Yet another experiment with this belly band...
I put a sensitive piece of wire on purpose to the FB point of the amp and a little hum appeared @ the output.
Then I just put my post factum belly band on the trafo loosely as you can see
at the attachment and it worked beautifully... The hum disappeared ~95%-ly.
So a great thanks to Bonsai once more to mention this in his article..!!
Funny: during switch on this shield "tape" shakes a bit.
I asked at the manufacturer about the material and its some kind of Si alloy material.
Its magnetic, I tested. (I mean it sticks to a magnet...)
I put a sensitive piece of wire on purpose to the FB point of the amp and a little hum appeared @ the output.
Then I just put my post factum belly band on the trafo loosely as you can see
at the attachment and it worked beautifully... The hum disappeared ~95%-ly.
So a great thanks to Bonsai once more to mention this in his article..!!
Funny: during switch on this shield "tape" shakes a bit.
I asked at the manufacturer about the material and its some kind of Si alloy material.
Its magnetic, I tested. (I mean it sticks to a magnet...)
Attachments
The results of this experiment confirm that somewhere inside your amplifier is unusually sensitive to radiated hum field.
I think this points to a wiring error.
I think this points to a wiring error.
Yes, there is still some work to do, but there is solid progress.
The 'belly band' makes a significant difference in my view.
Interesting,y, my Marantz PM7000 uses an EI core transformer, and if has a bely band. Now,mother reason I raise this is its a mass produced Amplifier that really meets the bang for the buck - anything they can do to cut costs they would. But, the belly band is important enough to include in this product.
Cortez, have you decoupled your output stage?
The next thing to look at is your signal vs power grounding. This can make a significant difference in my experience.
I assume the stability issues have been solved at this stage?
The 'belly band' makes a significant difference in my view.
Interesting,y, my Marantz PM7000 uses an EI core transformer, and if has a bely band. Now,mother reason I raise this is its a mass produced Amplifier that really meets the bang for the buck - anything they can do to cut costs they would. But, the belly band is important enough to include in this product.
Cortez, have you decoupled your output stage?
The next thing to look at is your signal vs power grounding. This can make a significant difference in my experience.
I assume the stability issues have been solved at this stage?
Hi Guys
PTs with core bands have been around since tube days. For EI they use a copper band. For toroids they use a strip of core material.
In my amps, I've always specified core bands even for output transformers. Anything that reduces the stray field is a good thing. On the toroid, the manufacturer builds the PT as usual, then makes the core band as a separate piece - it has to be completely covered in tape - then slips the band over the PT and adds another layer of tape. This helps in another way inasmuch as the toroid is less vulnerable to puncture if mishandled or exposed to the unexpected.
Toroidal PTs mounted without using the steel cup washer will radiate much more than one with the washer. That bit of steel helps to confine the field.
And the spray from the toroid is either right at the flylead break out or "around the clock" a bit from there. It depends on how many windings there are and how tightly the thing is made. There can never be complete coverage of the core by each winding, simply because of traditional winding methods and the fact that the inner and outer circumferences being different. Special winding techniques that step back and forth a bit do provide full core covereage in each layer, but this is only done for output transformers.
The lowest-price toroids will not have core bands or electrostatic screens. Higher-priced lines might. Custom devices cn have anything you want and do not cost much these days considering the number of transformer houses operating.
As far as noise in an amp, grounding is the biggest issue and the easiest to make an error with.
Have fun
PTs with core bands have been around since tube days. For EI they use a copper band. For toroids they use a strip of core material.
In my amps, I've always specified core bands even for output transformers. Anything that reduces the stray field is a good thing. On the toroid, the manufacturer builds the PT as usual, then makes the core band as a separate piece - it has to be completely covered in tape - then slips the band over the PT and adds another layer of tape. This helps in another way inasmuch as the toroid is less vulnerable to puncture if mishandled or exposed to the unexpected.
Toroidal PTs mounted without using the steel cup washer will radiate much more than one with the washer. That bit of steel helps to confine the field.
And the spray from the toroid is either right at the flylead break out or "around the clock" a bit from there. It depends on how many windings there are and how tightly the thing is made. There can never be complete coverage of the core by each winding, simply because of traditional winding methods and the fact that the inner and outer circumferences being different. Special winding techniques that step back and forth a bit do provide full core covereage in each layer, but this is only done for output transformers.
The lowest-price toroids will not have core bands or electrostatic screens. Higher-priced lines might. Custom devices cn have anything you want and do not cost much these days considering the number of transformer houses operating.
As far as noise in an amp, grounding is the biggest issue and the easiest to make an error with.
Have fun
Those bands are "GOSS" steel (grain oriented silicon steel).
Aiming the "spray' away from the amps did the trick , did not have to
go all the way with a belly band.
OS
Aiming the "spray' away from the amps did the trick , did not have to
go all the way with a belly band.
OS
I think the static screen between the primary and secondary windings is copper but yes the outer wrap or cup is goss.
I agree with AndrewT, Cortez. any high current wires should be twisted as close to their terminations as possible. So twist the trafo wires right up to where they come out of the trafo.
I tried it but with this layout it makes no difference.
As I said I added whis wire on purpose to test the belly band.
But consider now the hum is alread very very subtle.
I am just playing with it because its fun to completely eliminate such an "error". 🙂
Not yet, I am still at experimenting my IPS HF comp. I'll post further details in the other thread.
I already tried the 10R lifting resistor but for some reason it just added a big hum in my case...
Good tip Struth, thanks! Unfortunately I dont have a washer right now,
I thought its not involved with stray fields at all, but I'll try it soon...
