"The Compulator was born after I solved an engineering problem of biasing an optical unit with only a single 9V battery. I had always loved the sound of optical compressors and designed and manufactured tube units in the pro audio market for a number of years. I wanted to make a pedal, but it took years to come up with a method to do it the right way. The result is the Compulator, winner of Guitar Player Editor's Pick Award and the only compressor that does not suck away your tone." - James
The sound of classic studio optical compression of the 60's and 70's at your feet! The first compressor pedal not to suck the life out of your tone.
Operation is fairly straightforward. There are two inputs on the front side of the unit: a 1/4" input jack on the right and a 1/4" output jack on the left with a battery-ground switch on the input jack.
There are two controls on the unit: compress and volume, plus a foot switch to bypass the effect, and an LED to indicate effect operation. On the side there is a trim pot to set the overall gain of the unit.
Compress affects the amount of gain reduction (compression) of the input signal. Turning this clock wise will give you up to 30dB of gain reduction (depending on input gain). Please note that the Compulators max gain is 26dB (see Trim Pot) so in some circumstances if your instrument is very hot you could achieve less than unity gain if you turn up the compress knob too much.
Volume increases and decreases the output volume of the Compulator. Use this for level matching between the effected and unaffected signal.
Trim pot sets the gain of the compressor's pre-amplifier. If distortion occurs turn this down until the signal is clean. The unit is set at the factory at 20dB of gain which is perfect for most instruments. If you have weaker pickups or want to push the envelope turn it up to its max gain 26dB.
The sound of classic studio optical compression of the 60's and 70's at your feet! The first compressor pedal not to suck the life out of your tone.
Operation is fairly straightforward. There are two inputs on the front side of the unit: a 1/4" input jack on the right and a 1/4" output jack on the left with a battery-ground switch on the input jack.
There are two controls on the unit: compress and volume, plus a foot switch to bypass the effect, and an LED to indicate effect operation. On the side there is a trim pot to set the overall gain of the unit.
Compress affects the amount of gain reduction (compression) of the input signal. Turning this clock wise will give you up to 30dB of gain reduction (depending on input gain). Please note that the Compulators max gain is 26dB (see Trim Pot) so in some circumstances if your instrument is very hot you could achieve less than unity gain if you turn up the compress knob too much.
Volume increases and decreases the output volume of the Compulator. Use this for level matching between the effected and unaffected signal.
Trim pot sets the gain of the compressor's pre-amplifier. If distortion occurs turn this down until the signal is clean. The unit is set at the factory at 20dB of gain which is perfect for most instruments. If you have weaker pickups or want to push the envelope turn it up to its max gain 26dB.
Update: There was a missing cut between the top of the 619R and the 10K, so if you've been having trouble with this layout then give that a try. Layout updated below.
Just finished this for a friend. I don't have much compression experience, is there supposed to be a great deal of volume loss? I'm testing with a guitar equipped with a DiMarzio Super Distortion.
ReplyDeleteI'm not aware of a problem with volume loss. Are you getting any compression? And can't you reach unity even with the volume pot on maximum?
DeleteIf I keep the compression knob below 50% I can get unity gain with the volume near max, but if I go over 50% on the compression knob, I can effectively get almost zero output. This can be adjusted small amounts with the internal trim pot, but not a great deal. I'll study it some more, there must be an issue with my build.
ReplyDeleteI'll check over the layout to double check everything, but if you could upload a high res front and back pic and post the links then I'll see if anything else stands out.
DeleteThe bottom lead of the 4K7 in between the two 47Ks is going to the wrong row. Drop it by one row (it should be on the 2nd from bottom row) and see what happens. I also noticed a couple of the links were in different position when comparing the layout to the bare board, but that didn't matter because the same connections were being made. Layout above has been corrected.
DeleteCaught that, but I figured out the biggest issue on my end was using a 1nF cap in place of the 1uF. Doh.
DeleteDoes it work now then?
DeleteIt does, but don't take that as a verification. Sorry to say I took the schematic plus your layout and worked up my own layout, so mine does not match yours. I don't mind standup resistors much, so I compressed everything a bit to utilize a smaller board.
