Preamp. Low power for one 9V battery

When using battery supply there is best to only use devices with low current consumption.
This way the battery will last much longer.
The circuit shown uses OPA244, a very low power opamp.
The idle current is only 50uA = 0.05mA.
There are opamps with even lower current.
But OPA244 was chosen as it has acceptable GBW, 430kHz and also has fairly low THD distortion.

The circuit has a voltage gain of 4.7.
The THD is 0.00006%.
The upper bandwidth is like 100kHz.


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But that chip is far far too slow for quality audio - its slew rate is 0.1V/µs, limiting it to 0.55Vrms output at full bandwidth. The open loop gain at 20kHz is a very low 27dB. The full-swing bandwidth at +/-15V supply is only about 1kHz - another sign its well slow.

Audio opamps tend to need more like 70dB+ open loop gain upto 20kHz and typically have >10MHz gain-bandwidth products, so that the open loop gain is sufficient for low distortion.

Basically if the current consumption is less than 2mA per opamp, its likely too slow for quality audio - unless you're happy with a few percent distortion, that is.
The THD is 0.00006%.
How do you figure that? It takes 0.15ms to settle to 0.01% for instance, which cannot be reconciled with that figure in any way (well perhaps it that's distortion at 1Hz rather than 1kHz!!)

Its hard to find audio opamps that are significantly less than 4mA per amplifier, but perhaps ADA4610 family is a good choice, 1.6mA per amp and 0.00025% at 5Vrms - its bandwidth product is 16.3MHz, slew rate 17V/µs minimum - exactly what I'd expect for a low distortion audio opamp.

9V batteries are often about 300mAh, so 5 opamps each consuming 4mA still means an endurance about 15 hours, 5 opamps of 1.6mA means 37 hours. For a less bandwidthy device like a guitar effect you can probably find an opamp with 0.5mA consumption even, as you're not needing to go upto 20kHz, perhaps more like 5kHz, and you may want distortion even.