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Next place to check is the phono connectors on the phono amp. They are renowned for developing faults. Sometimes interconnects have slightly varying pin sizes and weights of cable+connector can make a difference. Could be cold solder joint or wear and tear in the connectors.
Airhead-
Next place to check is the phono connectors on the phono amp. They are renowned for developing faults. Sometimes interconnects have slightly varying pin sizes and weights of cable+connector can make a difference. Could be cold solder joint or wear and tear in the connectors.
It's a pre and power amp but yeah, I'm basically expecting dry solder and/or worn RCA connectors on both amps. I'll have all the caps replaced at the same time to be safe. The confusing thing is that when you look in to the different test scenarios, the results don't actually make much sense other than there must be several problems overlaying each other. It's useful to have a reference point s0 I can test them after they've been serviced.
I spent an hour this morning beforehand cleaning the interconnect plugs with alcohol (Lidl's finest Gin as I didn't have any contact cleaner).
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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.
freddo
Cross-posting from the CU forum to see if anyone (particularly the phonophiles here) can help.
I have a 50Hz-60Hz hum on one channel with only preamp and power amp connected. This problem has only manifested itself with new interconnects. The obvious conclusion is that the ICs are faulty, but I believe it is something more fundamental to the pre or power amp. Here's the results of my testing two sets of ICs, IC1 is a cheap set and IC2 are the new ones.
Possible conclusions:
Despite the lack of CE markings on either the pre or power amp, I believe that both units are double insulated (ie. no earth connection to the case) as there are only two pins on the mains cable socket. Therefore a ground-lift circuit will not help here.
Because PreTest 3 shows hum on the right speaker I can assume that the R channel on the Power amp is faulty and it is somehow picking up a current on the R channel from somewhere inside the power amp.
I seem to be able to also create hum on the L channel of the Power amp using either of the L or R preamp channels as sources, but only using IC2, not IC1. I don't have a decent explanation for this. Is it possible that the small amount of resistance in IC1s would isolate the signal sufficiently? Or that interconnects have a sound profile such that they might allow a given frequency to flow or be impeded? That would blow my mind.
Perplexingly I seem to be able to kill the Power amp R channel hum with IC1s but not IC2s from either L or R pre-amp source. What might explain this?
I'm going to get both the units serviced but I would really appreciate any thoughts as to what might be going on here as I don't feel qualified to make sense of the results.