But not the same amp as you're testing, because you could make a positive feedback loop and cause it to oscillate.
I was actually hoping to plug it into my POS scope but it would only show something on very noisy areas. A separate amp and headphones would likely be best.
anode choke
Hello,
What i usually do is using a lundahl ll1668 25mA anode choke which is 50 Henry so a lot of wire and i guess that will make it more sensitive and connect to an AC multimeter.
I did use this also to find out how to mount power supply chokes from Lundahl that use the same principle when they are close to my R core power transformer.
Which now is encapsulated in a 2 mm iron '' box '' now the values are even lower.
I will use choke input power supply which will not have charging currents which will diminish radation from wires and transformer a lot.
Dinner is ready.
Greetings, Eduard
Hello,
What i usually do is using a lundahl ll1668 25mA anode choke which is 50 Henry so a lot of wire and i guess that will make it more sensitive and connect to an AC multimeter.
I did use this also to find out how to mount power supply chokes from Lundahl that use the same principle when they are close to my R core power transformer.
Which now is encapsulated in a 2 mm iron '' box '' now the values are even lower.
I will use choke input power supply which will not have charging currents which will diminish radation from wires and transformer a lot.
Dinner is ready.
Greetings, Eduard
Attachments
The generic rule with EMC is that above 377 ohm impedance it is a capacitive/electric field problem. Below 377 ohms, it is magnetic.
Sensitive to touch I would think is electric and capacitive.
No.. shorted turn needs the flux to go through the turn. The band will attack stray parasitic fields.
Agreed.
Another concern for me would be the input jacks are not close to each other. A pair of IC's to another device would create a loop. I would have put the jacks as close together as possible, and twist the IC's between the devices.
In addition, I would also twist the source device line cord with the two IC's, and plug the source device with the amp in the same duplex.
Nice work, good debugging to all.
John
Jn maybe you can answer another question from me. If I place the aluminum or ferrous cover on one of my amps (in development) there is 6-10 dB drop in hum. The cover is not touching any part of the transformer (a torroid). I have assumed that what is happening here is the stray electric field from the transformer is being captured by the cover with the whole case forming a loop around the transformer. So rather than intersecting any cabling or local circuits, it flows in the amplifier casing. It has a belly and and a screen.
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Hi Guys
Have you never seen an EI transformer with end bells? Those do the same thing as the metal cover you placed over the toroid.
As I stated above, the core band and the steel cup washer help to contain the field because metal has a lower resistance to magnetic lines than does air. It has the effect of "containing", "focusing" or 'redirecting" the EMI. The end bells on an EI PT do the same thing. There is significant leakage from an EI and the end bells vibrate with the changing flux through them. Dipped or potted PTs are mechanically quieter but still have EMI the same issues.
Making a mu-metal box around the PT is a way to greatly minimise the harmonics of the field. Like all other metals, mu-metal's ability to block EMI improves with the frequency of the noise. Blocking mains-frequency noise is pretty difficult.
With large PTs like all the power amps around here must have, it is very important in our modern time to use a DC blocker as the transit of DC-like noise (anything asymmetric) through the PT greatly exacerbates the EMI output.
Is your PT made by Buddha, and thus it has a "belly"? Everywhere else it is called a CORE BAND or FLUX BAND.
Have fun
Have you never seen an EI transformer with end bells? Those do the same thing as the metal cover you placed over the toroid.
As I stated above, the core band and the steel cup washer help to contain the field because metal has a lower resistance to magnetic lines than does air. It has the effect of "containing", "focusing" or 'redirecting" the EMI. The end bells on an EI PT do the same thing. There is significant leakage from an EI and the end bells vibrate with the changing flux through them. Dipped or potted PTs are mechanically quieter but still have EMI the same issues.
Making a mu-metal box around the PT is a way to greatly minimise the harmonics of the field. Like all other metals, mu-metal's ability to block EMI improves with the frequency of the noise. Blocking mains-frequency noise is pretty difficult.
With large PTs like all the power amps around here must have, it is very important in our modern time to use a DC blocker as the transit of DC-like noise (anything asymmetric) through the PT greatly exacerbates the EMI output.
Is your PT made by Buddha, and thus it has a "belly"? Everywhere else it is called a CORE BAND or FLUX BAND.
Have fun
A like the name "belly band", it reminds me, that what has a belly is good. 😀
BTW: if the washer helps reducing the EMI, maybe another one should be put to the bottom as well..?
BTW: if the washer helps reducing the EMI, maybe another one should be put to the bottom as well..?
Hi Guys
Yes, a bottom washer helps confine the EMI field.
Many companies use aluminium chassis for its nonmagnetic properties, so there is electrostatic shielding but not magnetinc shielding. The same applies to the grades of stainless steel that are actually "stainless" and thus nonmagnetic.
CORE BAND and FLUX BAND are accurate terms that describe what the piece does and make sense. Electronics uses precise terms so people can understand what is being discussed. Belly-band sounds like something for an obese and disgusting slob with a genetic issue or poor will power. - certainly clinging to ignorance Why not thorax band, or head band, or around-the-outside band...
Have fun
Yes, a bottom washer helps confine the EMI field.
Many companies use aluminium chassis for its nonmagnetic properties, so there is electrostatic shielding but not magnetinc shielding. The same applies to the grades of stainless steel that are actually "stainless" and thus nonmagnetic.
CORE BAND and FLUX BAND are accurate terms that describe what the piece does and make sense. Electronics uses precise terms so people can understand what is being discussed. Belly-band sounds like something for an obese and disgusting slob with a genetic issue or poor will power. - certainly clinging to ignorance Why not thorax band, or head band, or around-the-outside band...
Have fun
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