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Why use 15V for symmetrical supply in amplifiers?

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Pferd:
Hello community!:)

I was wondering, why is it so common to use +/-15V symmetrical supply in operational amplifier circuits? Wouldn´t it just be ok in most cases to use +/-5V? The (in my case audio) signal is in the 500mVpp ranges anyway.
In my case it could possibly save me one transformer, which is specifically for the operational amplifiers supply in my design.
Am I missing something here? Does it has to do with the potential difference to the power rails? (not using rail to rail op amps)

Thanks in advance!

TimFox:
Operational amplifiers were, as stated in the term, originally designed for analog computer use ("operational").  The older vacuum-tube amplifiers usually had full-scale outputs of +/- 100 V, but the solid-state amplifiers used +/- 10 V full scale outputs for the calculated voltages.  To reliably obtain +/- 10 V output, +/- 15 V power supplies were reasonable.  Of course, modern operational amplifiers do not have a "ground" terminal, so you can play all sorts of variations on the splitting (on non-splitting) of the power supplies, so long as you remain within the minimum/maximum range of the total voltage from positive to negative supply terminals, and keep the input terminals within the allowed range of voltages with respect to the two terminals.  Some amplifiers suitable for audio are perfectly happy with +/- 5 V:  check the data sheet.  Split supplies are handy for audio, and can avoid extra coupling capacitors with signal voltages referenced to ground.

tooki:
Indeed, many audio op-amps are happy with ±2.5V (5V total, with a virtual ground). TI alone has nearly 1200 op-amps that suffice themselves with 5V total or less. 37 of those are expressly categorized as audio op-amps. For consumer line level audio signals (2Vp-p) that more than suffices.

Terry Bites:
 Unless you need large output swing lower supplies are fine. Nowadays any opamp that runs on over 5V is commonly called "high voltage". When I was a newbie that meant >44V!

armandine2:

--- Quote from: TimFox on September 23, 2021, 04:39:11 pm --- solid-state amplifiers used +/- 10 V full scale outputs for the calculated voltages.  To reliably obtain +/- 10 V output, +/- 15 V power supplies were reasonable.

--- End quote ---

might be good to see this reasoning in documents of the time - I had a quick look at my recently acquired copy of Roberge (1975) Operational Amplifiers: Theory and Practice but nothing there.

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