SSM2166 compressor build

[askwho69]

If you're etching a board then SOIC is easy enough to deal with, just make sure you account for the "flipped" pin layout you get by soldering to the bottom (copper side) of the board. If you use a program like ExpressPCB then it will take that into account for you. Another option is to get a SOIC to DIP adapter board, but that's likely to cost more than just buying the DIP version from small bear
-Matt

PS. I'll be posting a revised version of the layout soon. I have run into some issues getting my initial board layout to fit cleanly inside a standard stompbox enclosure so I reduced the board footprint and simplified the connections.

ohh nice i'll wait for the layout! by the way what company will give free sample SOIC version? can please tell me? i'll order too

[jefe]

ohh nice i'll wait for the layout! by the way what company will give free sample SOIC version? can please tell me? i'll order too

The answer to your question is right here in this thread. 

[askwho69]

ohh ahahaha got the link!... wooh it said that analog.com doesnt offer free samples in our country! this is sad!      

[fpaul]

If I build this to use with a microphone, would it work better with or without the input buffer?

[armstrom]

The buffer shouldn't impact use with a mic one way or another. The buffer simply provides a high impedance input. The main thing to consider is if the circuit has enough gain for your mic. Also, if your mic has balanced output and requires phantom power, then you'll have to deal with those issues separately. For microphone use you may want to consider changing R4 to 10K (as indicated in the datasheet) to increase the front-end gain on the circuit. Also you could consider a larger pot for the gain control so you can make use of the full range available from the chip. A 25K pot for VR4 should do the trick. That will get you a max VCA gain of ~19dB.  I would leave out R9 as well  (just jumper it). All of these things is the schematic are meant to keep the gain under control for use with a guitar signal. Other than that the circuit is fine for mic use once you've addressed the issue of a balanced line receiver and phantom power. However, by the time you've done all that you might want to just ditch my PCB and integrate those components directly

[Govmnt_Lacky]

SOIC chip from Analog Devices...... Free 

14-pin SOIC to PDIP converter board..... Free 

Soldering the SOIC to the adapter board..... Challenging but done well 

Getting this all done WITHOUT paying $9 + shipping just for the PDIP chip......... Well, not PRICELESS but it saved me $12 

[armstrom]

did you complete your build? How do you like the effect? (I'm assuming you used my layout, any problems?).

I'm delaying releasing my new layout because I'm having some feedback problems at high gain and volume settings. I had no such problems with the version I've posted here so it should be safe to use. My attempts to simplify the offboard wiring seem to have had more reprocussions than I would have hoped for I think I'm going to go back to the drawing board and redesign the board with NO offboard components. This will not be ideal for DIY builders though since I'll be converting to the SMT version of the chip (I may still provide through-holes in case someone has the old DIP version) and use of the new board will require careful machining of the enclosure to ensure everything fits correctly.

I can share some tips on building/using the design I posted though.

1) Try a bigger cap for C7. Maybe even up to a 15uF. It will provide a more substantial difference between fast and slow modes. Or you can just omit the toggle switch all together and swap out the cap (C6) until you find one that you like best and just stick to it.

2) You can use a 100K linear pot for VR3 (compression adjustment) in order to extract even MORE compression from the pedal. I can't promise that you won't get feedback problems but it's worth a shot! a 100K pot will let you  get up to 15:1 compression vs. the 10:1 you get from a 50K pot (as called out in the PDF)

3) Think of the noise gate as a sustain control as well as a noise gate. As you turn that pot clockwise you're DECREASING the signal level at which the noise gate takes over and clamps down on the signal.

Here are some setup tips:
First, you most likely want to use the pedal as the first one in your signal chain. Obviously, some people will disagree with this and insist it should be later, but I believe it works best right after the guitar. YMMV though.

Next you need to adjust your limiter (the 50K trimpot VR1). The way the board is setup maximum limit voltage (no limiting) occurs when the trimpot is turned fully CCW. For most setups this will result in distortion with a guiar signal with any sort of compression or gain dialed in. The trick here is to crank up the gain and the compression while keeping the volume down to ensure you're not clipping any devices after the compressor, we just want to eliminate clipping coming from the SSM2166 itself. Now strum a chord using your hottest pickups with the guitar volume all the way up. Keep turning the trimpot CW until you no longer get signal clipping. You should still be able to get quite a bit of clean gain out of the pedal even with the limiter in place.

