LA-4 Help Thread!

[briomusic]

Well, you've built the very first LA4 in 500 format !

When it's inside the rack, it looks very nice and professional.  ;D

but the wiring and the mounting.....  :

But this forum is where we share our darkest secrets, isn't it

 

[Matthew Jacobs]

Hi guys!

Well I decided to go with the LA4 and got it built to a usable state so that I could track with it and woah... it sounds good! hot!
I used it to record some hip hop vocals and cause it was quite a aggressive track I ended up squashing it hard and it distorted nicely.
I'm still waiting for canford to deliver my Sifam meters so I used a old meter but couldn't calibrate it properly. It distorts a little but I hope to sort that out once my meters arrive.

Big thanks to Lunytune and Gustav for making this project available. And big thanks to Gar381 for sharing his FPE file with me.

Anyway, I've been thinking of some mods for this project. Last night I experimented with replacing the input sensitivity switch with a 10K pot to give me a input level control. It worked but didn't give me enough range. Should I use a 100K instead and should I remove the 30K R7 resistor off the board? Is this the correct way of adding a input volume control? The reason I what a input control is that I like what the compressor does when driven hard but it would be nice to back it off a little.

Any thoughts?

Cheers

J

 

[helterbelter]

But this forum is where we share our darkest secrets, isn't it

Hahaha, well, yes, of course !

But I'm sure that when you've done a bit of tidying-up (is that correct english ?!?), the unit will look fabulous !!! 

 

[maxime]

Hello guys,

could someone give me the pcb dimensions?
I am in the process of buying the components and I am guessing about the perfect enclosure..
thanks
best regards

Maxime

 

[helterbelter]

Maxime : 10x 16 cm.

Hi guys!

Well I decided to go with the LA4 and got it built to a usable state so that I could track with it and woah... it sounds good! hot!
I used it to record some hip hop vocals and cause it was quite a aggressive track I ended up squashing it hard and it distorted nicely.
I'm still waiting for canford to deliver my Sifam meters so I used a old meter but couldn't calibrate it properly. It distorts a little but I hope to sort that out once my meters arrive.

Big thanks to Lunytune and Gustav for making this project available. And big thanks to Gar381 for sharing his FPE file with me.

Anyway, I've been thinking of some mods for this project. Last night I experimented with replacing the input sensitivity switch with a 10K pot to give me a input level control. It worked but didn't give me enough range. Should I use a 100K instead and should I remove the 30K R7 resistor off the board? Is this the correct way of adding a input volume control? The reason I what a input control is that I like what the compressor does when driven hard but it would be nice to back it off a little.

Any thoughts?

Cheers

J

Have you calibrated it correctly ? You should be able to get a clean signal from it without modifications.

Well, I don't have the time to look deep into it right now, but what you say makes sense, although 100K seems too much to me.

few things come to mind :
1. If you have a 1 Meg pot around, you could also try this : leave the 30k resistor in place, and put a 1meg pot in the place of the switch. But only if you have a 1 meg pot laying around.
2. Try a 25 KLog pot, and add a 5k resistor to it, lift one leg of the 30k resistor.

 

[Matthew Jacobs]

Have you calibrated it correctly ? You should be able to get a clean signal from it without modifications.

Well, I don't have the time to look deep into it right now, but what you say makes sense, although 100K seems too much to me.

few things come to mind :
1. If you have a 1 Meg pot around, you could also try this : leave the 30k resistor in place, and put a 1meg pot in the place of the switch. But only if you have a 1 meg pot laying around.
2. Try a 25 KLog pot, and add a 5k resistor to it, lift one leg of the 30k resistor.

Hi helterbelter

Thanks for your responce

No I haven't calibrated it yet cause I am still waiting for the meters to get delivered  :'( :'(
At the momment it only distrots with extreme GR. It is clean with no GR and mild limiting.

I like how the compressor sound when overloaded with the switch in 'low' mode (sometimes). I will do some experimenting to find out how to vary the input level.

The main reason for an input control is to be able to push the input to distort and because it will make the front panel look nicer with a extra knob  ;D

J

 

[helterbelter]

Well, I was just writing this reply when you posted, hahaha....

so, here's what I have written in the meantime, even though I see much of it isn't apllicable anymore, haha :

Well, I thought about it for a while. Now I re-read your post I see that you couldn't calibrate it correctly either...

