help selecting an op-amp

Hi folks,

I'm helping a friend try to find an op amp that meets his requirements. They're currently using TL074s, and they aren't happy with the noise of them. They'd like to move to something like an OPA4134, but the current requirements are too high, and it puts a lot of strain on the power supply.

Have any suggestions on a quad amp with a quiescent current less than 3mA per amp that sounds reasonably good?

We really need to know the circuits they are embedded in to make a proper recommendation, or at least the nominal impedances and levels, particularly if noise is an issue.

per amp as in per channel or as in per part?

Maybe the mc33079 would fit the bill? It's a little high on the current though if you are talking per part..

OR:

LT1359

a very crazy, high speed opamp with pretty good specs but damn expensive at 12$ each..

OR:

LME49740

per channel... I think they're cost sensitive as well, so $12 apiece probably isn't going to work.

I'll look at the MC33079, I haven't seen schemes or anything, sorry I don't have more design info, just trying to help a friend out; the existing design uses JFET tl074, so I dunno if a BJT input amp will be as happy in the design or what... I'll just make suggestions and let them sort it out until they can provide me some more details!

How about Linear LT1125 - quad 2.7nv/sq.rt.hz typ. - $7/25 $6/100 use it only in noise sensitive areas such as inputs and summing amps. Use the MC33079 elsewhere.

It may be tough to dramatically improve upon TL074 using same or less current and low cost, but the bifet is getting a little long in the tooth.

I have no personal experience with these but the TLE2074 looks like a possible upgrade path with slightly lower noise, similar PS draw, improved speed/bandwidth, and not uber premium pricing (but not as cheap as old soldier tl074).

To get huge noise improvement may require upping current and dollar budget.

JR

> they aren't happy with the noise of them.

Noise isn't a problem in EVERY stage.

Figure out which stages are noise-critical, start with them.

First: run the input trim hotter. Until they complain about the clipping or blurred sound. There may be a happier medium.

When you have a specific stage which does not have enough range between hiss and clip/blur, look at the impedance into the amp. If it is over 20K, no amp will be quieter than a '072. If it is 1K-5K, try a bipolar.

Thanks and thus my caveat that I never tried it.

When I was developing my current battery powered product I experiemented with some of the newer ultra low current opamps for some simple filters and gain stages but likewise encountered funny results. I ended up falling back to the old TL06x series which is just a current reduced version of TL07x so a known performer.

This is why we breadboard circuits even when we think we know what to expect. Stuff happens.

I wholly expect there should be a newer generation sub for the TL07x series after some 30 years that is the same just better, or was the bifet that remarkable for 30 years ago? I know I liked both it and 553x back in their prime.

The 553x has been well eclipsed. perhaps bifet is tougher.

JR