Finally, if you're trying to use the pedal to increase sustain (I suspect most of you are) then you need to adjust the noise gate. The noise gate (downward expansion) functionality ALWAYS "wins" the battle for control of the VCA gain.  Think of it this way, the reason the compressor gets you more sustain is because as your guitar signal decays over time the compressor is adding more and more gain trying to keep the signal level high (compressing your dynamic range). However, once you reach the threshold of the noise gate it takes over control of the VCA and quickly attenuates the signal. So the longer you can delay onset of the noise gate, the more "sustain" you will have.

Here's how I suggest setting the gate control. Set your volume, gain and compression where you want them, the settings are not terribly important. Next set your noise gate to about 8 or 9 o-clock. If you have the gate set fully CCW you will likely not get ANY signal through so there's no point in starting there.  Now you want to increase the noise gate pot in stages, letting a note ring/decay all the way until the noise gate kicks in after each adjustment. What you will hear is the noise floor come up as gain is increased due to compression then suddenly everything will go quiet. You want to keep increasing the noise gate control until you can get the longest sustain while still having an "acceptable" noise level just before the signal is cut (that's the subjective part). Humbuckers will let you increase the sustain even further because they have less innate hum (go figure!).

Finally, you can try one other trick with the compressor that you may or may not find useful. Use a big cap for C7 (as suggested above). Again set your volume gain and compression where ever you like them but this time start with your noise gate control FULLY CCW. Now, you shouldn't hear anything when you pick a note on the guitar.  again start increasing the noise gate slowly and incrementally. After each increase pick a note then mute the strings fully. You want to adjust the noise gate so that your initial pick attack is not heard through the amp but the rest of the decay of the note is. What you're doing here is taking advantage of the slower reaction time of the RMS level detector to "miss" the pick attack (noise gate is still clamping down on the signal). After the pick attack occurs the RMS level detector finally "wakes up" and lets the compressor start to increase gain. The net effect is kind of a cut-rate auto-swell or "bowing" effect. It's not terribly easy to dial in and you really have to be careful to mute the strings before each time you want the effect to be heard. I'm not sure how useful this "mode" of operation is (you won't get as much sustain), but maybe you guys can find a use for it

[Govmnt_Lacky]

Hey Matt,

Thanks for all of the information and suggestions. Sadly, I have only prepared the SOIC chip to fit into the DIP slot. I have not etched, drilled, or even populated the board yet. I have so many projects backed up that it is about #8 in the cue. I am looking forward to it though. I would really like a GOOD compressor that I can keep on the pedal board! 

[armstrom]

ok, my friend had a chance to record a sound clip of the latest incarnation of this pedal. Note: this version has a 100K pot for the compression control to extract the maximum amount of compression from the chip.

http://www.mr2-power.com/cramittest2.mp3

The guitar is a gibson SG running into the compressor with the compression and noise gate maxed out. This gives the most sustain possible at the expense of a higher noise floor (you'll notice both in the clip). The distortion pedal is a John Landgraff Dynamic Overdrive into a solid state fender princeton chorus.

Enjoy

[Maudibe]

 

If anyone in the UK is after this chip I have just a couple for sale. I am gutted that I cant find more of these in the pdip form...

Check it out at Doctor Tweek.

[auden100]

Finished up a perf layout for this. Haven't verified, but I think it's okay. Loosely based on your original layout. Should be able to get everything into a 125b.

Really looking forward to eventually giving this a shot. Your clips make it sound really nice.

[Mark Hammer]

The part you will appreciate most is the stuff you don't hear.  I fired mine up last night for the first time in a while, and the downward expander, to quote my old grad school office-mate from Milan who was describing his experience renting some time on a Grand Prix track in a formula 1 car, "Itsa soooo nice!".  Gone is all that hiss that people repeatedly complain about in their compressor.

I recommend having a choice of averaging cap values for different decay/gain-recovery times.

[Govmnt_Lacky]

I recommend having a choice of averaging cap values for different decay/gain-recovery times.

Mark... Are you referring to the caps off of Pin 8?

[Mark Hammer]

Yes, that very one.  Consider selecting between, say, 4u7, 10u and 22u. 

[armstrom]

I'm not sure if you guys caught it or not but I posted another sound clip in someone else's thread. Here's a link to that clip. Warning, it's ~2mb
http://www.mr2-power.com/sustaaaaaaaain.mp3
The first 30 seconds or so consists of a single note held with the help of the cram it.  The guitar is a fender strat with single coils.
-Matt