FET "Grinder"

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Gustav

Well-known member
Joined
Jun 4, 2004
Messages
2,271
Location
DK
This is a standard circuit from a classic FET compressor. I have done the layout to minimize wiring and implemented a few, minor changes. You can mount all pots to the side of the board, or you can wire them, if you want to mimic the original layout. Its still pretty easy to work with

Took some attempts to get it working perfectly, and I had a lot of help from Jakob Erland and the info on the group doing this.

- So without further ado, here are some files for self etch enthusiasts.

https://pcbgrinder.com/download/FET_GRINDER/FET_Grinder_Docs.pdf

If you have any problems with the scaling, please let me know. It worked on my home printer.

UPDATE

I made a new layout, which is not self etch friendly, and named it PHAT PHET to distinguish. Circuit is the same and in my shop.

Gustav
 
Nice. It would really help however if you put the size of the pcb in the files. And maybe also some text in the small pcb so you know which side is up.
 
Cool! Very cool!

How would you describe it's sound (yeah, unpopular question!)?
I see there's a pot named "dirt"!
So I guess it's not on the transparent side. Right?
 
shot said:
Cool! Very cool!

How would you describe it's sound (yeah, unpopular question!)?
I see there's a pot named "dirt"!
So I guess it's not on the transparent side. Right?

You probably saw this description of the OPTO Grinder?  :)

Gustav said:
P.S. I have an intellectual barrier when it comes to entering the intersubjective realm of aesthetic judgments, so I am no good at communicating "how something sounds". If I were pressed, I would say this thing sound "old, like 70s Elton John records" when its pushed into the red and "Very pleasant" when its not.

The FET Grinder is based on a very popular circuit. If you look at the schematic for 5 seconds, you might be able to see which. I am just reluctant to  use those types of names on the projects I conjure up myself, since I have no illusions of grandure or even hope to live up to the genius of the people who designed them or make carbon copies of them.

The changes are minor, and the "Dirt switch" is really just a distortion trim calibration pot brought to the front. In my experience, it doesn't change much in its original range, but if you up the value a bit, you can make it growl a little if you push the unit and dial it "out of the sweet spot". Thats why I put it on the front and upped the pot value. If you use a 220R or lower pot value,  you probably won't notice much when you sweep it, but I think it gets mildly interesting at 1/3 of the range if I put in a 1K pot.

Print, etch, populate, try!

Gustav
 
mitsos said:
neat. thanks.  maybe make some cheap pcbs?

Ill offer some PCBs. Cheap is relative, but I sleep at night knowing that you can always self etch if your relative is cheaper than mine :)

Gustav
 
L´Andratté said:
Thank you very much!! I never did a FET comp
I´m such a single sided guy and I´ll be stirring my acid kettle soon! :p

Cool! I have never self etched, but in 2 months time, I will have a humble workspace where I can try it out :)

If you need a supply for the project, I put this together earlier today. Its untested, and its pretty ugly, but it should work.

https://pcbgrinder.com/download/FET_GRINDER/supply.pdf

Gustav
 
The etching process is really not as half as complicated as I thought it would be.
I´m using photosensitive boards and print the layouts (unmirrored) on selfadhesive transparent sheets. Set the printer presets to "high quality" for deep black.
I expose it to a simple 11W cfl bulb for ca.8 min. I´m stunned, how the results are flawless. The drilling is the full attention part.

I did a handful of thomas henry 4046 vcos and a friend put one at his wall as
artwork ;D yours is not particulary ugly by the way
 

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living sounds said:
Nice! May I ask why you changed the timing cap to 220nf, ten times the size of the one in the "classic" design?

Nice catch.

Forgot to correct a typo on the silk screen - never tried it with a 220nF, since I used the original schematic as reference for the prototypes to double check. I am not really sure what impact it would have to put in the 220nF instead, so its going on the errata list.

Gustav
 
Hello.
I have already a case (from frontpanels.De) for building a G1177.
I think we can bypass the dirt dial, cause i haven't the hole in the panel to put the POT ?
Thanx.
Tom
 
frereyvan said:
Hello.
I have already a case (from frontpanels.De) for building a G1177.
I think we can bypass the dirt dial, cause i haven't the hole in the panel to put the POT ?
Thanx.
Tom

The "Dirt" dial is really more of an experiment than anything else. It is very dependent on the signal you send to the unit, and it is not just a set and forget function at all.

I kept it in anyway, because it can do some nice things in the more "subtle" category, but I also designed the PCB, so you can just add a trimpot instead directly to the PCB to calibrate the unit for a set trim.

Gustav


 
Gustav said:
You can link it like an 1176.
Sorry for asking dumb questions, but is that available on the board itself or do I need another PCB for that? Also is it possible to order a matched stereo kit or do I tune something to match it? Can I hook up a toggle for linking/unlinking? I have bigger use for stereo compressors as I´m mostly ITB. Looking to get out of it though!  :D
 
And the ratio, I saw 2:1 in another thread made possible with changing up some resistor values, but what about SLAM / all buttons in?

Maybe SLAM is not needed with 20:1 and your DIRT pot?  8)

Looking at IGOR´s 500 1176 ratio circuit it looks like SLAM is achieved by bypassing the resistors? The lower the impedance the higher the ratio?

I´m a noob mind you!  ;)

MAIN_SCH.png
 
XAXAU said:
I´m a noob mind you!  ;)

In that case, I would get a working build going before thinking about modifications - then do some searches on the forum.

Everything has been covered numerous times, and I cannot stress enough how much more difficult a build is if you start adding mods without really knowing a lot, and then have a problem when you fire up the unit.

KISS!

Gustav
 
Gustav said:
In that case, I would get a working build going before thinking about modifications - then do some searches on the forum.

Everything has been covered numerous times, and I cannot stress enough how much more difficult a build is if you start adding mods without really knowing a lot, and then have a problem when you fire up the unit.

KISS!

Gustav
Hmmm, yeah I know that would be the smart thing to do. But I´m stupid and really want to incorporate some more functions!  ;D

And I realize I was wrong in my previous post too.

I can understand if you don´t want silly questions in the build thread I just thought that since this is "your" circuit you could help a beginner out?  ;) I´m learning more and more every day, some from books I bought, but mainly by asking (silly) questions! But if it´s inappropriate then I apologize of course!

I would of course never try to build something without knowing how to build it!  :p
 
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