Finally got back to it again. It was a false alarm. The humming noise and a crackling sound seem to be some hum and the crackling was a microphonic I believe. It is actually working. It still has a fair amount of hum if no input signal is coming. The moment there is any input signal - the humming becomes almost none. Now I need to hunt the humming down.
No surprise with the original filter cap still installed. Wait till you get the new one in.
Speaking of hum, once you have converted this unit to a 3-prong power cord, it can only be used trouble-free with floating sources (either 2-prong power cord with conventional transformer supply or battery-operated). Any PC or other device powered by a SMPS of a certain size is likely to exhibit ground loop noise.
Speaking of hum, once you have converted this unit to a 3-prong power cord, it can only be used trouble-free with floating sources (either 2-prong power cord with conventional transformer supply or battery-operated). Any PC or other device powered by a SMPS of a certain size is likely to exhibit ground loop noise.
Hi sgrossklass
I changed the filter caps with CDE electrolytics, 56mfd, 400vdc. I was using this with a portable mp3 player - so hopefully no groundloop. While the mp3 player is connected, it is quite humfree. However - the moment there is nothing connected, I get a fairly strong buzz. It happens even when the mp3 player goes to sleep. I did try with a raspberry pi via usb sound card, and like you said the buzz was much worse - perhaps the ground loop.
Thanks
I changed the filter caps with CDE electrolytics, 56mfd, 400vdc. I was using this with a portable mp3 player - so hopefully no groundloop. While the mp3 player is connected, it is quite humfree. However - the moment there is nothing connected, I get a fairly strong buzz. It happens even when the mp3 player goes to sleep. I did try with a raspberry pi via usb sound card, and like you said the buzz was much worse - perhaps the ground loop.
Thanks
You mean the input line from the audio signal to the ground ? Does it need to go through a bigger resister than the one between input line to the preamp grid? I have a 100 ohm there at present.
Also - raspberry pi is running with a 2 prong plug - 5v charger basically. So there should not be a ground loop right?
Also - raspberry pi is running with a 2 prong plug - 5v charger basically. So there should not be a ground loop right?
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