3 ms·

Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.

by achr2 4y ago

jleahy 4y ago
The core might saturate at these low frequencies?
klodolph 4y ago
"Wider bandwidth" is not so useful if the wide bandwidth does not include the frequencies you care about. Generally speaking, the higher the frequency, the smaller the transformer. Ethernet deals with very high frequencies, so they can make nice, cheap transformers. Try putting audio through an ethernet transformer and see how much comes out the other side... I bet it won't be much, and you'll get extreme distortion unless your signal levels are very low.
- achr2 4y ago
  Thank you for correcting me. I misspoke and said ethernet when I was thinking modem. Many are rated from ~300Hz. And I did assume low signal levels in a similar gain setup from the article.
  - klodolph 4y ago
    I think modem transformers might have a similar problem of limited bandwidth--they may be rated from 300 Hz, but they are also rated to 3.4 kHz or something similar. Modems were mass-manufactured, and transformers tend to be expensive, so you would expect any expensive part in a mass-manufactured product to be engineered to within a hair's breadth of the specification for modems, which have something like 300 Hz - 3.4 kHz frequency range. On the low end, you have core saturation. On the high end, you have parasitic inductance and capacitance, as well as loss from hysteresis and eddy currents. Solving these problems basically means making the transformer larger and more expensive. I did a quick search on Mouser, and found wideband (20 Hz - 20 kHz) audio transformers at around $6 in small quantities. Let's say that you get it for $3 in bulk. At that point, you're adding something like $20 or $30 to the retail cost of whatever it is you're selling. If you're okay with the telephone-quality of the simple modem transformers, then you might as well use the optoisolator--neither option sounds good, but the optoisolator is cheaper. You know, as long as you have a power supply on both sides--which is not a given.

Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.

by achr2 4y ago

Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.

jleahy 4y ago

The core might saturate at these low frequencies?

klodolph 4y ago

"Wider bandwidth" is not so useful if the wide bandwidth does not include the frequencies you care about. Generally speaking, the higher the frequency, the smaller the transformer. Ethernet deals with very high frequencies, so they can make nice, cheap transformers. Try putting audio through an ethernet transformer and see how much comes out the other side... I bet it won't be much, and you'll get extreme distortion unless your signal levels are very low.

achr2 4y ago
Thank you for correcting me. I misspoke and said ethernet when I was thinking modem. Many are rated from ~300Hz. And I did assume low signal levels in a similar gain setup from the article.
- klodolph 4y ago
  I think modem transformers might have a similar problem of limited bandwidth--they may be rated from 300 Hz, but they are also rated to 3.4 kHz or something similar. Modems were mass-manufactured, and transformers tend to be expensive, so you would expect any expensive part in a mass-manufactured product to be engineered to within a hair's breadth of the specification for modems, which have something like 300 Hz - 3.4 kHz frequency range. On the low end, you have core saturation. On the high end, you have parasitic inductance and capacitance, as well as loss from hysteresis and eddy currents. Solving these problems basically means making the transformer larger and more expensive. I did a quick search on Mouser, and found wideband (20 Hz - 20 kHz) audio transformers at around $6 in small quantities. Let's say that you get it for $3 in bulk. At that point, you're adding something like $20 or $30 to the retail cost of whatever it is you're selling. If you're okay with the telephone-quality of the simple modem transformers, then you might as well use the optoisolator--neither option sounds good, but the optoisolator is cheaper. You know, as long as you have a power supply on both sides--which is not a given.