Aussie Compressor Build Report Pics and Problems

[comfortably_numb]

Okay, so I built the Aussie Compressor or OZ Compressor, or whatever we're calling it.  I used MartyMart's modifications as listed below, and I used the power filtering and polarity protection from Toney's layout.  This was all done on perfboard (which I will never use again!).
Soldering is so much easier and cleaner on PCB.

Problems:  At first I had this hooked up with only the DC power jack but it was getting no power, so I installed the battery snap - POWER!

Now I have sound...very very interesting sound.  It is quite distorted.  A little bubbly maybe?  It chirps.  It buzzes.  It's LOUD. 

What's up?

If anyone has any ideas I'd be much appriciative.  I don't have a meter yet, but may get one in the next few days, so if there's anything specific I need to test let me know what the values should be and I'll get on it ASAP.

Oh...and how to wire that DC jack.  It's a metal one, not the plastic kind.  It has a connection on the middle, then the side, then further down the side.  I compared this to the plastic jacks pictured at GGG for reference and thought I had it right.  Center is Negative, farthest out on the side is Positive.  I switched to the other side connection for positive and this didn't work either.  Power supply is A-Ok. 

Anywho - here's some pics:

The original schematic:

and the mods are:
100k input resistor before first 0.1uf cap
8k2 and 10uf between pins 1 and 8
10k pot and 100k vol pot "as is"
1M log pot replaces the mosfet 1M to ground, wired as variable resistor ( lug 3 -- lugs 1&2 joined  with lug 1 to ground )
4.7uf cap changed to 2.2uf

PLUS

a 1N4001, 100uf, and .1uf, in parallel for power and polarity.

The top side:


The bottom:


The whole damn thing:


Thanks a million,
CJD

[comfortably_numb]

Something else that was wrong with this at first - I wired the volume pot backwards.  After I fixed this I decided to box the thing up and try it again.  Fully enclosed, all the weirdo noises went away.

What I'm left with is a rather pleasant soundind overdrive!  Ha ha.  The only problem with the overdrive sound is a hard clipping choppy type sound at the attack when I play hard, and a sputtery decay when I let a chord sustain.

I'd like a compressor. 

It occurs to me that maybe this circuit just isn't that great...I've seen mixed reviews.  If I can't have a clean compressor, can I have a compressed overdrive? 

Can anyone remedy the sputtering decay?  Maybe I could add a diode or two on the output as well eh?

[MartyMart]

You have a error .... somewhere !
I have a "working" compressor..... which does "ripple" a bit as it decay's and when
pushed too hard it distorts "ever so slightly' BUT it's not an overdrive sound 
For this reason it works best with my strat/tele but not a HB equiped gtr.
Setting the 1M pot etc correctly does produce a decent compression so go over it with
your DMM and check the mosfet connections/values etc .... it WILL work

Marty.

[Toney]

Right, first you'll need a DMM.

First I would absolutely tripple check my soldering, esp for bridges.

Then after you've tested your voltages, post as per "what to do when it doesn't work" sticky.

You are aware of the static sensitivity of the mosfet, right?

I wouldn't question the circuit as a first step... Brett Robinson shared his design out of goodwill, I worked on the Vero layout to share with the community, others are contributing tweaks and fine tuning it.

[Paul Perry (Frostwave)]

I know the LM386 is a standard amp chip & lots of people have used them (on this board) with great success.
But, I'm not a fan...... because, in my experience, it's easy for them to go into ultrasonic oscillations. Unless layout is very rigorous. That's what I would suspect.

[comfortably_numb]

I meant no harm or disrespect to Brett.  I have just read a lot of reviews where people have said this was distorted and lo-fi sounding, possibly due to the chip.  But...  I got a DMM today!  On to testing!

[comfortably_numb]

Got the DMM and I have some readings.  Someone please help me interpret these.  It looks like the Mosfet is bad for starters, but who knows?

Battery
8.02V

IC
1. 1.35V
2. 0V
3. 0.01V
4. 0V
5. 4.11V
6. 7.97V
7. (not used) 4.02V
8. 1.35V

Q1
No Voltage

D1
No Voltage

So is it a bad Mosfet?  A bad diode?  What's up?

[Toney]

Check carefully for correct component orientation and soldering errors.

Have you checked the pinout of your particular transistor?
They can differ... and they are also static sensitive.

[brett]

Hi.
It seems that most things are ok.
At least one thing is happening: uncontrolled gain.
In this circuit, the MOSFET reduces the input until the average output is less than 3 volts p-p.  At this level, the 386 WON'T be distorting.

To find out why the output is high and loud (indicating that the MOSFET isn't turning on), play your guitar through it and look for a DC voltage on the MOSFET side of the rectifying diode.  When you play a chord, you should see 2 or 3 volts all the way along the line from the diode to the 4.7uF cap (2.2 in your case) to the gate of the MOSFET. 

IF there is a voltage at the gate that rises quickly and subsides slowly as your volume decays, the problem is with the MOSFET.  Either blown or the wrong way around.  (NB - BS170s and 2N7000s have different pinouts)

IF thewre's no voltage during playing at the MOSFET gate, work backwards to find out where there IS voltage, then replace parts or re-solder or unsolder until you establish voltage through to the gate.

Hope this helps.
Good luck.