Ordered a audio grade transformer from James transformers and they forgot the screen. My OCD is killing me, very miffed, James even ignored my complaint. They are normally very good. The screen is normally a standard item in their products I think (didn't specify one before and it was included)
Convince me all is well, how vital to the audio experience is the screen, the noise is generated between the power lines and ground right?
Is the screen is built between the windings and connected to OV?
Can the difference be measured?
Convince me all is well, how vital to the audio experience is the screen, the noise is generated between the power lines and ground right?
Is the screen is built between the windings and connected to OV?
Can the difference be measured?
The shield is usually used for electrostatic isolation of the two windings. It does not work in the magnetic realm at all, and care must be taken to not inadvertently created a shorted turn condition with the shield material.
It also helps prevent noise on the AC line from being capacitively coupled from the primary to the secondary winding(s). That's useful.
Only if screen is made of oxygen free copper hand forged by the Nibelungs.
Or 999 alloy Silver.
Electrostatic screens became popular in the era of AM tube receivers: they shielded the ground side from mains-borne interference ( receivers had antenna and ground connections).
Nowadays, they are almost useless, because of the regulations and ways of implementing things.
They can still have a role, when used properly (especially dual screens), but they are mostly a thing of the past: even the last contemporary AM receivers don't rely on a wire antenna or ground connection; they just use a loopstick antenna
Nowadays, they are almost useless, because of the regulations and ways of implementing things.
They can still have a role, when used properly (especially dual screens), but they are mostly a thing of the past: even the last contemporary AM receivers don't rely on a wire antenna or ground connection; they just use a loopstick antenna
Has anyone with a quasimodo noticed better stability or less ringing with screened transformer?
This means a good mains filter circuit / DC blocker would make the screen unnecessary?
This means a good mains filter circuit / DC blocker would make the screen unnecessary?
Audio related OCD may want to use two screens.
One screen to funnel currents induced by the mains voltage (and its harmonics/noise) coupling by capacitance into that screen, which is terminated at the mains PE terminal. The other screen to funnel currents induced by the secondary winding voltage (and its rectifier related harmonics and noise) coupling by capacitance into that screen, and perhaps terminated at the first filter cap negative terminal.
If you only have one screen then you get all in a tiz about where the screen should terminate to.
Some transformer standards and applications dictate the need for a screen that is rated to take worst-case fault current - that type of screen is related to protection and mitigating risk from a fault. It likely has a different function to what the OP appreciated.
One screen to funnel currents induced by the mains voltage (and its harmonics/noise) coupling by capacitance into that screen, which is terminated at the mains PE terminal. The other screen to funnel currents induced by the secondary winding voltage (and its rectifier related harmonics and noise) coupling by capacitance into that screen, and perhaps terminated at the first filter cap negative terminal.
If you only have one screen then you get all in a tiz about where the screen should terminate to.
Some transformer standards and applications dictate the need for a screen that is rated to take worst-case fault current - that type of screen is related to protection and mitigating risk from a fault. It likely has a different function to what the OP appreciated.
"Audiophile" OCD makes some people deeply worry about non-problems and paying dear $$$$$ for non solutions.
Not talking transformer screening, which Is a physical real fact of course, but stuff such as:
https://reference3a.com/features/?f...quy-CeHAQdgwDNncJaVdhy3Jv1XLgqfTIqQSFyvoq-zZY
The patented Surreal Acoustic Lens is used to prevent formation of air vortex’s generated by condensed air particles and turbulence in the deep center of loudspeaker driver cones. Inherent noise caused by this vortex is drastically reduced
All connectors, internal wiring, and metal driver parts are now treated with a -320F deep level cryogenic process.
Our cabinets are now coated with the patented material known as Nextel©. It’s a matte textured coating that absorbs light and sound.
The appropriate thickness of wire is used for each driver, such as 0.6 mm for tweeter, 0.8 mm for mid range and 1.2 mm for bass driver.
Not talking transformer screening, which Is a physical real fact of course, but stuff such as:
https://reference3a.com/features/?f...quy-CeHAQdgwDNncJaVdhy3Jv1XLgqfTIqQSFyvoq-zZY
The patented Surreal Acoustic Lens is used to prevent formation of air vortex’s generated by condensed air particles and turbulence in the deep center of loudspeaker driver cones. Inherent noise caused by this vortex is drastically reduced
All connectors, internal wiring, and metal driver parts are now treated with a -320F deep level cryogenic process.
Our cabinets are now coated with the patented material known as Nextel©. It’s a matte textured coating that absorbs light and sound.
The appropriate thickness of wire is used for each driver, such as 0.6 mm for tweeter, 0.8 mm for mid range and 1.2 mm for bass driver.
I had a solid state headphone amp and forgot to tie the screen to ground. I listened to it play and was taping it on and off to ground and could not hear any difference. I think the quality of the transformer and proper mounting and orientation play a more important role. If you can it is always a good idea to move the transformer around the project before it is cased to make sure not to pick up indused hum.
Looks like there are different opinions on the usefulness of static screens. However, you do see them used in high-end equipment, and they might still make sense. On the technical side, here are some excerpts (Google translation) on the subject, taken from the technical pages of a local transformer manufacturer (https://tauscher-transformatoren.de/html/technik.html). I think this sums it up pretty well:
"The screen serves as a static shield to attenuate network interference and voltage peaks in the high-frequency range (EMC transformer). The static shield has a green/yellow connection. ...
