Hi!
I finished preamp K8020. Left channel works fine, but the right one not. Volume is much lower than the left, and when I add volume the sound distorts, but not totally. I have checked all the solderings and changed places of the capacitors and measured all the resistors. Tubes are both working properly.
Any ideas before I reassembly whole preamp? Voltages are normal (an should be, because the left channel is okay)
The poweramplifier K4040 I have had years, and it works fine, but only after I replaced the metallic cover of the chassis with a thick plastic one. With the metallic plate there was a lot of hum, and it did not react to the turning of the transformers as adviced in the manual. Solutions to stop the hum with the metallic cover?
[quote=“VEL417”]As both channels are identical, you can compare signals from input to output.
This will allow you to locate the cause of troubles.
As for K4040, most likely a hum loop is created.
Check cabling and make sure all panels are grounded.[/quote]
I continue with checking. I presume that I don’t have to mind the transistors as they are not connected to the audiosignal. Are the connectors of the tubes critical?
It´s strange with th K4040, the metallic plate don´t have to be connected, only when you lower it, so that it surrounds the tubes and the humming starts. Sort of magnetic field? The grounding I checked many times. But with the dark brown stained plastic cover it works nice, and look’s okay (you can even see the inside LED lit)
It is very strange that there is a hum problem when the metallic cover is put in place.
This has never been reported.
Normally, this cover shields the circuit from external radiation.
Can you determine if the hum is 100Hz or 50Hz?
If it is 100Hz, it is power supply induced.
If it is 50Hz, then it is magnetically induced, via the transformers.