TL072 vs. better ones / Replacing 4OPa chips with 2x 2OPAs

Funky40

there was a post from 3 Phase.
The Thread is overall meant that i like to hear more about cheap OPAmps ( TL 072) versus better ones ( 2134, and what there exists).
But my post now is about a converter PCB ---> Quad OPA--> 2x dual OPA

Scott Stites · Posted: Mon Apr 02, 2007 6:41 am Post subject:

Looks right to me! I don't normally put caps across the rails, but that doesn't mean it's not right.

One alternative you might consider is that TI still manufactures the OPA4134 in SMT (OPA4134UA). If you don't mind soldering SMT, you might be able to make a little surf-board to mount them on - you could easily make it fit the footprint of a DIP part. The added advantage is that all four packages are on the same substrate, and the OPA4134 has an excellent cross-talk spec.

Downside is it's SMT Evil or Very Mad

I can deal with it, but I still don't like it. Main reason I hate'em is you have to do something like the above if you want to breadboard with them.

Take care,
Scott

toppobrillo · Posted: Mon Apr 02, 2007 11:44 am Post subject:

OPA4277s are what i have, it's a quad 177 are they no longer available?

Scott Stites · Posted: Mon Apr 02, 2007 11:55 am Post subject:

Why, yes! Yes they are (according to TI).

Cheerios,
Scott

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Uncle Krunkus · Posted: Tue Apr 03, 2007 2:28 am Post subject:

Wouldn't it be more important to put a bypass cap on the main board from the +ve to GND and from the -ve to GND? Therefore, you wouldn't need to worry about them on the daughter board at all.

Funky40 · Posted: Tue Apr 03, 2007 11:49 am Post subject:

the thing with the Caps i don't understand really.
an electronic expert sayd in the german Synthesizerforum that both works,
from Ve- to Ve + and from Ve- to Ground plus Ve+ to Ground.

In another disscussion it was sayed that the Ground is very very important,
and one gets the risk to "disturb" a proper Ground when decoupling into the Ground.

So i draw my modules, -just very simple ones as Mixer, Buffer and Inverter-, with decoupling between VE+ and Ve-.
But now i changed this, because i was not shure about how to do when putting OpAmps in series.

Ok, i think i see some more clear about this and the converterboard.
I read between all the words that it is not in general a Problem to deal with such a Board,
also when there's a need to stack Ic sockets.

It's good to know that the decoupling is not needed when the basic Ic allready is.
In one way i decouple all ICs.

As with all this things, i was really unshure.
But hey: i have allready own modules running Very Happy

Thanks alot for Replays

zipzap · Posted: Tue Apr 03, 2007 12:16 pm Post subject:

Just some thoughts - for discussion:
when high gain is needed or smaal signals are processed the choice of opamp is important to me because of noise (and distortion).
in most cases on a synth i think it doesn´t really matter, since your generating audio on high level from the start, rather than amplifying a tiny signal from a mike or LP. With a 10v signal noise is no big issue.
I´ll make some experiments if i can hear the difference from a tl072 and say an opa627 at different gains. some switch for direct comparing. Maybe one is more silky, the other more grainy. don´t know but it interests me. I think the main difference is the input noise.
in other non audio aplications like cv summing in vcos, integrators etc the right opamp can make a big difference.

I read some hifi forums from time to time. There are many questions about opamps. Some people say that the surrounding like layout, correct decoupling, right source impedance etc is more important than the amp itself. Some bipolar highend low noise opamps are said to perform worse on high source impedances (in the circuit) than the old 5534 or tl072.