newbie IC questions!

[phector2004]

Hey everyone, I'm planning a few builds but I prefer to design perf layouts before I order so I can figure out what enclosure/board I can fit it on.

One of these builds involves an IC. I've read up on gaussmarkov's beginner IC project and it makes perfect sense, but I have a few questions remaining:

1. The schematic shows the ICs with (+) and (-) inputs and an output. I've had some experience with 555 timers in high school, and I remember them requiring a power input. Is this just an abbreviated way of drawing the opamp, or is the power required for the circuit supplied by the inputs???

2. More specific to the board I'm laying out now, I've looked at the datasheet of the chip I'm using and its max Vcc is 18V. I'm building Aron's Shaka Express pedal and it has a 9v input into the first opamp and has a later opamp section after a JFET section powered at 18v. There's a capacitor after the FETs followed by a 9v connection leading into the opamp. Here's the link in case I don't make any sense: http://www.diystompboxes.com/pedals/ShakaExpress.pdf

a) Is the 2nd opamp input 9v as well?
b) Can I use both sets of inputs on one IC instead of using 2 ICs?
c) In any case, would I power the IC(s) with 9v or 18v?
d) Should the IC power supply come from the voltage-halver (right terminology???) or from before the voltage doubler?

I know some of these are trivial, and I could solve them on my own, but I don't have a breadboard yet and I'd rather make one large order than a few small ones. Another one of my planned projects also uses ICs, and although I haven't started laying out a preliminary perf design yet, I'm sure similar questions would arise.


Thanks for any help!

[amptramp]

Answers in oder of your questions:

1. The + and - connections are not power.  They are non-inverting and inverting signal inputs to the op amp sections.

2. It appears that the designer intends to power the op amps from + 18 VDC and GND (0 VDC).  The power connections to the op amp are not shown at all.

3. The 9 volt connection is a half-voltage point which is used as a bias supply to both op amps (3a).  As stated, the + and minus connections are signal inputs, not power inputs (3b).  18 V (3c). If you are using two batteries or two wall-warts to power the unit, VR could be the centre point that connects them; you may not need the resistive divider witht eh 47 uF cap on the right (3d).

[phector2004]

Answers in oder of your questions:

1. The + and - connections are not power.  They are non-inverting and inverting signal inputs to the op amp sections.

2. It appears that the designer intends to power the op amps from + 18 VDC and GND (0 VDC).  The power connections to the op amp are not shown at all.

3. The 9 volt connection is a half-voltage point which is used as a bias supply to both op amps (3a).  As stated, the + and minus connections are signal inputs, not power inputs (3b).  18 V (3c). If you are using two batteries or two wall-warts to power the unit, VR could be the centre point that connects them; you may not need the resistive divider witht eh 47 uF cap on the right (3d).

1. Hmm I got that, hadn't worded it right, but you answered it in 2.

Would 18v be the correct power input for the chip, though? I'd assume it's not exactly a great idea to power something near its max

thanks for the help!

[GibsonGM]

The power supplies to the opamp(s) are +18V.  The V.R. is 9V, 1/2 the supply, to provide proper bias as stated above.  This makes the opamp work in the middle of its characteristic curve so it can amplify BOTH sides of the AC signal input.

Good question there about the ratings.   Most often-used IC's like the TL072, great for this project, list a maximum voltage, but it's with respect to the inputs.....that chip says max is 18V, but with 9V applied in bias, you're not really 'maxxing it out' so to say.  It is really max +18V and -18V, if that makes sense!  It's a known good layout, and should work fine. 

[phector2004]

thanks for the input, makes sense!

now i gotta figure out how to lay this beast out