ReplyDeleteBTW, thanks for all the work you do with this blog. It's appreciated by way more people than say so, I'd venture. If I had one suggestion it would be to post the schematics for the pedals you cover as well as the vero, but it'd merely be a convenience and isn't strictly necessary. Cheers!
ReplyDeleteI would always post the schematics because it could potentially save me a lot of time, but I decided it was a bad idea simply because a lot of the schematics I use have notices refusing permission to repost, so I'd end up chasing around trying to get permission off the author. I could redo the schematics but that would mean each layout would probably take me 3 times longer to do and it gives another potential source of error going from schematic > schematic > layout.
DeleteIn the end I decided I'd get more layouts done by excluding them, especially as most people know that I get most of my material from Freestompboxes.
Logical and appropriate. Hope you're finding some time to build a few of these cool pedals now that you're bench is up and running. Happy soldering!
DeleteI really dont know much about vactrols. I just built the flatline and it's not working, no matter how many times I check it-thinking my vactrol is not working. I'm a huge compressor fan and wanted to build this anyways- I have a vtl5c9- do you know if that would work?
ReplyDeleteThe VTL5C9 has a much bigger off resistance than a VTL5C10 (50M instead of 400K), so I really don't know. It's just a case of use sockets and try it and see.
DeleteI've built this and i'm getting a strange response. When the compression knob is fully CCW It has a very quiet, slightly distorted sound. This gets every so slightly louder as the compression knob is turned CW until about 80-85% where the guitar signal comes through perfectly, with some compression. The volume knob works fine regardless of where the compression knob is. Any ideas?
ReplyDeleteAlso I've connected Main LED + and GR LED+ to the + LED wire and the GR LED - to the same spot on the 3pdt switch as the - LED wire. Is that correct?
The cathode of the Gain Reduction LED needs to be connected to the "GR LED-" point on the board. That would definitely cause problems because that connection will be grounding parts of the circuit which shouldn't be grounded.
DeleteSo there should be two LEDs? the indicator LED and another one?
DeleteAlso i have a green LED wired into a lunar module i built from here that lights up but it's really dim. Sorry for loads of questions im really new to this.
Thanks
The main LED comes on when the effect is on and is switch through a 3PDT (as you usually do with the main LED). The second LED is a gain reduction LED which should be connected directly to the points shown on the board, but you don't have to use if you don't want to. If you prefer to omit it The GR LED+ and GR LED- shown on the board should be left unconnected
DeleteI removed the gain reduction LED. I'm getting hiss along with a really faint guitar signal through the majority of the compression pot except between 80-85% which is clean and clear.
DeleteI've done everything in the fault finder guide.
I've been tweaking a bit, changing over IC chips (i got a few lf353n) and i've found that two yielded no sound at all. The 3rd chip gives sound throughout the compression pot but the first two thirds are distorted.
ReplyDeleteCould a bad IC cause this problem?
I'll debug some more in the morning. Almost works right.
ReplyDelete+m
No. I played around with this for quite some time. I noticed couple of minor errors, that i thought could contribute to the oddish behaviour..
DeleteI've compared the layout to schem from Briggs' blog, and noticed that upper lead of 4K7 is connected to 9V row. That should be one row lower - to ground. Other thing is with 470R and the trimpot. According to the schem, 470 should go to "lug" 1 or three of the pot, while other two would create voltage divider from ½ voltage row. In the current version of the layout it's just acting as a rheostat between 470R and comp 3 (which should be +½V).
I fixed those to match the schem, but to no avail.
Last 5% of the comp pot gives out ground noise and kills the signal and volume needs to be at 95% to get unity.
It could be that i've damaged some of the components while i had 9V where ground should have been... And did i socket the VTL5C10? Of course not...
Mark, could you check those areas again? Just to be certain..
+m
Cheers for the heads up mate, I'll go over it
DeleteYou're right about the 4K7 don't know how I managed that. The trimmer is right though, whether the centre lug is linked to the unused outer lug or not, it's still just acting as a simple variable resistor, and the row the upper trimmer lug is on is the VCC/2 row (which is why Comp 3 attaches to it). I did this from the scheme by Max Greco which shows the trimmer with just the two connections, but they're still essentially the same.