About the input sensitivity pot : Most of us don't need it, since you could vary the gain with the device you put in front. So, I remember that you said that you use a G9 as mic pre. I don't have one, but IIRC it has an outputcontrol. You could use this one for gaincontrol. Together with the gain switch it should be enough control.

But talking about distortion, could it be that the common mode trim is set wrongly ? You can apply some audio to the gainswitchpin that's in front of the 30k resistor.  Set the threshold as high as possible, so the compression is off. Now you have just the lineamp of the LA4 that you hear. Distortion? * ? put the outputlevelpot a bit lower. Still distortion ? post again.

* : (In case you don't have distortion this way, apply the audio to the input, and check again. If there's distortion at this stage, then you know where it's at.)

Oh, and I'm guessing too, I'm an electronics starter as well.  

 

[helterbelter]

At the momment it only distrots with extreme GR. It is clean with no GR and mild limiting.

Ah, well, then the unit is set up pretty decent ! It could be that the unit distorts a bit at high GR settings if you use an NSL32 opto. At least, that's what a few people discovered if I'm not mistaken.

I like how the compressor sound when overloaded with the switch in 'low' mode (sometimes). I will do some experimenting to find out how to vary the input level.

The main reason for an input control is to be able to push the input to distort and because it will make the front panel look nicer with a extra knob  ;D

J

About the inputgain, check the G9 as said in my previous post.

 

[maxime]

thanks helter,

the pcb will fit in a danner module!

maxime

 

[Rybow]

Well, I just put in my order for the PCB from Gustav, and I am going shopping for parts tomorrow. I just have a couple of questions about some of the parts. This is my first build, so you guys might be seeing a lot of me! I apologize in advance for any stupid questions.

1) I was thinking of building my own optos. How do the different values of photo resistors affect the compression characteristics? I read in this thread that if using the Silonex opto cell, you need to change the trimmer value. If I build my own, do I still need to keep this value? Or go off the one in the BOM.

2) Are there any places on the PCB that would benefit from some higher quality capacitors?

3) What size of case should I be looking at? I was hoping to build this into a 1U full rack case.

4) The meter on the BOM is an AL 29, but I was thinking of using an AL 15 for aesthetics. Does it matter which meter I use as long as the power requirements are the same?

Thanks for all the help. I can't wait to build this puppy!

One more thing that I forgot. Reading through the thread, there was some dispute over using 1/4 watt and 1/2 watt resistors. What is the final verdict on that one?

 

[helterbelter]

Hi,

well, I can answer a few :

1) I was thinking of building my own optos. How do the different values of photo resistors affect the compression characteristics? I read in this thread that if using the Silonex opto cell, you need to change the trimmer value. If I build my own, do I still need to keep this value? Or go off the one in the BOM.

I thought the different trimmer value was for the Silonex only..... am I right, Lunytune ?

2) Are there any places on the PCB that would benefit from some higher quality capacitors?

Uh, well maybe, I'll leave that up to the other guys here.
However I do suggest to use tantalum caps instead of the 6.8uF Elco's. Voltagerating 35v is fine. For the other Elcos I have chosen for normal 105 degrees caps. They're not in the audiopath anyway.

3) What size of case should I be looking at? I was hoping to build this into a 1U full rack case.

That should fit fine, depending on the outputtransformer that you want to use. When using 2boards in a single housing, make sure the depth of the case is right. I'd say 240 mm.

4) The meter on the BOM is an AL 29, but I was thinking of using an AL 15 for aesthetics. Does it matter which meter I use as long as the power requirements are the same?

a Sifam AL15 will be just as excellent as an AL29. Be shure that it's a VU meter.

Thanks for all the help. I can't wait to build this puppy!

One more thing that I forgot. Reading through the thread, there was some dispute over using 1/4 watt and 1/2 watt resistors. What is the final verdict on that one?

If you haven't ordered the resistors yet, I'd suggest to choose 1/2 watt for all of them. Do choose metalresistors though, they are the same size as 1/4 watt. If you have most of the resistors already in 1/4 watt version , you could consider to change the 15 ohm resistors to 1/2 watts.  Maybe the 47 Ohms as well.

And last but not least : Have fun building it !
And welcome here. Don't be afraid to ask !  

 

[Rybow]

Thanks for your reply helterbelter! I think I will have a lot of fun building it, and hopefully a lot more fun using it as well, but that will depend on how the build goes.

