Buzzing is nonexistant in your transformers because you design for less magnetizing force. Not as far up the BH curve, more turns per volt. Takes more iron and copper but that’s how you make them quiet. The varnish gives them a nice professional feel, keeps them from developing surface rust, and stabilizes the windings themselves (which can buzz under heavy load - especially low voltage high current windings).
No amount of varnish, rubber grommets or prayer will fix a transformer running in saturation. If you got an Edcor that’s being run too hard, it was just a design mistake. It happens. Not really a mistake, as it will run properly - utility transformers are run pretty hard into saturation too, and often you can hear them at the end of the block. That’s a “mistake” for a trafo designed for audio where one EXPECTS quiet.
I personally have quite a few Hammond 270 series transformers and so far none have made any noise.
They are all under 200VA size, wonder if that is a a factor.
Some districts power line distortion is higher than others and perhaps the 270 lacks the magnetic margins to handle the harmonics without noise.
When I lived on the west coast the power line looked almost like a square wave it was so distorted.
Could that be a factor why some users find the 270s fine and others are bothered by them?
Good to know the 370s are better so I will have a fall back if I find I have a project with a noisy 270 transformer.
They are all under 200VA size, wonder if that is a a factor.
Some districts power line distortion is higher than others and perhaps the 270 lacks the magnetic margins to handle the harmonics without noise.
When I lived on the west coast the power line looked almost like a square wave it was so distorted.
Could that be a factor why some users find the 270s fine and others are bothered by them?
Good to know the 370s are better so I will have a fall back if I find I have a project with a noisy 270 transformer.
Surprised that no one here mentioned the number one issue causing power transformer hum. That's a power supply design with far too low a conduction angle forcing extreme current spikes in the transformer secondary. Can sometimes be fixed simply by keeping the first capacitor relatively small. Sometimes a choke input supply will fix the issue if the current requirements are high. This is especially a problem with DIY supplies using solid state rectification.
I’ve had some that make as much racket as under designed EIs. Run the flux density too high and it hums, no matter how it’s made.
yes, temperature rise is tops in my list of priorities, aside from looking for high quality cores, i run them at low flux densities....
Surprise, surprise, run a component outside of spec and it doesn't perform as intended. My experience with Edcor PTs is disappointing within specs.
Oh, they were in spec. 115 volt 50/60 Hz primary and they were loud enough at 60 Hz. Made for 48V telecom power supplies, so if they buzzed up a storm no one would care. I ended up putting an extra winding in series with the primary, and running them at lower output. Then they were quiet enough to use in PA amplifiers.
The same is probably true of the Edcor, but it’s far harder to add the extra turns on them than it was on toroids.
The same is probably true of the Edcor, but it’s far harder to add the extra turns on them than it was on toroids.
Flux density seems to be important. I bought some small Hammond EI transformers and chokes last year to build a rather ambitious DHL filament power supply. Turned out most of them were unusable due to vibrations. Bought new chokes from Lundahl instead (much more expensive) and 400/24V industrial control transformers to be used as 230/14 transformers.
Good, because industrial control transformers operated at nominal voltage tend to make a lot of racket. I used to use 240 to 120/240 units at 120 V to make the 60-0-60’s required for 400 watts per channel at 4 ohms (solid state of course). Before Antek, that was the only sanely priced option for this. At half voltage they are quiet.
There are two main buzzing causes in a power transformer.
1. Core magnetizing forces. This manifests itself at unloaded transformers. With EI transformers, the culprit is loose laminations that could be glued together into a solid block using varnish. For C cores, it could be a loose lamination or loose core surfaces. It is mandatory for C cores to be glued together for noise free operation. For torroids, it could be loose laminations too.
2. Secondary peak current draws. These happen during loading and capacitor input filters. To fix it, secondary layers need to be fixed together as best as possible and the bobbin needs to be tight to the core. Potting helps a lot for this. I find this problem manifests more with higher leakage inductance designs.
1. Core magnetizing forces. This manifests itself at unloaded transformers. With EI transformers, the culprit is loose laminations that could be glued together into a solid block using varnish. For C cores, it could be a loose lamination or loose core surfaces. It is mandatory for C cores to be glued together for noise free operation. For torroids, it could be loose laminations too.
2. Secondary peak current draws. These happen during loading and capacitor input filters. To fix it, secondary layers need to be fixed together as best as possible and the bobbin needs to be tight to the core. Potting helps a lot for this. I find this problem manifests more with higher leakage inductance designs.
#2 resulted to #1, they are closely related...
magneto motive force or mmf, or ampere turns per inch is pretty much fixed once the transformer is built up, so it is down to the load current draw that leads forward to core saturation..
the obvious fix is to not allow current draws that lead to saturation....
magneto motive force or mmf, or ampere turns per inch is pretty much fixed once the transformer is built up, so it is down to the load current draw that leads forward to core saturation..
the obvious fix is to not allow current draws that lead to saturation....
Lower voltage high current windings with relatively few turns tend to make racket from the windings themselves. With low current tube power trafos you have not only low current but many layers of turns so they tend to be constrained even before varnishing. Battery chargers are loud enough idling, even worse while charging. In a tube amp, a filament transformer rectified to DC would probably be about the worst case for this. Loudest trafos I’ve ever heard in audio equipment are the power trafos on the Crest CA18’s (Moderately high volts at very high current). Yeah, they hum a little at idle. Several members here have dipped them and cured that. Crank it to WAR VOLUME and you’d swear that transformer was going to come apart. Normally you can’t hear it over the music, but if it’s running in a remote location or on a dummy load it’s unnerving….
Core saturation is related to alternating voltage, not current.
Ba = Vrms / 4.44 * Afe * T * f
However windings noise, bobbin noise depend on current draw. They need not be confused. The type of noise will also depend of current draw waveform and bobbin construction.
A transformer can become highly noisy on high current draw, it can also become hot due to Rdc losses + poor cooling, but this is no conclusion that a core saturates.
A good indicator a core is potentially saturating is hot temperature during idle, unloaded operation.