DIY Compresor build

Hello GDIY! This is my first entry here, so greetings to all!

I am searching for a diy analog compressor project, in order to present in my bachelor's thesis.

I seek for a rack-mount format unit, with basic controls like thresh, ratio, attack, release and some visual indicator for GR monitoring. One channel is enough, no prob. Im on a budget of around 100 euros, so expensive rare parts for vintage replication could be a pain..

I have been asking and searching about it, but most units ive come across are in a guitar pedal format, so not many controls or VU meters.

The best option would be a kit, or a ready to transfer PCB design. Im not experienced in designing pcbs from schems alone or debugging "beta" projects..

I know there are some very experienced techs around who could pinpoint some interesting stuff..
Cheers!!

PS(im located in Greece so EU retailers are much easier for me)

Welcome here!  8)

Maybe a simple Fet compressor without transformers? Or what do you think?
Do you already have a case you could rip, or a meter you could use?
One could spend a 100€ alone for a VU Meter, but you could also get a used one from an old Tape deck or alike.

What will your bachelor thesis be all about?
In what environment do you want to use it? Do you need balanced in/out or will unbalanced be ok?

Maybe you don't need a pcb and you could do it on a simple breadboard.

As I'm not too much into kits and have no overview therefore, maybe someone else has.
But if you give a little more info on what you require I'm sure we find a suitable circuit.

If it has to be hell cheap you could consider diode limiter Not sure about Vu then, but doable.

Sorry my english is a mess today.

DerEber said:

Welcome here!  8)

Maybe a simple Fet compressor without transformers? Or what do you think?
Do you already have a case you could rip, or a meter you could use?
One could spend a 100€ alone for a VU Meter, but you could also get a used one from an old Tape deck or alike.

What will your bachelor thesis be all about?
In what environment do you want to use it? Do you need balanced in/out or will unbalanced be ok?

Maybe you don't need a pcb and you could do it on a simple breadboard.

As I'm not too much into kits and have no overview therefore, maybe someone else has.
But if you give a little more info on what you require I'm sure we find a suitable circuit.

If it has to be hell cheap you could consider diode limiter Not sure about Vu then, but doable.

Sorry my english is a mess today.

Click to expand...

Thank you for your reply, let me get into some more details:
I am an Automation Control engineer, but because of my love for music and sound, i try to bring it into audio territory, so what better example than one of the most basic AUTOMATED audio circuits, compressors/limiters.
The project will be split in two, the first will be general theory and the second will cover the build that i present (Schematics, some maths, pictures and steps of construction).

The basic purpose of the unit i make will be the presentation. Of course it would be nice to be able to use it for gigs or studio and have a "standard" commercial comps features, if we stay close to the budget and moderate complexity of the project.

In my mind it would be a dbx 166-like unit. An "old school" warm and coloring unit would be nicer but  I believe tube designs are out of my skill/knowledge/budget. Maybe i could find some ready box to fit it in and make a custom front plate.

Balanced/unbalanced is not a problem, anything could work.

As far as the visual indicators, i could use some guidance as i am not axperienced at all. Meter or leds is fine for me, unfortunately i dont have any spares from old equipment.

I hope to cover some basics with these info, if u need any additional details, ill happily provide!
thanx again, cheers!

Ok cool, so Diode Limiter is out of the game.
You want a controllable Attack and/or Release. Maybe if automated circuit is your toppic you could even think of 2 Release and Attack times. One for short overs and one for overall level.

So either a Fet comp or VCA?
I never messed with VCA, so I can't say if the VCA's are cheap to get.
Maybe you even find a suitable circuit in VCA- Datasheets to start with. Check it out.
THAT2180 is a VCA chip for example.

Fet- Compressor could be made very cheap.
Do you have a basic understanding of Fet and VCA circuits? Check out Datasheets and get your hand on a 1176 schematic/manual.
Should be somewhere around.

best,
Stephan

I believe sticking to a pair of Att/Rel is fine for start, but im always open to suggestions. Im not yet familiar with FET/Vca.  Just started looking into thery on them, but i believe we're talking about opamp or transistor based circuits. So far i have been informed about THAT 4301 Comp, and the GSSL (THAT 2180 based?)  who appear to be Vca designs. I will look into 1176 asap, could you provide some FET designs? Not too advanced if possible..

Regards

For that budget you can build the Gyraf 1176 version with IC input (instead of transformer)
you can buy an already made PCB or even etch your own,
info here:

http://mnats.net/1176.html

http://groupdiy.com/index.php?topic=646.0

and for a case you could scavenge some sheet metal from local companies, blacksmiths, metal work shops, dumps etc ask your neighbours. if your school has a metal work area, speak to them and knock up a nice case, even better if they have CNC machine or something that could etch the front panel.
G1176 is a nice project and pretty easy to do self etched pcb, again you could ask around local companies and schools to see if they could help with materials. doesnt hurt to ask.

good luck.

regards

Spence.

Google spits out this picture:



The Fet is like a variable Input Pad here. Maybe someone can comment on C2.
For me it looks like if the Fet conducts there is less audio  on Vbe of Q2, yes?