Good luck, i've never succeed to get rid of the magnetostriction noises on large transformers.
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at the moment in the condition where before was buzzing and humming
(hair dryier or washing machine or coffee grinder)
seems to be solved with the circuit above.
(hair dryier or washing machine or coffee grinder)
seems to be solved with the circuit above.
If the hair dryer has a diode in it to give it a half power setting, that could possibly put a small DC offset on the powerline when the dryer is used on its low setting, and toroids are very sensitive to any DC component in the power.
Does somebody has experience with the attached Crown circuit ?
Is DC current blocking possible without capacitors?
..applying the basic superpositioning law (right english term ?) for the AC domain here :
a DC Voltage source (example 100mV) in serial connection with a sinus source (230V eff), currents can be analyzed seperatedly (sinus source made 0V results in a DC current only, then 0V DC results in a sinus current only, then addition of the two..
well, it is more complicated : imagine a rectifier as voltage dependand switch. It is switching on, when the secondary voltage applied to the big reservoir capacitors there behind the rectifier has fallen below the applied secondary transformer voltage before (time domain, the polarity turn of the diode bridge left out).
A voltage dependand switch basically renders AC Analysis not applicable. But it helps nevertheless :
as long as the switch is open the transformer approximatedly is unloaded, so the so called magnetizing current (from the hopefully huge primary inductivity ) and the DC current (dc resistance of the primary side) are left over..in this "unloaded voltage band" the ~0.6V Diode (here 1.2V) conduction voltage Voltage suppresses DC current as long as the dc source voltage is much smaller...
So indeed, the crown circuit should block dc current without bulky electrolytics.
The voltage curve behind the primary diodes should look like a non biased class B amplifier around the zero crossing, but this is not seen by the secondary dc voltage, as the transformer secondary bridge rectifier trustworthy is turned off here..
As a con there is switching noise, but a pro is no possible serial resonance of the blocking caps and the main transformer inductivity, or a partly activated serial resonance by parameter shift (dc voltage change eg)..
Did I miss something, or is the Crown circuit simply working ?
I hope I have not oversimplified..
Have fun, Philipp
Is DC current blocking possible without capacitors?
..applying the basic superpositioning law (right english term ?) for the AC domain here :
a DC Voltage source (example 100mV) in serial connection with a sinus source (230V eff), currents can be analyzed seperatedly (sinus source made 0V results in a DC current only, then 0V DC results in a sinus current only, then addition of the two..
well, it is more complicated : imagine a rectifier as voltage dependand switch. It is switching on, when the secondary voltage applied to the big reservoir capacitors there behind the rectifier has fallen below the applied secondary transformer voltage before (time domain, the polarity turn of the diode bridge left out).
A voltage dependand switch basically renders AC Analysis not applicable. But it helps nevertheless :
as long as the switch is open the transformer approximatedly is unloaded, so the so called magnetizing current (from the hopefully huge primary inductivity ) and the DC current (dc resistance of the primary side) are left over..in this "unloaded voltage band" the ~0.6V Diode (here 1.2V) conduction voltage Voltage suppresses DC current as long as the dc source voltage is much smaller...
So indeed, the crown circuit should block dc current without bulky electrolytics.
The voltage curve behind the primary diodes should look like a non biased class B amplifier around the zero crossing, but this is not seen by the secondary dc voltage, as the transformer secondary bridge rectifier trustworthy is turned off here..
As a con there is switching noise, but a pro is no possible serial resonance of the blocking caps and the main transformer inductivity, or a partly activated serial resonance by parameter shift (dc voltage change eg)..
Did I miss something, or is the Crown circuit simply working ?
I hope I have not oversimplified..
Have fun, Philipp
Attachments
thank you, good quote from rod elliot..
I forgott the blocking diodes also are switches, rendering simple ac analysis not applicable..
but the magnetizing (idle) current is mainly inductive...I wonder, if crown made a parallel network around the transformer...I will follow this road a bit longer..
anyone got a crown circuit diagramm showing the transformer neighbourhood circuit ?
I forgott the blocking diodes also are switches, rendering simple ac analysis not applicable..
but the magnetizing (idle) current is mainly inductive...I wonder, if crown made a parallel network around the transformer...I will follow this road a bit longer..
anyone got a crown circuit diagramm showing the transformer neighbourhood circuit ?
mmmh, blind current compensation for the magnetizing (idle) current with a capacitor in parallel (maybe on the secondary before the rectifier bridge) ?
Mains frequency is fixed - but transformer inductance ?
idea is parallel resonance at 50Hz, meaning current resonance among transformer inductance and an added parallel capacitor - magnetizing current would be handshaked between inductance and capacitor - not flowing through the diodes in steady state..but behavior when rectifier turns on ?
good simulation task..
Mains frequency is fixed - but transformer inductance ?
idea is parallel resonance at 50Hz, meaning current resonance among transformer inductance and an added parallel capacitor - magnetizing current would be handshaked between inductance and capacitor - not flowing through the diodes in steady state..but behavior when rectifier turns on ?
good simulation task..
The way is to put caps in series to primary, no other solution if you got the problem
The noise from tor comes for two reasons. One is the quality of the nucleus, it is possible that in some condition the lamination is poor so in presence of dc the efficency goes low and foils can vibrate. In addtion if the trafo is calculated with a high induction to save space (and money) so the magnetization amplify the issue.
To have a good trafo you have to spend money.
When I ask for a trafo to my pusher I know that he will use a toro painted and "coocked" , in addition the calculation is made at around 50% of the nominal specs.
In this way it is impossible to have a poor stuff.
Walter
The noise from tor comes for two reasons. One is the quality of the nucleus, it is possible that in some condition the lamination is poor so in presence of dc the efficency goes low and foils can vibrate. In addtion if the trafo is calculated with a high induction to save space (and money) so the magnetization amplify the issue.
To have a good trafo you have to spend money.
When I ask for a trafo to my pusher I know that he will use a toro painted and "coocked" , in addition the calculation is made at around 50% of the nominal specs.
In this way it is impossible to have a poor stuff.
Walter
i have wounded my toroid myself on a tormach at my previous working facility.
The calculation was done by my former boss. the flux was -30% and the trafo is 3x. has a regulation that is perfect.
The nucleus is an Italian made, wetted in resin and cured under vacuum.
Btw, with the schematic attached in my previous post the problem went away. I guess is also a matter of the "un-loading" of the trasfo @ idle.
is capable of more than 20A over 24Vac, and @ idle it draws just 3 amp.
If this is OT, apologies. I'm still new to DIY and learning quite a bit. I have a previous model of one of these I got ages ago https://www.richardgrayspowercompany.com/wp-content/uploads/2017/09/RGPC-INFO-400Pro-01-web.pdf
It seems to work well for reducing hum, but I am not sure if that's from DC or some other cause. Does anyone know the innards of one of these and whether it has DC-blocking or other functions? Audiophoolery that I bought into??
It seems to work well for reducing hum, but I am not sure if that's from DC or some other cause. Does anyone know the innards of one of these and whether it has DC-blocking or other functions? Audiophoolery that I bought into??
To me seems like a balanced isolation transformer... but not sure...
Different purpose... but nonetheless useful in some situation.