LA3A 500 BUILD

[sonic02]

Stupid me, the ol' mix up blue and red  . All working good now. The meter is a little off, can only get about 4db of compression showing. But after a little while of calibration have a fair idea of where the -5, -10 & -15db positions are. Looks like it will be 'all ears mode'  . btw, this sounds fantastic Peter, can't wait to send tracks through its 3 trafo, t4 cell goodness.

 

[peter purpose]

Great stuff.
Did you use 10k for R13? Should sort your metering if you didn't.

 

[sonic02]

R13 measuring 9.38K. Should be close enough to 10k? or does it need to be closer?

 

[peter purpose]

That should do you.... strange.

 

[Ianbryn11]

Hey, Fellas, im almost done with mine. i just need to wire pots and meter and calibrate. Quick question. it probably doesnt mater, but do you guys attach the board to the frame before you wire the pots and meter? Or wire them up and then hook the whole thing up to the frame? (EDIT - never mind, i figured this out gonna wire it before putting in the frame. )

Also, what equipment is needed for calibration? i only have a multimeter at the time... I see a bunch of gear in pics that i dont have for calibration. Is there a way to calibrate it with just the multi meter?

 

[peter purpose]

1. Either or.
2. A multimeter will be plenty. Just use your lug holes.

 

[sonic02]

Any idea what I can do to make the meter a bit more accurate Peter?
I can pick up a new meter from JLM Audio which are the same size, there are used in there LA500 project and are very accurate.

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=20

What are the specs for the current meter supplied with the kit?

 

[zayance]

Any idea what I can do to make the meter a bit more accurate Peter?
I can pick up a new meter from JLM Audio which are the same size, there are used in there LA500 project and are very accurate.

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=20

What are the specs for the current meter supplied with the kit?

I got mine tracking "ok" until 5db's maybe using 10K there..., after that ears are there..
You should also consider the fact that these meter are not super expensive
and don't have super accurate ballistics. A good meter would cost maybe 80Dollars so....

 

[sonic02]

I have about 9.38K in there. Should be close enough. maybe another value will do the trick.

I know the meter with the kit is a fairly inexpensive one, but I also built the JLM Audio LA500 at the same time as this, and it has a very accurate meter. They can be bought for $20 here is Australia.
Just wondering if it would be a compatible swap, for the $20 it would be def worth it.

 

[zayance]

Jlm's are the same....

 

[sonic02]

thanks for the help, will take the plunge and swap them over. Will post the results/differences when its done.

 

[ShandonSound]

Looks like I've screwed up with amp 3 somewhere Q5 & 6 are getting very hot. I suspect a short on amp 3 board itself but, before I cook any more components, what voltage should I see on +/-v arriving at amp 3 please?

Thanks,

Steve

 

[zayance]

Looks like I've screwed up with amp 3 somewhere Q5 & 6 are getting very hot. I suspect a short on amp 3 board itself but, before I cook any more components, what voltage should I see on +/-v arriving at amp 3 please?

Thanks,

Steve

looking at the Schemo, +/-16V i presume.....

 

[ShandonSound]

Thanks that's what I thought, just looking for some reassurance, before I plough on make things worse!

Cheers!

 

[horvitz]

OK, so about a year later I'm finally motivating myself to finish my pair of these things.  I've actually got them both up and running and everything seems real good with the exception of trying to get a somewhat more accurate GR indication on the meter, but I haven't given that much thought yet.  Seems I'm not the only one with that problem though.

I just notice one peculiarity.  It seems that with the meter looking at the out signal, it is actually inducing some harmonics on the output.  They go away if I set the meter to GR.  Is this expected behavior?

  Brian

 

[jensenmann]

My pair of LA3A-500 even performs a slight leveldrop when output level is engaged for the meter. Reason is that the rectifier and meter are loading the output transformer. Since this is not a resistive load it will create distortion.

 

[horvitz]

That makes perfect sense.  Thanks.

 

[ShandonSound]

Hi,
I have one channel complete and passing audio but it doesn't actually seem to be compressing at all. So I have moved to calibration hoping this might sort things out. Looking at the earlier posts on calibration there's a few things I either don't understand or don't feel clear on, so I wonder if someone could please clarify these for me?
My voltage at TP1 is sitting just above 6volts so that looks good I think, beyond that though I could do with some help.

For the meter:
R24 NI
R13 10k
R22 47k
RV36 - 3.9k
RV23 - adjust to zero meter

Re R24, what does NI mean/stand for?
Re R13, R22, RV36 are these three just the values that we need to use are or are they measurements that need to be made?
Re RV23 adjust so GR is at 0vu when idle presumably?

RV36 and i think Rv3 have to be done with no DC power to get the measurements right. I thought i had a faulty trimpot until i tried this.

What does 'no DC power mean', to me it suggests the LA3A is turned off is this correct?

RV3 - compress / limit option, 1.3k nominally, adjust to taste I suppose

Where do you take this measurement?

As ever apologies if these are very stupid questions but I'm here to learn. Hopefully I might not be the only one to benefit from the answers!

Many thanks for any help you can offer.
S.

 

[peter purpose]

Re R24, what does NI mean/stand for? Not used (in Septic).
Re R13, R22, RV36 Values.
Re RV23 adjust so GR is at 0vu when idle presumably? Yes.
What does 'no DC power mean' No clue.
Where do you take this measurement? Across the pot/resistor.

 

[ShandonSound]

Re R24, what does NI mean/stand for? Not used (in Septic).

Thanks Peter, I have R24 at 270k should I remove it then?