Unbalanced mic input

[tedbar]

There are some great op amps for microphone pre amps available (INA849, That 1512 etc). The "typical application" circuits in the data sheets all use balanced microphone inputs. Can these op amps be used with an unbalanced input? If so what is the correct topology for the input?

[richnormand]

This should help:
https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.305.873
Download the pdf link to the Jensen document.

[tedbar]

Thanks, that certainly sheds some light.

[magic]

These are integrated instrumentation amplifiers, not op amps.

You could ground IN- of those chips and drive IN+ with single-ended signal. Bandwidth will be same as normally, not sure if there is distortion penalty for doing that, you could try.

At low closed loop gains low noise opamps in ordinary noninverting configuration could work - LT1028, AD797, OPA211, NJM2122, depending on price, other specs and which brand you are a fanboy of.

At high closed loop gains the in-amps will win on bandwidth and maybe on distortion.

[Zero999]

Those are instrumentation amplifiers.

I agree with the above, especially the NJM2122.
https://www.mouser.co.uk/datasheet/2/294/njrc_s_a0009641155_1-2279373.pdf

[SiliconWizard]

I don't see the benefit of using an instrumentation amplifier if you're going with a single-ended input here.
And we don't know what kind of microphone and gain you are talking about. If this requires high gain, single-ended is likely to be pretty disappointing in terms of noise, even with an instrumentation amp. If this is low gain, then any decent opamp will do.

[magic]

I don't see the benefit of using an instrumentation amplifier if you're going with a single-ended input here.

3GHz gain-bandwidth product (THAT1510 at +60dB) is not something even AD797 could match

Not sure if there are current feedback opamps with similar low frequency noise specs?

[Terry Bites]

You can, but its wise to ground the unused leg with a resistor similar to the mics output Z.
It can be useful to bring the single ended mic' ground back to the amp. A pseudo differential connection.
Make sure you have an isolated jack with a switch so you can lift it above chassis ground via the 10 Ohm resistor.
Make that part a SE Diff switch and keep your options open.

In general Inst amps make poor audio amps. They're designed with low frequncy and DC in mind.
Add RFI protection or you'll have an expensive AM radio on your hands.

The masters of Mic amps are the "THAT corporation". Their app notes a goldmine.