EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: e100 on March 28, 2018, 04:30:11 pm
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USD $70 or thereabouts for something that is small and appears to be made using the same materials as a normal power transformer.
What am I missing?
Mike
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One factor is the core material. Usually very thin laminations to minimize losses, and the material needs to be optimized for the wide frequency range of use.
Still your price seems very high
paul
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The audio snake oil treatment ;)
Serious, the small series, small market, logistics, and indeed materials (silver wire anybody) that is probably what makes them expensive.
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There are tons on digi-key for a tenth the price you are quoting for example https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701 (https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701) so IMOP somebody is trying to rip you off. If you cannot access digikey there is always fleabay but buy from us/european if you want something that meets the spec :)
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There are tons on digi-key for a tenth the price you are quoting for example https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701 (https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701) so IMOP somebody is trying to rip you off. If you cannot access digikey there is always fleabay but buy from us/european if you want something that meets the spec :)
The $70 price came from the Jensen web site
http://www.jensen-transformers.com/transformers/line-input/ (http://www.jensen-transformers.com/transformers/line-input/)
My investigation started when I went looking for a pre-built audio isolator box and found retail prices in the USD $150 range. They all appear to be using transformers to do the isolation.
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Those are flat from 20Hz to 20Khz, they are not cheap audio transformers. Their cores are most likely made of pure nickle not iron to get that frequency range and they are well shielded.
The prices you see there for these type of studio grade transformers is standard for today. It's cheaper to separate your audio electronically, or, if you just need cheap sound for phone lines or modem, go with the digikey transformer.
See here:
http://www.lundahl.se/pro-audio/ (http://www.lundahl.se/pro-audio/)
10hz-100khz, +/-1db audiophile transformers (These will cost ya royally! :) )
http://www.lundahl.se/input-and-line-output-application/ (http://www.lundahl.se/input-and-line-output-application/)
If you want, I bet I can find even more expensive stuff.
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Yeah. Basic transformers are easy to design and manufacture. Transformers having very low distortion in the audio frequency range are a lot more difficult to get right and require expensive R&D, tools and materials.
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The audio snake oil treatment ;)
Serious, the small series, small market, logistics, and indeed materials (silver wire anybody) that is probably what makes them expensive.
A measured spec of 20hz through 20khz, with a flatness response +/-0.05db with a +21dbu range through an isolation transformer is one thing which is not snake oil, it is ridiculously difficult to achieve.
Compare that to Digikey's 5$ 600:600ohm transformer, 660hz to 3.5Khz, +/-1db. What do you expect the performance of Digikey's 5$ transformer is at 20hz if it is already at -1db at 660hz? And Digikey's transformer is only sensitive from -45dbm to +10dbm. The 70$ transformer operates from 1hz(-1db) to 50Khz(-1db), measured, and has a CMMR of 107db...
That transformer is worth 70$.
Though the Lundahl aren't so perfectly flat from 1hz to 50khz, instead of 250vac isolation, they have 2-4kvac isolation. Lundahl also has many more configurations and an excellent IV transformer/or/MC phono cartridge adapter (1:32 output if I remember) for use as the IV stage in current output audio dacs making your voltage output. You go for Lundahl if you want extra serious voltage isolation or different gain and multi-output configurations. Go with Jensen's if you don't need as much serious isolation, but need a tighter flatter response.
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22 years ago I designed an 8 channels active microphone splitter
Each channel had one electronic balanced input and tree balanced outputs, two of them electronic balanced (one for front-of-house and one for stage monitor mixers) and one with output transformer (we needed separate grounds for an external video production mixer, that was usually powered via a different power system).
The output transformer, with very high specs (similar to the Jensen's) was priced the equivalent of 30 dollars, in lots of 100 pieces !!!
I visited the factory where it was built, and I was really impressed by how difficult it was to make them, from thin wires that were practicallly invisible to the MuMetal screening can.
The ladies in the assembly line had to wear cotton gloves to avoid touching the wire and contaminate it with skin oil, that seems to be, in some days of the month, corrosive (or so I was told).
The 70 dollars for one piece is an honest price, I think.
Best regards
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I've used these.
Not cheap, but worth every penny!
http://www.opamplabs.com/products/logic-module-plug-in/transformer-audio/t-25.html (http://www.opamplabs.com/products/logic-module-plug-in/transformer-audio/t-25.html)
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Does an ADC to opto isolator to DAC combination come anywhere close to the performance of a transformer at the same price point?
