Friday, 18 January 2013

Bearhug FET Compressor

Jon Patton's Bearhug FET Compressor (Yeah! That's the same cool dude who demoed Valvewizard's Engineer's Thumb a while back!) As requested.

From Jon: The Bearhug is a (fairly) low-parts-count, quiet, tonally transparent compressor using only transistors. It can do subtle peak limiting or squishy sustaining, with a decent amount of boost (probably ~6-12db).

Notes & mods:
- The hold cap is the reversed 4.7uF. This sets the overall compression and decay. The 10K + 47K in parallel with the hold cap set the decay. Larger values may be used, but these were the most natural sounding overall.
- The High/Low switch is there for "more." A 100K instead of the 47K would provide a much more dramatic change.
- You can use substitute Schotkey, germanium, or other diode with forward voltage under ~.35v for the 1N60Ps.
- The best tone control for this circuit, if you want to add one, is Jack Orman's version 2 of Mark Hammer's SWTC.
- The 100pF cap is primarily to eliminate noise and can be adjusted to change the overall brightness.





Turned out pretty compact. I've been through it a few times, but you should still grab the schematic for reference from DIYSB...


42 comments:

  1. Nice! That was FAST! it will be a few days till I can slap this together as I am probably missing some of the parts needed. Very much looking forward to checking this out. I've been on the long search for the right compressor.

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  2. Replies
    1. Looks like it, here is a good BOM...
      https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Bear%20Hug%20BOM.pdf

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    2. Added notion about the switch...
      +m

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  3. Been waiting for this one to be designed for veroboard! Thanks!

    Questions, what does the double link signify? Link from a link from row 1 to row six as well as a link from row 6 to row 11?

    Thanks again!

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    Replies
    1. Hi. That means that two links are sharing one hole.
      +m

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  4. Oh, neat, I didn't know you did a layout of this one until someone told me they built it. Thanks! :)

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  5. It looks like this layout is missing a 10k resistor in parallel with SW1/SW2, right?

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  6. Dan, the 10K is in series with the switch. The 47K is in parallel with the switch (i.e., bypassed).

    However, the 47uF cap from Comp 1 & 2 to ground is backwards. Should be - to ground. I'll let you guys know if I see anything else.

    -Jon

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    Replies
    1. Yup. I see that now. For some reason, I saw "R10" as 10k on the schematic....

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    2. Thanks forr noticing.. I'll reverse it right away.
      +m

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  7. This one can be marked, finished the other day and works like a charm!

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  8. When i connect the 9V and ground wires to my power source, my power source seems to shut off and my amp starts rumbling. Any ideas?

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    Replies
    1. Definitely a short somewhere on the board. Knife the strip gaps and check everything visually - maybe with a magnifying glass.
      +m

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    2. could it be that my 9V and ground are connected together somewhere?

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    3. Doh! Had a micro solder bridge somewhere. Problem Resolved!

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  9. I seem to get clipping when i play hard, is that normal?

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    Replies
    1. Could it be the FETs causing clipping?

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    2. Possibly. Did you use a socket so you can swap it? All FETs seem to been not than consistent... Your symptoms point to that, especially now that Adam and Kinski built this successfully.
      +m

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    3. A bad solder joints on one of the capacitors was the problem. Resoldered, it sounds great!

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  10. This thing sounds great. i just built it. FINALLY got the parts order in that I needed. I've been looking for a good, clean, quiet, smooth compressor for a while now. I've build a ton, and this one is the best for sure. At least for my purposes.

    I might leave off the switch and keep hard-wired in the "high" position. We will see see...

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  11. I'm adding some recent changes to this design here. I don't know if Mirosol will see these, but these changes make it sound about twice as good. Briefly, these give a larger compression range (both more and less compression) and much, much more output.

    1. The 2.2K connected to the drain of Q1: Change this to 4.7K (or slightly higher. Target voltage on drain is 5V-5.5V).
    2. Remove the 1K in the bottom right.
    3. Use a 1KC for the comp pot. It'll be much easier to dial in.
    4. Use 1N4148 (or any other generic silicon) for D3&D4.
    5. The 1M in the lower right, connected to the gate of Q3: Make this 1K. This is a MAJOR change and you must change D3&D4 when doing this!
    6. The two resistors in the top right, 10K and 47K, set the decay. I prefer 22K and 100K for these now. It sounds much more natural.
    7. Finally, I prefer 47pF rather than 100pF for the bypass cap on Q1 for a little more sparkle.