DeleteYou're a brave man soldering in a Vactrol, I refuse to solder anything that costs me more than £1 :o)
Sometimes overconfidence isn't exactly a virtue... :)
DeleteI guess i need to rebuild it. There could be some damage somewhere from the 9V at the 4K7. I'll do it soonish. I have something else at the crosshair for tonight...
+m
I've tried troubleshooting this one again. I realised i'd put a 470k where the 4k7 should be. I put a 4k7 in along with the relevant position changes and, the volume pot now works as expected. I can get a volume boost with the comp pot in any position.
ReplyDeleteProblem is now there is loads of distortion regardless of where the comp or volume pot it. If i pick really lightly it goes away, but a full strum and it's there. Adjusting the input gain resistance doesnt seem to make a difference.
Any ideas?
by the way, you can hear that the guitar signal is being compressed and that changes based on where the comp pot is, as expected.
DeleteHey man, before complaining to you about my electronics issues, I want to start out by thanking you for all you contribute to the community. I've used a few of your vero layouts recently with great success (The Woolly Mammoth, Super Duper 2 In 1, and SHO layouts all worked fantastically)
ReplyDeleteI'm having issues with the compulator for some reason. For starters, the gain reduction LED is responding in the opposite manner that one would expect. When the compression knob is all the way down, the LED stays lit up. As soon as you turn it up, the LED turns off and doesn't blink any more.
Secondly, the compression knob seems scratchy; Not in the sense of a bad pot, but moreso the way the SHO knob crackles. After about 1 or 2:00, it starts to break up and sound more like a fuzz, and just after that the signal is out entirely. The counter to this is that at around 12:00, the compression is pretty ideal and responds fantastically, so really one would be inclined to just set it there and leave it, but it still irks me a bit.
Anyhow, great work, and let me know if you can think of what the issues might be.
I have nothing to add. Some of your symptoms are close to the ones i had when i was battling with this.
DeleteThere are at least 4 people have tried to build this to no avail. The layout seems to be correct to the schematic, and Lowbrow made his own, working layout from the same schem..
Makes me wonder if this one should be redone from scratch. Maybe with quad opamp?
For TheMorphineSea, i would recommend building dyna or ross comp until this one gets verified...
+m
Yup! Works! Tag it!
DeleteThat missing cut was the cause.
There's one slight quirk though. Controls are not working as the demo with log taper pots. Linear tapers should work much better - haven't swapped them myself yet...
Works and sounds as squishy as it should. Now i need to play with this and my Dyna clone as comparison - I've grown to love it over the last month or so, so decision of replacing it can't be done light hearted.
+m
Excellent cheers matey.
DeleteSo when I originally built this I felt like it was super duper transparent with tons of sustain and no pumping. Really nice. Now that I've boxed it up its got a TON of squish and it has a ton of sustain but it 'pumps' pretty obviously. Could I have damaged something (like a burnt resistor or cap from reflowing solder and replacing wires for the box) that ruined the transparency? It has a lot of squish even with the compression knob set pretty low.
ReplyDeletealso, the compression knob seems to be backwards. clockwise is less compression and more volume. I checked my wiring of the pots and it looked correct- is this how the pedal is supposed to function?
And one more thing, it feels like the pot tapers are not very smooth. has anyone tried linear yet? I know miro mentioned it above, just wondering if it has been verified that linear taper will improve the circuit?
Sorry for all my super long posts- I really appreciate any help I can get here! Thanks so much!
Hello, can i use a VTL5C3/2 ?
ReplyDeleteI don't think that'll work.. It has dark resistance of 10M, while the VTL5C10 has 400K. Plus it has double LDRs in it, so you would have to sacrifice the other LDR altogether.
Delete+m
What is the pinout for the vactrol? Is #1 the LED+ on the Vac?
ReplyDeleteAlso is there a recommendation for the Gain Reduction LED?
This gives the info:
Deletehttp://www.uk-electronic.de/PDF/vtl5c9_c10.pdf
For GR LED just use any LED, not super bright though
Strange I have the comp pot wired correctly but it almost seems reversed. but really low volume/squish ccw. Louder less obvious squish CW. Only able to get unity at full volume maybe a little less than unity. The trimmer doesn't appear to do anything. It's a25 turn from tayda but it just keeps spinning and I hear no audible difference
DeleteI'm going to try replacing the trim and hope for the best
DeleteMiro, did you notice any obvious differences with the trimmer?