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all correct. Mostly it has to do with the low quantities that are made in and that it is a luxury type purchase. Nobody really needs one, so the price goes up. a That corp balanced receiver chip is cheap, and does a great job, but you don't get the warm fuzzy feeling. Warm fuzzy costs, and there you go. Also good quality ones are hard to make. To get the high inductance for low frequency response without introducing lots of winding capacitance that reduces high frequency is complicated. Add to that the high DCR to get that inductance in a small transformer and you find a transformer that is to handle small signal at tiny power is actually surprisingly large. I have all the equipment to make them myself for prototypes as transformer companies don't want to mess around with it. If i specify a exact design that will make it, otherwise they just have no time to fiddle about with them and leave it to the likes of Lundhall and jensen, and such.
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Welp, I suppose this rules out line in/out transformers in my ~$700 Cambridge Audio stereo integrated amplifier. And likely any other manufacturers products in the same price range.
And also why they chose not to include a phono stage in said IA. Instead, they make an accompanying phono stage that runs another ~$600-$700. Don't even know if that uses transformers or a higher end electronic solution. "Higher end" as compared to an AV or integrated amp that includes a phono stage for the same money, that is.
I'm tempted to stress on the thought that hopefully the IA's budget wasn't blown entirely on the massive toroidal power transformer & beefy construction, leaving little for the signal input, it's path, and output stage(s).
But I think I'll just keep reminding myself that I chose the Cambridge through "blind" auditioning. I was lucky enough to have a dealer that sold gear ranging from ~$300 to upwards of ~$100k. Who was also nice enough to oblige my request of setting up several products within my "lowly" budget of $1500 prior to my arrival. Along with not tipping his hand as to which product I was hearing.
At the end of the day I walked out with the $700 Cambridge Audio IA even though I listened to several pieces of gear that were more expensive and also "reviewed" much better than the CA. Because, to my ears at least, that was what sounded the best.
Yet I've already downloaded the old spec sheets, reviews, and marketing for what I've got. LOL. Audiophile = a freaking disease!!!!
Sent from my SM-G900V using Tapatalk
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Yes, be careful what you buy - most if it is telephony stuff and the true audio frequencies (20-20k) are expensive.
Don't buy from ebay - tried that, didn't work out.
If you find some good ones, please post them - I still need 2 for a broken 4 DI 19" rack unit.
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Those are flat from 20Hz to 20Khz, they are not cheap audio transformers. Their cores are most likely made of pure nickle not iron to get that frequency range and they are well shielded.
...
Pure nickle is a poor choice for the core. The "normal" Fe-Si alloy and just a bit thinner sheets is probably OK. Other options would be Permalloy (classic, expensive and sensitive to stress) or a nanocrystaline material like nanoperm (http://www.magnetec.de/de/produkte-aus-nanopermr/ (http://www.magnetec.de/de/produkte-aus-nanopermr/)).
Otherwise it can be a more or less normal ring core. Much of the higher price is from the small series an limited market. Rather Similar common mode chokes are not that expensive, just lower impedance due to less turns.
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There are tons on digi-key for a tenth the price you are quoting for example https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701 (https://www.digikey.co.uk/product-detail/en/tamura/TTC-105/MT4134-ND/285701) so IMOP somebody is trying to rip you off. If you cannot access digikey there is always fleabay but buy from us/european if you want something that meets the spec :)
The $70 price came from the Jensen web site
http://www.jensen-transformers.com/transformers/line-input/ (http://www.jensen-transformers.com/transformers/line-input/)
My investigation started when I went looking for a pre-built audio isolator box and found retail prices in the USD $150 range. They all appear to be using transformers to do the isolation.
Jensen transformers are expensive because they are the real deal. A line input transformer has to handle signal levels on the order of +24 dBu (12.7 Vrms or 36 Vp-p) without saturating and without low-end roll-off, and it has to have a frequency response out to 20 kHz. In other words, it has to be transparent. There are a lot of people who claim they want to use transformers for their "sound," but quality transformers like these Jensens do not have a "sound."
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See if you can find old Western Electric telephone transformers. They were 600 ohm, audio range, and might be findable in some piece of old phone equipment surplus. key systems (old electromechanical PBXs) used to have a bunch of them. Old style phones might too. Some newer phones sold now are basically modern day clones of those old phones, they may even still contain whats called the network which is a complex transformer which includes a 600 ohm matching transformer.
Most people would probably see the parts from old phone systems as worthless old junk but they are chock full of now-expensive, useful parts. The transformers they used were extremely good quality ones.
