LA-4 Help Thread!
- Thread starter Luny Tune
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Help Support GroupDIY Audio Forum:
mylesgm
Well-known member
Are you using that transformer for balanced out? is it a suitable transformer given the freq specs or am I missing something?
Hi,
There were a number of reasons for choosing that transformer - the main one being space. I also seem to remember a discussion in this thread where that particular option (wired backwards IIRC?) was discussed and suggested as a good alternative.
The LA4 isn't exactly an uber clean compressor anyway so I wasn't too bothered about colouration (obviously I didn't want to ruin though!
) and in all honesty I don't hear that I'm missing anything when I engage the comps with those transformers...
Ian
There were a number of reasons for choosing that transformer - the main one being space. I also seem to remember a discussion in this thread where that particular option (wired backwards IIRC?) was discussed and suggested as a good alternative.
The LA4 isn't exactly an uber clean compressor anyway so I wasn't too bothered about colouration (obviously I didn't want to ruin though!
) and in all honesty I don't hear that I'm missing anything when I engage the comps with those transformers...Ian
Just got a couple of minutes whilst the missus is in the shower... Here's a quick freq. sweep of one of my LA4s with a TM019:
This is the first time I've done this - it helps me understand why I like it to just very gently compress on vocals. ;D
Thanks for the prompting!
Ian
This is the first time I've done this - it helps me understand why I like it to just very gently compress on vocals. ;D
Thanks for the prompting!
Ian
mylesgm
Well-known member
that's a pretty decent curve! especially when you consider that compression often 'dulls' the tone a little... and those txs are cheap as chips!
Hello everyone!
I just ordered 2 PCBs for your version of the LA4 and I am waiting for them to arrive so I can start the build.
I got them pretty cheap at Gustav's PCB grinder and I have to say he is a really nice guy.
He told me the schematic was pretty much the original one. I am still wondering if there is a specific schematic for this very LA4 tho because you are mentionning it on the first page and I can't seem to find it...
Maybe I am not properly awaken...?
Best,
Thomas
I just ordered 2 PCBs for your version of the LA4 and I am waiting for them to arrive so I can start the build.
I got them pretty cheap at Gustav's PCB grinder and I have to say he is a really nice guy.
He told me the schematic was pretty much the original one. I am still wondering if there is a specific schematic for this very LA4 tho because you are mentionning it on the first page and I can't seem to find it...
Maybe I am not properly awaken...?
Best,
Thomas
Hi all!
I completed the first of my 2 units today, wired up really fast just to test it, as it is not even racked yet and it passes no audio...
I think I have a forgotten a basic thing somewhere. Also, the meter circuit is not wired, but I guess it doesn't make a big difference?
Thomas
EDIT:
It now passes audio, but the sound gets very distorted depending on the threshold setting. It also overloads pretty easily when doing a simple insert in my DAW. The output level is weak too, with the volume all the way up I cannot match unity gain.
As I told you guys, it is not calibrated yet, so maybe things will be better after that.
What I really dig right now is the hi / lo switch that allow to get some nice distorted tones... Will it still be possible when the unit will be calibrated?
I completed the first of my 2 units today, wired up really fast just to test it, as it is not even racked yet and it passes no audio...
I think I have a forgotten a basic thing somewhere. Also, the meter circuit is not wired, but I guess it doesn't make a big difference?
Thomas
EDIT:
It now passes audio, but the sound gets very distorted depending on the threshold setting. It also overloads pretty easily when doing a simple insert in my DAW. The output level is weak too, with the volume all the way up I cannot match unity gain.
As I told you guys, it is not calibrated yet, so maybe things will be better after that.
What I really dig right now is the hi / lo switch that allow to get some nice distorted tones... Will it still be possible when the unit will be calibrated?
thomasdf said:Hi all!
I completed the first of my 2 units today, wired up really fast just to test it, as it is not even racked yet and it passes no audio...
I think I have a forgotten a basic thing somewhere. Also, the meter circuit is not wired, but I guess it doesn't make a big difference?
Thomas
EDIT:
It now passes audio, but the sound gets very distorted depending on the threshold setting. It also overloads pretty easily when doing a simple insert in my DAW. The output level is weak too, with the volume all the way up I cannot match unity gain.
As I told you guys, it is not calibrated yet, so maybe things will be better after that.
What I really dig right now is the hi / lo switch that allow to get some nice distorted tones... Will it still be possible when the unit will be calibrated?
Don't do anything drastic until you've followed the calibration instructions properly.
Which Opto-cell are you using?
This can affect the characteristics a lot.
I am using the VTL4C4/2 and it sounds pretty good to me. I still need to get VU meters and rack the whole thing before I start calibrating them.
Audioman
Well-known member
Hi Guys,
I connected everything and it seems to work and sound very well (I used two custom transformers of turin ELTRA I had lying around)
The thing that I do not understand is how to make the correct calibration of the unit.
I downloaded the manual and I followed on page 18 is the gain reduction meter zero adjustment (4.1) and the Gain Reduction Meter Calibration (4.2) by using the two trimmers in the middle of the PCB.
The thing that I do not understand is how to calibrate the ratio and treshold with the two trimmers on the lower right corner of the PCB (the ratio in the lower right corner, near is the treshold)
And then the trimmer at the top left (common mode) I do not know what is, and how goes calibrated
Can you give me some tips about calibration?
Let me know
Thanks in advance!
Fabio
I connected everything and it seems to work and sound very well (I used two custom transformers of turin ELTRA I had lying around)
The thing that I do not understand is how to make the correct calibration of the unit.
