MAC Rack kit Build Thread from October 2016 with slow attack led

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asidd
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by asidd »

hello again, I'm on the SCv3 pcb and the kit comes with two 10R resistors that don't seem to have a place on the board. The build photo has a place for them in the corner but my pcb instead indicates two 1uF caps.

I'm assuming the resistors are not needed on this board?

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

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asidd wrote:
Fri Mar 17, 2023 2:03 pm
hello again, I'm on the SCv3 pcb and the kit comes with two 10R resistors that don't seem to have a place on the board. The build photo has a place for them in the corner but my pcb instead indicates two 1uF caps.

I'm assuming the resistors are not needed on this board?
You are correct the parts kit is shared between the LA500A and MAC so there are some extra parts.

You will not need the 2 x 10R. The newer PCBs have 78L & 79L regs instead. Follow the pcb overlay on the pcb you have.

Be careful to put the 78L12 & 79L12 in the correct places and DIP8 opamps around the correct way.
Joe :-)
JLM Audio
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asidd
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by asidd »

Hello again, when connecting the SCv3 to the chassis, how should we connect the board to the meter? The photos show the meter tabs lining up with the pads on the pcb -- do we eventually solder them directly? Or do we connect them with wires in a similar way to what the older design shows?

Also, at what point in the build should we go ahead and solder all of the switches to the SCv3 board? The photos show one foot soldered, which I assume is to hold it in place until future steps are completed.

Lastly (just to be sure), the switches can go in either way, correct? The on/off/on nature seems like this is the case.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

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asidd wrote:
Wed Mar 22, 2023 10:38 am
Hello again, when connecting the SCv3 to the chassis, how should we connect the board to the meter? The photos show the meter tabs lining up with the pads on the pcb -- do we eventually solder them directly? Or do we connect them with wires in a similar way to what the older design shows?

Also, at what point in the build should we go ahead and solder all of the switches to the SCv3 board? The photos show one foot soldered, which I assume is to hold it in place until future steps are completed.

Lastly (just to be sure), the switches can go in either way, correct? The on/off/on nature seems like this is the case.
The MAC sc PCB is made to go under the 4-meter metal tabs and sit flat against the back of the meter. Solder a couple of the toggle switch legs so the PCB stays flat with the meter and doesn't touch the back of the pull pot switches on the pot PCB. Then just bent the 4-meter tabs down and solder them to the PCB. Then if everything looks in the right place solder off the rest of the toggle switch legs.
Joe :-)
JLM Audio
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asidd
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by asidd »

Apologies, I've deleted my original post as I think I've answered my question.
I'm now just wondering how the Link function works on the MAC. It seems to almost "stack" the settings (GR and Ratio) rather than one channel dictating the stereo settings (what I'm used to). Slow Attack and Makeup Gain seem to be independent.
Is this correct? I just want to check that I've assembled it properly. Thanks again for all the help.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

asidd wrote:
Sat Mar 25, 2023 10:36 am
Apologies, I've deleted my original post as I think I've answered my question.
I'm now just wondering how the Link function works on the MAC. It seems to almost "stack" the settings (GR and Ratio) rather than one channel dictating the stereo settings (what I'm used to). Slow Attack and Makeup Gain seem to be independent.
Is this correct? I just want to check that I've assembled it properly. Thanks again for all the help.
The link works like most vintage comps like LA2A & 1176 it just joins the side chains so both comps have to be set the same settings before linking. Only since modern VCA comps with DC controls have comps handed control over to one channel.
Joe :-)
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saxmonster
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by saxmonster »

Hello,
Just curious what is the difference and over all sound quality with this stereo rack version vs two LA500A link together. Besides the obvious of not taking two slots up on my lunch box, which is a good reason for me, lol and its $80 bucks or so more that two la500a's. I know that this rack version comes with 2 opamps on each channel what does that do to the sound vs on having one like the la500a has. Sorry for the questions as I am still learning all the little details. I will be using this as a stereo compressor on my 2 buss.

-Scott

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

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saxmonster wrote:
Sat Apr 22, 2023 1:14 am
Hello,
Just curious what is the difference and over all sound quality with this stereo rack version vs two LA500A link together. Besides the obvious of not taking two slots up on my lunch box, which is a good reason for me, lol and its $80 bucks or so more that two la500a's. I know that this rack version comes with 2 opamps on each channel what does that do to the sound vs on having one like the la500a has. Sorry for the questions as I am still learning all the little details. I will be using this as a stereo compressor on my 2 buss.

