------Question for LME49724MR Please Put your question below----
Sir, I’m building a 1khz low distortion audio generator and the original design uses
2 9vdc batteries. The distortion value is .0.000125%. So my question is will the gen still
have the same distortion value if I use a 5vdc to +/-9 v dc to dc converter Digi Key
part number 1470-2535-5-ND or 1470-1539-5-ND? If I can use the converters does it
matter what voltage supply I want to use either 9vdc the original design or use +/- 15 V
dc to dc converter?
Thank you.
Jeff Miiller
Hi jmelect,
The reason they use 9V batteries in the original design you mention is because the 9V batteries introduce essentially zero noise into the system. Any switching-based power supply will introduce noise. One can filter it to varying degrees by several means, but you’ll always have more noise in your output than if using a pure DC power supply.
Regarding the two DC-DC switching supplies you mention, the XP Power 1470-2535-5-ND (ITX1209SA) takes a 9V to 18V input and outputs a single isolated 9V output. That part would not work with a 5V input.
The other part, the 1470-1539-5-ND (IR0515S) does take a 5V input and will output +/-15V at 100mA each, so is capable of powering the LME49724MRX/NOPB. At full load, it’s output ripple and noise is typically 50mV pk-pk, measuring on a 20MHz bandwidth. The switching frequency is in the 60-85kHz range.
As I said, if you need to use a switching DC-DC supply to power a very low noise amplifier, you are going to introduce some noise, so then you need to figure out how to minimize it. Adding capacitance and inductance on the outputs of the DC-DC converter, such as in a low-pass Pi-filter arrangement, can be very helpful.
In addition, adding a positive and negative linear regulator, or a dual output with both, between the positive and negative outputs of the DC-DC converter and the power supply inputs of your amplifier can greatly reduce the noise. Linear regulators with greater PSRR (power supply rejection ratios), specified in dB’s of attenuation, will do a better job of minimizing input noise from passing to the output.
Thanks so much for your answer. After reading your answer I decided to use 2 9 vdc batteries.
Best regards,
Jmelect
