Very simple compressor. Works well IMO

[Noplasticrobots]

We'll be speculating for 6 more days on this one...

[markm]

We'll be speculating for 6 more days on this one...

Ya know, I  really needed that kinda laugh tonight!
Very good 
I've moved on fer now......it's too painful to continue on this one tonight!

[Noplasticrobots]

I've moved on for now too. I still want to see how this thing works but I found another schematic for a simple compressor I think I'm gonna try until Brett gets back from holiday.

[markm]

5 days to go 

[Noplasticrobots]

4 more days to go...

[markm]

bumpity-bump-bump

[Noplasticrobots]

You beat me to it Mark. Hasn't it been 6 days yet?

[markm]

Maybe seven but, who's counting! 
He's on the other side of the world though.

[brett]

Hi
thanks for understanding about time off.  The kids (10 and 16) loved the beach.

Now....what's going on?
First, that symbol for the MOSFET may be wrong, because I can never remember which way the diode goes.  But I always make sure the DGS labels are right.  In this case, I think it makes sense for the drain to go to the signal path, and the source to go to earth (as always).  My MOSFETs have DGS pinouts when looking at the flat side, if that helps

NPR said

Source of 2N7000 has a 2.2uf cap and a 47k to ground and a 1N34A with the negative side connected towards the Source, Gate is grounded.

The gate of the MOSFET should have the cap and 47k, and is connected to the negative (banded) of the diode.  It's the source that is grounded.

I'll check out the updated layout and report back.  I'll build and test one in a coupla days.  Apologies for confusing everyone. 

Thanks for the interest and persistence.  I feel in my gut that this will work out in the end.

[brett]

Hi
Looking at markm's current layout, there is a bugs for those using J201s.  Also, there is a difference between the pinout of BS170s and 2N7000s.

The pinout for a J201 is DSG, whereas the layout is DGS.  There might be DGS JFETs, but I suspect most people use J201s and similar, so the layout should reflect that.

The MOSFET orientation is correct for a BS170, but a 2N7000 is SGD and needs to face the other way (flat side to the right).
cheers

[markm]

Brett,
Maybe you have an older layout.
I beleive the pinouts on this one are correct;

[brett]

Hi

Yeah, the layout is right.

Here's something more:  I forgot that the JFET buffer is an OUTPUT bufffer as well as an input buffer.  This will prevent some, maybe even most, of the compression from happening.  The solution is to place a 33k resistor between the JFET drain and the V+.  Then take the JFET output from the drain instead of the source. 

These changes will make the JFET an input buffer but not an output buffer, and should give the circuit a source that is more like a guitar pickup.
I'll build one tonight using a modified version of markm's layout.
cheers

[markm]

Shouldn't the 33K from V+ go to the source?

  The solution is to place a 33k resistor between the JFET drain and the V+.  Then take the JFET output from the drain instead of the source. 

Shouldn't the 33K from V+ go to the source?
And the the output from the drain??
Like this>>>>>>>>>>>>>>>

[Noplasticrobots]

I agree with Mark, wouldn't having the +9v connected to the input cancel it out?

[brett]

Hi
The idea is to convert the JFET from a voltage follower to a common source amplifier. 

The new JFET circuit is similar to the JFET buffer circuit that is widely used as a pre-amp: except the resistor values are higher.  There are resistors on both the drain (Rd) and the source (Rs).  The output impedance is approx Rd, or in this case 33k.  We need this output impedance to create the effect we want - signal loss when the MOSFET becomes active and its impedance falls.

cheers

[brett]

Hi
This is a schematic of what I built tonight.


It works quite well (ie sustain is good, dynamic range is substantially reduced).  The details to fix are:
1.  with the compression turned down, the gain is high and the signal is quite clipped (in a nice gritty way).  With a booster turned on it got a bit nasty.  This issue can be fixed by either rolling the guitar volume back or turning the compression pot up (it's a compressor, right?  ).  If the distortion isn't wanted, the compression could be arranged so that there is at least a minimum amount that prevents clipping.  A small resistor (330/470/whatever ohms) between lug 1 of the compress pot and ground would achieve this.
2.  with the compression pot turned all the way up, the output is feeble or nothing, coz it has been compressed out of existence.  The 5 k pot is a bit large and might be better if it's a 1k (especially if used with the "minimum compression" resistor mentioned above).
3.  I'm not sure that the response (rise) time is fast enough.  Release sounds real good to me, but I don't really know much about compressors.  Someone who uses a compressor could try different values of the 3.3uF cap.  Maybe try 1uF?

It's still quite simple!  And it works!

cheers

[markm]

Great!
Okay, I'll do the Layout tonight and post it up ASAP.
Thanks Brett 

[Bagge]

Since you no longer uses pin 1 and 8 for controlling gain(it's set at 20), could a transistor or Jfet be used instead of LM386?

[Noplasticrobots]

Brett, since we've had a quick discussion here about confusing Mosfet pinouts, could you possibly label them on the schematic? It might help clarify things from the beginning and leave out discussion here about which is D, S or G. just my two cents!

[petemoore]

Brett, since we've had a quick discussion here about confusing Mosfet pinouts, could you possibly label them on the schematic?
  I used to add that to all schematics, any type transistor I thought I /would could use, it's pinout would be drawn on the schem. It helped...but I still have trouble nailing those pinouts from memory.