Almost any decent quality analog phone should contain a 600 ohm transformer.
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The problem with telephone transformers is that they will have a bandwidth of perhaps 100Hz - 4kHz and lousy distortion, on the order of a few percent minimum, possibly worse. They will have great DC HV isolation, but that is the only figure of merit for which they are likely to be 'good'.
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They use that deoxygenated super conductor cable in them don't they
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Decent 1:1 audio transformers (and the mic to -10 line level types) with flat-ish response and low distortion / good headroom, have always been expensive and always will be
Don't hold your breath waiting for them to get knocked off easily by OneHungLow Industries any time soon,
and chucked on Ebay for "two dollar each 4U, ten dollar for six..Paypal only..."
That's assuming you need a realistic 40Hz to 15Khz performance with no resonating frequencies silly business in between
Pay the money for the good stuff, look after them and they'll go for years
and don't drop the suckers or leave them idle in a damp place, and keep them away from freaky magnetic fields, otherwise game over :(
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Still if you ask a company with skills to duplicate that transformer and order five million pieces you will get them for $6 a pc tops.
It is the r&d costs, extreme small market and low sales that makes them $70 and the margin is incredible higher than for instance on modern tvs. Logic because the plant, people , etc have to live of it.
Are they worth it is a non sense question because for every person there is a different answer.
There are wooden oil filled audio capacitors selling for $400 a piece and for some persons that is really worth it.
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i went and did a little googling out of curiosity
XL = 2pi()*F(hz)*H(henry)
@ 20Hz, for 600R reactance, the inductance needed is 4.8H. i didnt think it would be this huge. do they actually have to use reactance?
i am guessing this parameter is a factor. and it appears many xfmrs i could find on mouser are over 10H.
if i then toy with the idea to wind this 1:1 xfmr (ie : assume 2 x 4.8H coils), assuming i use the equations correctly. a 2uH/N2 core material, will take about 2500 turns (thats about 200m+) over about 25mm diam to make the 4H++. one would need to use something like AWG38. not easy not matter how i look at this. but should be "fun" to do :P and likely close to USD70
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i went and did a little googling out of curiosity
XL = 2pi()*F(hz)*H(henry)
@ 20Hz, for 600R reactance, the inductance needed is 4.8H. i didnt think it would be this huge. do they actually have to use reactance?
i am guessing this parameter is a factor. and it appears many xfmrs i could find on mouser are over 10H.
if i then toy with the idea to wind this 1:1 xfmr (ie : assume 2 x 4.8H coils), assuming i use the equations correctly. a 2uH/N2 core material, will take about 2500 turns (thats about 200m+) over about 25mm diam to make the 4H++. one would need to use something like AWG38. not easy not matter how i look at this. but should be "fun" to do :P and likely close to USD70
:scared: Holy Shit, 0.2km of wire, per side! That's almost 1/2 Km! :scared:
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Still if you ask a company with skills to duplicate that transformer and order five million pieces you will get them for $6 a pc tops.
It is the r&d costs, extreme small market and low sales that makes them $70 and the margin is incredible higher than for instance on modern tvs. Logic because the plant, people , etc have to live of it.
Are they worth it is a non sense question because for every person there is a different answer.
There are wooden oil filled audio capacitors selling for $400 a piece and for some persons that is really worth it.
You seem to be approaching this as if the use of audio transformers is some sort of audiophool preference. It is not. Transformers firstly provide galvanic isolation, this is a safety and circuit protection feature and allows one to mitigate ground loops - a typical studio or live performance rig contains 100s of interconnections, each one coming with the risk of a ground loop. Transformers also provide impedance transformation; if you have a microphone with a 200 ohm output impedance and an input stage with input impedance in the megohms region you can get some noise-free gain for 'free' using a microphone transformer. They come with drawbacks, relatively poor distortion, poor frequency response, large size and cost; the very fact that professional audio gear still uses them, in the face of the drawbacks, is an indication that their disadvantages are outweighed by their advantages.
Your $6 audio transformer pipedream is just that, a pipedream. The materials for a decent audio line or microphone transformer will cost more than $6. You need low hysteresis core materials, you can't use the cheap silicon steel that you use in mains transformers, you need fine gauge wire, lots of it and for most low level audio transformers you need a mu-metal screen and the wherewithal to manipulate and heat-treat it. Then you have the irreducible production cost of the machine time that fine, high count windings requires. Jensen et al have been making audio transformers since before you and I were born, the designs (and hence the NRE costs) of some transformers haven't changed in 40+ years - do you really think that if there was some way to reduce production costs and hence clean up in the marketplace that they wouldn't have taken them?
