Does anyone have recommendations for mounting toroidal mains transformers to reduce hum please?
I have 2 power supply supply boxes each with 2 toroidal mains transformers. There’s an initial hum after power-on (probably powering up the tube rectifier and other tube heaters) which dies away for a few seconds. Then it gets quite loud when the HT tube rectifiers kick-in. The hum then subsides to a level that is audible up close.
I was thinking maybe replacing the standard rubber disk with a felt pad might help.
I have 2 power supply supply boxes each with 2 toroidal mains transformers. There’s an initial hum after power-on (probably powering up the tube rectifier and other tube heaters) which dies away for a few seconds. Then it gets quite loud when the HT tube rectifiers kick-in. The hum then subsides to a level that is audible up close.
I was thinking maybe replacing the standard rubber disk with a felt pad might help.
Electromagnetically induced acoustic noise - Wikipedia
A lot of this hum can be put down to quality of design , the rubber disc was initially designed to stop turns of the transformer being "shorted out " by the casing.
But it is also the case if hum is present then a more audible insulated material could cut down the direct transmission of the transformer hum to the casing which acts like an "amplifier" in increasing the audibility of the hum.
A lot of this hum can be put down to quality of design , the rubber disc was initially designed to stop turns of the transformer being "shorted out " by the casing.
But it is also the case if hum is present then a more audible insulated material could cut down the direct transmission of the transformer hum to the casing which acts like an "amplifier" in increasing the audibility of the hum.
Try to rotate it.
In some cases helps.
I have here in Roma a supplier that for toroidal trafo use a low induction for calculation and a screen between primary and secondary plus a external coil
This reduce the flux
In some cases helps.
I have here in Roma a supplier that for toroidal trafo use a low induction for calculation and a screen between primary and secondary plus a external coil
This reduce the flux
I had also loud hum with certain toroidals which was completely removed after putting a DC blocker in front.
As usual the OP does not give away any usable data which is strange on a technical forum... So dch53:
1. Are you sure the toroids are the right VA rating for the job they are doing now?
2. Have you measured anything?
3. Can you tell the first diagnosis of peak currents etc. combined with a small calculation how much power the transformers deliver at start up?
4. Steel PSU boxes or aluminium?
5. Brand and types of the used transformers?
6. rectifier tube type?
The DC blocker also seems a must with many toroids. Another common made mistake is to sandwich the toroid between 2 metal plates that are in connection with eachother. There will then be a shorted winding.
IF the VA rating is right, a DC blocker is used and the hum persists... one could think of potting the toroids but only if it is mechanical hum by the windings and the transformers don't heat up (so overdimensioned a little).
1. Are you sure the toroids are the right VA rating for the job they are doing now?
2. Have you measured anything?
3. Can you tell the first diagnosis of peak currents etc. combined with a small calculation how much power the transformers deliver at start up?
4. Steel PSU boxes or aluminium?
5. Brand and types of the used transformers?
6. rectifier tube type?
The DC blocker also seems a must with many toroids. Another common made mistake is to sandwich the toroid between 2 metal plates that are in connection with eachother. There will then be a shorted winding.
IF the VA rating is right, a DC blocker is used and the hum persists... one could think of potting the toroids but only if it is mechanical hum by the windings and the transformers don't heat up (so overdimensioned a little).
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Thanks for all the responses. Perhaps I was too brief with my first post.
How would I measure any DC component in the mains supply?
I'm rebuilding a four-way tube crossover; separate left and right units with separate power supplies for each. I didn't build the original.
The transformers are rated at 153VA and provide 200VAC x 2 (only one used), 12VAC and 6.3VAC. There are no currents shown on the label. Each transformer is supplying
The rectified 12VAC has 10,000uF on it.
The rectified 200VAC has 10uF > 10H > 220uF > 1.5k > 220uF.
I haven't done any in-rush current calculations.
I'll try a felt pad between the transformers and the 5mm plates they're mounted on. Also some high-density foam pads between the plate and the bottom of the chassis.
How would I measure any DC component in the mains supply?
I'm rebuilding a four-way tube crossover; separate left and right units with separate power supplies for each. I didn't build the original.
