I tried to use compact PCB mount power transformer for my updated headphone hybrid. I've got an unpleasant surprise: a lot of buzz in audio path as well as from transformer itself. Even a screwdriver vibrates in my hand, if I bring it close to the transformer.
I admit that my PCB layout can be non optimal, but abnormally high level of flux leakage is obvious too.
So I'm asking for advise: should I try another flat pack transformer, or go back to toroid?
http://www.mouser.com/ds/2/643/LP-892507.pdf
I admit that my PCB layout can be non optimal, but abnormally high level of flux leakage is obvious too.
So I'm asking for advise: should I try another flat pack transformer, or go back to toroid?
http://www.mouser.com/ds/2/643/LP-892507.pdf
Turn it 90 degrees and the induction will reduce. I can't see your output transformer positioning.
It doesn't have output transformer. It has BJT CFP push-pull output stage instead. Common cathode stage is DC coupled with power amplifier through bipolar inverter which "flips" 45 volts of cathode voltage around 30 volts point to produce 15 volts (the middle point of low power side). The output is AC coupled but nevertheless I have added DC servo circuit to keep push-pull perfectly centered. It required some brainstorming and finally I came to decision to use servo-driven voltage controlled current source which controls cathode current through Wilson mirror.
First design with manually adjustable cathode current source and toroidal power transformer works pretty well for months.
Many successful designs have a copper band soldered around the windings of the transformer. they also keep a frame transformer 10 cm away from high gain circuits, and put a ferrous steel box around the transformer. You have a fuse right next to the transformer, making a steel bulkhead a short hazard. Looks as if you have a vacuum tube 4 cm from the transformer. I'd get a pair of tin shears & a roll of .006 ferous shim stock, forming a box around your transformer. This might work but distance would help even more. You could tape the steel edge near the fuse to cut the hazard of it touching the fuse. Or some scrap appliance, there is no shortage of sheet steel going to the dump weekly. Debur the edges with a file or wear gloves when handling cut steel. I bend thin steel by clamping in a vise & hitting with a hammer. I have no access to a $4000 press brake.
The advantage of a frame transformer, they have some built in RF interference suppression. My daily use amp amp, with only a .01 uf disk cap across the output of the EI transformer, rejects interference from CB police and aircraft band radios, cell phones, an AM radio station, and lamp dimmer hash, coming in the power feed. I know about the prevalance of all these sources because I had to treat the signal input to get rid of them. A toroid transformer likely would need significant number of parts on the AC feed to keep RF interference out.
The advantage of a frame transformer, they have some built in RF interference suppression. My daily use amp amp, with only a .01 uf disk cap across the output of the EI transformer, rejects interference from CB police and aircraft band radios, cell phones, an AM radio station, and lamp dimmer hash, coming in the power feed. I know about the prevalance of all these sources because I had to treat the signal input to get rid of them. A toroid transformer likely would need significant number of parts on the AC feed to keep RF interference out.
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The transfromer shown in the pic resembles a door bell tranny. So no need to wonder...
Best regards!
Best regards!
I've used those as filament supply transformers and never noticed any issues with hum or vibrations from them.
What is the transformer rating and the load of your circuit?
What is the transformer rating and the load of your circuit?
Do you use it properly?
This kind of transformer normally has two identical sets of winding on each leg, and sometimes, for some applications, it would be tempting to use them separately, but they are intended to be connected by pairs, generally in series, sometimes in parallel, to balance the induction.
If you use one leg (or part of) as a primary, and the other as a secondary, you will get all the symptoms you describe, because all the flux needs to pass through the iron, and when the secondary is heavily loaded, it tries to block the flux which tends to escape from the naked iron parts.
It also leads to a high leakage inductance
This kind of transformer normally has two identical sets of winding on each leg, and sometimes, for some applications, it would be tempting to use them separately, but they are intended to be connected by pairs, generally in series, sometimes in parallel, to balance the induction.
If you use one leg (or part of) as a primary, and the other as a secondary, you will get all the symptoms you describe, because all the flux needs to pass through the iron, and when the secondary is heavily loaded, it tries to block the flux which tends to escape from the naked iron parts.
It also leads to a high leakage inductance
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