A while ago I build a wooden housing for a K-16LS tube amp kit. However, its been sitting my lounge for some time collecting dust. Although it works, it's got a noticeable hum. I live in NZ so have 230V/50Hz power supply and the hum is clearly 50Hz and it's harmonics (I measured it using a simple audio spectrogram).
Attached are some photos. The housing is entirely wooden, except for the back plate for the audio input/output and the front plate for the volume knobs.
After turning the amp on it takes a few seconds for the hum to appear, it's quiet at first, but then gets louder over a minute where it reaches maximum hum. The hum increases linearly as I increase the volume. The hum gets worse a while after I put the top cover on the amp housing, I presume because it's getting much warmer. This hum is louder and sounds "angrier".
Sometimes when the amp has been running for a while, maybe 10 to 30 minutes it can make some really intense hums... very angry noises. I've noticed this when the music being played is stopped, then the normal hum is there for 0.5 to 1.0 seconds, but then a very loud hum appears for 1 to many seconds and then disappears, all this time the music has been stopped.
Any ideas on how to troubleshoot? My equipment is limited.
Attached are some photos so you can see the layout of the amp.
Attached are some photos. The housing is entirely wooden, except for the back plate for the audio input/output and the front plate for the volume knobs.
After turning the amp on it takes a few seconds for the hum to appear, it's quiet at first, but then gets louder over a minute where it reaches maximum hum. The hum increases linearly as I increase the volume. The hum gets worse a while after I put the top cover on the amp housing, I presume because it's getting much warmer. This hum is louder and sounds "angrier".
Sometimes when the amp has been running for a while, maybe 10 to 30 minutes it can make some really intense hums... very angry noises. I've noticed this when the music being played is stopped, then the normal hum is there for 0.5 to 1.0 seconds, but then a very loud hum appears for 1 to many seconds and then disappears, all this time the music has been stopped.
Any ideas on how to troubleshoot? My equipment is limited.
Attached are some photos so you can see the layout of the amp.
Attachments
The volume and tone pots and the piece of metal that holds the pots are connected to each other by green wires. I assume these wires connect the ground sides of the pots to each other and to the metal plate. This creates ground loops between the two tone pots (since they are already grounded at the circuit board) and between the two circuit boards (the grounds of the two circuit boards are already connected to eachother by one of the the small white wires so connecting the grounds of the volume pot and the tone pots creates a second ground connection).
What happens if you unsolder/cut the left and the middle green wire at the pots?
What happens if you unsolder/cut the left and the middle green wire at the pots?
Last edited:
Hum can cause by many issues. In order to trouble-shooting, you want to disconnect the input wire until you hear no hum. Just connect the speakers and amp, then try one thing at a time. It's pretty hard to look at the picture if you solder all the sockets correctly. You have to check every single of them and all the wiring.
Edcor OPT in S5 Electronics K-16LS kit?
You can disconnect RCA interconnect cable from one channel to test if the hum is caused by multiple ground loop in screen of interconnect cable. The screen of 2 cable should be joined together and ground at one place (you probably has another ground at the sending side?). There is a video should there is no hum problem in unmodified amp: Model K-16LS 16 Watt Stereo Vacuum Tube Amplifier Kit - YouTube
You can disconnect RCA interconnect cable from one channel to test if the hum is caused by multiple ground loop in screen of interconnect cable. The screen of 2 cable should be joined together and ground at one place (you probably has another ground at the sending side?). There is a video should there is no hum problem in unmodified amp: Model K-16LS 16 Watt Stereo Vacuum Tube Amplifier Kit - YouTube
Check your heating supply. Try disconnecting the heater for a second when the amplifier is hot and running; does the hum disappear? Do you have your heater connected to a DC voltage (heater elevated)? And you can try a DC source for your heater and listen to the effect.
Regards, Gerrit
Regards, Gerrit