opamps in the voodoo vibe - teach me how to replace quads with dual opamps

[ulysses]

hey guys

ive started my RM voodoovibe on vero project

i have a quick question for those with more technical experience than me.

can i sub the 2 quad opamps (LM324N) (only 6 of the opamps are used) for 6 dual opamps (TL072)?

maybe someone can teach to how they arrived at the answer - im interested in the theory too.

cheers
ulysses

[petemoore]

  Yes, but not very easily or neatly without amazing effort of some kind.
  The pins are pretty whacky, making two duals work where one oa with more pins and only a few pins matching means...you'll have quad OA that fits, or Dual OA's that have had major messing with to be made to fit.
  I would try to leave as many pins straight to go in the socket directly as possible, then bend the pins that dont' match to the outside of the socket, [after having added jumper wires to the tips of their pins, carefully not to overheat etc.]...nope, I think the quad'll look better in a quad position than two duals ever can.

[ulysses]

hi pete

thanks for the reply - i am making a brand new layout on vero - so i dont need to actually make two opamps fit into the same physical space as a LM324N - also a LM324N has 14 legs, and 2 tl072's have 16 legs - so that would be very difficult to bend legs

im starting off with the second part of the circuit - the lfo section

here is a copy of the lfo section

http://web.archive.org/web/20040123175441/www.green-fuz.freeserve.co.uk/effects/voovibe2.gif

you can see that it would break up quite nicely into 3 dual opamps

my real quesiton is - would a single opamp inside the tl072 amplify the signal more, less or the same as a single opamp inside a LM324N

cheers
ulysses

[ulysses]

my original thought was to leave off the external speed control

but on closer inspection it looks like the opamp for speed is not only for the external foot controller

which means - 7 single opamps - in which case its prob easier to use the two quad opamp ic's

thanks anyway

cheers
ulysses

[BN]

my real question is - would a single op amp inside the tl072 amplify the signal more, less or the same as a single opamp inside a LM324N

The gain of an operational amplifier is solely determined by external components (ie. resistors and caps). Google for something like 'inverting amplifier op'. So the answer is no, but they might have other preferences when it comes to speed, frequency response and supply voltages etc. Check the datasheets!

Hope that will set you on the right track

/BN

[slacker]

Some circuits that specify an LM324 won't work with TL0** opamps so it's probably best to use LM324s or at least try the circuit on breadboard before doing the layout.
If you did want to use duals instead of quads all you need to do is get the datasheets for both so you can figure out which pins are the + and - inputs and outputs of each individual opamp in the package.
Personally I'd just stick with quads, I know some people say using duals can make layouts easier but I prefer quads.

[petemoore]

Personally I'd just stick with quads
  Definitely, when it comes to attempting to 'dual oa' a working vibe pedal.
  If yer doing or choosing a layout, use of anything is more straightforeward.

[swt]

there are times where oscillators won't work with certain op amps. I believe there's a reason for the lm324 here. That's why sometimes we use lm1458, instead of rc4558, or lf 3xx. And the tl072 is a jfet op amp, and the lm 324 it's a regular opamp.

[R.G.]

The LM324 is one of a type of opamps optimized for working from a single power supply and ground. It's claim to fame is that its inputs work fine at ground. Many normal opamps will only work if their inputs remain at least a volt or two away from both the most positive and most negative power supply to the chip.

The LM324 is also cheap to buy.

There is a dual version of the same chip, the LM2904.

The peculiarities of opamps for how widely their inputs and outputs can swing compared to the power supply is a big distinguisher for which opamp to use. Look for 'input common mode range' and 'output voltage swing' on the datasheet. Also look for "no latchup" or "latchup free" on the datasheet. Some opamps latch their outputs high or low if you exceed the input common mode range, and can't be gotten out of that except by cycling the power supply.

[ulysses]

thanks for the replies guys.

cheers
ulysses