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The typical materials used in audio transformers are Grain Oriented silicon iron, for transformers that are to handle any appreciable power, 50% nickel/iron which has a square BL curve and low distortion, and 80% nickel with offers the highest permeability. What that gives you is nigher inductance with fewer turns therefore better low frequency response with less winding capacitance which preserves high frequency response. This material however has the lowest core saturation point and is not suitable for any appreciable power. They can generally saturate and cause distortion very easily and have great difficulty handling DC offsets. Therefore it is typically only used in low signal level AC only applications, or extremely well balanced DC applications (Condenser mics, etc) I have 50% material I use for Mic input transformers and line out transformers. Its kinda funny. Sometimes the numbers actually work out better for a given core size using silicon iron. Audio transformers are really a trial and error design thing. Anybody who says otherwise is wrong. Apart from the gross inductance and amp turn saturation calculations for power transformers you can never have more than a vague idea what the inductance or frequency response will be until you actually make it and test it.
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You seem to be approaching this as if the use of audio transformers is some sort of audiophool preference.
Where did I say that, you are putting words in my mouth.
Jensen et al have been making audio transformers since before you and I were born, the designs (and hence the NRE costs) of some transformers haven't changed in 40+ years - do you really think that if there was some way to reduce production costs and hence clean up in the marketplace that they wouldn't have taken them?
Ofcourse they are not lowering their prices, they are selling so why would they? Besides as I said earlier an entire company has to make a living of their niche products.
Are you really thinking that the BOM for such transformer is higher than $30 think again.
That does not mean that they are not good, they are probably very goid that is why they are upselling for that money, there us demand so there is a matching price. All I am saying is that they make a large margin on them, good for them.
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Are you really thinking that the BOM for such transformer is higher than $30 think again.
That does not mean that they are not good, they are probably very goid that is why they are upselling for that money, there us demand so there is a matching price. All I am saying is that they make a large margin on them, good for them.
The $70 cost is the single-unit price. Ask them for a quote if you're going to buy a few thousand for production; the cost will be significantly lower.
Just like it would be for anything you buy. You're participating on a professional engineering-design forum and you don't grok that?
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You seem to be approaching this as if the use of audio transformers is some sort of audiophool preference.
Where did I say that, you are putting words in my mouth.
No I'm not:
Are they worth it is a non sense question because for every person there is a different answer.
There are wooden oil filled audio capacitors selling for $400 a piece and for some persons that is really worth it.
Sure sounds like a reference to audiophoolery to me. Would you care to retract that claim that I'm putting words in your mouth?
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Having personally worked on a specialty transformer company, one thing to consider with these types of transformers is the production yield loss.
Never wound audio transformers, but we did wind some MIL-spec transformers for the US Navy.
Winding long runs of 38AWG wire is difficult to do without creating defects like wire stretching, breakage and pinholes.
And then it still has to meet all the parametric testing.
As other poster mentioned previously, it is also a trial and error approach of what your yield will be.
One never gets 100% yield. And one has to scrap some expensive materials.
Expensive compared to "normal" transformer.
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Winding long runs of 38AWG wire is difficult to do without creating defects like wire stretching, breakage and pinholes.
And then it still has to meet all the parametric testing.
As other poster mentioned previously, it is also a trial and error approach of what your yield will be.
One never gets 100% yield. And one has to scrap some expensive materials.
Expensive compared to "normal" transformer.
Interesting, you've made me think. I'd have put them in the "put them on the old slow careful, winding machine" not the "new whizzy, fast, messy one" category. That is, I'd assume there would be higher production costs because one had to me more careful, slower, circumspect in making them, rather than in terms of the far end of the production process in yield terms. Obviously it can cut both ways, but it reveals something about one's approach to how to do things.
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The $70 cost is the single-unit price. Ask them for a quote if you're going to buy a few thousand for production; the cost will be significantly lower.
Just like it would be for anything you buy. You're participating on a professional engineering-design forum and you don't grok that?
That is what I am saying all the time *big sigh* but everyone here claims the $70 is a very good price. Yes it is for the seller.
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Sure sounds like a reference to audiophoolery to me. Would you care to retract that claim that I'm putting words in your mouth?
