You are reading a single comment by @ChainBreaker and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
ChainBreaker
@Airhead @danb
Regarding my rogue hum between pre and power amp.
I am an idiot.
I got some great advice on the CU forum to plug in just one end of the interconnect and test for resistance between centre pin of the other end of the IC and chassis ground.
I spent a while testing and recording the results before the penny dropped. Outer connection (return) to chassis ground gave me around 10kΩ resistance with the old ICs but 0Ω with the new ones. So why would that be?
The new ICs have a slightly shorter centre pin and so the RCA plug seats more deeply than the originals. The return connection of the outer RCA plug on the new IC was making a connection between the two cases. Because both pre and power amps have double insulated cases (ie. they are ungrounded) and each contains a toroidal transformer, the cases were getting mildly excited by the electromagnets. Pushing the RCA plug on too far was introducing this to the return path of the interconnect signal.
Solution: don’t push the IC plugs on quite so far. Hum now completely gone.