Hello!
(From what I have seen, to make a balanced transmitting do their job well we must retain an equal impedance to "ground" between "hot" and "cold" line. However, many schematic available on internet seem not take care of it.)
Instrumentation amplifiers seem be "perfect" (OK, nothing can) for receiver sections of balanced transmitting. So why I have never seen it popular (or I have missed ?) in audio (especially in line level audio)?
Thanks!
(From what I have seen, to make a balanced transmitting do their job well we must retain an equal impedance to "ground" between "hot" and "cold" line. However, many schematic available on internet seem not take care of it.)
Instrumentation amplifiers seem be "perfect" (OK, nothing can) for receiver sections of balanced transmitting. So why I have never seen it popular (or I have missed ?) in audio (especially in line level audio)?
Thanks!
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Analog Devices, THAT Corp and TI all make chips for interfacing balanced inputs or outputs to the unbalanced internal circuitry of an audio device.
THAT IC Datasheets
Professional Audio Line Receiver | Products | Audio | TI.com
Audio Line Drivers and Receivers | Analog Devices
THAT IC Datasheets
Professional Audio Line Receiver | Products | Audio | TI.com
Audio Line Drivers and Receivers | Analog Devices
Thanks everyone for info,
The transformers are unbeatable but only with enough effort on materials and winding technique. So it is clearly less attractive to many people (include me).
I choose instrumentation amp since current Delta-Sigma DAC chips come with differential output, and I only want sufficient noise rejection for 3m cable, so really high CMRR is not needed
The transformers are unbeatable but only with enough effort on materials and winding technique. So it is clearly less attractive to many people (include me).
I choose instrumentation amp since current Delta-Sigma DAC chips come with differential output, and I only want sufficient noise rejection for 3m cable, so really high CMRR is not needed
It is a very good question and one I pondered as an undergrad when introduced to the IA. Taken me over 30 years to get around to implementing this in my system.
In reality for home audio with everything in a rack balanced is not that big a deal, but if you are worried about signal integrity it makes a lot of sense. Also hand as means your control amp can be 30ft from the power amp with no worries.
The THAT 1206 is a nice, cheap and proven single chip solution for audio.
In reality for home audio with everything in a rack balanced is not that big a deal, but if you are worried about signal integrity it makes a lot of sense. Also hand as means your control amp can be 30ft from the power amp with no worries.
The THAT 1206 is a nice, cheap and proven single chip solution for audio.
Lots and lots of inamps built out of tl072s, too. Not just transformers. Not to mention the linked ic's Kevin provided.
Not in pro world. Today, transformers are considered to be a device for coloration and saturation. Chip solution is chosen for transparency (cleanness) today. I guess that is why most of pro ADA converter do not come with transformers, but most of the "real" professional (not prosumer) consoles, preamps and outboards still come with the transformers.
Somehow you managed to contradict both me and yourself by citing a whole bunch of devices where you may still find line to line and bridging transformers.. LOL
There are many situations where their use is not required or even necessarily the best solution, note my remark about high CMRR and galvanic isolation, that would clearly be a small subset of mostly pro applications.
Jensen, Lundahl and Cinemag I suspect still sell a lot of transformers for pro audio applications.
It's true I did not see a lot of transformers in pro audio equipment in the 16 years I designed consumer, MI and pro gear professionally, but I did see some, most notably in applications driving long lines in buildings or outdoors, and places where signal levels were very low and RFI and AC mains related noise were likely to be problems..
There are many situations where their use is not required or even necessarily the best solution, note my remark about high CMRR and galvanic isolation, that would clearly be a small subset of mostly pro applications.
Jensen, Lundahl and Cinemag I suspect still sell a lot of transformers for pro audio applications.
It's true I did not see a lot of transformers in pro audio equipment in the 16 years I designed consumer, MI and pro gear professionally, but I did see some, most notably in applications driving long lines in buildings or outdoors, and places where signal levels were very low and RFI and AC mains related noise were likely to be problems..
Well, sorry for the confusion. I was talking about the professional recording studio equipments, not SR equipments. I don’t really know SR world, but I don't think transformer is commonly used for RFI reduction. No SR console has transformer input these days as far as I know. I'm curious what kind of pro equipment you have designed with a transformer.
What I was going to say is, the chip solution is used when the coloration is not required (or should avoided), and they are also chosen to simply cut cost especially for prosumer audio equipments. Transformer is still a more common solution for high end outboards and consoles in the pro recording studios.
You've pretty much answered the question in the above quote. Nothing I've said contradicts this.
If by SR you mean sound reinforcement, I have rarely seen a transformer used in such equipment, and generally only where there was a problem such as a large difference in potential between equipment grounds that can exist in large venues or between buildings, this is one instance where galvanic isolation provided by transformers is useful.
I have never, ever used a transformer in a commercial design, but I do occasionally use them in some of my own gear.
Just for later clarity: the "instrumentation amp" in post #1 is NOT commonly used as a Line Input because it has significant gain but must take arbitrary inputs. If you are taking output from a +/-15V console's balanced output near clipping, you take over 20V peak input. As the single opamp can't swing much over 10V peak, the diff-input stage should often work at a *loss*, to be made-up after a gain-trim.
There is a 1 opamp 4-R differential input with theoretical flaws which is WIDELY used in near-Pro audio and even a fair number of Pro gear.
The input impedance of this is complicated, which matters in extreme situations. There are three or a dozen designs using 2 or 3 opamps which can be "essentially perfect" (though not all implementations go all the way).
If you want your mind bent, study "Super-Bal input". It eats its own output. It looks like an oscillator. It was once invented by a respected maniac. It works very well. But there are several less-crazy-looking diff-inputs for gain of 1.0 or 0.5.
In the last few years, all but the cheapest and the most exotic machinery considers the THAT and similar special diff-line-in chips. The chip costs more but the matching and frills are baked-in.
And variants of the post #1 IA *are* the basis of most MIC inputs today. Only diff is that the input "opamps" are either specialized large-area inputs or add discrete transistors for low hiss.
There is a 1 opamp 4-R differential input with theoretical flaws which is WIDELY used in near-Pro audio and even a fair number of Pro gear.
The input impedance of this is complicated, which matters in extreme situations. There are three or a dozen designs using 2 or 3 opamps which can be "essentially perfect" (though not all implementations go all the way).
If you want your mind bent, study "Super-Bal input". It eats its own output. It looks like an oscillator. It was once invented by a respected maniac. It works very well. But there are several less-crazy-looking diff-inputs for gain of 1.0 or 0.5.
In the last few years, all but the cheapest and the most exotic machinery considers the THAT and similar special diff-line-in chips. The chip costs more but the matching and frills are baked-in.
And variants of the post #1 IA *are* the basis of most MIC inputs today. Only diff is that the input "opamps" are either specialized large-area inputs or add discrete transistors for low hiss.
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I totally agree with you.
The overall gain is a crazy problem. We may need divider circuit for both input in case the "Theoretical" output swing is so large. But it bring more problem on matching.
But the instrumentation amplifier seem be the most advance in the the list of simple ideas if crazy gain problem is treated in an entire system, as I would go for lowered voltage from I/V converter stage.
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