Unknown 958Hz peak in amplifier/ADC with any input (shorted, opened, signal generator, real signal) [closed]

Question

Update 2: I disconnected the ground between channel 1-4 from channel 5-16 and the 958Hz peak disappears. It could be crosstalk but i wonder why crosstalk can produce 958Hz noise.

Update: Using the g.USBamp demo didnt produce the unknown 958Hz peak at the FFT (that BCI2000 software does). See below. Instead there is shift upward in the frequencies.

In both tests. I shorted the differential inputs of channel 1 (In+, In-, ground). I set sampling to 4800Hz, 0.5Hz High Pass and 1000Hz Low Pass using 8th order Butterworth filter and 58-62Hz Notch filter.

Here is the signal and FFT of the g.USBamp.

Why do the lower frequencies shift up? Do you call it baseline shift?

Here is the FFT from the output of the BCI2000 software. All settings the same. Including taken in same sitting and both within 10 minutes.

Why is there no shift of any kind in the BCI2000 output? Instead there is a 958Hz peak that is not seen using the g.USBamp software? What is the cause of the strange 958Hz peak?

Which FFT is the correct one (the one from g.USBamp software shown in the first figure or the BCI2000 software)?

Original question;

I have this second hand g.USBamp 16 channel bioamplifier. There is unknown peak at 958Hz when FFT (both in Sigview and Matlab) when the bandwidth is set to low pass of 1000Hz (or even 2000Hz) with 4800Hz ADC sampling. The 958Hz peak is the same whether the input is shorted, opened, with signal generator input, real bio-signal, etc., with battery only or using AC adaptor. Does anyone any idea where the 958Hz noise could be coming from inside the circuit? Have you encountered anything like it? Does it occur in the amplifier or ADC? The specs of the g.USBamp is also shown.

The following signal is 9600Hz sampling without any passband nor notch filter, FFT at Matlab. It forms harmonics or multiple of 958Hz (except the peak near 1400Hz). All 3 inputs shorted (in+,in-, ground). Both 5V USB powerbank and AC adaptor shows same peak at 958Hz and harmonics.

The following signal is 4800Hz sampling (2400Hz sampling shows same peak) with 5Hz to 1000Hz bandpass and notch filter, Sigview display (Both Sigview and Mathlab used the same data from BCI2000 software). All 3 inputs shorted (in+,in-, ground). Both 5V USB powerbank and AC adaptor shows same peak at 958Hz and harmonics.

https://www.gtec.at/product/gusbamp-research/

Answer 1

I can't be 100% sure if this is the source in your case, but many USB devices have a problem that causes disturbance around 1000 Hz.

The USB data packets are generally transferred every 1ms so either the data transmission itself or just the increased power consumption to transfer the data may lead to the 1000 Hz disturbance coupling inside a device, maybe through power supplies.

Try it with different PCs to see if the USB polling rate of the specific USB host controller has any effect, or different ports like USB2 and USB3 ports on same PC, etc.

It could also have suffered some damage like a drop or ESD, or have a manufacturing defect or some broken component that now appears as near 1000 Hz frequency everywhere.