    Here's a demo of version 2.0:
    http://www.youtube.com/watch?v=WPm8x4hEwZ4

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  12. Reporting from the battle field: I have just built version 2.0 with all values suggested above by Jon himself. Works and sounds excellent but:

    - the switch doesn't seem to do much - I'll continue debugging/experimenting
    - I used 12v Zener but I doubt it may have any effect on the sound.
    Bart

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  13. Ola sou brasileiro fiz o pedal e gostei so gostaria se poder mandar o esquema do pedal pra mim obrigado

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  14. Bart, the switch is pretty subtle but you can hear or 'feel' the difference in compression,especially at higher compression settings.

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  15. Hi Bill, I finally figured that. Once I tried the compressor at a bit higher than bedroom volume, the change was indeed noticable. Great compressor.

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  16. To anyone else who's built this... is this about the subtlest comp ever? I built it, tested it, and spent an hour trying to figure out what was wrong because I had output just fine, but no compression. Then after swinging the comp knob back and forth a couple dozen times I *think* I can hear a very slight difference between the two ends of the spectrum. Sound about right? If there's supposed to be some serious compression, I'm missing it completely, somehow.

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    Replies
    1. Try converting it to version 2.0 specs.

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    2. levis, thanks man. I must have seen the changes somewhere else because I'd done some of them, somehow... but I went through and did the rest, and now everything is perfect. It doesn't seem like those changes could have been such a big change, so maybe I had a solder bridge somewhere I accidentally got rid of.

      Great pedal, very versatile. Everything from a light comp, to a total clampdown (with the comp maxed and the More switch on).

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  17. I am getting a pronounced drop in high frequencies that I can't pinpoint, could it possibly be the input cap value that is cutting them out?

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    Replies
    1. No the input capacitor acts as a high pass filter so it won't affect high frequencies, and will only cut bass. Try removing the 100p cap and see if that helps, that'ss a low pass filter and so will be cutting some top end.

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  18. Going a little nuts here. I've got this wired up properly. Checked it a dozen times. And it's wired to the 3PDT properly. Somehow, the volume control is controlling the volume of my guitar when the pedal is on, and when the pedals is OFF! I don't know if I'm just not seeing the forest for the trees, but I can't find anything wrong. Any ideas on that one?

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    Replies
    1. Well I opened the pedal up and everything works as expected. Perhaps when the back of the pedal was on, something was touching that shouldn't have been. But I still don't understand the pedal being off and the volume control working... Goes against everything I thought I knew about true bypass... I'll put it back together very carefully.

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  19. I spotted something that is causing me great confusion with my limited knowledge. There appears to be some discrepancies with this board layout above and the schematic and perf board layout at DIYSB. In the circuit above, and in the schematic at DIYSB, the Comp pot has no direct connection to ground, but in the other schematic that is linked from the DIYSB page and on the perf board layout it does. Also, the perf board layout at DIYSB and the linked schematic show the ground connection to the Comp pot on different pins, the perf board layout shows it to pin 3, the linked schematic shows it to pins 1&2.

    I am very keen to build this with all the mods added so would like to know which circuit is correct, please help.

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  20. Something else I forgot to ask, where do you connect the LED? It isn't shown in any of the circuits

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    Replies
    1. Didn't know that all my questions have answers in the thread at DIYSB, so having read through it I can now see that the discrepancies are all due to mods being made. I also figured that the connections to the Comp pot can be reversed without any effect as it will still reduce the resistance to ground when turned clockwise no matter which way around pins 1&2 and pin 3 are connected to the circuit. I also figured that by using a 3PDT foot switch I can achieve true bypass and use one pole to power the board and use a 4.7K resistor to power an LED.

      So, I have solved all my queries, but please correct me if I have anything wrong. Have not messed with any electronics for about 20 years, so this is a good refresher course.

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  21. Does someone know if mods like threshold, ratio or attack could be added? The switch and associated restistors could be replaced with a decay control from what I discovered so far.

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  22. Hey all, having a bit of trouble with this build. I've built it as per the schematic and checked it a bunch of times over, I'm not getting any signal whatsoever when plugged in. Oddly enough, when I remove the power jack, I get a really strange rising pitch (it sounds like Sonic the Hedgehog jumping, if that rings any bells!). I assumed it was a capacitor discharging, but all of the polarised ones are oriented correctly and there are no shorts. It's the original schematic posted above, so I haven't implemented the mods that Jon suggested yet, but I should be getting something. Going to go through it with a probe and see where the signal is dying this evening, but I thought I'd post up in case any of the more experienced of you were able to diagnose it straight off, or suggest something specific to look for?

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    1. I should add, the 1 uF capacitor below the 10 uF electrolytic on the left hand side is a tantalum (oriented in the same direction as the electrolytic and D1) as it's all I had to hand, and D3 & D4 are 1N34As as I didn't have the 1N60P. Could this be it?

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    2. You should definitely implement the mods suggested by Jon. They will make it more "compy". Not sure about your other weird issues, probably just a stuff up somewhere!

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