently that has made some difference in the behaviour.
I noticed that the original sounded a little bit different. Difficult to explain but I've touched on it a bit before... I've mentioned earlier that there might be "something" with the attack time and as it turns out the original does behave slightly different. It's really not a lot when you listen to it and if you allow for the different margins and tolerances and thereby accept that you may have to set the threshold at 12:30 instead of on 12 o'clock on the original and little things like that then it's not too difficult to dial in a setting where you virtually hear no difference.
However, I did notice that the original seemed to be faster to dial in. I quickly found the right settings for the track I used it on whereas the DIY version seemed a bit more unforgiving. It sounds great, but a little too low threshold and you get punished with a slightly squeezed result... And I distinctively remember years ago I was working on a silverface LA-4 and I could just squash material and I still didn't think it killed the sound. It maintained good transient integrity and introduced no annoying pumping... The DIY version certainly has all the right character and I love it as it is but once you fall for certain details, it's hard at least for me to let it go until I've completely nailed it. Well, this is it...
Let me start by giving you the recipe I have found to give the sound of the original. Well, with one little difference. Our diy version is slightly brighter. Only in a good way and I'm not gonna do anything to change that. here's what I've found to be the perfect combination:
DIY optos: 2 x red LED + NSL 6910 LDR (EDIT: It seems the red LEDS is not so "standard" after all. Or rather: Many different types fall under the catagory of being "standard". The ones that work for me right now is 2V, 20mA, 150 mcd, 50 degree angle.)
Opamps: 2 x TL074 in the signal path + 1 x MC33079 in the sidechain
My explanation for the different opamps is that the TL074 has a bit of a "smiley curve" to it. I love the sound of it and I think it aids the overall sound so that we can live without a transformer even beefier than the OEP, Cinemag or even the cheapos I've mentioned earlier...BUT the smiley curve is not helping us in the sidechain because a smiley curve there actually makes the sidechain react to a slightly different signal than what we're hearing coming through the damn thing. Experimenting back and forth has proven me right...at least to myself. The more neutral MC33079 lets it work a bit more freely and there's a perfect coherence between the sound you hear and the effect you're putting on it.
And now to the optos. I must admit that they do mean more for the behaviour of the LA-4 than I have thought myself and led others to believe. I apologize if that has in any way messed up anybody's plans.
Here's what I experienced when comparing the original to my diy version:
The first clue was the meter actually. The needle returned to 0 veeeery slowly. I did see that the manual stated that somewhere but I was thinking that we just have a different view on what "slowly" is. I was thinking in the way that a VU meter reacts slowly compared to a peak LED meter... But it really DOES move sloooowly when it's releasing.
I then put two diy optos (Red LED and 6910) in there and voila!...there's the exact same needle movement.
I had of course made the first two test files at this point and this next test file was just right on the money straight away. Listen to the pauses between notes. You can hear the very slow release of it. And then listen to the NSL-32 version and the release whipping up right after the signal is gone.
So the NSL-32 does indeed sound good, but it doesn't quite sound exactly like the original. And this experiment shows us that it IS the opto that makes that difference. (And more difference that which opamps you use where.)
So how about the VTL5C4/2 from Vactec? That's the opto I believe JBL recommends as a direct replacement for the original optos. Obviously that one is very interesting to check out. Well, it sounds more like the NSL32 than like the original but I also think that it has a slightly weird distortion sound to it. BUT that could be due to inadequate adjustment!
I'm not able to tell the original and the diy opto apart in a blind test either so there you have my recommendation and the one that rank #1 in my opinion.
A close second is the NSL-32 and third is the VTL5C4/2. (Remember the Vactrol may sound better with adequate and accurate adjustment!)
Now give it a look and listen yourselves:
24 bit test files here in one zip file! (They're levelled by ear so you shouldn't have to compensate although they look different. That was my aim anyway.
)And the picture montage:
So, Insomniaclown! Don't give up on your plans just yet if you hear some interesting differences. I would though, after my test here, recommend the option to switch between the diy opto and the NSL 32. The NSL32 sound damn good in it's own right but there's something odd going on with the Vactrol as far as I can tell.
Maybe there are other Vactecs that'll give different flavours...(?)
EDIT: Just tested the Vactec VTL5C1. No good at all unless you like distortion a lot: LA- 4 with Vactec VTL5C1 opto
pedroplanet
Well-known member
Hey luny,
I couldn't find any source that would ship NSL 6910 LDR to Brazil, so I'll stick with the nsl32...
Is the MC33079 for sidechain pin compatible?
I couldn't find any source that would ship NSL 6910 LDR to Brazil, so I'll stick with the nsl32...
Is the MC33079 for sidechain pin compatible?
Matthew Jacobs
Well-known member
Thanks Luny for the in-depth analysis on the characteristics of this comp vs. the original.
I'll experiment with the DIY optos.
Does anyone have a source for the NSL 6910 in UK? I have a feeling they are banned because they have mercury in them or something...
If someone knows where I can buy then that would be cool.
Pedroplanet, I could always post some NSL 6910 to you in Brazil if you want.