I haven't gone shopping for parts yet, so I will just pick up the 1/2 watt metal resistors. I might also pick up some of the silonex optos as well just in case mine don't work out. I still have to figure out some sort of casing for the homemade optos.

I am just going to build a mono version of this badboy, so I only need space for one board. I was thinking of grabbing the Lundahl or Cinemag transformer that is listed in the BOM. They are easy to find here in Vancouver. I figured a 1U case would not have too much wasted space, and still give me enough room to work in.

Thanks for the advice on the caps. I know there is a lot of discussion out there regarding different caps providing different sonics and whatnot. I am totally in the dark on this one.

Man, I can't wait to get on this project. I only ordered my PCB on Monday, but the anticipation is already killing me.

 

[MrZpliff]

Got one channel up an running yesterday. Sounds really promising with all the trimpots just set about halfway 
Gonna finnish the wiring for the second one and start adjusting it tonight, hopefully.

One thing: I usually test all the voltages before installing the IC's but in this case one of the transistors (BD140) and the 7918 Reg did run really hot, so I just checked for mistakes, but couldn't find any... then thought what the heck and plugged them in and all was fine.

 

[Rybow]

Got one channel up an running yesterday. Sounds really promising with all the trimpots just set about halfway 
Gonna finnish the wiring for the second one and start adjusting it tonight, hopefully.

One thing: I usually test all the voltages before installing the IC's but in this case one of the transistors (BD140) and the 7918 Reg did run really hot, so I just checked for mistakes, but couldn't find any... then thought what the heck and plugged them in and all was fine.

Sounds Awesome! Are you willing to post some pictures when its all done?

I looked at the meter options again, and I noticed that the one I want is a DC meter. Will that work out?

Thanks.

 

[MrZpliff]

Sounds Awesome! Are you willing to post some pictures when its all done?

I looked at the meter options again, and I noticed that the one I want is a DC meter. Will that work out?

Thanks.

I think you need some kind of VU meter, don't think  the DC meter will work...

Will post some pictures next week... going away for the weekend, so no diy in a few days.

 

[helterbelter]

I think you need some kind of VU meter, don't think  the DC meter will work...

It won't work as it should... But, check this nevertheless :

http://www.groupdiy.com/index.php?topic=7473.0

 

[Rybow]

This meter is a VU meter, but it requires DC power. Here is the one I am looking at.

http://www.multimeter.com/?&Class=4&SubClass=008&Model=00014&PartNumber=00197

Let me know if this will work out. I went shopping for parts today, but it looks like I'll still have to order parts from mouser. Some of this stuff doesn't exist in this part of the world. Such as a 1/2 watt 3.6K resistor. I can only find 1 watt 3.6k resistors. Weird.

 

[briomusic]

hi insomniaclown,

you can definitely use the sifam al15 - I am using one in my 500series build which you can see on the previous page.

as for resistors - electrically you can always use a higher wattage rating then specified, you only have to start watching component sizes at some point. as for the 3.6k you should be fine with a quarter watt, it is particularly the small Ohm values around the power transistors that actually require the higher wattage.

briomusic

 

[helterbelter]

This meter is a VU meter, but it requires DC power. Here is the one I am looking at.
http://www.multimeter.com/?&Class=4&SubClass=008&Model=00014&PartNumber=00197

Haha, the specs are a bit misleading ! It says 12v DC, but that's for the illumination ! Look further, in the description they say this
"A low range ac voltmeter suitable for connecting across a 600 ohm line and self contained except for requiring an external 3.6k ohm resistor.".
So, it's an AC meter !
(By the way, I used AL15´s in my 1176. Nice meters ! I was so lucky to get a pair of new AL15´s for 8 gbp through ebay. )

by the way, the 3k6 resistors : try 1% tolerance 3k59 resistors. 1/4 watt is fine, just like Briomusic said. Only the 15 ohm resistors need to be 1/2 watt.

 

[Rybow]

Wow! Thanks a lot guys. As you may have figured out, I have very little experience with electronics. Carpentry is more my forte, but I am excited to pick up this skill. Got me a soldering iron, solder, and some wick today. First soldering iron I have ever owned. I am going to pick up a kit tomorrow to practice my soldering. Some silly LED flashing thing. Should be fun. I am also going to pick up a book on electronics for some light table reading. Hopefully there is a pop up book I can get.

The guy at the store said I only needed a 25 watt iron. I hope he wasn't lying.

The parts hunt continues...