I have a question regarding transformer hum. I have completed the psu and aleph J board for one channel (I am making mono blocks). The psu and the psu with Aleph board passed the DBT. I have set the bias and dc offset without problem. I hooked up a speaker and my iphone and it sounds great. With my ear right up against the speaker I hear no hum whatsoever. However, the transformer is humming. If I disconnect either the positive or the negative rail from the Aleph board, the hum disappears. Is this typical? Maybe once in the chassis the hum won't be noticeable? I have attached a few pictures so you can get an idea of the setup.
Thanks,
Jazzzman
Thanks,
Jazzzman
Attachments
Any chance you might have some dc on the power line? That might come from things like fluorescent lighting or power equipment on the same circuit.
I'm guessing your transformer is 250VA which should be adequate for a single channel.
I'm guessing your transformer is 250VA which should be adequate for a single channel.
The transformer is 250 VA. The power line is a dedicated line from the electrical panel in the house to my backyard workshop. That line powers the overhead LED's in the workshop and the outlets. The only thing plugged into the outlets at the time of the test was the transformer.
Your picture shows the power supply pcb sitting directly on a metal platform. Do you have insulating material between the two?
My question wasn't about the transformer. Or did you place that pad between the pcb and the metal platform? I was concerned that the bottom of the pcb may be shorting against the metal.
![IMG_8637[7838].jpg](/community/data/attachments/1010/1010527-69608c193a66682f469fbce1f39b5978.jpg?hash=aWCMGTpmaC)
Disconnecting one rail will prevent any current from running through the MOSFETs - hence no hum (the transformer is not loaded).
You may need to dampen the transformer. There are provisions for that on the PS PCB.... give it a go. I think there's a thread called Quasimodo or something like that.
If the transformer is buzzing only when loaded (when there's a quiescent current running through the MOSFETs) - you probably don't have a DC in your mains.
Otherwise... it's just a noisy transformer.
Okay, I read through the threads. It seems I would need a scope to find the correct values for the snubbers. I don’t have a scope, so I am out of luck as far as that goes. Although it appears that the snubbers help if one has oscillation. I don’t think my hum is from oscillation, but then what do I know.
Maybe putting a bigger rubber pad under the transformer would help? I have another identical transformer for the other channel. I could try that one to see if is a problem with the transformer.
Maybe some transformer hum is to be expected?
Maybe putting a bigger rubber pad under the transformer would help? I have another identical transformer for the other channel. I could try that one to see if is a problem with the transformer.
Maybe some transformer hum is to be expected?
Thank you. That is a great resource! Happily, my transformer is listed😀. Avel Lindberg 250VA 18-18 volts. 18R and Cx 10nF and Cs 150nF. I am using the discrete bridges instead of the diodes on my universal psu. I believe the snubber circuit goes on the AC side of the bridge, but I would appreciate confirmation that I am correct or incorrect before I hook it up.
Thanks in advance.
Thanks in advance.
The snubber is connected across the transformer secondary. For a 250VA transformer with 2 x 18VAC secondaries, you'd want a first snubber across the first 18VAC secondary, and a second snubber across the second 18VAC secondary.
Thanks, Mark. It is too bad they closed Frye’s and Radio Shack. I’ll have to bite the bullet and place another order with Mouser.
Would these fit the bill:
18R Vishay 5% metal film resistor; 3W
https://www.mouser.com/ProductDetai...R03000201809JAC00?qs=LCMWAU1DZczMyMZeEfOnFQ==
.01uF Kemet 5% film capacitor; 30V AC; 50V DC
https://www.mouser.com/ProductDetail/KEMET/SMR5103J50J01L4BULK?qs=9OvERMBOKbb1GzMQFaudZA==
.15uF Vishay 5% film capacitor; 40V AC; 63V DC
https://www.mouser.com/ProductDetail/Vishay-BC-Components/BFC236612154?qs=Ypa0Bugdmhqh6NfswsKAew==
18R Vishay 5% metal film resistor; 3W
https://www.mouser.com/ProductDetai...R03000201809JAC00?qs=LCMWAU1DZczMyMZeEfOnFQ==
.01uF Kemet 5% film capacitor; 30V AC; 50V DC
https://www.mouser.com/ProductDetail/KEMET/SMR5103J50J01L4BULK?qs=9OvERMBOKbb1GzMQFaudZA==
.15uF Vishay 5% film capacitor; 40V AC; 63V DC
https://www.mouser.com/ProductDetail/Vishay-BC-Components/BFC236612154?qs=Ypa0Bugdmhqh6NfswsKAew==
They are all good. The resistor will probably have to be soldered vertically... but that's okay,