Electronic noise in audio preamplifiers

[m_t_c]

Hi all

I am driving a preamplifier in frequency range of 3 KHz to 40 KHz with 60 dB Gain with 12V DC Power Supply (R&S bench power supply). The noise floor at preamplifier output observed on oscilloscope is around -60dBV (in frequency range of 3 KHz to 40 KHz) when input is being short. However, i have to power ON a single board computer (SBC) from same 12V supply. As soon as SBC (PICO-KBU4) is being power ON, the output noise floor at preamplifier output suddenly rises to around -15 dBV in desired frequency range on oscilloscope. If SBC is power OFF, the noise floor at preamplifier output again drops to -60 dB.

What can be possible causes of this noise induction upon SBC power ON and what may be possible remedies to resolve this noise issue? Please help me.

Thanks & Regards

 

[betwixt]

The SBC probably has low frequency switching signals within the amplifier passband and also may have an on-board switching voltage regulator. These are notorious for drawing short but large bursts of current that are probably not dampened by the bench supply output filtering. Try adding a choke in line with the supply to the SBC and adding a low ESR capacitor on the SBC side of it. Suggest values of around 1mH and 100uF as a starting point.

Brian.

 

[m_t_c]

Try adding a choke in line with the supply to the SBC and adding a low ESR capacitor on the SBC side of it. Suggest values of around 1mH and 100uF as a starting point.

Brian.

Thanks. I will try them

--- Updated Nov 10, 2020 ---

Try adding a choke in line with the supply to the SBC and adding a low ESR capacitor on the SBC side of it. Suggest values of around 1mH and 100uF as a starting point.

Brian.

Do i need to introduce inductor only in positive supply line or in ground line also? Should i connect capacitor b/w + and - supply terminal of SBC? Thanks

 

[KlausST]

Hi,

show a photo of your wiring. Especially GND, Supply and audio signals. Also all connections to your measurement devices.
Then we can give you recommendations.

Klaus

 

[crutschow]

A common-mode choke connected between the power supply and the preamp for power and ground and/or for the SBC may also help.

 

[BradtheRad]

Although a choke is more effective (as already suggested)...

You might have a mild case where a resistor (with capacitor smoothing) provides a degree of isolation from noise on the supply.