as above.
What specs should I be looking for?
As an example, I looked at these 3 transformers
What specs should I be looking for?
As an example, I looked at these 3 transformers
- All 3 are 1:1 and all 3 have different impedances.
- Lundahl LL1545e (https://www.lundahltransformers.com/wp-content/uploads/datasheets/1545e.pdf) - all 4 windings have a resistance of 295ohm
- Hammond 560G (https://www.hammfg.com/files/parts/pdf/560G.pdf?v=1697661949) - the static resistance for the 4 windings are less than 20ohms
- Jensen transformer (https://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-11ssp-6m.pdf) - the windings for all 4 are less than the Lundahl.
- The frequency range seems be similar (the max for all 3 is well beyond human limit)
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I'm curious, and hope you will back up a little bit and give a bigger picture on the problem you are trying to solve? In what application is this (pro audio, home audio, etc) and why do you want to isolate the input and use a transformer? I ask as much for wanting to learn as wanting to help.
I understand input isolation, but I have not seen it except for automotive applications where floating ground is a problem. I have seen audio engineers pipe a line signal through transformers for effect to flavor the audio, in fact in-line transformers are a major component in tube and germanium amplifiers and helps to give them their unique sound. Are you looking for best high fidelity? If so I would not expect you to use transformers, but again I'm not sure what the problem is you are trying to solve.
I understand input isolation, but I have not seen it except for automotive applications where floating ground is a problem. I have seen audio engineers pipe a line signal through transformers for effect to flavor the audio, in fact in-line transformers are a major component in tube and germanium amplifiers and helps to give them their unique sound. Are you looking for best high fidelity? If so I would not expect you to use transformers, but again I'm not sure what the problem is you are trying to solve.
Hi
Have you looked at the Hammond 140UEX ?
It is in a mu-metal can with four leads. Having no taps on either winding allows the frequnecy response to be super flat and extend up to 100kHz and down to 10Hz or so. It is rated as 10k:10k and I think it is a better choice for line level inputs. 140UEX has the flattest, widest response in the line and can handle huge signals. See the attached data sheet from Hammond.This series should be better known, and at least this specific model should be much better known!
I bought an LG TV and made a point of getting the "this year" model instead of the "next year model" for various reasons. I only use it with a bluray player and listen to the sound through a stereo NOT home theater. I wanted to be able to use the TV's remote volume control, but the only analog circuit point is the speaker output. ( If you turn off the TV speakers using the TV menu, the remote volume no longer works - they expect you to be using a "smart" system connected via HDMI.) So...
On the day I brought the TV home I opened it up and added a switch to disconnect the internal speakers and direct the signal to some jacks while placing a load across the PA. Each speaker output in the TV is actually a pair of bridged amps, so the jacks have to float. The TV has a SMPS running off the mains, so ground needed isolation to the stereo, but I brought out the PA ground to another connector.
I made an interface box using a pair of the 140UEX transformers that allows the signals to go to RCA jacks to connect to the stereo, or to external speakers with or without the line out feed. I added an attenuation switch to the line out and found it worked best unattenuated into the stereo. There is no hum or other noise and I have not used the ground of the TV.
In a previous situation, I used 1:1 transformers to get rid of a hum from a VCR into a stereo. Those were again single windings with no taps, but a custom piece from Hammond.
Also, where the legacy 600-ohm line was necessary for telecom and was adopted in early public address systems, it is more usual to use 10k loads for audio line in/out. There is no need to transfer power, just voltage.
Have you looked at the Hammond 140UEX ?
It is in a mu-metal can with four leads. Having no taps on either winding allows the frequnecy response to be super flat and extend up to 100kHz and down to 10Hz or so. It is rated as 10k:10k and I think it is a better choice for line level inputs. 140UEX has the flattest, widest response in the line and can handle huge signals. See the attached data sheet from Hammond.This series should be better known, and at least this specific model should be much better known!
I bought an LG TV and made a point of getting the "this year" model instead of the "next year model" for various reasons. I only use it with a bluray player and listen to the sound through a stereo NOT home theater. I wanted to be able to use the TV's remote volume control, but the only analog circuit point is the speaker output. ( If you turn off the TV speakers using the TV menu, the remote volume no longer works - they expect you to be using a "smart" system connected via HDMI.) So...
On the day I brought the TV home I opened it up and added a switch to disconnect the internal speakers and direct the signal to some jacks while placing a load across the PA. Each speaker output in the TV is actually a pair of bridged amps, so the jacks have to float. The TV has a SMPS running off the mains, so ground needed isolation to the stereo, but I brought out the PA ground to another connector.
I made an interface box using a pair of the 140UEX transformers that allows the signals to go to RCA jacks to connect to the stereo, or to external speakers with or without the line out feed. I added an attenuation switch to the line out and found it worked best unattenuated into the stereo. There is no hum or other noise and I have not used the ground of the TV.
In a previous situation, I used 1:1 transformers to get rid of a hum from a VCR into a stereo. Those were again single windings with no taps, but a custom piece from Hammond.
Also, where the legacy 600-ohm line was necessary for telecom and was adopted in early public address systems, it is more usual to use 10k loads for audio line in/out. There is no need to transfer power, just voltage.
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If the hum is from a TV or VCR connected to cable TV, you can save a lot of money by using a small, cheap RF transformer to break the DC connection to the TV cable. Cable TV connections are grounded at the utility pole, which is inevitably a different "ground" than at the breaker box. An RF transformer breaks this connection and the ground loop.
Hi
Although I do buy a few electronic parts from Aliexpress I am not impressed with most of the 1:1 audio transformers I checked out there. They may be completely fine. I do not normally mind waiting to get stuff from them (it is a minor miracle to get stuff from half way around the world in three months or less) but I wanted to build the interface quickly and I get a discount from Hammond. A friend was considering buying encapsulated PTs from Ali, like the Telemas, and the price was okay until you added shipping, then there was no advantage and you had to wait longer to get them compared to using Digikey or Mouser.
Hammond, like Jensen and the others mentioned by the OP, provide complete data sheets and have a known standing in the industry. You can get good or bad parts from everywhere, but a reassurance is in the documentation available, which is often lacking with the Aliexpress stuff.
Back with the VCR, I had not thought of using an RF transformer. If I had, I likely assumed there would be a loss. Using the audio isolation transformers was quick and easy since I had them already. Of course in the mean time, my VCR died and the replacement for it did not work from Amazon. So, piles of tapes that cannot be viewed, but I still have the memories - haha. On top of that, the TV has no RF input since it really is not a TV in the historic sense.
Although I do buy a few electronic parts from Aliexpress I am not impressed with most of the 1:1 audio transformers I checked out there. They may be completely fine. I do not normally mind waiting to get stuff from them (it is a minor miracle to get stuff from half way around the world in three months or less) but I wanted to build the interface quickly and I get a discount from Hammond. A friend was considering buying encapsulated PTs from Ali, like the Telemas, and the price was okay until you added shipping, then there was no advantage and you had to wait longer to get them compared to using Digikey or Mouser.
Hammond, like Jensen and the others mentioned by the OP, provide complete data sheets and have a known standing in the industry. You can get good or bad parts from everywhere, but a reassurance is in the documentation available, which is often lacking with the Aliexpress stuff.
Back with the VCR, I had not thought of using an RF transformer. If I had, I likely assumed there would be a loss. Using the audio isolation transformers was quick and easy since I had them already. Of course in the mean time, my VCR died and the replacement for it did not work from Amazon. So, piles of tapes that cannot be viewed, but I still have the memories - haha. On top of that, the TV has no RF input since it really is not a TV in the historic sense.