Nelson suggested to try 2 different (cheap) solutions:
1 To use a MU-metal shield for the input transformer (see his link for a company you can source them)
and
2 use steel band to shield your transformer.
Generally, (low frequency) magnetic fields are only being lowered in their strength if you use ferro-magnetic metals of high permeability. Copper is not helping with low frequency magnetic fields, only with high-frequency ones, which in out case can only be brought into the system by the power cable.
Instead to use a separate case, you can also use the measures Nelson suggested or buy a transformer, which is radiating less.
Also try to rotate the transformer arround its axis, and then flip it by 90 degrees. Toroids have a highly directional radiating field.
Good luck
Matthias
1 To use a MU-metal shield for the input transformer (see his link for a company you can source them)
and
2 use steel band to shield your transformer.
Generally, (low frequency) magnetic fields are only being lowered in their strength if you use ferro-magnetic metals of high permeability. Copper is not helping with low frequency magnetic fields, only with high-frequency ones, which in out case can only be brought into the system by the power cable.
Instead to use a separate case, you can also use the measures Nelson suggested or buy a transformer, which is radiating less.
Also try to rotate the transformer arround its axis, and then flip it by 90 degrees. Toroids have a highly directional radiating field.
Good luck
Matthias
Both of those solutions have already been implemented and are still fitted to the components
Full - MuMetal box enclosure over the Edcor
Full - steel metal can DIY enclosure for the toroidal
Both methods did not work
Next option was to test the removal of the toroidal from the case before embarking on sourcing shielded replacements for the Edcor transformers if it did not work
Now that I have the answer to the problem was the toroidal I will enquire about a fully sealed at factory units
FR
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@ Full Range
Check if Your two signal wires who go from RCA's are connected first directly to pcb audio signal IN and IN-G ?
Normaly two stranded together.
One more OUT-G wire point on the pcb who go to the black cold speaker connection
( stranded together with red wire from pcb audio OUT btw )
PSU-G go after that to your main earth star groud with the chassis
Is total of 2 psu wires ( V+,V - ) 3 ground wires ( IN-G, PSU-G, OUT-G ) 2 audio ( IN, OUT ) = 7 wires connected to one amp pcb.
All ok or find missing wires ?
I always learn from Mr. Pass amplifier pictures. Thanks FW
Greetings 🙂
Check if Your two signal wires who go from RCA's are connected first directly to pcb audio signal IN and IN-G ?
Normaly two stranded together.
One more OUT-G wire point on the pcb who go to the black cold speaker connection
( stranded together with red wire from pcb audio OUT btw )
PSU-G go after that to your main earth star groud with the chassis
Is total of 2 psu wires ( V+,V - ) 3 ground wires ( IN-G, PSU-G, OUT-G ) 2 audio ( IN, OUT ) = 7 wires connected to one amp pcb.
All ok or find missing wires ?
I always learn from Mr. Pass amplifier pictures. Thanks FW
Greetings 🙂
I kinda tried that in a loose way, and while the toroidal was still housed in its can and it added a whistle to the hum
Yep all wiring is spot on and a few ways were tested
Eventualy settled for the minimalist star earth you see now
The only 2 things that worked was
1) Mr Pass asked for a specific earth test - it stopped the hum
2) Removing the toroidal from the chassis
The detective in me will ask
Why do most M2 builders have NIL or few easy to fix issues ?
It's entirely possible that my toroidal is faulty or overly active in RF / EM emissions even though it was the Audio spec unit
So I'm searching for a Zero emission toroidal
Happy to be pointed in a makers / brand direction ( link )
FR
I will suggest when you do decide on another toroidal get a 300VA one instead of the larger one since you are having hum problems.
I use 500 VA in all my first watt amps, probably a different transformer would solve the problem.
My BA 3 uses a 1000VA and is dead silent, even with 98 and 100+ dB speakers.
The 500 VA are Antek, the 1000 VA is a Sumr.
Russellc
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Something I have always done on FW amps is to rotate the toroid +/-60 deg
in operation, as one position will give minimum noise. Usually there is a
lobe of radiation, and pointing it at (or away) from the right spot is a big help.
in operation, as one position will give minimum noise. Usually there is a
lobe of radiation, and pointing it at (or away) from the right spot is a big help.
I don't know if it's zero emission, and not sure what shipping would run, but Antek makes a shielded 400VA/18 V torroid AS-4218
AS-4218 - 400VA 18V Transformer - AnTek Products Corp
Thank you all for the feedback and noting what toroidal transformers you use that are silent
What would be the difference at the speaker end when using a -
300VA - 400VA & 500VA
I am in comunication with a local supplier for Noratel Transformers at the moment and working through the shielding options
Now that the toroidal is on long leads I can give it a try as a test and report back my findings
A few days ago the toroidal was tested standing upright on the side coils and a whistle was added to the hum
Tricky little buggers these toroidal's
FR
What would be the difference at the speaker end when using a -
300VA - 400VA & 500VA
I am in comunication with a local supplier for Noratel Transformers at the moment and working through the shielding options
Now that the toroidal is on long leads I can give it a try as a test and report back my findings
A few days ago the toroidal was tested standing upright on the side coils and a whistle was added to the hum
Tricky little buggers these toroidal's
FR
Update
Tested the toroidal in all manner of positions including upside down
Always hum produced
Think I have a rouge or possessed toroidal 🙂
On a positive note I am just about to place an order for a Noratel toroidal as used by Pass Labs and others but have also ordered it with a can just in case
FR
Tested the toroidal in all manner of positions including upside down
Always hum produced
Think I have a rouge or possessed toroidal 🙂
On a positive note I am just about to place an order for a Noratel toroidal as used by Pass Labs and others but have also ordered it with a can just in case
FR
Hi full range,
I've been using the cheapie torroid's from altronics and Jaycar. I haven't bought one of these yet Audio DIY needed Metal Shield plate cover for toroid transformer with many size | eBay but that might be a cheaper and easier solution?
Failing that, ZM oft suggests a large tin of tuna can be turned into a torroid's cover easily.
I've been using the cheapie torroid's from altronics and Jaycar. I haven't bought one of these yet Audio DIY needed Metal Shield plate cover for toroid transformer with many size | eBay but that might be a cheaper and easier solution?
Failing that, ZM oft suggests a large tin of tuna can be turned into a torroid's cover easily.
Hello Full Range!
I hope you have finally found a solution to the problems with your transformer that works. I have been follwing your search with interest, since I'm a bit concerned about hum myself. I'm thinking of using a Mini Dissipante chassis, which I guess could be troublesome because of its size.
When looking at the pictures of your chassis I noticed that you are using the galvanized steel baseplate. Could it be that the "magnetism" of the baseplate is making things worse? Just a thought...
//Ronny
I hope you have finally found a solution to the problems with your transformer that works. I have been follwing your search with interest, since I'm a bit concerned about hum myself. I'm thinking of using a Mini Dissipante chassis, which I guess could be troublesome because of its size.
When looking at the pictures of your chassis I noticed that you are using the galvanized steel baseplate. Could it be that the "magnetism" of the baseplate is making things worse? Just a thought...
//Ronny
Shouldn't
I have sanded the earth point - it's just something I do automatically
Smallest size I would go is a 4U chassis as the heatsink size is very important for heat dissipation
Run to hot and you get transistor failure
FR
It seems you're not the first one Full Range...
http://www.diyaudio.com/forums/tubes-valves/110458-magnetic-shields-transformers-2.html#post1331218
http://www.diyaudio.com/forums/tubes-valves/110458-magnetic-shields-transformers-2.html#post1331218
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