A probe comprises a small “consumable” probe substrate permanently mounted to a circuit-under-test. The probe substrate includes a high-fidelity signal pathway, which is inserted into a conductor of the circuit-under-test, and a high-bandwidth sensing circuit which senses the signal-under-test as it propagates along the signal pathway. The probe substrate further includes a probe socket for receiving a detachable interconnect to a measurement instrument. Power is alternatively supplied to the probe by the circuit-under-test or the interconnect. When the interconnect is attached, control signals from the measurement instrument are supplied to the sensing circuit and the output of the sensing circuit is supplied to the measurement instrument. In one embodiment, the sensing circuit uses high-breakdown transistors in order to avoid the use of passive attenuation. In a further embodiment, the sensing circuit includes broadband directional sensing circuitry.