DeleteCan't remember. I recall testing it back when i built it, but i've scrapped the board since..
Delete+m
Hmm according to the post just above mine from splashsplish the Comp knob also seems to function backwards for them as well.
DeleteIt has sounds like the same issue with their build, now that I'm not posting on my phone I can describe it a bit more clearly.
The volume knob works like a charm.
The compression knob however when turned CCW decreases volume greatly but also increases the squish. With the Comp knob FULL CCW and the volume full CW it's under unity gain but definitely and intense squish.
As you turn the comp knob to the right the squish becomes more subtle and the volume increases. I'm 100% confident that the pot is wired as per the layout so it definitely sounds backwards.
Does anyone have any ideas on why the extreme volume loss?
Update:
DeleteI replaced the trimmer turns out it was defective.
I also swapped the comp knob 1 and 3, pretty certain those are backwards on the layout.
it's better now, still less than unity at max comp and volume but rolling the comp knob down slightly gets it there.
I got this one working and it sounds great. Reverse 1 and 3 on the Compression pot. This will probably become my main compressor to replace Dyna Comp, Ross, Orange Squeezer.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteGuys, could this thing be used for bass guitar?
ReplyDeleteOr would you advise to change a few part values for doing so? If so, which parts and values would that be?
Thanks a lot!
Hey guys, decided to pick this one up and give it another go. I cut the new trace and moved the 4k7 on the left side to it's proper location. Seems like it's working now, but the the GR LED stays on now if I pass about 7:00 with it. I get the impression it's supposed to blink when the compressor is working, but no joy. I am admittedly using a rather bright white LED. Do you think that's the source of the problem?
ReplyDeleteMmmm, silonex nsl32 works similar to vtl5c10? 500 vs 400
ReplyDeleteso the compress control on this works by gain reduction. When I turn the knob clockwise I get more volume (which is how most other comrpessors I've used work), but it sounds like i'm getting less compression (this is pretty subtle sometimes, so its hard to tell)- Shouldnt I be getting less volume when I turn the compress control clockwise? Ive just checked my wiring and I definitely have the pot wired correctly
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteI also confirm the inversion of comp 1 and 3.
ReplyDeleteI have the same squish as Nicholas.
I tried to change the trimmer, the GR led, but this little fuzzy noise stays, especially when the compress knob is CW.
Notice that this squish appears with my Les Paul but not with my Strat....
Can anyone understand?
thx
I've had effects in the past that were perfect with a strat but clipped easily with my Les Paul, the Jacques Meistersinger being a prime example (although a different type of effect of course). Some effects are fine tuned to a single coil output, and when that is the case it can cause issues with humbuckers or high output singles which may be the case here.
DeleteI'd suggest looking through some of the threads on FSB about it. There were a few people who had problems with this clipping.
This comment has been removed by the author.
DeleteI build this last wekend and it didn`t work right until I put in the VTL5C10 and 2 LF353 (which I didn`t have at hand), so....
ReplyDeleteWorks great, but I'm finding the gain reduction led very faint unless the trim pot is cranked to a high level where distortion sets in and the amount of compression is severe. Currently using a 3mm red, tried a blue which was useless, any suggestions or resistor swaps? Thanks!
ReplyDeleteHello fellow diyers! Anybody knows how many mA this guy needs?
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ReplyDeleteThis comment has been removed by the author.
ReplyDeleteHey all.
ReplyDeleteAnyone familiar with this build know what resistor or combo there of responsible for "Attack"? and what the hell, "Decay" too. :)
Thanks in advance!
I would really like to make one of these but it seems the world's supply of VTL5c10 (and most Vactrol optocouplers) has dried up. Does anyone have a source tha may have a couple of these left or has anyone been able to successfully roll their own suitable alternative? I would be happy to try making my own if anyone has suggestions on which LED/LDR combo could reproduce similar performance.
ReplyDeleteI have 2 would you like one
Delete