What makes a 600 ohm 1:1 audio isolation transformer so expensive?

[iampoor]

Why use all that copper to break a ground loop? We aren't talking about large voltages, do it actively.

The voltage differential can be pretty large. Plus, when you bring a few millions of dollars of equipment to record a performance, having a 10,000$ transformer based splitter is worth its weight in gold, and its a pretty small investment compared to having ground loop noise in your production feed!

So how many have you bought and do you use personally?

Quite a few. I have some clients that love the Jensons on professional audio inputs, especially on passive equalizers. :-)

For anyone who is interested, Jensen has a little factory tour on their website. 70$ for the best audio transformer money can buy is really not that expensive. Here is a factory tour for all who are interested.
http://www.jensen-transformers.com/factory-tour/

[BrianHG]

I think what marco means is can you use a linear optocoupler, or, digital RF/Optical isolation.

Does a linear optocoupler exist?

Yes: https://www.digikey.com/product-detail/en/on-semiconductor/H11F3SR2M/H11F3SR2MCT-ND/1794002
I used 2 for a telephone line interface in place of a transformer.  Very clean and strong signal, though, I only tested to a 4khz BW.

[Audioguru]

I agree that hardly anybody buys a high quality audio transformer anymore. They are difficult to make and are rare so of course they are expensive.
Why do you need one?

[Cerebus]

Why do you need one?

What is the utility of asking a question, halfway down page three of a thread, which has been answered several times already?

[floobydust]

I've tried cheap 600 ohm transformers from Edcor, their PC series for $7.23 each pretty cheap and M6 silicon steel laminations.

They sucked- not bi-filar wound so noise and hum were still terrible, due to longitudinal-balance being crappy. In other words, stray capacitance between primary and secondary was not symmetrical.
Frequency response was meh, you really need mumetal nickel-iron core for low distortion and wide bandwidth. This is part of the high cost.

I use Sowter or Jensen or Cinemag for high-end transformers. Hammond has both low cost and studio-grade parts.
I've also used Lundahl but don't like them, they are very small and op-amps oscillated driving them. Very small core and very fine wire.

[Marco]

Plus, when you bring a few millions of dollars of equipment to record a performance, having a 10,000$ transformer based splitter is worth its weight in gold, and its a pretty small

You're also bringing multi-millions of dollars of human capital, you could argue that the almost universally not double insulated equipment saturating when you leave it floating is an useful feature. As long as everything is earthed and none of your high power equipment is using earth as the return path, the voltages are low enough for an active solution to work. If it can't work, you're fucking up and working around that fuck up is a really bad idea.

The music industry routinely electrocutes its members and it's not a healthy habit (nor a profitable habit, "the show must go on" mentality is almost always loss generating).

[Brumby]

Even from my early days in electronics, I had my reservations about audio transformers.  Just the idea of a linear response from 20Hz to 20kHz through an inductor seemed a hard ask.  Not having done anything requiring audio transformers over the years means I didn't get any hands on experience, so it was a subject of mine that was lacking real knowledge.

Just reading through this thread has filled in a lot of detail that shows my intuition was pretty good - and the efforts to achieve high quality were not trivial.

I'm glad I'm not buying such things.

[calexanian]

So by looking at this thread I cannot tell if i should be making interstate input and output transformers. Pretty much everything said here has been true. So ask yourself would a serious manufacturer try to step into this market? Would you? Will this sell any better than some other new electronic trinket targeted for a broader market? There are already known vendors in the market with good product, and there are even low cost ones with mediocre product too. Is there room for another? All serious questions with no specific answer.

[floobydust]

I think interstage and output transformers are a niche market for the audio industry. Today, everyone wants compact and cheap. The signal transformer is expensive and pretty much outlawed unless you understand the benefits.
Or you are cloning a Pultec

Transformer manufacturing is labour intensive. That is most of their cost.
So getting them made in china is the only way to be competitive, or invest in expensive automation for winding machines.

There is technology in how they are wound and the core material used. This is pretty much what separates the good, bad, ugly, cheap manufacturers. Transformer performance varies widely for level, distortion, frequency response etc.

Old brands, like Jensen, Peerless, UTC, Triad etc. were proven in their day to be excellent.
The core material and heat-treating is the "voodoo" that would be very hard to replicate and cost a lot of money measuring and evaluating.

Today, I would not spend 100's dollars on an unknown make. I think that would be the hard part, establishing a name, a brand.

[cdev]

If you can find old PBX equipment particularly "key systems" made by Western Electric, they had multiple very nice encapsulated 600 ohm transformers in cans in them. Very high quality.

I remember going to their factory and getting a tour when I was an Explorer Scout in high school.