Fostex MN50 compressor ideas

[FUZZZZzzzz]

So, yesterday I found this compressor on a 2nd hand website and found out these are pretty cheap and work great as cool drum compressor for many studio. Rumour has it, it was used on a couple of flaming lips albums as well. In my book thats a cool thing and as I'm in the proces of having my new studio space I need some extra stuff.

I found the schematic online, which I will post and looking at it I want to modify it a little  as well. I want to remove all the inputs except for the microphone. I read somewhere that it lacks a makeup gain. So it would be nice to add that as well (could it be as easy as adding a booster at the end?). Pretty compact and works on 9V. Any ideas or suggestions? Maybe put two together as a stereounit?

[amz-fx]

You do not need to remove the other inputs. Just move sliders 1 through 4 down to zero and the tape inputs are out of the circuit.

The gain can be changed, but doing so will have an effect on the response of the compressor since it is tapping off its signal from the output.

Best regards, Jack

[FUZZZZzzzz]

sorry.. i was a bit unclear . I dont own this model. I just want to build a clone and modify it a little bit to my liking

[amz-fx]

Leave out R25 - R28 and their pots, R102 - R105. You also do not have to include the meter in the bottom right corner built around U4.

regards, Jack

[Mark Hammer]

Interesting circuit.  Pretty much a fancy-schmancy Orange Squeezer, with a better input stage and a better rectifier sidechain.

As with the OS, one could modify U2, the sidechain "driver", to have a bit more gain, by either upping R11, reducing R12, or both.  Since that would affect not only the output level but also the sensitivity of the sidechain, you might run into problems there.  To some extent, those issues could be offset by simply padding down the input level with R101, or even making the value of R5 a little bigger (e.g., 2k2 or 2k7).

The basic underlying strategy is that you can find ways to "push" the signal, without having to substantially change the circuit, just a few passive components.  I vary the gain on my Orange Squeezer, to get more "squish", but that also requires including an output-level pot to compensate.  In this instance, replacing R31 with a 47k log pot would be appropos.

[FUZZZZzzzz]

yes. the meter (red and green led) reminds me of the old DBX compressors. the hifi models for home use. it says -20 dbv on the output. If the original output is already a compressed signal? what will happen if i put a booster at the end? will it function as a makeup gain or am I forgetting something? (it would probably colo(u)r the sound a bit)

replacing r31 seems like a good and easy way to start thank you!

[FUZZZZzzzz]

I will be using it for dynamic microphones mainly. kick / snare / guitar amps that kind of stuff.

[snk]

Wonderful !
I have one, and it is great (if not those RCA plugs, grrr) !
I wanted to clone it, too, and add a couple mods or tweaks, i'm glad this project might come alive 

I remember making a web search, a couple years ago, here a couple links i had found :
https://avensonaudio.com/avenson-audio-mn-50-smash-compressor-colour-diyre-colour-module/
https://www.diyrecordingequipment.com/products/mn-50-smash-compressor-colour?variant=22383267908
https://cdn.shopify.com/s/files/1/0698/2265/files/Avenson_Audio_-_MN-50_Smash_Compressor_Colour_-_ASSEMBLY_GUIDE.pdf?3070671290224496846
http://www.muzines.co.uk/articles/fostex-mn-15-mixer-compressor/4125
http://pecktronics.blogspot.com/2015/01/fostex-mn-50-mixer-schematic.html

The release control is faithful to the original, and goes from a very fast 50ms to 1 sec. I found the fast times far more useful than the slower settings (which sound more like a ducking effect) so I decided to get in touch with Avenson Audio to ask about changing the release pot value. They were very helpful, and suggested I changed out the 500k log pot for a 100k lin pot. That was a major improvement - now the release time can be more finely tuned, and also matched on two modules for stereo operation.

I also tweaked the input pad, as in my system I found the module to be compressing too hard too early, and I would have to pull back my sends by a good 6dB or so. So I contacted Avenson Audio again, and with their advice changed R3 from 3.6K to 820R. This inverts the pad jumper, meaning that the low setting gives around 14dB attenuation and the high setting gives around 20dB attenuation, which gives the drive knob far more range/control.

[FUZZZZzzzz]

Something like this? Yes.. its untested.

[Slowpoke101]

Looking forward to this. One of these would free up one of my studio compressors from a rather overkill type of job.

A 2SK30A would be fine to use. So would a 2N5457 or BF245B....If you can still get hold of any real ones.

Good luck with the project and please do keep us posted as to your progress.

[FUZZZZzzzz]

it's going to be a vero build at first so not to everyone's liking. these mods are easy to undo even for vero layout. let's see if it fits in a standard 1590b. should be cool to have a microphone compressor in the size of a stompbox. maybe a little bigger and you can use it on location with a 9v battery even.

[FUZZZZzzzz]

Does anyone know the function of the R107 trimmer?

[snk]

it's going to be a vero build at first so not to everyone's liking.

It will be to my liking at last

should be cool to have a microphone compressor in the size of a stompbox. maybe a little bigger and you can use it on location with a 9v battery even.

One thing which could be nice imho is to have two inputs : one mic input, and one instrument/line level input.
If i build it, I will be using it as an AUX in a mixer, with synths and drum machines, so line level is a must.
But sometimes I like to drive a mic input to get both compression and overdrive

Looking forward to your layout, Fuzzz ! 

[FUZZZZzzzz]

adding the line input back again is not very hard. just a couple of components and a switch. I will start a vero and will see about the size maybe do two versions. one with and one without the line input

[duck_arse]

that trimpot would appear to be reading a voltage from the zener, to bias the fet. if you follow those lines to above the dotted box, there is a dotless junction showing and a shorted pair of lines on your last diagram draw.

[FUZZZZzzzz]

I see that d1 and d2 are not specified. Will a common type like 1n4148 suffice?

[bluebunny]

I see that d1 and d2 are not specified. Will a common type like 1n4148 suffice?

I would imagine so.  I can't see why it should be anything more exotic.

[FUZZZZzzzz]

So.. some part of me wants to see if I can fit this layout into a 1590B enclosure. I split the board in half (just connect the numbers). Its a big board and mistakes are easily made. Therefore, don't start building if you're not into troubleshooting. I have not yet build it myself, but will very soon.

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?

EDIT: IM NOT BUILDING THIS FOR 1580B ON VERO.

[FUZZZZzzzz]

I also need to figure out the comp in switch. Am I the only one having trouble with reading switches on schematics?

[FUZZZZzzzz]

Well.. I'm going to try and build it this week. The components are easy to obtain. Nothing fancy here.