Anyone built the "Really Cheap Compressor"? How is it doing?

[Ben Lyman]

I've been playing around for awhile now with the mods and stuff but one quirk I am getting stock or otherwise, I feel like there is not enough compression on a certain area of notes on my guitar. Specifically, between the 3rd and 7th frets of the low E and A strings, so low G up to second E. It creates a strange unevenness when playing single note runs in that zone. Lots of nice squish until that zone and then volume boost on those notes with less comp.
Anybody know why that might be?

[Groovenut]

I've been playing around for awhile now with the mods and stuff but one quirk I am getting stock or otherwise, I feel like there is not enough compression on a certain area of notes on my guitar. Specifically, between the 3rd and 7th frets of the low E and A strings, so low G up to second E. It creates a strange unevenness when playing single note runs in that zone. Lots of nice squish until that zone and then volume boost on those notes with less comp.
Anybody know why that might be?

If it were all the notes on the low E up to the 7th, I would say the cap feeding the second opamp needed to be bigger. However, if it's between the 3rd and 7th on the low E, I haven't a clue what might cause that within this compressor circuit. It sounds as if your guitar has a low output range in that area and it's not triggering the compressor the same way the rest of the instrument is. That's a head scratcher.....

[Ben Lyman]

Okay, thanks. I might be wrong about the exact notes, I will try to examine it closer to see if those last few low notes are behaving the same way.
It might be my guitar, I put the pickups in myself a long time ago and maybe I tried to lower the bass side to keep a sort of trebley sound, I dunno. They are DiMarzio Area pickups and I seem to recall they had a higher output and more bass than the original Van Zandt and Seymour Duncan single coils.

[PRR]

> between the 3rd and 7th frets of the low E and A strings

And the open strings?

(As Lawrence says) The 1uFd driving the LEDs and 1K looks skimpy. Assuming this network bottoms out at 1K, 1uFd into it is blocking bass below 170Hz. Which is essentially the bottom octave of guitar. I will not be shocked if this droop (failure to compress) does not become obvious for another half-octave, the range you are pointing to.

Tack 10uFd across the 1uFd and take a run to the bottom. Is that different?

[Ben Lyman]

Yes, thanks, upon further noodling and wanking, it has come to my attention that the loss of compression is occurring from the 7th fret down to the open low E & A strings. I will see what I can do about it with that 10uF tomorrow at some point.

Other than that, this comp is very nice, sounds great with my Electra distortion, the bright mod is great for clean and I have some other mods of my own going on right now on the BB. Instead of a 470pF across the 2k2 input r, I have a A100k pot in series with a 1nF for a variable cap. I'm not even sure if I've got it hooked up right and it is probably changing a lot of the intended plan but it's sounding really good. I don't really want more knobs but an internal tone trimmer might be useful.

For playing with distortion I think the 470pF mod needs a switch because, while brightness is good for jangly cleans and hot chicken pickin', it doesn't work so much with distortion if you want to shake the walls.

[Ben Lyman]

10uF across 1uF did the trick. 100x better, thanks.
So, this makes 11uF total and I can omit the 1uF as long as it sounds fine without it, right?
I'm not sure if you suggested "tack across" for a specific reason. Its still on the BB.

[PRR]

> if you suggested "tack across" for a specific reason

So if I was totally wrong the mod could be UN-done without more surgery.

Now that we have a clue, you can salvage the 1uFd and put 10uFd in right.

> on the BB.

Ah, missed that, no heavy work to make the change.

[Ben Lyman]

Okay, thanks again PRR. One more thing I noticed, as the notes decay there is a very quiet fuzzy crackle, almost like static or a wax paper and comb kazoo. I was wondering if it might be the LEDs "consuction noise" that groovenut mentioned, so I tried a lot of different caps across them but the kazoo persists no matter what. It only seems to happen when the sustain control is from 2:00 (60%ish) up to full CCW. I have bypassed the effect to test my own amp/guitar for this noise but it is definitely only from the comp

[PRR]

Power rail bypass as CLOSE to the chip and LED return as you can manage.

The LED driver must distort in heavy action. Large spikes in the power supply. These could be sneaking back via power rail or round-the-BB ground path.