-Scott
Basically no real tone difference at all. The form factor is the only real difference. The rack runs on +/-24v with JLM99v input just as no DIP8 runs on that voltage anymore. This in theory gives more headroom but both LA500A and MAC can output +28dBu which is about the limit of the output transformer and way more than any A/D can handle. The input opamp only runs into a 47k load so the LA500A uses a NE5532A as it will run Class A into that 47k load so if hard to tell a difference between the input JLM99v and NE5532A.
Joe :-)
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saxmonster
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by saxmonster »

Thanks Joe,
I will be selling my original LA500 with the slow mod to help fund getting the MAC Rack kit so to save space in my 51X rack for other future items, lol. I see you have one kit in stock, not sure how long it will take to sell this LA500 I have but will you be getting new stock in if this one rack that is left sells out?

Thanks again.
-Scott

materialstooutlet
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by materialstooutlet »

Hello-
I just finished my MAC kit, but when powering it on, it comes up for a brief moment, then shuts off again. Then, in about a second or two, it does the same thing, then over and over until I get freaked and turn it off. I put a meter on the power in and it's sitting at 48v before the switch comes on, then it drops to 0 in the cycle down, comes back and drops again, and over and over. Is this a switching PSU thing or is it maybe something to do with the Zerners? I just don't know if a fault in the MAC circuit is going to make the PSU switch off or not. If it does do potentially make the PSU behave this way, it seems like someone else was having a slightly similar issue and it was recommended to replacing the 24v 1W Zerners (I did pull the opamps and didn't see any scorching or anything.)
Any advice is appreciated-
Thanks!
Jake.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

materialstooutlet wrote:
Sun Nov 12, 2023 6:06 am
Hello-
I just finished my MAC kit, but when powering it on, it comes up for a brief moment, then shuts off again. Then, in about a second or two, it does the same thing, then over and over until I get freaked and turn it off. I put a meter on the power in and it's sitting at 48v before the switch comes on, then it drops to 0 in the cycle down, comes back and drops again, and over and over. Is this a switching PSU thing or is it maybe something to do with the Zerners? I just don't know if a fault in the MAC circuit is going to make the PSU switch off or not. If it does do potentially make the PSU behave this way, it seems like someone else was having a slightly similar issue and it was recommended to replacing the 24v 1W Zerners (I did pull the opamps and didn't see any scorching or anything.)
Any advice is appreciated-
Thanks!
Jake.
HI Jake
OK the power supply is seeing a short circuit and going into protect mode and will retry to start every couple of seconds.

Unplug the ribbon cables from the 2 dingo or dingo-T going to the front pcbs and see if the power supply stay on or not? If power stay on the zeners are fine and the fault is on the front PCB. Check you have the NE5532A plug in the correct way around and that you have the 78L12 & 79L12 to92 regs in the correct places on each Sidechain pcb.

If still powering on and off. Disconnect the left channel +/-power and try powering up with only right channel? If it doesn't power up with only right dingo unplug all the JLM99v and take some photos of the pcb tops so I can check them over for you.
Joe :-)
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materialstooutlet
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by materialstooutlet »

Hey Joe,
thanks for getting back!
I unplugged the ribbon cables from the dingo cards and the power kept cycling on and off. I then disconnected the left channel and it powers on and stays on.
I assume that means the fault is on the left board- would the Zerners be a good place to start?
Thanks!
Jake.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

materialstooutlet wrote:
Wed Nov 15, 2023 4:11 am
Hey Joe,
thanks for getting back!
I unplugged the ribbon cables from the dingo cards and the power kept cycling on and off. I then disconnected the left channel and it powers on and stays on.
I assume that means the fault is on the left board- would the Zerners be a good place to start?
Thanks!
Jake.
Yes you should find one or both zeners are short with ohmmeter. Check the dingo pcb for solder shorts and reversed parts like polarised 100uF caps etc and replace the zeners and reconnect it to power wires and power up with no ribbon cable again. If you found no problems on the dingo except the zeners then check the MacSC pcb for reversed parts or solder shorts. Take clear well lit photos of the top and bottom off any pcb you have removed encase you need any help you can send those to me to double check for you.
Joe :-)
JLM Audio
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materialstooutlet
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by materialstooutlet »

Hey Joe,
Found the issue on the SC board (I think) after re-checking every component-I had the 79L12 and 78L12 line voltage regulators switched.
(I am supposed to have the C18 .1U cap installed- correct?)
Pretty sure I fried them in the process of getting them out so are these fine replacements?
(from Mouser)
LM79L12ACZ/LFT4
LM78L12ACZ/LFT3

Thanks!
Jake.

materialstooutlet
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by materialstooutlet »

Also, here is the Dingo T Top & Bottom-
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