# for an audio signal within the rails of an opamp, can its quality be improved by the + and - rail voltages?

I have a high end audio application in which I'm using the NE5532 opamp. I'm processing an audio signal with 10Vpp swing (so between +5V and -5V) in an audio ADC input stage. Does it make any difference for the audio quality whether I use +/-14V or +/-11V as supply rails? If yes, why?

Additional info: my converter takes differential inputs, each input between 0 and 5V. My circuit feeds it two signals centered around 2.5v, each 2Vpp so after subtraction the ADC sees a 4Vpp signal. This is a 32-bit converter and the sample rate I'm using is 192kHz. I cannot change the converter. Given this scenario, does it matter sound quality wise to use 11V or 14V rails?

• What does your ADC datasheet specify as the input voltage range? Commented Oct 17, 2017 at 0:47
• @BlairFonville for +/-15V supply voltages the input voltage range is -15..+15V according to the datasheet Commented Oct 17, 2017 at 0:54
• It looks like you will be ok at +-11 though you can not guarantee any output over +-8V. Commented Oct 17, 2017 at 1:00

In general, you want your input signal to swing close to the rails of the ADC’s specified input voltage range, in order to maximize the converter’s dynamic range.

Make sure you back off a little to accommodate any gain error of the device.

From TI doc SBAA004A

The signal amplitude should be closely matched to the analog input range of the A/D. This is done to maximize the dynamic range of the converter. For example, if a 12-bit converter with a 20-V input range is selected, the value of one LSB is 4.88 mV. It would be ineffective to use only a small part of that range, for example, if the input signal was 2 V. A better solution would be to select a converter with a more optimal input range, or to insert a gain block in front of the A/D (keep in mind new errors which the gain block will introduce). Many high speed converters, due to process voltage breakdown limitations, have small input ranges. If the signal bandwidth is small and a high degree of accuracy is needed, it may be advantageous to consider using a lower speed A/D with a larger input range.

edit per comments: The voltage level of the rails to the op-amp won’t have any affect on noise, so long as it’s in spec and the amp stays thermally cool and regulated.

• Edited to remove the bit about the preamp’s NF - didn’t notice you specified the amplifier in the post. Looks good. Commented Oct 17, 2017 at 1:38
• I added a few more details Commented Oct 18, 2017 at 21:25
• @b20000 No, the actual level of the supply rails you use doesn’t matter. What does matter are the details I provided above. Also read through the TI link. It’s full of useful information. Commented Oct 18, 2017 at 23:04
• My question was whether there is anything lost or won in terms of audio quality (linearity, distortion, noise ...) by using higher voltage rails when using the NE5532 opamp. I am aware that the input signal has to be scaled to maximally use the supported analog input range of the converter and that is already the case. Commented Oct 20, 2017 at 0:01
• @b20000 Ok. Since you stated that this was to condition the signal at an ADC input stage, it read as though you were asking about signal level. So the answer is that the voltage rail level doesn’t matter. As long as the amp is thermally quiet, your current setup sounds great. Commented Oct 20, 2017 at 0:07