On 2/2/2021 6:35 PM, gareth magennis wrote:
How can I force this motorboating to happen on my bench, so I can deal with it?
I've not seen it yet.
If it only happens when connected to a patchbay, it's likely due to the
cable capacitance hanging across the output.
You should ask the owner with the problem a couple of questions:
1. How long are the cables between the EQ and the patchbay? If it's
going to a normalled jack, add the length of the cable between the
normalled jack of the pair to wherever it goes.
2. If it's going to a normalled jack, what's that jack going to?
or
Does it motorboat if the normalled connection is broken (stick a cable
in the "destination" patchbay jack)
You could experiment with loading the output with a capacitor. Start
with 500 pF and go up in value to about 0.01 uF to see if you can make
it take off.
I agree than 100 ohms sounds like a pretty hefty load, but you can see
what the source impedance really is by putting in a tone and measuring
the open circuit voltage at the output. Then hang resistance across it
until the voltage drops in half (6 dB if you're using a meter calibrated
in dB). The resistance value that gives you the 6 dB drop will be
representative of the output impedance of the unit.
--
For a good time, call
http://mikeriversaudio.wordpress.com