Dual Toroids in Close Proximity...An Issue?

EchoWars · 30th March 2010, 12:36 AM

Any problem with setting two toroid transformers closely side by side? In close proximity to the two amp driver boards?

I have a rather rare Rotel RA-1412 integrated amp (110WPC), with a missing transformer. The unit uses separate power supplies for each channel, with a separate transformer (43-0-43, unknown VA rating). The channel with the missing transformer works, as I had a 35-0-35 transformer sitting around and connected it to see if the channel was operational.

So, to straighten this out, I thought of removing the remaining EI-core transformer and replacing it (and the missing transformer) with a pair of Plitron 300VA 40-0-40 transformers. I can just squeeze them into the available space, side by side. Not enough room to put one on top of the other, as I have seen others do with toroids.

Feasible? Or is there a possibility of interference of one with the other, or with the toroids interfering with the driver boards causing hum?

Thanks gentlemen...

bob91343 · 30th March 2010, 01:09 AM

One important characteristic of a toroid transformer is its lack of external field and its insensitivity to external fields. So you can probably mount them any way you like.

EchoWars · 30th March 2010, 03:48 AM

I've not always found this to be the case, although it should hold in theory.

PMA · 30th March 2010, 05:38 AM

Depends on placement. Do not mount them axially on the same axis. The radiated field is NOT negligible.

EchoWars · 30th March 2010, 07:29 AM

As I said, the only way to fit them in is to mount them side by side.

View from above: -> OO <-

h_a · 30th March 2010, 07:40 AM

Quote:

Any problem with setting two toroid transformers closely side by side?

Quote:

Do not mount them axially on the same axis.

I built a dual mono PSU with two large toroids on the same axis and don't see any particular problems. In fact I have the worst case scenario, two magnetically shielded (even more magnetic field along axis) in rather close proximity (less than 10cm) to the VAS.

With a little mu-metal and optimised wiring, no humm. Spectrum analyzer says humm is about 80dB below 0.7V (gives more than 100dB dynamic range for ~90W amp).

I get about the same numbers with only a single toroid in place.

Interestingly, I got about the same result with a single R-core mounted in the same position, which I think is fairly good for a R-core.

Quote:

In close proximity to the two amp driver boards?

Depends on exact situation, including sensitivity of your speakers, how far you sit away from them and how much humm annoys you.

I guess not much of a problem as the drivers do not have gain, the real problem starts when humm enters voltage gain stages as it gets amplified.

Have fun, Hannes

EchoWars · 30th March 2010, 08:10 AM

By 'driver boards', I mean everything it takes to boost a line-level signal to drive an 8 ohm speaker to 100W levels. Diff-pairs, VAS, driver, outputs. The toroids will be within 4cm of them.

I'm asking because the Plitron transformers cost about $100 each. If this fails, that's $200 I can kiss goodbye to. I do not want to fool with MU-metal, as I've never seen the stuff have any effect when trying to battle EMF issues. Yeah, it's supposed to. Maybe I'm doing it wrong, but if I have to play around with that junk I'd rather just part this thing out and not fool with it.

h_a · 30th March 2010, 08:55 AM

Yeah, 4cm to VAS is really close, you should definitely expect humm.

Of course that also depends a bit on bias, for ClassAB current draw is light, so is magnetic field (in comparison to high bias ClassA or so). But still it's likely a problem.

I have no idea how you could get around that problem, maybe with an external power supply. SMPS emit at other frequencies, maybe also an option.

By the way, mu-metal works ok (6-10dB damping if I remember correctly), it's not a wonder material. It cannot really shield the magnetic field in most cases (except for 100% encapsulation), that's the nature of magnetism. It redirects the field, something to keep in mind when working with this stuff.

Have fun, Hannes

EchoWars · 31st March 2010, 08:08 AM

Why then were the original transformers able to be mounted so close to the driver boards, when they are supposed to be so leaky with EMF? If the toroid has so much less leakage, wouldn't it be an improvement over the stock units?

bobodioulasso · 10:17 AM

Locate the input circuits. I bet they are far enough from the transformers.

Quote:

wouldn't it be an improvement over the stock units?

I think it would.

30th March 2010, 12:36 AM	#1
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	Dual Toroids in Close Proximity...An Issue? Any problem with setting two toroid transformers closely side by side? In close proximity to the two amp driver boards? I have a rather rare Rotel RA-1412 integrated amp (110WPC), with a missing transformer. The unit uses separate power supplies for each channel, with a separate transformer (43-0-43, unknown VA rating). The channel with the missing transformer works, as I had a 35-0-35 transformer sitting around and connected it to see if the channel was operational. So, to straighten this out, I thought of removing the remaining EI-core transformer and replacing it (and the missing transformer) with a pair of Plitron 300VA 40-0-40 transformers. I can just squeeze them into the available space, side by side. Not enough room to put one on top of the other, as I have seen others do with toroids. Feasible? Or is there a possibility of interference of one with the other, or with the toroids interfering with the driver boards causing hum? Thanks gentlemen...

30th March 2010, 05:38 AM	#4
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Depends on placement. Do not mount them axially on the same axis. The radiated field is NOT negligible. __________________ Pavel Macura, consultant http://cz.linkedin.com/pub/pavel-macura/4/783/637

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30th March 2010, 01:09 AM	#2
bob91343 diyAudio Member Join Date: Mar 2010	One important characteristic of a toroid transformer is its lack of external field and its insensitivity to external fields. So you can probably mount them any way you like.

30th March 2010, 03:48 AM	#3
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	I've not always found this to be the case, although it should hold in theory.

30th March 2010, 07:29 AM	#5
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	As I said, the only way to fit them in is to mount them side by side. View from above: -> OO <-

30th March 2010, 08:10 AM	#7
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	By 'driver boards', I mean everything it takes to boost a line-level signal to drive an 8 ohm speaker to 100W levels. Diff-pairs, VAS, driver, outputs. The toroids will be within 4cm of them. I'm asking because the Plitron transformers cost about $100 each. If this fails, that's $200 I can kiss goodbye to. I do not want to fool with MU-metal, as I've never seen the stuff have any effect when trying to battle EMF issues. Yeah, it's supposed to. Maybe I'm doing it wrong, but if I have to play around with that junk I'd rather just part this thing out and not fool with it.

30th March 2010, 08:55 AM	#8
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	Yeah, 4cm to VAS is really close, you should definitely expect humm. Of course that also depends a bit on bias, for ClassAB current draw is light, so is magnetic field (in comparison to high bias ClassA or so). But still it's likely a problem. I have no idea how you could get around that problem, maybe with an external power supply. SMPS emit at other frequencies, maybe also an option. By the way, mu-metal works ok (6-10dB damping if I remember correctly), it's not a wonder material. It cannot really shield the magnetic field in most cases (except for 100% encapsulation), that's the nature of magnetism. It redirects the field, something to keep in mind when working with this stuff. Have fun, Hannes

31st March 2010, 08:08 AM	#9
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	Why then were the original transformers able to be mounted so close to the driver boards, when they are supposed to be so leaky with EMF? If the toroid has so much less leakage, wouldn't it be an improvement over the stock units?

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