The transformers are rated at 153VA and provide 200VAC x 2 (only one used), 12VAC and 6.3VAC. There are no currents shown on the label. Each transformer is supplying
- 200VAC secondary:~60mA
- 12VAC secondary: ~0.7A
- 6.3VAC secondary 1 (6X4 rectifier heater): 0.6A
The rectified 12VAC has 10,000uF on it.
The rectified 200VAC has 10uF > 10H > 220uF > 1.5k > 220uF.
I haven't done any in-rush current calculations.
I'll try a felt pad between the transformers and the 5mm plates they're mounted on. Also some high-density foam pads between the plate and the bottom of the chassis.
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Have you tried to use both 200V windings in parallel? I would first determine what the root cause is before changing anything mechanically, certainly to non standard things.
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Excellent suggestion. I'll try that.
When I received the units to rebuild both windings were used on each transformer to generate a rectified and filtered 250V. I reconfigured the power supply to produce ±150V and had an extra winding left over in each transformer.
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A plethora of sources pollutes today's AC power mains with all sorts of trash. 😡 Disposing of any DC bias is easy enough for a DIYer. Use "Da Blok"!
Another thing to do with toroidal power trafos is placing ferrite beads on the primary side connections. Toroids exhibit a large bandwidth and can pass crud into PSUs.
Another thing to do with toroidal power trafos is placing ferrite beads on the primary side connections. Toroids exhibit a large bandwidth and can pass crud into PSUs.
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First of all you have to look if it is 50 (or 60) hz or 100 (120Hz) Hz with a scope and a corret test set
Il it is 50 or 60 hz is concatenation with toro.
If it is 100 or 120 is coming from power stage ( filtering or bad ground topology)
Walter
Il it is 50 or 60 hz is concatenation with toro.
If it is 100 or 120 is coming from power stage ( filtering or bad ground topology)
Walter
Like SMPS have a false good reputation at the dark side of audio toroids also have a false good reputation with audio DIYers. Truth is that they are not the best and that they're much too wideband and much too sensitive to DC component in mains voltage.
People, stuff that is produced most is not best, it is cheapest to manufacture!
People, stuff that is produced most is not best, it is cheapest to manufacture!
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Toroidals make bad power supply transformers and good Output transformers for the very reason that they are wideband. They are smaller and lighter than EI transformers and so they are popular with manufacturers.
However I have to say that a properly designed audio grade SMPS is hard to beat in terms of power delivery and lack of hash and noise.
Shoog
However I have to say that a properly designed audio grade SMPS is hard to beat in terms of power delivery and lack of hash and noise.
Shoog
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I'm still waiting for a real scope trace showing DC on their mains line. So far nobody can produce one
Anyone can when it occurs en when the right equipment is there but not many have a scope that is safe for mains measurement use. Mine is the required differential one and I still have sweaty hands when measuring straight on mains lines. Anyone that is professionally in electro has followed at least 1 course where the DC part is discussed. Same at short circuit theory and practice where a large DC component occurs.
So, one can deny facts 🙂 but then why do the DC blockers work?
Sometimes it maybe is better to accept knowledge and get along with the newly acquired wisdom.
So, one can deny facts 🙂 but then why do the DC blockers work?
Sometimes it maybe is better to accept knowledge and get along with the newly acquired wisdom.
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The input wiring on one channel is close the toroid. I would put the mains inlet on the left and the inputs on the right so they don't cross.
I'd have had the mains entering on the left too but I had the cutouts back-to-front in the drawing I gave the laser cutter! The lovely chassis came from China and ordering new back panels isn't an option.
Sorry I got confused. This is just a power supply box and the hum is coming from the box correct? If the toroid's are mounted on a steel panel, then space them away from the panel or use aluminum. It possible its acting as a sound board.
Yes. It's mounted on a 5mm aluminium plate. There are 15 screws into spacers on the bottom of the chassis.
When I put the second one together I'll try a felt pad under the toroid and some high-density foam rubber between the base plate and the bottom of the chassis. If there's a major improvement I'll retrofit the same to the first one.
I'll also wire the 200V secondaries in parallel in both units.