Probe schematics and spikes

Hi to all!
I would display output signal from differential output amplifier: Out+, Out- and signal ground/shield.
Signal outputs through a 3-way PCB screw terminal block, due I am using oscilloscope probe I only get ground and Out+ using a two short wires, just to collect signal using oscilloscope probe.
Using oscilloscope probe I read clear signal, I used different oscilloscope probes (I don't remember models, that ones are default probes for MSO46 and TDS210).
Issue starts when I use direct coaxial cable with BNC connector instead oscilloscope probe: I see spikes I can't understand where they come from.
I changed cable type (RG58 and others) but with no effect.
It looks like a low-pass filter on the oscilloscope probe.
Are there available probe schematics?
Do you suggest specific cable for homemade probe?
I'll post image as soon I can.
Any suggestions/ideas?
Thanks.

Hello Michele,

I don't have a clear understanding of the setup and the spikes you observe.
we can follow-up via email: massimiliano.fiaschetti@tektronix.com