Greater attenuation is achieved by installing two static shields. One shield is connected to the protective conductor connection and has a green/yellow connection. The second shield has secondary potential and the connection color is black.
Copper foil is usually used as the material. However, highly permeable foil is more suitable for EMC purposes, as the attenuation is greater at higher frequencies. With highly permeable foil, attenuation increases of up to 20 dB can be achieved even at relatively low frequencies compared to Cu foil..."
"The screen serves as a static shield to attenuate network interference and voltage peaks in the high-frequency range (EMC transformer). The static shield has a green/yellow connection. ...
Greater attenuation is achieved by installing two static shields. One shield is connected to the protective conductor connection and has a green/yellow connection. The second shield has secondary potential and the connection color is black.
Copper foil is usually used as the material. However, highly permeable foil is more suitable for EMC purposes, as the attenuation is greater at higher frequencies. With highly permeable foil, attenuation increases of up to 20 dB can be achieved even at relatively low frequencies compared to Cu foil..."
While were at it, here is an opinion from someone producing high end gear. Unless I am mistaken he was even active on this forum in the past: http://vinylsavor.blogspot.com/2011/02/power-transformers.html
Dual screen windings
This is a very important feature of power transformers and it is surprising that it is not more commonly used.... Check his blog entry to see the full statement.
Dual screen windings
This is a very important feature of power transformers and it is surprising that it is not more commonly used.... Check his blog entry to see the full statement.
I approached an engineer who works for an US company(made in USA transformers) and he gave me some answers regarding audio toroidal transformers:
"The purpose of the grounded electrostatic shield is to filter any transient voltage spikes and noise that might be present as a result of capacitive coupling between two windings with different voltages....
The electrostatic shield is not absolutely necessary for an audio transformer, but it will help with the noise to a certain degree. Some of the customers request the shield and some others do not.
Adding it to the custom design will add to the cost.....
The core's magnetic flux density is the more significant factor affecting the operation of an audio transformer."
"The purpose of the grounded electrostatic shield is to filter any transient voltage spikes and noise that might be present as a result of capacitive coupling between two windings with different voltages....
The electrostatic shield is not absolutely necessary for an audio transformer, but it will help with the noise to a certain degree. Some of the customers request the shield and some others do not.
Adding it to the custom design will add to the cost.....
The core's magnetic flux density is the more significant factor affecting the operation of an audio transformer."
Say, you have a 5 layer primary, top layer carries normally 80-100% of the primary voltage. Without screen, layers are not only magnetically, but also capacitively coupled. Now, suppose a steep rising voltage spike on the primary. What would be the voltage coupled to a low voltage secondary wound on top of the primary?
Depends on many things, but one thing is sure, a steep rising spike will couple and divide first of all capacitively, highly unrelated to the winding ratio.
Principally, no matter what the nominal step-down ratio of a transformer, a short duration, say 1000V spike, could get capacitively coupled almost entirely to the secondary.
A properly done and grounded, so called static shield, intercepts this capacitive coupling.
Easy to do in a transformer with stacked laminations,
Most effective in transformers of large step-down ratio.
In an opt the fb-winding propably wants to be a shielded against capacitive coupling.
With only magnetically coupled windings the voltages relate to the winding ratio.
Depends on many things, but one thing is sure, a steep rising spike will couple and divide first of all capacitively, highly unrelated to the winding ratio.
Principally, no matter what the nominal step-down ratio of a transformer, a short duration, say 1000V spike, could get capacitively coupled almost entirely to the secondary.
A properly done and grounded, so called static shield, intercepts this capacitive coupling.
Easy to do in a transformer with stacked laminations,
Most effective in transformers of large step-down ratio.
In an opt the fb-winding propably wants to be a shielded against capacitive coupling.
With only magnetically coupled windings the voltages relate to the winding ratio.
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The consideration of a screen in an output transformer is imho a completely different topic, especially for hi-fi and where global feedback around the output transformer puts a lot of attention on the high frequency coupling and resonances (ie. >50kHz) that radically influence stability.
With a power transformer that uses screening to mollify spikes (either from mains side, and/or from using solid-state diode rectification on the secondary side), the screen's lead inductance can have a significant impact, so construction awareness is needed to gain benefits.
There is also a case for having additional screen between secondary HT winding and heater windings, to suppress ss diode rectification spikes coupling into heaters and then into the audio chain.
But heh, it seems that many want to spend lots of $$ on valves and output transformers and aesthetic appeal, so its a counterpoint that nearly everyone ends up being happy with a common commercial power transformer.
With a power transformer that uses screening to mollify spikes (either from mains side, and/or from using solid-state diode rectification on the secondary side), the screen's lead inductance can have a significant impact, so construction awareness is needed to gain benefits.
There is also a case for having additional screen between secondary HT winding and heater windings, to suppress ss diode rectification spikes coupling into heaters and then into the audio chain.
But heh, it seems that many want to spend lots of $$ on valves and output transformers and aesthetic appeal, so its a counterpoint that nearly everyone ends up being happy with a common commercial power transformer.