J
I'll experiment with the DIY optos.
Does anyone have a source for the NSL 6910 in UK? I have a feeling they are banned because they have mercury in them or something...
If someone knows where I can buy then that would be cool.
Pedroplanet, I could always post some NSL 6910 to you in Brazil if you want.
J
strangeandbouncy
Well-known member
Matthew,
that'll be the Cadmium in 'em methinks! They are CdS (cadmium sulphide) cells iirc. SLionex and vactrol are the same i believe, so unavailability is probably not due to ROHS stuff. VActrol and silonex seem to be available.
Who knows if the rumours are true as to wether optos are banned or not?
ANdyP
that'll be the Cadmium in 'em methinks! They are CdS (cadmium sulphide) cells iirc. SLionex and vactrol are the same i believe, so unavailability is probably not due to ROHS stuff. VActrol and silonex seem to be available.
Who knows if the rumours are true as to wether optos are banned or not?
ANdyP
Luny Tune
Well-known member
Updated my post above with a test file from a VTL5C1.
chrispbass
Well-known member
Matthew Jacobs said:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2508662347
Luny Tune
Well-known member
Just saw this old post by 3nity...
http://dl.dropbox.com/u/1683654/DIY_LA-4_VTL5C1.wav3nity said:
Luny Tune
Well-known member
...and...chrispbass said:
http://www.alliedelec.com/search/productdetail.aspx?SKU=6991020
Luny Tune
Well-known member
The manual explains all that.
Luny Tune
Well-known member
: I'm sorry about these late notes, but I'm literally learning as I go here.
For practical reasons I bought standard red LEDs that are 10 mm because it would be easy to wrap them in shrink wrap, iso tape or whatever's at hand because they can just face and touch eachother and the light will still be evenly distributed over the LDR like it would be with a smaller LED and a bit of distance between the that and the LDR... And now changing another LA-4 to use diy optos I had to use 5 mm LEDs because I'm out of the big ones...but now I've had to learn that "standard" does not mean "standard". They do have to meet some specs.
The large LEDs I'm using are 20 mA, 2V, 50 degree angle, 150 mcd ones and they work as intended.
The ones that didn't work well was 10 mA, 1,7V, 54 degree angle, 0,6 mcd.
I will update the documentation but I'll see if I can find more exact specs to meet. In the original there's 5mm LED which are available today. I'm just having a hard time finding LEDs that meet the specs of my big ones. I will find out which specs are the important ones (in this particular design) and post them of course.
I'm sorry about these late notes, but I'm literally learning as I go here.For practical reasons I bought standard red LEDs that are 10 mm because it would be easy to wrap them in shrink wrap, iso tape or whatever's at hand because they can just face and touch eachother and the light will still be evenly distributed over the LDR like it would be with a smaller LED and a bit of distance between the that and the LDR... And now changing another LA-4 to use diy optos I had to use 5 mm LEDs because I'm out of the big ones...but now I've had to learn that "standard" does not mean "standard". They do have to meet some specs.
The large LEDs I'm using are 20 mA, 2V, 50 degree angle, 150 mcd ones and they work as intended.
The ones that didn't work well was 10 mA, 1,7V, 54 degree angle, 0,6 mcd.
I will update the documentation but I'll see if I can find more exact specs to meet. In the original there's 5mm LED which are available today. I'm just having a hard time finding LEDs that meet the specs of my big ones. I will find out which specs are the important ones (in this particular design) and post them of course.
pedroplanet
Well-known member
Hey Luny, have you tested VTL5C9 optos as you said on the first page?
Luny Tune
Well-known member
No, I decided to sell the 8 x What? box I made. I expect it will work fine like the NSL32 optos.
Another thing is that the NSL 32 comes in a lot of different versions. I've decided to just use diy optos in my machines but yet I'm comparing specs of the different NSL32 versions to see if one of them should match the 6910...
Another thing is that the NSL 32 comes in a lot of different versions. I've decided to just use diy optos in my machines but yet I'm comparing specs of the different NSL32 versions to see if one of them should match the 6910...
Rybow
Well-known member
Luny Tune said:
Luny Tune
Well-known member
Yes, we're going in on the secondary side and out on the primary side. Is that what you meant?
Rybow
Well-known member
Sorta. I have it going in secondary and out primary, but I am wondering if I have the + line coming back to the board is in the right place on the primary. On the A262a2C, The primary has S1, S2, F1, F2. Right now, the + From transformer wire is going to S1 (start winding 1), and the other wire is going to F2. When I look at the wire instructions from my last post, it appears that I have wired my primary connections going back to the board in reverse.
I should add that I have the secondary wired the same way. + going to the start of winding 1, and the other connection going to the finish of winding 2.
I should add that I have the secondary wired the same way. + going to the start of winding 1, and the other connection going to the finish of winding 2.
Luny Tune
Well-known member
I think it's correct the way I described it. Would you try and follow that and then tell me if it flips the polarity? If it does, just switch the wires in + and - on one side of the transformer. It won't do any damage if it's wired wrong at all.
Rybow
Well-known member
I'll give it a shot when I get a chance. Thanks Luny!
