Friday, 29 January 2016

5-knob Compressor

Drew this one up some time ago and thought i'd post it up. It's basically Mark's layout for Keeley 4-knob style compressor with slight tweaks and more notably, an addition of mix/blend/ratio knob. As some of you already know, the basic CA3080 compressors like Ross, MXR and derivatives reverse the signal polarity and thus, the simple blend circuit additions won't work with it. So here's the Ross compressor with tons of usable mods on it. I've built a number of these already, so consider it verified.

2017/05/08 - One cap was reversed on the layout. Now fixed, but i had to redraw this completely due to lost source files. Anyway. Here's the "V2".


33 comments:

  1. Do you know if this is similar to the BYOC 5 knob?

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  2. Yes i do. No it's not. BYOC's take on parallel comp is closer to Ibanez CPL/CP10/CP5 compressor with added tone and blend controls than any of the ones listed here. Completely different VCA and thus, completely different circuit.
    +m

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  3. Nice! Do the transistors need to be matched?

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    Replies
    1. No, they do not. And any NPN will work just fine.
      +m

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  4. going on my list right after the engineers thumb . I love compressors !

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  5. Sorry but where's the COMP 1? and thank you !

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  6. Built, thank you for that post it works very well. I'm very happy of the mods. Thanks again.

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  7. Sorry for the newb question, but I'm super new to pedal building (and electronics, generally) and I have a question about the layout.

    What's the blue square just left of center? There are a few cuts, with a 2K mark and three blue dots. Sorry, just not familiar with this particular set of symbols.

    Thanks!

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  8. can I use this cOmpressor on my bass? .

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    Replies
    1. Yes. As you can use any compressor that is based on dyna or ross.
      +m

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    2. This comment has been removed by the author.

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    3. Finally getting around to building this.

      Is the 1u cap just below the 2k trimmer drawn backwards?

      Should the + side be connected to the Collector and the (-) side to ground?

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    4. True. Thanks for heads up. I'll fix the layout as soon as i'm back at my desk
      +m

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    5. Did the layout get updated for this cap orientation? I'm having a hard time debugging this one, it's my first compressor. I tried it both ways, but nothing. Does anyone have any voltages I can compare to? I tried tracing it but so far this one is pretty complicated.

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    6. Hi, doesnt look like the layout has been uodated, the 1u cap just below the trimmer needs to be flipped.

      Do you have an audio probe handy for troubleshooting?

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    7. Thanks, yes the layout hasn't been updated, the cap needs to be flipped. I found my problem, I had a small solder bridge. Working great now! Thanks for the response.

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    8. No, the cap isn't fixed. It's a long story, but last summer i lost all of my data due to currupted disk controller. Home and mirrored backup drives were both rendered unreadable. So i do not hold the source files anymore and to fix any of my layouts would mean to redraw them completely. I might do some of those at one point, but this hasn't been a high priority.
      +m

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    9. It is fixed now. As noted on the update.
      +m

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  9. What does the trimpot control?

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    Replies
    1. Noise balance between the inputs. Nothing to be conserned about when using this circuit with a guitar or a bass. You won't notice any difference turning it with guitar/bass signal levels.
      +m

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  10. I built a slightly modified version of this one(added the BYOC tone control).

    I'm getting an uneven compression, when I strum a chord and let it ring out, the volume seems to increase in waves.

    The controls all appear to be working, but the compression is not smooth.

    Would that indicate a bad CA3080?

    What else could cause this unevenness?

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    Replies
    1. I boxed it and swapped out Q5, the waviness seems to be gone now.

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  11. Thanks again mirosol!!!

    I've been playing this pedal all night through the headphone jack of my practice amp and wow! Really quiet and the blend control is definitely the money!

    There were times I literally wasn't sure the pedal was still working, until I turned it off!

    Couple observations/suggestions:
    1. Did I mention the Blend control is the money?
    2. There may be something to using matched sets for Q1,Q2 and Q3,Q4 as well as using higher gain transistors for the Q1 and Q5 buffers. I went with matched MPSA18 for Q1&2, matched 2n3904 for Q3&4 and 2n5089 for Q5 (Mark Hammer suggestions I think?) The pedal sounded cleaner and had more punch than the random set of 2n5088s I also tried. (It's possible I was fooled by the slight increase in volume the MPSA18s and 2n5089 seemed to provide, but it sounded better so I stuck with the matched sets)
    3. TL072 sounded better than the NE5532, I did not notice any improvement in noise levels with the 5532. The TL072 sounded a bit warmer to me.
    4. I added the BYOC 5 Knob Compressor tone control, highly recommended if/when using the neck humbucker. Country players will probably like it too.
    5. For me, the Attack control seems like it's going to be a set-and-forget control. I had converted the clip control to a trimmer to keep the pedal at 5-knobs. It might have been more useful to keep the clip control on the outside (especially if using with multiple instruments/pickup styles, Les Paul/Strat/Bass etc or using after a boost or dirt pedal) and change the Attack control to a on/off/on switch selecting 3 presets. 150k, shorted and something in between like 30k-40k giving the two extremes of the original 150k attack pot and something in between-to taste. (Another Mark Hammer suggestion referring to the original Ross design)

    I may just go with a 6 knob version on the next one :0)

    Finally, for everyone who has built the Keeley 4-knob and like it, you really ought to give this enhanced version a try.

    (I'll most likely be posting the converted layout I used with the added tone control in the Forum)

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  12. I'd like to give just the dry signal a boost so when the Compression control is at noon, both the dry and compressed signal levels are about the same at both extremes of the Ratio control.

    As it is now, the compressed signal is much louder than the dry signal with the Comp control at noon. Also, with the Ratio control full CCW and the Volume Control full up, the dry signal is just at unity, I'd like to give the dry signal a slight boost with those settings.

    To increase the Dry gain, Would it be better to lower the value of the 100k resistor feeding pin 2 of IC2 or increase the value of the 130k resistor?

    I'm guessing the latter to keep the input impedance of the inverting op amp the same at 100k.

    Thanks

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    Replies
    1. That should suffice. 220K would nearly double the clean level.
      +m

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  13. What's the chance of getting the schematic for this guy? I would like to create a pcb using the LM13700. I would really appreciate it.

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    Replies
    1. Zero. This being due to the fact that one doesn't exist. Take Ross, read up on Keeley mods and use the blend section from here:
      http://www.diystompboxes.com/smfforum/index.php?topic=40292.msg288800#msg288800

      If you fab them, i'd want a few :)

      (edit - posted a wrong link from my clipboard, sorry - now the link is what it was supposed to be)
      +m

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