I've always found buzz/hum issues to be one of the hardest issues to track down in amps. Anyone have any general methods or tips to share? Is there a way to prove it is or isn't big power supply caps without spending a lot of money to replace them? Sometimes I've used the scope and see some noise only to find it isn't the noise I am hearing. Any way to tell grounding issues apart from power supply issues?
I mostly work on vintage solid state gear.
I mostly work on vintage solid state gear.
Unless your home is next to a utilities company dropdown transformer hum is usually connected to the power supply which gets through old/faulty filtration components in your gear.
If its RF induced you or your neighbor has gear that is transmitting radiation.
If it is mains induced then you have "dirty mains " .
To test for RF buy a small broadband spy detector /RF radiation detector --I have one its handy .
Your post can generate very many replies as it will take a webpage or more of the issues that need to be attended to if you have problems.
If its RF induced you or your neighbor has gear that is transmitting radiation.
If it is mains induced then you have "dirty mains " .
To test for RF buy a small broadband spy detector /RF radiation detector --I have one its handy .
Your post can generate very many replies as it will take a webpage or more of the issues that need to be attended to if you have problems.
I disagree, hum is nearly always caused by ground loops and loop area in designs. You should design the ground network and not wait until you are putting things together.
I see "buzz and hum" as two separate issues.
A buzz possibly occuring in the transformer may be due to vibration, DC on AC supply or vibration of transformer laminates. Secure transformer mounting screws, try a "dc blocker", some also suggest dipping the transformer in some sort of varnish, no experiance so wont comment further.
Hums may be mains 50/60Hz or rectified 100/120Hz. First step always work out which.
An oscilloscope is helpful, eg, if you have 50/60Hz at the main filter caps then suspect the rectifier. Don't confuse the normal +ve/-ve ripple as hum. Start at the speaker posts so you know what the hum "looks like". Also, hum the increases with volume is most likely introduced before the volume pot. Hums are tricky to track down, difficult to generalize. Certainly groud loops are an issue.
A buzz possibly occuring in the transformer may be due to vibration, DC on AC supply or vibration of transformer laminates. Secure transformer mounting screws, try a "dc blocker", some also suggest dipping the transformer in some sort of varnish, no experiance so wont comment further.
Hums may be mains 50/60Hz or rectified 100/120Hz. First step always work out which.
An oscilloscope is helpful, eg, if you have 50/60Hz at the main filter caps then suspect the rectifier. Don't confuse the normal +ve/-ve ripple as hum. Start at the speaker posts so you know what the hum "looks like". Also, hum the increases with volume is most likely introduced before the volume pot. Hums are tricky to track down, difficult to generalize. Certainly groud loops are an issue.
First thing I do is disconnect everything except the speakers. If the hum goes away then you likely have a ground loop with whatever other equipment was previously attached.
You can also try re-orienting the transformer. If there is any radiated noise, it is not normally uniformly radiated and one orientation may be better or worse than another. If not too difficult (or dangerous) try moving the transformer outside the case temporarily to see if that reduces the hum.
If you haven't already, have a read of this article. Audio Component Grounding and Interconnection - diyAudio note some of the images seem to have died. The wayback machine has them though. Audio Component Grounding and Interconnection - diyAudio
Tony.
You can also try re-orienting the transformer. If there is any radiated noise, it is not normally uniformly radiated and one orientation may be better or worse than another. If not too difficult (or dangerous) try moving the transformer outside the case temporarily to see if that reduces the hum.
If you haven't already, have a read of this article. Audio Component Grounding and Interconnection - diyAudio note some of the images seem to have died. The wayback machine has them though. Audio Component Grounding and Interconnection - diyAudio
Tony.
Asking mostly for existing equipment that has been designed correctly and used to work without a buzz then one snuck in.