Fostex MN50 compressor ideas

[snk]

Great !
Thank you, Fuzzzzz 
It's a big layout, but a nice sounding compressor
As soon as i find some time, I'll try to build it.

[FUZZZZzzzz]

I put the line input back in as well. I was thinking of building a couple of them together in a 19 inch rack. But, first we need to take out all the mistakes and test the mods.

[snk]

Yes, once the "basic" layout is verified, I may be interested into gathering two and build a stereo module as well 

[FUZZZZzzzz]

I was thinking about a 19 inch rack (1HE) and put 4 of them next to each other. maybe put in a transformer.. is this the kind of effect that will benefit from running on 12 volts instead of 9?

[snk]

is this the kind of effect that will benefit from running on 12 volts instead of 9?

On the enclosure, it is written "9V-15V"...

[FUZZZZzzzz]

have you tried opening it up before? Im still looking for the value of r38 on the schematic

[snk]

No, I never opened it (it is a compact enclosure in good condition, and I usually open only crappy boxes with dust, missing screws and requiring fixing)...
It didn't occure to me that i could get some measurements from the PCB 

[snk]

Would this be of any help, in the meantime (maybe the BoM features the missing resistor value ?) ?
https://cdn.shopify.com/s/files/1/0698/2265/files/AA_MN-50SmashCompressorColourTH-BOM.pdf?7188324099458706996
https://cdn.shopify.com/s/files/1/0698/2265/files/AA_MN-50SmashCompressorColourTH-BOM.pdf?7188324099458706996
https://www.diyrecordingequipment.com/products/mn-50-smash-compressor-colour?variant=22383267908

[FUZZZZzzzz]

Unfortunately not. They only based it on the MN50 its not a clone or replica. When you look at the schematic theres a resistor between lug 2 and 6 of the 2904 ic. according to the datasheet thats:




Can anyone tell me what would be an appropiate value?

[snk]

I will try to open mine this evening, and see if it is easy to take a picture of the PCB (by the way, mine is a MN15, not a MN50).

[FUZZZZzzzz]

cool! I think the mn15 is pretty similar. If you could make a straight photo of both the pcb sides then maybe its possible to make a digital trace of the pcb as well. Will save a lot of space possibly and we can modify it a little for the mods.

[snk]

Hello,
I managed to open the enclosure of the MN15 today.
I will not be able to take a picture of the back of the PCB, but i can take pictures of the top of the PCB, with components.
However, with the height of the faders and some other components and many standing resistors), it is a bit tricky to make a clear picture of everything.

One thing I notice is that R42 & R43 are not present.

Could you tell me which resistor you need to know the value ?
I can take a good picture of the resistors surrounding U4, and a not so good picture of the ones surrounding U1 & U2 (because all are standing resistors, in between faders). U3 is not really visible (because under a 2nd PCB layer).

[snk]

Also, R38 doesn't have any info whatsoever on the schematic. I thought I erased it in Photoshop, but alas. What would be a good candidate?

Hi, for R38, it's easy : golden / orange / blue / brown... which gives : 16K?





(PS1 :for the record, i have a MN15, not a MN50)

(PS2 : R32 and C20 are also not present on the PCB, as R42 & R43)

[FUZZZZzzzz]

thank you! I have a small update as well. I bought a MN50 last week. I took it apart yesterday. I wonder if the mn15 and mn50 are identical. Mine's missing R24 and C11, but they're also not showing on the schematic. If you take out the small plastic pins between the rca plugs (just push them with a plier or something) you can easily take out the pcb. I will make pictures of the front and back. Ive got some studio lights. The smaller board can also be taken out easily. Just unscrew the 2 small screws and you'll find a piece of soft material sticking to the 072 underneath it. Probably to level it out. The power adapter you can easily slide out. R38 is indeed 16k on my board as well. The diodes look like 1n4148. I have not been able to look at them closely. Too bad there's writing/values on the pcb side as well. Makes it a lot more work to photoshop a new pcb.

Also, I need to take the 4 RCAs and sliders out of the pcb to make the board a little bit smaller. Let's see how it goes. Fun times!

[snk]

If you take out the small plastic pins between the rca plugs (just push them with a plier or something) you can easily take out the pcb.

AH, I thought it was "rivets" (I don't know the english word for it. It is something you can put, but can't remove and put back again).

Let's see how it goes. Fun times!

[rankot]

Why do they use NJM2904 and NJM4558? What's the difference between the two? They look very similar to me.

[diffeq]

Why do they use NJM2904 and NJM4558? What's the difference between the two? They look very similar to me.

NJM2904 is LM358 under another name - it can pull all the way down to the negative rail, which is used for level indication comparator. Red led would always be lit otherwise. The 4558 is picked for less noise than LM358, I assume.

[FUZZZZzzzz]

I made a bunch of pictures for the two separate boards. One big and a smaller board for the leds part. I thought I wanted to trace this by drawing a pcb over the back images of the boards. But, what software can I use? Is there a free (preferably MAC) software available for this?

BTW Missing resistor R38 is 16K

[snk]

Interesting : so, between the MN15 and the MN50, the PCB is the same (same reference), but the MN50 features R43 & R42, R32 & C20, while the MN15 features C11 & R24...

[FUZZZZzzzz]

But does the MN50 also sound 35 better?