Never recycled magnet wire? Not even to build speaker crossover chokes? I find that a little hard to believe, for someone who builds trafos from scratch.
In my experience, for a given volt-ampere rating/capability, toroids have better regulation than EI. To get an equivalent power supply, with the same unloaded and full load voltages, you need a much bigger (Higher VA) EI than you do a toroid. That will make the EI “better”, but a LOT heavier and more expensive.
In my experience, for a given volt-ampere rating/capability, toroids have better regulation than EI. To get an equivalent power supply, with the same unloaded and full load voltages, you need a much bigger (Higher VA) EI than you do a toroid. That will make the EI “better”, but a LOT heavier and more expensive.
Get a new transformer wound on a stabilized core and specify its for audio. That one looks like a general purpose component.
Try Tiger Torroids (Norfolk).
Hi js
a genuine question, how did you establish there was no DC offset on the mains voltage, I don't know if latest multimeters do show the DC component embedded in a VAC signal, my old one certainly don't show it.
If interested, you could try out a DC blocker as shown in this link (fig 3): Mains DC and Transformers
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Okidoky the empirical test is the quickest way to figure it out it seems, I searched the net for some answers on how to measure DC offset on the mains but apparently it's not that trivial after all so I started a new thread if some bright minded feel compelled telling how to. 
How to measure DC offset on the mains voltage?
How to measure DC offset on the mains voltage?
A quick test for DC on the mains is to plug a hairdryer in and switch it to medium or low heat. They often just half wave rectify the heater element supply. My wife had one that would cause big non-Audio torroids to ‘growl’.
I actually have two big transformers - one for audio and the other bog standard. If I get a chance in the next week or so I’ll put them side by side and record them. The non-Audio spec one growls at the slightest provocation.
I actually have two big transformers - one for audio and the other bog standard. If I get a chance in the next week or so I’ll put them side by side and record them. The non-Audio spec one growls at the slightest provocation.
I tried that in my youth. ALmost impossible to wind a decent transformer with used wire - and especially the secondary’s! But ok to reuse for coils etc.
We used to go to a local motor re-winder. He’d weigh the roll(s) of wire we selected and we’d take it away wind our transformer and take the rolls back and it would get re-weighed and we’d pay for what we had used. Later when I earned a bit more money, I’d just get the transformer wound to spec - they were EI cores (late 1970’s/ early eighties).
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Exactly; saturation due to "normal" operation (audio power amplifier) will usually not be noticed because of the high level coming from the loudspeakers.
The advantages of toroidal transformers (very steep magnetizing curve, no air gaps, max flux concentration, low core magnetization losses and low resistance of the windings therefore very high effiency)lead to the two common problems, very high inrush current (when switch on at the "wrong" phase angle) and core noise (the growl that you've mentioned).
The before mentioned vacuum impregnation helps against other noises coming from loose metal sheets and/or windings and betters the insulation, but can't do next to nothing against the growl coming from the magnetostriction of a saturated core.
The common cure is to make the toroidal transformer a bit less optimal, by reducing the flux (winding calculation) and usage of other core materials with less steep magnetization curve and more losses.
i got a toroid from a well known winder, antek, it was a china job, and the toroid came to me doa, open primary windings....
if you look a the toroid there are no signs of damage the one can see...
so what i did was to dismantle the thing, lo and behold, the primary winding was broken in several strands in one place, so i thought then, someone must have dropped the thing and the toroid landed edge first....
so this is one thing with toroids, do not drop them.....
if you look a the toroid there are no signs of damage the one can see...
so what i did was to dismantle the thing, lo and behold, the primary winding was broken in several strands in one place, so i thought then, someone must have dropped the thing and the toroid landed edge first....
so this is one thing with toroids, do not drop them.....
there is a reason why i never reused copper wires, when i was 14, i attempted to make a traffo using copper wires taken from ballast transformers for fluorescent lighting....
my first attempt went up in smoke and scared the hell out of me....
so from thereon, i never used used copper wires ever again...
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