Electronic noise in audio preamplifiers

Thread Starter


Joined Feb 19, 2016
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


Joined Aug 1, 2013
Post a block diagram of your system components and *all* individual wired connections.

Without that, just guessing ... power supply decoupling. As a start, you need a noise filter between the 12 V source and *each* of the system components (preamp, SBC, etc.). then, based on a schematic of the preamp (???), there are noise reduction methods to apply.

The good news is that this is entirely solvable - for a price. I did a system with 120 dB isolation among three system areas all running on a common power source. Not cheap, but it passed on the first test run.



Joined Feb 24, 2006
@AnalogKid mentioned, (guessed(?)) that conducted noise might be the primary source of your problem and I would tend to agree. Besides conducted noise there are three other sources of noise to consider:
  1. Capacitive coupling
  2. Inductive coupling
  3. Radiated coupling
That is why the block diagram and possibly even detailed schematics may be necessary to do an analysis and suggest remedial steps. The effort you are willing to expend depends in large part on managing your expectations. Knowing how much is enough is almost as important as getting there.