No it is not, its the same firm Jensen that sells $200-$400 audio capacitors, thought they were wood but they are oil with paper and alufoil, whatever.
http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx (http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx)
The whole question is when is a price too high and when is it right, as said earlier that is personal, I think the $70 is too much and $30 would be more in the right ballpark.
For the audio capacitors, I would never spent that kind of money.
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Perhaps Jensen has been bought out at some time, and audiowank marketer trash have slithered in
to drum up business selling baking tray foil and oil filled cardboard toilet rolls in wood for $200 to $400
Hopefully they haven't gone cheap on the transformer quality and still charging top dollar
Nah, can't happen, who would do that? ::)
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Sure sounds like a reference to audiophoolery to me. Would you care to retract that claim that I'm putting words in your mouth?
No it is not, its the same firm Jensen that sells $200-$400 audio capacitors, thought they were wood but they are oil with paper and alufoil, whatever.
http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx (http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx)
The whole question is when is a price too high and when is it right, as said earlier that is personal, I think the $70 is too much and $30 would be more in the right ballpark.
For the audio capacitors, I would never spent that kind of money.
Jensen Transformers, in California, does not make and sell capacitors, and to my knowledge, they never have. You might be thinking of Jensen Capacitors (http://jensencapacitors.com) in Denmark, which does.
BTW, Radial Engineering, a manufacturer of all sorts of audio goodies and who were possibly Jensen's largest customer, bought Jensen four years ago. Bill Whitlock, who was running Jensen, wanted to retire and found a good buyer in Radial, as the Jensen product line is still going.
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Also do not confuse Jensen speakers. They are a separate company producing speakers in Italy and using CE distribution in the US as their master distributor.
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Sure sounds like a reference to audiophoolery to me. Would you care to retract that claim that I'm putting words in your mouth?
No it is not, its the same firm Jensen that sells $200-$400 audio capacitors, thought they were wood but they are oil with paper and alufoil, whatever.
http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx (http://jensencapacitors.com/products/audio-capacitors---aluminium-tube/aluminium-foil---paper-in-oil---pure-silver-leadout.aspx)
The whole question is when is a price too high and when is it right, as said earlier that is personal, I think the $70 is too much and $30 would be more in the right ballpark.
For the audio capacitors, I would never spent that kind of money.
Jensen Transformers, in California, does not make and sell capacitors, and to my knowledge, they never have. You might be thinking of Jensen Capacitors (http://jensencapacitors.com) in Denmark, which does.
BTW, Radial Engineering, a manufacturer of all sorts of audio goodies and who were possibly Jensen's largest customer, bought Jensen four years ago. Bill Whitlock, who was running Jensen, wanted to retire and found a good buyer in Radial, as the Jensen product line is still going.
Does anybody know the Dutch for "Laughing up ones sleeve"...
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That is what I am saying all the time *big sigh* but everyone here claims the $70 is a very good price. Yes it is for the seller.
Really? Go compare the audio quality that comes out of a $10 "ground loop isolator" like this one (the exact same thing that Radio Shack used to sell for $15-$20):
https://www.parts-express.com/audio-system-ground-loop-isolator-kit--265-007 (https://www.parts-express.com/audio-system-ground-loop-isolator-kit--265-007)
... with the output of a high-quality, $50-70 audio transformer. Go ahead, see what the response is like at 20 Hz, try to shove a square wave through it, sweep it around from down at 20 Hz to up in the 20+ KHz range and watch the output on your scope.
There is a reason that companies that make things like a quality Radial DI box use a transformer like a Jensen, not the cheap transformer made from Chinesium that is in the $10 isolator.
On the other hand, one of those transformers from a cheap isolator is perfectly acceptable in many coupling applications and would certainly sound better than a 600:600 telephony transfomer in an audio application.
It really depends on precisely what the OP is looking for for their application. I've used those cheap "ground loop isolators" with great success in many applications, though it is certainly not audiophile grade or even anywhere close to proper Hi-Fi if your application needs quality.
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So how many have you bought and do you use personally?
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So how many have you bought and do you use personally?
Personally - none, and that's probably true for everybody as few people have professional audio gear for personal use. But I soldered a few hundred into the radio production consoles I used to build.
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... with the output of a high-quality, $50-70 audio transformer. Go ahead, see what the response is like at 20 Hz, try to shove a square wave through it, sweep it around from down at 20 Hz to up in the 20+ KHz range and watch the output on your scope.
