Lower noise equivalent to 5532

[tackleberry]

Im building a SS FX loop and reverb set up for my epi Vjr. The TL072 is called for as the dual opamp in the FX loop buffer and booster. I have found the 5532 can be substituted and is lower noise. And the OPA2134 is even lower noise. Any real advantage to using them versus the cheaper 072.

[Mark Hammer]

It'll depend what's going in the loop.  No chip imposes low noise on what gets fed to them.

[R.G.]

I guess more to the point, does anything else in the amp limit your returns by making more noise than the opamp that does the effects loop?

There is a reason the TL072 is cheap - the industry uses them by the shipload. This is in turn because they are a great value for the money spent. It's funny, but humans think that just because something is expensive, it must be good; that is definitely not the case always, and it is something that marketing types know. Many "boutique" pedals try to convince you that just because something was hand wired, point to point it must not only be good, but also it's worth every penny of its high price. I've seen marketing class exercises where one of the variables to put in for pricing is that customers will buy more of the more expensive of two identical (although not obviously so) items just because it costs more so it must be better somehow.

There are situations where the bipolar-input 5532 has more noise than the JFET input TL072 because of source impedance. It may be that the 5532 was chosen because it drives a 600 ohm balance line better than the 072, which it does.

Picking an opamp only on "noise" requires an in-depth knowledge of noise considerations far outside just "which one's got the lowest noise?"

[Mark Hammer]

Which is why the article on page 8 here is always an appropriate read.  http://hammer.ampage.org/files/Device1-8.PDF

[tackleberry]

Then let me rephrase my question. How do I do the math to chose the the best opamp for this situation. 

[R.G.]

Read Ott's "Noise Reduction Techniques", still regarded as the source on low noise design.

You need to know what signal levels, bandwidth, and source/load impedances are involved in what you connect to your effects loop to do that right. Without knowing those, any selection is a mixture of insight, hunches, experience and raw guesses.

Another way is to put in a socket and try them all fairly and with all the effects you'll ever use in the loop.

[George Giblet]

Check out,

http://www.national.com/an/AN/AN-104.pdf
http://focus.ti.com/lit/an/slva043b/slva043b.pdf

[oldschoolanalog]

(Very) simplified:
http://www.muzique.com/schem/opcalc.htm

[grapefruit]

If you want to take the hunches with some insight route: generally if you have a high source impedance (like a guitar) a fet input op amp like the TL072 will be lower noise. If you have a low source impedance a bipolar op amp like the LM833 or NE5532 (or better) would be lower noise. If you need to drive a 600 ohm load go with the LM833, NE5532 or better, that are specified to do just that.

The "Art of Electronics" has some insight into these matters.

Personally, if you have a lowish source impedance I'd use the LM833. I get them for about the same price as a TL072.

Cheers,
Stew.

[R.G.]

Personally, if you have a lowish source impedance I'd use the LM833. I get them for about the same price as a TL072.

I like the LM833 very much. It was designed specifically to correct common complaints about opamps used in audio.