Can Toroidals be stacked?

[ben62670]

I have a project I am working on. I have two Toroidals (one for each channel), and it would make life much easier if I could stack them. Is this a bad idea.
Thanks
Ben

[Tweeker]

Assuming your not even close to pushing any thermal limits I dont see a problem. If you are, it will aggravate it badly.

You wont have the most magnetic separation between the transformers, but this should not be an issue for a psu.

[ben62670]

Thanks much. I was woried about having a problem ith magnetic fields or other noise/perforance issues. They will both be seperated by rubber spaces.
Thanks again.
Ben

[Symon]

Just a thought but would probably be a good idea to make sure the primaries are wired so that the magnetic fields are going in the same direction.

I would also make the rubber washer between the two quite thick say 8mm as this will reduce the capacitive coupling between the transformers.

[Tweeker]

There are both going to have the same input noise anyhow.

It is possible in theory that there could be some loss of channel separation on a class B amplifier if there isnt much filtering (the transformer doesnt directly see the final rails) with magnetic coupling between PTs. Ideally the transformers are 90 degrees to each other, which is not very conducive to stacking. Toroidals should have low leakage fields, though stacked is about the worst case.

Steel or more exotic materials could be used as a magnetic shield.

[ben62670]

My project is going to consist of 2 LM3886's per channel with 34vdc+-(34+ 34-). I am doing this because the chips can share the load with 4 ohm speakers quit well. With each trany at 28.7 0 28.7 and 2 amps I should be looking at 100wpc clean. I will post when I am done. While I am here can you guys recommend a good source for the pcb's for the LM chips?
Thanks
Ben

[Symon]

Tweeker,
I agree this isn't the ideal setup in terms of magnetic separation.
I was thinking more of the capacitive coupling as the secondary
windings will be practically touching. This would transfer the HF
noise from the rectifiers which could be at different times due to
different loads on each transformer.

But, as you say provided there is enough power supply filtering
this may not be significant in practice.

Symon

[Tweeker]

Yes, several mm of low k additional separation between toroids should pretty much wipe out capacitive coupling. Interposed grounded shield would also, careful to avoid shorted turn.

Polyethylene foam sheet is nice for this, sold in hardware stores, at least around here.

[seventenths]

I'm using stacked single secondary transformers for my chip-amps and i find no noise or drawbacks at all.


7/10

[Nordic]

yep, I have not tried it, but have certainly seen enough photos of such a stacked arrangement, to not dismiss it without trying.