I have been using a N.E.W A-20.1 amplifier (based on Pass design?) for a while. Today, for no reason, the transformer started to hum very loudly.
I didn't make any modifications to the amp, change any components in my system, move the amplifier, etc. There was no hum yesterday
I opened the top cover to check out the transformer. It is very securely fitted between two metal plates with rubber sheets in between. Don't know what is wrong.
Anyone who can recommend a way to fix or diagnose the problem?
I didn't make any modifications to the amp, change any components in my system, move the amplifier, etc. There was no hum yesterday
I opened the top cover to check out the transformer. It is very securely fitted between two metal plates with rubber sheets in between. Don't know what is wrong.
Anyone who can recommend a way to fix or diagnose the problem?
The problem fixed itself after I reconnected everything on the amplifier. Lucky 
arrgh! The hum randomly resurfaced. Guessing something is wrong with the amp after all. Don't have a schematic because the amp is like 15 years old and there is no literature on it. Is there anything that can be figured out from these pictures?
http://www.cs.mcgill.ca/~nyu3/IMGP1971.JPG
http://www.cs.mcgill.ca/~nyu3/IMGP1972.JPG
http://www.cs.mcgill.ca/~nyu3/IMGP1971.JPG
http://www.cs.mcgill.ca/~nyu3/IMGP1972.JPG
hello again.. i had an amp that had a similar symptom, it was caused by a diode in my bridge(using discrete diodes like yours).
diodes are easily tested with a dmm just unsolder one leg and measure resistance both ways, should be close to 0 ohms one way and infinite resistance the other. thats an interesting looking p/s looks like your toroid has 2 sets of secondary windings with 2
diode bridges, i don't see any fuses between the bridge rectifiers and the driver boards, how many fuses does it have??
Elwood
diodes are easily tested with a dmm just unsolder one leg and measure resistance both ways, should be close to 0 ohms one way and infinite resistance the other. thats an interesting looking p/s looks like your toroid has 2 sets of secondary windings with 2
diode bridges, i don't see any fuses between the bridge rectifiers and the driver boards, how many fuses does it have??
Elwood
hummmm
You can use you DMM set at DC at the proper volts range and check the AC, you should see 0 or possibly a dancing reading around .001 or so, if you get more then that look into a DC trap they are easy to build.
You could also have some windings going bad "short" in the trans, check the AC out before the rectifiers with out the humm and check it with the humm active if there is an appreciable difference the transformer could be on its way out. A bad rectifier will load the trans if shorted, but will cause humm at the speaker same goes for an open diode it will not load the trans but produce AC on the DC to the amp and you get hum.
You can use you DMM set at DC at the proper volts range and check the AC, you should see 0 or possibly a dancing reading around .001 or so, if you get more then that look into a DC trap they are easy to build.
You could also have some windings going bad "short" in the trans, check the AC out before the rectifiers with out the humm and check it with the humm active if there is an appreciable difference the transformer could be on its way out. A bad rectifier will load the trans if shorted, but will cause humm at the speaker same goes for an open diode it will not load the trans but produce AC on the DC to the amp and you get hum.
Is there anyway that the top-cover-plate can be pressed down to touch the bolt through the toroid? That could form a shorted winding which would lead to noise and buzzing.
Are there any metal object or wires that could touch the toroid top-plate?
My apologies for the bad explanation.
You could probably search for "shorted turn" or something like that.
Regards TroelsM
Are there any metal object or wires that could touch the toroid top-plate?
My apologies for the bad explanation.
You could probably search for "shorted turn" or something like that.
Regards TroelsM
The transformer does not get hot, but I haven't let the amp run very long when it was humming... at most 3 minutes. The transformer does not make contact with the case, as it is covered by a plastic film and is mounted between rubber sheets. I will have to wait until the next time hum appears to test your hypothesis. For better or worse, it may be a while before it happens again.
Look for a solid state lamp dimmer in your house, or similarly
controlled appliance. The Triacs in such circuits often do not
trigger symmetrically, putting a net DC on the AC line, which
drives toroidal transformers into saturation, making them
noisy. The clue here is the intermittent nature of the noise.
controlled appliance. The Triacs in such circuits often do not
trigger symmetrically, putting a net DC on the AC line, which
drives toroidal transformers into saturation, making them
noisy. The clue here is the intermittent nature of the noise.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.