I breadboarded a DOD 280 Comp from http://www.tonepad.com/getFile.asp?id=40 and here's what I found out:
The LED will not light until I cover the LDR with my finger. The LED will pulsate for two or three seconds then will fade gradually for a second. This LED activity is repeated again and again as long as the LDR is "blackened".
Is that really how it should be?
Sound-wise, I haven't really scrutinize it because my amp is currently weak for unknown reason, even when the volume is cranked up. I can barely hear it. I still have to check it out.
Thanks for any help :wink:
I dont know that particular unit, but it probably needs to be inside something to work unless you put the LDR/LED combo inside a lightshield ( heatshrink tubing).....if you have it all on a breadboard and sit in the light, the LDR probably allready is in the lowohmsection and the unit is allready compressing....
just a geuss..
Johan
Quote from: zenerThe LED will not light until I cover the LDR with my finger. The LED will pulsate for two or three seconds then will fade gradually for a second. This LED activity is repeated again and again as long as the LDR is "blackened".
Is that really how it should be?
:
Almost certainly not, in my opinion, if you mean it is doing this without a signal input! If it is doing this without an input signal, you have an oscillator, either from feedback or maybe from a flattish battery.
Although my initial reaction was "That doesn't sound quite right", in retrospect most certainly YES, in my opinion.
Why? Because the gain applied to the signal that will eventually light up the LED depends on the resistance value of that LDR to set the gain. Cover the LDR and the resistance/gain in stage 1 goes up which will light the LED.
But there is no input, you say. Yes there is, the bias voltage. There is also no DC blocking cap between the bias voltage applied at the + input of the first stage and the envelope follower.
It is the natural behaviour of LDR-based compressors, that in the absence of signal, their gain goes up.
So now, what accounts for the rate at which things go up and down. That's where I don't have a specific answer. However, I *am* curious about what the compression pot (the gain control on stage 1) does to the rate of LED re-illumination, and also what the 47uf cap at the junction of the two transistors does when you change the value.
Sorry guys for the wrong info I posted earlier :? .
I plug it in again and I found out that the blinking of the LED happened when I accidentaly shorted the LDR from pin 1 to the Vb. I mistaken that as constant blinking and fading off, what a shame :? .
Anyway, I was able to shove in a generic PC speaker into my Little Gem to check it out again. It's hard to tell whether there's really compressing going on. I can barely hear any difference. Honestly, I really don't thoroughly know how a compressor works aside from the common knowledge that it gives added sustain and that's just I'm looking for :? .
The LED is not lighting, with or without signal. When I turn the lights off in my room and turn it on again, I can see that the LED lights a bit but fades out in a second o two.
When I cover the LDR, it is muted, no sound at all.
Thanks :wink: .
A compressor works by cranking the gain when there is little or no incoming signal, and turning the gain down in response to larger signals. The gain is slowly raised back again as the note/chords die out. The end result is the production of a relatively constant output level which *sounds like* (but isn't) longer sustain. Think of it like holding a note with your voice and moving closer to the mic as your voice starts to peter out. Same effect.
You'll know its working when you can slam the strings and it doesn't seem to be any louder than simply playing single notes.