Garbage Compactor - Super simple compressor circuit

[Perrow]

This circuit relies quite heavily on deadastronauts "sound to light" layout, actually just added an ldr (and depending on leds used, a diode). It's the simplest such circuit I've seen and my own attempts failed miserably.




Depending on the leds used the diode could be excluded and replaced with a jumper. When I used regular leds, ~1.8V, it made the sound to light work much better. When I changed the led facing the LDR to a brighter, 2.7V, it wasn't needed. As the ldr reduces the in signal when the leds light up, there is little risk of burning any leds and thus no resistor should be needed.

The rightmost led should be facing the ldr. In and out are the same, this circuit essentially just bleeds the signal to ground. There's quite some signal loss, so you might want to add a booster before the out jack, or at least after this.

The gain pot (should be 1k, maybe 5k) changes the amount of sustain as well as the attack.

I've only tested this with a Ruby amp (loaned my Orange to my brother) so I don't really know how good it sounds, but it does sound quite nice as far as I can tell, and it's not that difficult for anyone interested to breadboard.

For an even simpler circuit, just jumper pin 1 and 8.

[Gurner]

It seems you are using an LDR as a variable resistance to ground on the signal input of the LM386?

In isolation (ie as per your diagram), that particular configuration might work (on account there's likely to be some 'in series' resistance after the pickup's output prior to hitting this circuit), but what you really need here (for maximum effect) is a voltage divider ...with the LDR forming part of a resistor divider chain (I'm assuming you got results with the ruby due to some resistance being in series with the LDR)

An LDR working on its own, affects the signal current not the voltage (think about it, if your signal is 500mV peak to peak & the LDR is 500k, then 500mV gets dropped across the 500k LDR. If the LDR now changes resistance to 10k (due to changes in light shining on it), then the same 500mV gets dropped across the LDR's 10k...the signal voltage has not changed...but the current has)....but put a resistor in series with the LDR and the signal voltage starts being affected.

[nexekho]

If that works how I think it does, that's ingenius.

[Perrow]

Gurner, you're probably quite right. The Tiny Trem used an ldr similarly and some people reported better results with the guitar volume turned slightly down. I'll redesign and stick a small resistor in there.

[deadastronaut]

nice one perrow...another tiny project yay!......i'll try it later....

[Perrow]

I thought you'd like it

[markeebee]

Just a thought.....and not wishing to complicate the elegance of your circuit......but would it work if you used Rob's Darklight ldr reversing thing instead of (or as well as) the gain pot?  That way, you get increased output as the input signal decreases as well as vice versa.

Would probably take a bit of monkeying to find the right led/diode combo, and similar monkeying to get the resistance across the gain lugs right.  If any body wants me this weekend, I'll be in the shed with a breadboard. 

[Perrow]

Bring some milk and give that breadboard a run for its money

(that comment will look so odd when you change your sig )

[Perrow]

Source reference: http://www.diystompboxes.com/smfforum/index.php?topic=82843.043.0

[Perrow]

....but put a resistor in series with the LDR and the signal voltage starts being affected.

I assume you mean something like this, got it in keeping the same footprint



Was about to breadboard this (adding the resistor shouldn't be that much problem on the breadboard) but GF called first shot on my time, but after an episode of "Lewis" I'll pop down to my workshop and see how it turns out.

Any guesses on a good value for the resistor? I guess that the greater the value, the greater the effect, but also lower output. Might have to pop in an LPB-1 in front or after (have one ready for insertion on the breadboard).

[Gurner]

I assume you mean something like this, got it in keeping the same footprint

Yes, that's how I meant.

Re the value.,..that's gonna depend very much on the dark resistance of the LDR....I've never actually dabbled with LDRs, but Ohms law suggests that if you match the series resistor to the LDR's dark resistance...then that'll likely have maximum impact.

[arawn]

Ihave a couple of those vtl5c vactrols, wonder if that would work instead of the led/ldr?

[Perrow]

I suppose vactrols should work.

Regarding resistor value, I tried a few different, 1k then 1M then 421k then a 100k pot. Found something like 1k to 5k to work best, higher than that and the 386 wouldn't drive the leds to light up. Guess I'll have to try with a buffer in front.

[deadastronaut]

@pelle,   did it work?...havent had time to mess with it yet...great name for it btw!..

my GF is taking up my time too....not with 'lewis' though...some other boring inane crap...


@mark, hmmmm... interesting idea!..

[Gurner]

Regarding resistor value, I tried a few different, 1k then 1M then 421k then a 100k pot. Found something like 1k to 5k to work best, higher than that and the 386 wouldn't drive the leds to light up. Guess I'll have to try with a buffer in front.

It'll be a fine line to walk....not enough series resistance then there'll likely be little effect, too much & the uncompressed signal level will be attenuated too much. I'd be surprised if adding a resistor the same size as the dark resistance of the LDR, that the gain of the LM386 couldn't be tweaked to ensure the LEDs are driven sufficiently well...the LM386 has 200x voltage gain on tap, so even if the input signal has been dropped (by adding in series resistance....same resistance as dark LDR loses half your signal)) then it should be counteracted by boosting the gain setting on the LM386.

[Perrow]

@Rob, the circuit works fine for me, I'm just with Gurner on that it should work better with the suggested series resistor. I'm a bit surprised that anything over (about) 10k killed enough signal to cancel the effect altogether. The ldr has a dark resistance of ~500k, I should be ok at least to 100k or even 250k. But it's easy enough to breadboard, give it a go

@gurner, yes, the Ruby amp after can easily distort the signal that's left, so I can't really see why it didn't work. Now, it was after midnight and I had more things to do before I could call it the night so I didn't spend all that much time tinkering with it.

[deadastronaut]

yep, just gave it a go, yep it works, but like you said drops volume a lot.... a bit of tinkering may be in order...

[deadastronaut]

hi guys: found this...386 compressor..nice n simple too..

http://www.aronnelson.com/gallery/main.php/v/BinOfBrett/Simple+MOSFET+compressor_small.jpg.html


this idea too...using ldr....interesting...so using the sound to light into this i guess?..

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=37383

[Perrow]

I'll give those a better look tonight, they look interesting.

[brett]

Hi
I like the idea of grounding a signal ahead of a 386. My CMOS circuit worked OK for me, but others got variable results.
One obvious thing that could be improved would be the impedance "matching". An in-line resistor (220k?) would make the compresor look like high input impedance to the guitar (maintaining tone), while making the guitar look like a high output impedance to the compressor. As Perrow said, the dark resistance of an LDR is high (500k+), and a MOSFET is way more (500M+), so a higher resistance than a pickup alone should work better. Also, it's needed if the compressor is used after another stompbox. For a 1c part it's worth a look.
cheers