It's perfectly square. No ringing at all as long as you match/terminate the designed output load spec as listed in the transformer's data sheet. That's why it's 70$. This will not happen on the 10$ RadioScrap junk no matter what output impedance you choose. No will that RadioScrap support +21db range.
Note that the RadioScrap transformer does ground loop isolate as expected.
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Any stock signal generator that puts out Sine, Square, Triangle and Pulses with any generic 2 channel oscilloscope, soon tells the story of why good audio range transformers cost big money,
and where cheapies reach their limits. A realtime spectrum analyser shows you the big picture all at once :clap:
The good transformers should come supplied with a very comprehensive detailed spec sheet, so you can test it for yourself to see if it meets and or exceeds spec
If it does, a listening test usually isn't necessary, but hey, why not have a listen once the things are hooked up ?
In a blindfold A / B listening test (the type of test Audiophools flee from, in shock :o horror :scared: and disgust :rant: ) you should hear no discernable difference
well, none that the average MP3 and iChunes phone brained listeners would care about ::)
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well, none that the average MP3 and iChunes phone brained listeners would care about ::)
They even cant tell the quality difference between their .mp3 and mid range audio cassette tape as long as the cassette player is new enough that it has no hiss.
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Why use all that copper to break a ground loop? We aren't talking about large voltages, do it actively.
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Why use all that copper to break a ground loop? We aren't talking about large voltages, do it actively.
When you are dealing with ground differences that exceed your op-amp's rails, you need a transformer. This is sometimes the case when there is a recording truck running on different power from the PA system.
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I think what marco means is can you use a linear optocoupler, or, digital RF/Optical isolation.
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I think what marco means is can you use a linear optocoupler, or, digital RF/Optical isolation.
Does a linear optocoupler exist?
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When you are dealing with ground differences that exceed your op-amp's rails, you need a transformer. This is sometimes the case when there is a recording truck running on different power from the PA system.
Your differential input is going to be AC coupled ... how much AC do you have on a truck body relative to earth with a couple inverters running? It can't be too much, or humans are going to get upset when they are part of the ground loop.
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I think what marco means is can you use a linear optocoupler, or, digital RF/Optical isolation.
Does a linear optocoupler exist?
Yes, something like the IL300 or HCNR200 series. They have an LED and two photo diodes. One photo diode is used for feedback in an attempt to linearise the whole thing, the other as output. Linearity only on the order of 0.25 - 0.5%, tempco +/-0.15%/°C, highly variable process that would require individual gain adjustment for paired signals or absolute measurements. Basically, pretty rough and ready, but better than nothing if you need what only they can do.
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Good luck with the other methods, they have their drawbacks and issues too ::)
Pay the money and get the good quality transformers
or...
set up the system to be noise free using fully balanced active lines, run the lot off the one single phase power point,
don't add or subtract any other gear ever...
and supply all the crew with garlic necklaces to be sure :popcorn:
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Your differential input is going to be AC coupled ... how much AC do you have on a truck body relative to earth with a couple inverters running? It can't be too much, or humans are going to get upset when they are part of the ground loop.
Voltage differences can be very high. Think about two systems (big, complicate systems) one near the stage, powered by a generator, and the other on a moble TV recording studio, powered by a different generator, located maybe 200 meters away... There are problems with different earth voltages, maybe slight AC frequency differences, some direct-injected amplifier thats leaks to ground... Result: ground noise.
You can go completely digital by putting everything on a network, and this is the current trend.
It is also the reason because my Active Microphone Splitters and Stage Boxes have lost a big lot of market...
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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/ (http://www.jensen-transformers.com/factory-tour/)
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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 (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.
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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?
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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?
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I've tried cheap 600 ohm transformers from Edcor, (https://www.edcorusa.com/pc_series) their PC series for $7.23 each pretty cheap and M6 silicon steel laminations.
They sucked- not bi-filar wound so noise and hum were still terrible, due to longitudinal-balance being crappy. In other words, stray capacitance between primary and secondary was not symmetrical.
Frequency response was meh, you really need mumetal nickel-iron core for low distortion and wide bandwidth. This is part of the high cost.
I use Sowter (http://www.sowter.co.uk/) or Jensen or Cinemag for high-end transformers. Hammond (http://hammondmfg.com/5caud.htm) has both low cost and studio-grade parts.
I've also used Lundahl but don't like them, they are very small and op-amps oscillated driving them. Very small core and very fine wire.
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Plus, when you bring a few millions of dollars of equipment to record a performance, having a 10,000$ 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).
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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.
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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.
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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.
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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. :)