I downloaded the manual and I followed on page 18 is the gain reduction meter zero adjustment (4.1) and the Gain Reduction Meter Calibration (4.2) by using the two trimmers in the middle of the PCB.
The thing that I do not understand is how to calibrate the ratio and treshold with the two trimmers on the lower right corner of the PCB (the ratio in the lower right corner, near is the treshold)
And then the trimmer at the top left (common mode) I do not know what is, and how goes calibrated
Can you give me some tips about calibration?
Let me know
Thanks in advance!
Fabio
The "common mode reject" trimmer you can mostly ignore, it is meant to make sure that any difference between + and - inputs is cancelled out.
Normally an input signal is reversed polarity between + and - (or the signal is present at + and zero at - as I found my soundcard does, I don't think that is quite "balanced" but...)
What the manual describes is connecting the same polarity signal to both + and - (you'd have to use aligator clips or something) and checking that the result is silence (they should cancel out)...
Ratio trimmer calibration is really easiest (in my opinion) if you measure input and output in a DAW or something.
What they say is I think:
- Apply a signal at some reasonable level.
- With the threshold turned way up adjust the output to the same as input level (or some nice round value), measured either on the units meter or with your DAW.
- Now turn the threshold knob down slowly while looking at the output level until you see it drop 1db - now the compressor has just started compressing.
- From this level you can increase the level of the signal in (the level from your DAW);
On ratio 4:1, increase the level by 4 db, the output should now only have increased 1 db (4:1!), you can keep going up to see that the compression ratio is ok.
Do the same for 8:1 (increase 8db input, see only +1db output etc) and the other ratios.
Threshold of limiting (not sure I did this actually)
This is for setting the absolute level at which the compressor starts to compress (you'll have to get you absolute levels figured out, as the levels in a DAW / soundcard is not necessarily dbu, mine shows dbFS where -18db on the meters corrsponds to 0 dbU "outside").
Set the threshold knob to it's lowest value (for maximum sensitivity to compression), then turn up the input signal to about -20dbU, now there should be about 1db of compression, but the manual says +/- 2 db from this is normal.
Use the threshold adjust trimmer to get it right...
I think that's basically how I did calibration.
EDIT: Got my db's turned around.
Normally an input signal is reversed polarity between + and - (or the signal is present at + and zero at - as I found my soundcard does, I don't think that is quite "balanced" but...)
What the manual describes is connecting the same polarity signal to both + and - (you'd have to use aligator clips or something) and checking that the result is silence (they should cancel out)...
Ratio trimmer calibration is really easiest (in my opinion) if you measure input and output in a DAW or something.
What they say is I think:
- Apply a signal at some reasonable level.
- With the threshold turned way up adjust the output to the same as input level (or some nice round value), measured either on the units meter or with your DAW.
- Now turn the threshold knob down slowly while looking at the output level until you see it drop 1db - now the compressor has just started compressing.
- From this level you can increase the level of the signal in (the level from your DAW);
On ratio 4:1, increase the level by 4 db, the output should now only have increased 1 db (4:1!), you can keep going up to see that the compression ratio is ok.
Do the same for 8:1 (increase 8db input, see only +1db output etc) and the other ratios.
Threshold of limiting (not sure I did this actually)
This is for setting the absolute level at which the compressor starts to compress (you'll have to get you absolute levels figured out, as the levels in a DAW / soundcard is not necessarily dbu, mine shows dbFS where -18db on the meters corrsponds to 0 dbU "outside").
Set the threshold knob to it's lowest value (for maximum sensitivity to compression), then turn up the input signal to about -20dbU, now there should be about 1db of compression, but the manual says +/- 2 db from this is normal.
Use the threshold adjust trimmer to get it right...
I think that's basically how I did calibration.
EDIT: Got my db's turned around.
audiophreak
Well-known member
got one of these PCBs from the BM a while ago , wanting do a pair , where can I get another PCB ??
Audioman
Well-known member
Hi All
I have measured 36 Volt Dc on the Led point on the PSU section on the board , is it correct or i have some problem ?
Anyone have the same voltage ?
I have measured 36 Volt Dc on the Led point on the PSU section on the board , is it correct or i have some problem ?
Anyone have the same voltage ?
audiophreak said:
Check with Gustav @ PCBGRINDER - he used to stock these (where I got mine) and may have one kicking about...
Audioman said:
I didn't use the PSU section for mine - but it looks like the LED is across the +ve and -ve rail so it makes sense that it'd measure 36V (18+18). Measure your voltage from 0>+ and 0>- you should see +18 and -18 respectively, in which case you're at a good starting point!
Ian.
Audioman
Well-known member
Audioman
Well-known member
Audioman
Well-known member
shot
Well-known member
I have two channel LA-4 that's been working without problems for many months.
But now I've noticed a strange thing that is happening.
After 20 minutes or so when second channel is in 1:2 ratio position, gain reduction slowly rises up to 20db or so, even though treshold is at CCW (not supposed to compress). If I turn off the unit and power it back again everything goes back to normal. It only happens in 1:2 ratio, all other ratios are okay.
Why is that? How do I fix it?
But now I've noticed a strange thing that is happening.
After 20 minutes or so when second channel is in 1:2 ratio position, gain reduction slowly rises up to 20db or so, even though treshold is at CCW (not supposed to compress). If I turn off the unit and power it back again everything goes back to normal. It only happens in 1:2 ratio, all other ratios are okay.
Why is that? How do I fix it?
Sounds like a bad cap somewhere?
