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New pedal project

Started by phatt, December 28, 2015, 03:24:11 AM

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Well after a very long and interesting journey into compressors and ODrive setups I'm having a ton of fun with this one. I've never liked compressor pedals as they sound wrong to my ears.
Unlike a lot of big name guitar compressor pedals this one adds the missing sizzle. 8)

Bear in mind I built this for a solid state amplifier which does not have the dedicated guitar circuitry so may not work so well in front of some guitar amplifiers, all the mojo is implemented in the pre stages and the power amplifier section is essentially flat and clean. 
I have found that a lot of dirt pedal circuits no matter how good often don't work so well when used in front of many ss guitar amplifiers.

Older valve Amplifiers always had a fair amount of distortion *even when played clean* there was always a little, shall I say Hair on the peaks of the signal this small distortion added a distinct sizzle to notes played giving the instrument a more dynamic feel.
When cranked up higher or boosted with a pedal that clipping is accentuated, helped along by some supply sag and other quirks or short comings of early Valve amp design. So they effectively had a built in compressor with no bypass.

Most SS amps don't have that luxury and one is forced to use compressors and all sorts of gizmos to replicate that magical feel and obviously some work better than others.

This circuit uses an optical compressor > a simple OD > cab sim.

The first A/B test is just some plane chords with no efx.
Signal path is; PhAbbtone > compressor > *OD OFF* > Cab sim > out to Laney Amp.
Mic at 600mm (2 foot) straight to computa no EQ or tone tweaks.
(I note some bass loss on my small desktop speakers.)

When I engage the compressor you get compression along with just a bit of sizzle.
engaging the OD simply increases the sensitivity but signal is still fairly clean so you still have plenty of scope for OD pedals for more serious lead work.

The second clip I whipped up on the fly;
Comp on, OD on for a little extra edge, Cab on, playing over a simple loop pedal. Engaging an OS2 for some solo. (using the Ditto Looper borrowed from a good mate). <3)

This circuit will work on 9Volts but performance won't be as good. :-\

Played on Sunday at the local open mic jam and everything went well I had no trouble with control over clean and dirt levels. The compressor really helps keep the SPL within a civilized range when jumping on dirt pedals.



Very nice!  <3) Me likey!

I may have to build this one. What op-amps did you use?

I have built a few compressor pedals and the one I like the most "so-far" is the MoRC from GuitarPCB.


Click on the Build Document in the above link to see the schem.
Oh ya, also click on the MoRC Compressor Demo just under the video.

It uses the now obsolete CA3080 (*watch out for fake china ebay chips*).
I have a stash of genuine CA3080's I got from a guy in Japan.

MoRC means Modified Ross Compressor, and it is a very good sounding comp.
"Can't tell when its on, Miss it when its gone" tho you can crank it and get some very squishy sounds
along with a bit of breathing/pumping, but even that is sometimes hard to tell.
If it ain't broke I'll fix it until it is.


Glad to hear you like it. :tu:
2x TL074 1x LF353.
I think most of the obvious chips will work much the same.

Just remember you will need some kind of tone control circuit in front of this otherwise it will be dark, on the other hand if your amp rig is already bright then it may work fine.

I've messed around with some of the circuits that use the ca3080 chip but never had much luck. I've had a Boss CS2, CS3, and a Marshall Ed all on my bench at the same time for comparison and Ed and CS2 are noise prone while the CS3 is very quite.

CS2 and Ed use ca3080 while CS3 uses THAT chip.

I also have a Ulite optical compressor which is also dead quite but pumps like mad at any decent setting. I ended up wedging a shim of plain paper between the Led and Photo resistor which helped a lot but still none of the compressor circuits I've built/owned/borrowed for testing have the Rattle on the edge I mentioned.

The circuit by Mictester is really simple to build and requires no great skill to get working. I've only added an extra stage to invert the signal so it's in phase when switching to bypass, if that is not an issue for you then delete it as it's not needed.

Original post by Mic here; http://www.freestompboxes.org/viewtopic.php?f=13&t=8581

The front end on my circuit has a buffer which is also not really that important but in my experience it's worth the extra fuss.


Thanks for the link and tips.  :)

I kinda figured the TL074 and others of that ilk would be ok.

Interesting about the comps, I had a CS3 at one time but sold it. As I recall I never was satisfied with it.

The Mictester looks great and simple and once I clear some other projects, plan on building a stand alone version too.

I really can't say enough good about the MoRC comp.
Decently quiet and as mentioned, pretty much "invisible" until you turn it off, or unless you crank the comp control.

I also built the GuitarPCB "Squishy Octopus" which is a 280 type optical comp but it really darkens my tone too much.
That might be my rig but others have had the same issue. Tweaking cap values helped some... but it just lost too much sparkle.
IMHO it's nowhere near as transparent as the MoRC.

Even tho you haven't had much luck with them, if you have any spare CA3080 chips I highly recommend trying the MoRC.
The board is cheap enough.  8)
It does require paying attention to the build document and adjusting the trimmer *precisely* but once set its good.

If it ain't broke I'll fix it until it is.


Well if I do happen to acquire another ca3080 I'll have another try,, meantime if you do build  mictester's compressor circuit I will be interested to hear how it compares to others you have built.

Only hickup might be the LDR section as you need normal green LEDS, not the high intensity led's. When the unit is working the led's don't glow at full brightness which is what you want.

Also note LDR's are not all the same,, different light/dark resistances and also the speed at which they change resistance can alter the outcome.

This is the unit I used;
Rise /decay time is around 40`50mS.

I tried several different LDR types and they all work but this one seemed to produce they best result.
The Leds are hard up against the LDR face and then slipped into a sleeve of black heat shrink.

My led's are the 5mm transparent green type but the frosted ones might be just as good.

In case you miss this subtle but very important point; 8)
Unlike other compressors as you turn up the guitar volume or even stomping on a clean booster the compressor Distorts more. <3)
That may not seem like a big deal but it's exactly what happens with some old classic Valve rigs.
All the other compressor units I've tried don't react that way,, they stay clean.  >:(
For a studio, clean all the way up is likely a big asset but for classic rock guitar it's dry and lifeless. :grr

Cheers, Phil.