JLM AUDIO

Although my first one is done and working well, I have a couple questions about the mac pcb:

-Following the guide and silk screen, there are 12 resistors installed, but both my kits shipped with 15 or 16 resistors in this package of the kit (the la500 pcb package had the exact # of installed resistors only); are these just some extras, or did I miss something?

-There are several unused through hole pads in the traces (seen in my underside picture in post above), correct?

I assume all is well as I followed the guide steps closely and the unit cals and sounds great with all functions working, but my ocd forces me to ask, lol.

PeteJE wrote:Although my first one is done and working well, I have a couple questions about the mac pcb:

-Following the guide and silk screen, there are 12 resistors installed, but both my kits shipped with 15 or 16 resistors in this package of the kit (the la500 pcb package had the exact # of installed resistors only); are these just some extras, or did I miss something?

Mac kit will usually have a spare couple of resistors as it is used in several rack and 500 kits which can have some differences so this is normal. Follow your build thread and you will be fine.

-There are several unused through hole pads in the traces (seen in my underside picture in post above), correct?

These are PCB vias which connect top and bottom tracks and are not for components. These are common to all multilayer PCB's

PeteJE wrote:Finished my first of two; really happy with these kits and Joe's great support! It sounds very, very good!

Great to hear

Got the second one done and working (with Joe's super responsive and patient help, once again)! Great units and using on shows already......

Noobish question.

Which 33R resistor (Carbon, etc) should I use regarding note 1. in the errata. The ones I bought (forgot which type) have effectively muted the compressor .

Cheers
Peter

lordnielson wrote:Noobish question.

Which 33R resistor (Carbon, etc) should I use regarding note 1. in the errata. The ones I bought (forgot which type) have effectively muted the compressor .

Cheers
Peter

Hi Peter any 33R will work in there. Make sure you have 33R not 3k3 or 33k. Measure with multimeter to be sure. If 33R and no output then there is solder short or transformer cable is not plugged in

Joe Malone wrote:
Hi Peter any 33R will work in there. Make sure you have 33R not 3k3 or 33k. Measure with multimeter to be sure. If 33R and no output then there is solder short or transformer cable is not plugged in

Just tried both units again and realised that they weren't muted but ultra low output which of course yells wrong resistor. They are 33k. Trusted the shop assistant so much that when I pre checked the resistors (always do before soldering in) I didn't notice the "k" damnit. Rinse & repeat

Thanks for the reply.

Peter

I have some questions and I figured I would put them all in one post and hopefully get them all answered.

1. I'm unclear about how to install the 3 switches because the ones included are different lengths than the ones that you have to straighten the legs of in the pictures. Is the goal only for the pcb not to touch the stereo link pull switch? I attached a picture, is it correct to do it this way?
Also, can I solder the 3 switches on the underside of the pcb instead of the top next to the resisters in the picture?

2. I bought a pair from you (for stereo operation), should i install the link switch mod on both?
Also, I have a Radial workhorse, do I need to pull the link switch on each and click the link switch between the 2 slots?

3. Should I just go ahead and do the stereo matching mod, or is it best to test the pair first and then if needed go back and do it? Also, looking at the slow attack mod, what do I do if I need the stereo matching mod and slow attack? Do I solder the red wire to the middle pin of the 2 trim pots that are soldered together?

Thank you,
Franklin

Franklin wrote:I have some questions and I figured I would put them all in one post and hopefully get them all answered.

1. I'm unclear about how to install the 3 switches because the ones included are different lengths than the ones that you have to straighten the legs of in the pictures. Is the goal only for the pcb not to touch the stereo link pull switch? I attached a picture, is it correct to do it this way?

With the new long leg switches you can actually mount the pcb parallel to the front panel by mounting the PCB straight on the end of the switch legs with only about 1mm of the leg sticking out. As this gives enough length to fit behind the pull pot switches in both positions. Or push the PCB down the switch legs and mount at the usual angle. Both work.

Also, can I solder the 3 switches on the underside of the pcb instead of the top next to the resisters in the picture?

Yes all holes are plated so solder on either side works.

2. I bought a pair from you (for stereo operation), should i install the link switch mod on both?

Yes

Also, I have a Radial workhorse, do I need to pull the link switch on each and click the link switch between the 2 slots?

Yes leave the link switch on the back of the rack on for those 2 slots so pulling the front 2 switches links both comps.

3. Should I just go ahead and do the stereo matching mod, or is it best to test the pair first and then if needed go back and do it?

You cannot do the stereo mod until you know which compressor compresses harder. If you bought a pair at the same time we match the optos so stereo matching mod shouldn't be needed as long as you put the correct optos in U1 and U2 positions on each MAC pcb.

Also, looking at the slow attack mod, what do I do if I need the stereo matching mod and slow attack? Do I solder the red wire to the middle pin of the 2 trim pots that are soldered together?

Yes or just follow that track down to the top of the 2 linked diodes and solder there.

Thank you,
Franklin[/quote]

Thank you Joe!

Hi Joe, i'm asking some help cause my second LA500 is not working, although things seemed easier to make compare to the first one :

So, when engaged, the vu meter is not iluminated although it responds well. Sound is passing through the unit without being processed even though the signal seems to pass through all the path due to the vu meter and knobs which respond.

If you have any idea of what is going on and how to fix it i'll be pleased.

Cheers . Lud.

other pics

Hi,

I just finished my first ever build, it worked the first time when I plugged it in too, thanks to the really good instructions on this thread. If anyone's just staring out, like I did, I recommend they pick up DIY synth kit to practice with - they're dead cheap and they teach you not to make mistakes with soldering.


Anyhow I'm now stuck on calibrating the VU meter. I have to idea what to do here. If I set the Test Oscillator in Logic X to make a 1KHz sine, at what level do Logic 's output meters need to peaking at?

Hi Joe,

I finished the pair and they sound wonderful! I'm really happy with them.
I did the calibration process and everything went according to your instructions.

I do want to verify, when I do the stereo link, they jump a little more than 1db in opposite directions. Is this acceptable or do I need to do the stereo match mod? They sound fine, it does not sound like one is compressing more than the other - I only used my ears though, no meters.

Also, one of my VU meters has some small cracks in the inside around the lower right screw. Could you send me a replacement? I can return this one to you.

Thanks,
Franklin

Lud wrote:Hi Joe, i'm asking some help cause my second LA500 is not working, although things seemed easier to make compare to the first one :

So, when engaged, the vu meter is not iluminated although it responds well. Sound is passing through the unit without being processed even though the signal seems to pass through all the path due to the vu meter and knobs which respond.

If you have any idea of what is going on and how to fix it i'll be pleased.

Cheers . Lud.

If the meter led doesn't light then the bypass relay will not operate so the comp will not be switched in. Add a wire across the back of the meter shorting out the two LED terminals to see if the comp switches in then, If so the led has been blown and will need replacing.