Help Debugging AMZ Q&D Compressor

[Giglawyer]

I put together an AMZ Q&D Compressor.   I am having some difficulties and was wondering if anyone can offer some insight.  

First - here is the tech page with the schematic - http://www.muzique.com/tech/2166.htm

It seems to work very well, except for the GATE pot.  When the GATE pot is cranked all the way up, it works.  If the GATE pot is anything less than dimed, I get horrendous feedback and squealing.  

I did some voltage testing -

Q1 - 2n5457

D - 4 v
S - 5.46v
G - 9 v

U1 - 78LO5
1 - 5v
2 - 0v
3 - 9v

EDIT - I had the pin numbers goofed up before.  They are correct now.   

U2 - SSM2166
1 - 0v          14 - 4.95v
2 - .14v        13 - 2.25v
3 - 2.47v      12 - 0v
4 - 2.47v      11 - 4.95v
5 - 2.26v      10 - 1.42v
6 - 2.26v        9 - 4.95v
7 - 1.56v        8 - .58v

D1 - 9v

Other notes:  I changed C6 to 10uf, as I play bass, and C8 to 100uf, to address any power supply hum.  

If I turn the GAIN all the way down, I can back off of the GATE a bit, but it is all but unusable unless it is fully dimed.  

I will post some pics, if that will help.  Also, FWIW, it is not boxed yet, just on my testing board right now.

Any thoughts?

[Mark Hammer]

I've made a couple, and the Gate control should not be doing what you describe.  WHY it does that is beyond me.

[Giglawyer]

I am glad to know that something is wrong, I just wish I could figure out WHAT!  LOL...

[Giglawyer]

I am glad to know that something is wrong, I just wish I could figure out WHAT!  LOL...

How did you like the compressor overall?

[Mike Burgundy]

It's unbeatable for what it is, a simple, good sounding comp/lim/gate all in one go.
If your voltages are as you stated them, there's some wiring errors.
Pin 14 should be V+ (5V), pin 12 should be grounded.

[Mark Hammer]

I second Mike's recommendation.

One of the most common complaints people have about compressors is that way in which they can increase noise when one stops playing.  Some, less familiar with the inner workings of compressors, convince themselves that there is something wrong with the unit, or that there is some magical mod they ought to be able to perform that will eradicate the audible hiss resulting from cranking the gain on an input signal containing only hiss.  The downward expansion on the 2166 magically solves that issue in a very transparent way.

For greater variation in compression amount/control, set your rotation point higher, to something like at least 200mv.  Keep in mind that the Rotation point is where hard limiting becomes imposed.  The Compression control only applies to content/levels between the Noise-gate threshold (downward expansion point) and the Rotation point.  So if the rotation point is too low, you won't notice that much effect of Compression pot settings.

[Giglawyer]

It's unbeatable for what it is, a simple, good sounding comp/lim/gate all in one go.
If your voltages are as you stated them, there's some wiring errors.
Pin 14 should be V+ (5V), pin 12 should be grounded.

I will pull the IC and check the pins on the socket for cold joints.  Maybe that's what's giving me fits.  Thanks for the info, I should have looked at the schematic closer. 

[Giglawyer]

It's unbeatable for what it is, a simple, good sounding comp/lim/gate all in one go.
If your voltages are as you stated them, there's some wiring errors.
Pin 14 should be V+ (5V), pin 12 should be grounded.

Mike:  I totally blew it on the pin numbers.  Here is the U2 voltages:

U2 - SSM2166
1 - 0v          14 - 4.95v
2 - .14v        13 - 2.25v
3 - 2.47v      12 - 0v
4 - 2.47v      11 - 4.95v
5 - 2.26v      10 - 1.42v
6 - 2.26v        9 - 4.95v
7 - 1.56v        8 - .58v

As you can see, 12 is grounded, and 14 has the right voltage.  Now I am back to square 1.  Maybe a bad pot?

[Giglawyer]

Gack....I am an idiot. I have my pin layout for Q1 mislabled. 

The Correct voltages are

D - 9v
S - 5.46v
G - 4.5v

[Giglawyer]

Links to a few pics...

http://giglawyer.files.wordpress.com/2014/04/img_0086a.jpg

http://giglawyer.files.wordpress.com/2014/04/img_0091a.jpg

[Mark Hammer]

The build looks fine, and the solder joints appear competent enough.  I'm pleased to see your use of heatshrink on the pot lugs.  That's an approach I use myself.

Despite that thumbs-up, I will say that there have been the odd occasions where I've found that a solder joint on a lug was cold, or the wire actually HAD fractured, and the heat shrink had created the appearance that everything was hunky dory between the board and pot, by hiding the fracture.  Just for the heck of it, you may want to simply confirm that the connection between the board and pots is fine for all wire leads.

That may not be much, but it's all I've got for now.

[Giglawyer]

The build looks fine, and the solder joints appear competent enough.  I'm pleased to see your use of heatshrink on the pot lugs.  That's an approach I use myself.

Despite that thumbs-up, I will say that there have been the odd occasions where I've found that a solder joint on a lug was cold, or the wire actually HAD fractured, and the heat shrink had created the appearance that everything was hunky dory between the board and pot, by hiding the fracture.  Just for the heck of it, you may want to simply confirm that the connection between the board and pots is fine for all wire leads.

That may not be much, but it's all I've got for now.

I have been over that pot twice now - replaced the wires and everything.  It seems to read 500k on my meter as well, so it appears to be all good.  Grrr...

Thanks for the follow up.

[samhay]

Not sure which version you built, but did you see this: http://www.muzique.com/news/ssm2166-update/

[Giglawyer]

Not sure which version you built, but did you see this: http://www.muzique.com/news/ssm2166-update/

I did not see that.  Hmmm...I will look into that.

I did want to give a big thanks to all who have commented, and further a big shout-out to Jack Orman, who has been e-mailing me advice to me as well.  I may have a bad SSM2166 chip.  I am going to replace that, and the pot in question, and I will keep everyone advised. 

[Giglawyer]

So, I built a second one of these, to see if I could figure out what the heck was wrong with the first one.  The second one did not have the squealing problem that the first one does, and sounds great.  I must either have a bad chip, a bad pot, or some other anomaly.  I just finished boxing this up today.  I am really impressed so far.

[amz-fx]

So, I built a second one of these, to see if I could figure out what the heck was wrong with the first one.  The second one did not have the squealing problem that the first one does, and sounds great.  I must either have a bad chip, a bad pot, or some other anomaly.  I just finished boxing this up today.  I am really impressed so far.

Great! I'm glad you got it working. Enjoy!

regards, Jack

[Giglawyer]

Here is a link to my build.

http://giglawyer.com/2014/07/11/amz-qd-compressor-2/

And here are links to a couple of pictures.