What does this do exactly?

[H4T]

Sorry for being such a n00b, but I am just wondering what this stomp box does. Does it allow one to modify treble, bass levels? Or something more? The name was confusing, then Googling "op amp" yielding confusing results lol. I'm an electronics n00b, but I am very excited about learning. Just kinda confused on this thing, lol.

[mutant_guitar]

i'm pretty new at this, too, but from what i know, an op-amp is a circuit that is used in most pedals, and in amps. i don't know exactly what an op-amp does, but you can use this homebuilt circuit instead of using an integrated chip (IC) op-amp. it just provides a different sound than IC chips, i guess.

[Marcos - Munky]

Op amp is operational amplifier. The most used ICs are opamps, like the 741, TL071, TL072 (two opamps in one IC), and others. This circuit is a homemade opamp, but using discrete parts and with a better sound.

[smoguzbenjamin]

What an opamp is is a most useful piece of circuitry. It allows you to change its gain by using a process called negative feedback, by feeding an inverted signal back into its input. And that's only using it as an inverting amp.

Consider this: you have a signal generator that is generating a 50Hz sinewave. One period of these waves (IE the time it takes for the wave to go from 0, to the top, past zero, to the bottom, and back to zero again) is 2ms. At 0ms the wave is at 0. At 0.5ms the wave is at its top. At 1.5 ms it's at its bottom value and at 2ms it is at 0 again. If you invert this it is the other way round, at 0.5ms the waveform will be low and at 1.5ms it is high.

Now feed the two signals together: what you get is that the waves subtract and cancel each other out, which means you can turn down the gain of an opamp by feeding it its own output. If you leave out a resistor you're cancelling the output entirely, but by adding two resistors you can easily calculate the gain. Now let's filter out low frequencies in the bit we're sending back (the feedback loop). You're negating and cancelling the low frequencies the amp is putting out, which leaves you with all frequencies higher than what you filtered out, meaning that an opamp can also be used as an active tone control. There are endless possibilities of what you can do with these little ICs. You can also just amplify a signal, ghehe  :lol: If you ever kill your portable CD/MP3/minidisk/cassette player, and pop it open, don't be surprised to see an opamp in there

I hope that was clear, I can ramble on and on you know

[Leftyrockr]

So, basically, you can substitute this in for an IC. Which IC's can you substitute this in for?

[saul_sabia]

Leftyrockr, i don't know much myself, but an IC is a piece of electronics that has lots of miniaturized electronics in one package. a good example of this is an Op-amp, for instance the 741. here's an example of what is all in that one chip...

http://www.play-hookey.com/analog/inside_741.html

this link shows the internal schematics of the 741 op amp.... but it's all in one chip, so instead of having to have all of that to wire up, you get the convenience of it all in one shot. as it appears to be in most cases with electronics, there are tradeoffs, however.

it's way easier to use a single chip instead of three or four transistors, resistors, caps, etc. the tradeoff is that usually you get less gain, more noise, with the opamp. wiring the transistors out means harder to do, more space, but you have the option of better components, which can mean better gain, less noise, etc.

which is the purpose of this project - better components means better quality distortion (we hope =)

hope that helps.

Saul

[tennisdude]

I think the most common IC you would switch this out for would be a tl071 or half of a tl072

[T-Man]

This is an interesting circuit, but I think it would have been wiser to have an actual effect as the 2nd beginner project.  2 circuits that only amplify is not that interesting to a beginner.  A DOD 250 or MXR Dist + or Bazz Fuss or any simple distortion would have been a better choice IMO.

[KORGULL]

This is an interesting circuit, but I think it would have been wiser to have an actual effect as the 2nd beginner project.  2 circuits that only amplify is not that interesting to a beginner.  A DOD 250 or MXR Dist + or Bazz Fuss or any simple distortion would have been a better choice IMO.

I believe this is simply "a project" -not necessarily another beginner's project. It is just listed along with the beginner's project under the general "Projects" heading.

[Joe]

It's not a complete pedal, you use it instead of an opamp in a distortion circuit. For example you can use this instead of a 741 in a Dist+, or instead of a 4558 in a TS9, and get a better tone.

The main point of the circuit is to get the diode before the opamp's output stage. That's where it needs to be for the compression effect to work. I only recommend using it in distortion stages, and IC opamps for things like tone controls, etc.

[Somicide]

...or instead of a 4558...

instead of half a 4558

[zeppelinchld]

...or instead of a 4558...

instead of half a 4558

are u sure? or is because a 4558 is a dual op amp?
could it replace a 4739? or would it only be half

[GibsonGM]

The project is 1 discrete op amp....the 4558 is a dually, so you'd have to build it twice!   The 4558 is just a souped up version of 2 LM741's in 1 package...look at the pinout for dual opamps to verify there are actually 2 separate OA's in there ;o)  As for replacing the 4739, I'm not sure, most likely it could, but could cause problems down the road (oscillation and things like that)...

[admanrocks]

so could i use this in something like the little gem? instead of the LM386?

[raulgrell]

I believe the LM386 is not an op-amp, but a Chip-amp, different in some ways... Look at it's datasheet on google, you'll find some more info...

[GREEN FUZ]

While the datasheet for the LM386 describes it as a "Low Voltage Audio Power Amplifier" it is, by definition, an op-amp.

[Transmogrifox]

An LM386 indeed is an op amp, but it interfaces external components for feedback in a different way, making it non-compatible with most standard op amp applications.  The LM386 includes some of the feedback network of its own internally, and the external components merely complete the feedback network so that the designer can modify the gain.

In short, the diode compression op amp could be used in something like a Little Gem.  It would require the addition of input DC biasing, and a higher power rated output section if it's going to be compatible with the Little Gem circuit.  It is not a project for a noobie since it requires some electronics knowledge to redesign the circuit to work in a little gem.

Again, this circuit is a good replacement for op amps in a TS, or a Dist+, etc.  It requires all the input biasing and DC decoupling treatment that any audio electronics op amp application would require.  The results from using this as an effect would be about as disappointing as connecting a power supply to an IC op amp, your guitar to one input, and the amp to the output...sputter, fuzz, pop...or maybe nothing.