My goal is to show how output relay contacts may worsen THD of a high power amplifier. The amplifier under test is this one:
and the output relay under test is Finder 40.31.9.024.0000 type with AgNi contacts. It has maximum contact current of 20A and is rated at 10A ac current with resistive load. The tested parameter was THD vs. output power at 1kHz into 4ohm and 2.2ohm resistive loads. Measuring bandwidth was 45kHz.
1. Load 4 ohm
Distortion is same up to 20W/4ohm. Then we can see and effect of nonlinear contact resistance, increasing THD (orange plot). Measurements were repeated with consistent results.
2. Load 2.2 ohm
This is a demanding load to any contacts in the signal path. We can see that up to 10W is distortion almost identical, above 10W we can see effect of the nonlinear contact resistance and increased distortion (violet plot).
Output mechanical relays are a two-bladed sword. They are easy to use, however their contacts are nonlinear and deteriorate with number of DC fault current breakdowns, due to arcing on contacts. I have not found yet a contact material that would not worsen amplifier parameters.
and the output relay under test is Finder 40.31.9.024.0000 type with AgNi contacts. It has maximum contact current of 20A and is rated at 10A ac current with resistive load. The tested parameter was THD vs. output power at 1kHz into 4ohm and 2.2ohm resistive loads. Measuring bandwidth was 45kHz.
1. Load 4 ohm
Distortion is same up to 20W/4ohm. Then we can see and effect of nonlinear contact resistance, increasing THD (orange plot). Measurements were repeated with consistent results.
2. Load 2.2 ohm
This is a demanding load to any contacts in the signal path. We can see that up to 10W is distortion almost identical, above 10W we can see effect of the nonlinear contact resistance and increased distortion (violet plot).
Output mechanical relays are a two-bladed sword. They are easy to use, however their contacts are nonlinear and deteriorate with number of DC fault current breakdowns, due to arcing on contacts. I have not found yet a contact material that would not worsen amplifier parameters.
