Discrete compressor. So simple.

[puzzle87]

Try J201, but delete R5 (variant 2). And you have bit more noises.

[Al Heeley]

I've just put this circuit together and I'm not getting much compression noticable, also the sound is breaking up like a fuzz box on the edge of distorting. i've followed the tweaks for the trim pots as per the notes in this thread. Any advice would be muuch appreciated.

[brett]

Which circuit did you build?  The original one with 2 x BJTs and a MOSFET or the JFET one?

[Al Heeley]

its the Jfet one = 3 X J201 and 1 x B170 - schematic calls it version 2

[SirBlend12]

It feels like a dumb question, but... where can I add in an attack control?

[psychedelicfish]

The schematic of a working prototype is below.

I can't seem to see the schematic

[Gram]

Can I ask what kind of caps you are using for the non-polarised caps?
i.e. C1, C2, C5 and C7.

I don't have any ceramic caps of those values so it'd be handy to know before I buy...

Is film the way to go?

Cheers

G

[duck_arse]

nothing special about those parts, use poly of any description. box, greencap, styro, mustard, orange drop, tropical fish, whatever you've got/can get/can afford/can fit.

[knutolai]

The picture of the original schematic seems to be broken. Is it only me or could you try to reupload it? Would love to give it a go

[tubegeek]

The picture of the original schematic seems to be broken. Is it only me or could you try to reupload it? Would love to give it a go

Note that the bulk of this thread is quite old.

Internet Archive to the rescue!

[Kipper4]

Do Let us know how it goes please Gram and welcome to the forum.
Rich

[duck_arse]

also have a look at this thread, a somewhat similar in principle at least.

http://www.diystompboxes.com/smfforum/index.php?topic=99892.0

[Kipper4]

Another old bump up....it's on the breadboard now
Problem = lack of output.
It is passing signal. but it's less than unity. I can hear the compression
Fet ver 2

Q1                 Q2                      Q3                      Q4
j201               BS170                 J201                    J201
D  5V4            D  0V                  D  9V                   D  9V
G  0               G  1V9                 G  0                    G  1V
S  0V2            S  0                    S  2V                   S  2V

Do they look like ballpark please?

[Kipper4]

Schematic is the fet version reply 16 page 1
subs
My R9 is a 2k2
25k Q1 drain trimmer.

[Kipper4]

If I make R12 33k it seem a little better.
I'll post the new voltages and see if anyone can see a problem.

[Kipper4]

Near as dammed it the same voltages as previous post.

[midwayfair]

That FET attenuator is going to load the guitar quite a bit. Unless you aren't compressing at all, it's going to be well below 1M. You could get more input headroom and a lower output impedance by using a BJT instead of the FET. Just move the FET to before the input cap and then move the pulldown resistor to be a base -> collector feedback resistor and you don't even have to add any parts.

The JFET for the rectifier buffer is also a waste of the FET -- might as well be a BJT to save a buck. Especially considering you've used a third type of transistor for it.

Ray Ring's MOSFET compressor has some thoughts on using the MOSFET as the attenuator. There's also a way to use a regular FET like the 2N5457, but it would require more parts for reasons I don't feel like typing out right now.

[Kipper4]

Brilliant thanks Jon
I'll work on it some more tommorow.
I have a buffer before it already because of the loading.

[GibsonGM]

This looks promising - please post a schematic when you get something, Rich!   

[Kipper4]

I think I totally messed up here. I havent breadboarded it like this yet.
Is this what you meant Jon?