Or may be something else.....

[Ben Lyman]

Okay thanks PRR. I've tried to make a new schematic in a way that I can more easily wrap my brain around, including part numbers. I hope it's all accurate, it should be almost the same as the original version, except I've included all cozy builder's mods and PRR's 10uF for my C9.
This is what's on the BB now, is "power rail bypass" my C1?
Is this an okay way to go with the bright switch or should I worry about it popping?

Edit: correct 220k input r, correct sus and lvl pot values

[Groovenut]

Okay thanks PRR. I've tried to make a new schematic in a way that I can more easily wrap my brain around, including part numbers. I hope it's all accurate, it should be almost the same as the original version, except I've included all cozy builder's mods and PRR's 10uF for my C9.
This is what's on the BB now, is "power rail bypass" my C1?
Is this an okay way to go with the bright switch or should I worry about it popping?

Power rail bypass will be C2 actually and it's physical location needs to be as close to the power pin of the opamp as possible for best results. you could do 100n as well there.

The inverting input of the opamp is a virtual ground. I dont think the bright switch will pop, but all thinkgs being what they are, it may 

For distortion/fizz in this circuit it's usually one of two things. LED conduction noise, in  which case placing a 10n cap in parallel with the diodes usually fixes this, or rail clipping the first opamp because of too much gain/high LDR dark spec, in which case you could try lowering the 2M2 resistor to 1M and see if it results in the changes you're after.

[Kipper4]

Have you tried a bigger C7 Ben ?
While its on the breadboard I'd try anything upto 470pf just to see if it improves the crackle.
It might work !!!!!!!

[Cozybuilder]

Just curious if you meant to replace R6 with 2K2 rather than 220K? I didn't see anything written on this (maybe I just missed it?)

[Ben Lyman]

@kipper4, okay, will do, I haven't had a chance to really delve deep into the mystery of the kazoo player. It persisted when I moved one leg of C2 right onto IC+ (pin8) but I *THINK* it went away when I moved the other leg of C2 right onto IC- (pin5). I'll report back later after I've had some more time with it.

@cozybuilder, good catch, my bad  thanks. I will update the schematic

[PRR]

> C2 right onto IC-

Yeah, like that.

[maiko]

hellow and good day sirs

ive built this but i notice my led barely lit up.   i cupped my hand over it and it did lit up.   im thinking maybe r8 1k might be too high a value.  and considering 470ohms.    i havenot actually tried it yet with a guitar.  Cause i populated it at the office and did not have a guitar here.  but signal seems to be getting through.

Also i notice alot omiting c1 will try that if its too dark.

[maiko]

swapped the 1k for a 470 works great for me.

I played with it quite a bit.  with the circuit on my bench i noticed that bypass was louder than with the effect.

as i strum a chord or hit a note and then i tried to cup my hand over the ldr and led.  it would get louder if i put totaly coverd it it would raise the volume so much it would break.  This as sustain on my guitar was dying out.  So i know its work and had fun with it 

i used aluminum tape.  the kind used for refrigeration.  to block out ambient light between the ldr and led and wow what a great sounding compressor.

i think 1k resistor needs to be a 1k trimmer. so you can adjust it depending on the led your using.   Initially i had typical red opaque led there then green and finally settle on yellow as it was brighter to me.     

Really happy with the compressor.   

[Nick C.]

I've been playing with a moded version of this, anyone know how an attack control can be added? Appears to be tied into the "sustain" amp and the led+ldr type (threshold?), but I'm trying to figure out how to impliment a seperate controlOr is it not possible with an optical?

[PRR]

> Or is it not possible with an optical?

It is incredibly difficult. To be simple, change the LDR, some are faster than others. This won't be an on-stage change because every LDR is different in other ways. To be complicated, add rectifier and DC filter, plus NFB around LDR...... and now you exceed the complexity of simple non-LDR limiters, and should go with one of them.

[Nick C.]

> To be complicated, add rectifier and DC filter, plus NFB around LDR

Is that what the Flatline does? I was hoping for a simple (cap-resistor) solution. Well, I like the simplicity of this one and it works well enough. I'll find a led/ldr pair that works and go for it.