> You need a nice flat bed to start off with if you are going to wind a ton of thin wire layers.
True. But in this case we are looking at a few-tenths to few-K transformer. The few-K side will be the same as any other few-K winding, such as a 1:3 200Ω:1K8Ω standard mike input transformer for discrete or chip input. Nothing new on that side.
As a general rule, the pounds of wire in primary and secondary are the same, and they take equal areas of the core-window. Sometimes you want to put more in one than the other: very-high-Z windings have many-many turns and thus a lot of varnish, so for equal-copper they have to take more than half the window area. Or the "ideal" size is too thin to wind without breaking, so you use "oversize wire" on that winding and use "too small" wire in the other winding, and try to find a happy balance.
The few-tenths side is tougher. If we did not need good power transfer (we don't) and don't need low-low noise (ah, but we do) then we could wind ~20 turns of anything handy. But we do want winding resistance "low" compared to ribbon resistance to avoid adding noise. That suggests a fairly fat wire. And fat wire resists being laid neat and tight. In some big-power work, you bring the wire (more like a rod) through the window, and beat it with a hammer to make the bend around the corner. At #18 size you just mash it with a popsicle stick to flatten it around the corner without bruising your thumb.
>> copper foil winding primary trafo for ribbons yet?
> would give quite high winding capacitance, wouldn't it?
What is "high" capacitance on a 0.1Ω winding? Something like 100uFd for 20KHz response, no? And in fact the capacitance is mostly proportional to transformer size, and the number of interleavings, not much about the shape of the wire. You have to try very hard to get more than a few hundred pFd.
On the few ribbon-mikes I've autopsied, they use like #18 wire to link the ribbon to the transformer, and at that point it makes sense to just carry the #18 around the core 20 times. I suppose they could foil-wind the primary and use the foil to link to the ribbon, but foil costs MUCH more. At at 20 turns, round-wire works OK. If it were 1 turn, foil would make more sense.
Crack open a Weller soldering Gun.
The secondary is a tube hammered flat so it will fit neat inside the core window. They start with a tube because they need stiffness outside the transformer to support the heating-tip. The tip runs about 0.1V 500 Amps or 0.000,2 ohms.
True. But in this case we are looking at a few-tenths to few-K transformer. The few-K side will be the same as any other few-K winding, such as a 1:3 200Ω:1K8Ω standard mike input transformer for discrete or chip input. Nothing new on that side.
As a general rule, the pounds of wire in primary and secondary are the same, and they take equal areas of the core-window. Sometimes you want to put more in one than the other: very-high-Z windings have many-many turns and thus a lot of varnish, so for equal-copper they have to take more than half the window area. Or the "ideal" size is too thin to wind without breaking, so you use "oversize wire" on that winding and use "too small" wire in the other winding, and try to find a happy balance.
The few-tenths side is tougher. If we did not need good power transfer (we don't) and don't need low-low noise (ah, but we do) then we could wind ~20 turns of anything handy. But we do want winding resistance "low" compared to ribbon resistance to avoid adding noise. That suggests a fairly fat wire. And fat wire resists being laid neat and tight. In some big-power work, you bring the wire (more like a rod) through the window, and beat it with a hammer to make the bend around the corner. At #18 size you just mash it with a popsicle stick to flatten it around the corner without bruising your thumb.
>> copper foil winding primary trafo for ribbons yet?
> would give quite high winding capacitance, wouldn't it?
What is "high" capacitance on a 0.1Ω winding? Something like 100uFd for 20KHz response, no? And in fact the capacitance is mostly proportional to transformer size, and the number of interleavings, not much about the shape of the wire. You have to try very hard to get more than a few hundred pFd.
On the few ribbon-mikes I've autopsied, they use like #18 wire to link the ribbon to the transformer, and at that point it makes sense to just carry the #18 around the core 20 times. I suppose they could foil-wind the primary and use the foil to link to the ribbon, but foil costs MUCH more. At at 20 turns, round-wire works OK. If it were 1 turn, foil would make more sense.
Crack open a Weller soldering Gun.
