Flatline WAY too hot! Anyone got any ice?

[David]

I've got a Flatline on breadboard.  It sustains pretty good.  It also thinks it's an overdrive -- a heavy metal overdrive -- which would be fine if I wasn't trying to build a compressor!  Anyone got any ideas to cool this thing down and get the dirt out of it?

[petemoore]

Just glad when I get signal to pass sometimes.
 But somehow it must be getting gained up...isn't there a little feedback resistor between output and input of the OA [10k?] that sets gain?
 Make sure it's not 100k...
 I had one 'working' for about a week...
 Problem a simple probably...simply finding it is the complicated part

[Mark Hammer]

Two things can make it behave so:  a) too much gain applied for the input signal being fed, b) too little padding down for the next device in line.

[David]

1)  guitar used:  Strat clone with 3 single-coils
2)  built according to values on Hollis' schematic
3)  I agree that something is "off".  It worked fine during my initial tests.  Then I got the boneheaded idea to swap out the LED/LDR for a CLM6000 -- with unsatisfactory results.  I put the LED/LDR back in and put them in a light-tight tube.  Ever since, it's been a distortion monster.  I've been over the schematic a half-dozen times and found a few mistakes on my board, which I've cleaned up.  Haven't cleaned up the sound yet, though.

By the way, I checked to make sure, and I am getting 4.5 volts from the bias network, and that's what's going to the noninverting input of op-amp "B" (pin 5).

[Alex C]

How does it sound when it's clipping?  I get what I think is a pretty neat sound when I slam my dyna-comp with the boost from my sparkle drive.   Just a thought.  

Alex

[Johan]

did you check that the LED in the LED/LDR are in the with the right polarity?..if it is not lighting up when you play, its in backwards and it wount compress..probably just clipp...

Johan

[David]

Johan:

Yeah, I checked, and it's lighting up.

[jrc4558]

One of the IC stages is probably distorting. Without any signal to the input and preferrably without ny power to the cirquit, try to see what is the resistance in the feedback loop and what is the resistance to ground. Add one to another and divide by the resistanceto ground. That will give you a gain factor. Post it here.
Anyway if the number is too high, like in the 400 range, it's probably the op-amp clipping on itself due to runnig at very high gain. That's why people sometimes report tubescreamers clipping even with no diodes in the feedback loop.
Good luck.

[David]

Constantin:

Thanks for checking in.  Your build report is what led me to breadboard this thing.  Now I assume that you're referring to the "audio" op-amp, not the "rectifier" op-amp, right?

[jrc4558]

Yeah, that thing. I remember mine distorted too and then I discovered that 220k resistor in the feedback loop was not connected to the output of the op-amp.
I love that compressor now by the way. I gave it to my bassist and whoa, now his guitar can easily withstand some stick-like tapping. All thanx to Joun Hollis's design.  

[casey]

hey, does it sound good as a distortion box?  you might have
a "new" design there.  

[David]

Casey:

Yeah, it's not bad.  Obviously, the sustain is really nice.  The thing is, I'm not going to waste 4 germanium diodes and an optocoupler on a stupid DISTORTION, for heaven's sake.  I can do distortion in myriad ways -- all of them easier!

[David]

Mark and Constantin:

Thanks for your collective advice.  My Flatline is MUCH cooler now!  Turns out that I had one of the wires for the 220K resistor that parallels the LDR connected after the 10K resistor going to the sustain pot.  I moved that and got instant smooth, cool sustain.  That baby sounds NICE!

[Mark Hammer]

Congrats.  

A *very* familiar scenario.  Probably deserves its own acronym like WTHIIDT (what the hell is it doing there?) :lol: for those instances where you were absolutely sure you wired it up right on breadboard or perfboard and after weeks of staring at the existing wiring and troubleshooting, you finally realize that the connection you had come to accept as fine (because it had become familiar by now) is dead wrong.  Something like, oh I dunno, wiring up V+ to pin 8 on a single op-amp because you're so used to doing it with duals. :wink: