Weird impedance balancing behavior

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gepicaster

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If record to a balanced Input use a 600Ohm transformer. Be saure you do not have any galvanic connection - all other experiences are lost time.
 

EmilFrid

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If record to a balanced Input use a 600Ohm transformer. Be saure you do not have any galvanic connection - all other experiences are lost time.
Yes, it seems this is the way to go for noise in the low frequency band, but for a more even rejection across the audible spectrum it seems to me @abbey road d enfer offers a superior solution.

Edit: and the solution discussed by @MisterCMRR
 
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MisterCMRR

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It's the total impedance you're trying to match. If you leave out the capacitor, the impedances will not track each other as frequency goes down. It's significant in most cases for 50 or 60 Hz rejection. More modern electrolytics come in ±20% if the tolerance issue really bothers you. But even a slightly mismatched pair of caps is better than leaving one out.
 

abbey road d enfer

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If record to a balanced Input use a 600Ohm transformer. Be saure you do not have any galvanic connection - all other experiences are lost time.
This a rather extreme statement. There are enough cases of non-transformer based balanced connections that work perfectly well.
Transformers have their advantages, but they also introduce non negligible distortion and frequency response alterations, particularly when they are grafted on elements that were not designed specifically.
 

MisterCMRR

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And, of course, a GOOD transformer is the preferred solution for a "universal" output. It can drive either balanced or unbalanced inputs gracefully. But the key word is GOOD. Specs on most transformers don't reveal how much distortion they add at high levels of low frequencies (where most of the energy in music actually is) because of their too-small core stack. All Jensen parts are specified for distortion and high levels at 20 Hz - it's a high bar (and increases the size and price). Most competing parts spec at 30 Hz, 50 Hz, or not at all.
 

Newmarket

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If record to a balanced Input use a 600Ohm transformer. Be saure you do not have any galvanic connection - all other experiences are lost time.

This is simply not true. There are non-transformer solutions that work very well.
Take a look at THAT 1200 "INGenius" parts.
Also the "600 Ohm" transformer spec' is of no specific significance in the general case.
 

MisterCMRR

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As I've explained hundreds of times over the years, a transformer has no impedance of it's own. Transformers simply reflect, bi-directionally, the impedance on one side to the other, multiplied by the square of the turns ratio - period. So, if you have a 600 Ω load on one side of a 1:1 transformer, the other winding will appear to have a 600 Ω impedance (plus the DC resistances of both windings). But, change that load to 2 kΩ and the other side will have approximately the same 2 kΩ impedance. That being said, transformer designs (number of turns, wire size, etc.) to perform best across the wide frequency range of audio by optimizing them for a certain range of impedances. Only in slang are transformers optimized for medium impedances referred to a "600 Ω" parts - and because that impedance was the standard for telephone lines and it trickled down into early tube gear and passive filters ... they are rarely used today.

The best transformer to achieve high noise rejection is a Faraday-shielded "input" transformer designed for high-impedance (10 kΩ or higher) circuits. Used at the receive end of a balanced line, they often have CMRR of 100 dB or more. It's difficult and expensive to make a Faraday-shielded "output" transformer (designed for low impedance) ... as illustrated by the Western Electric 111C or Jensen JT-11SSP series transformers. They offer high noise rejection and are suitable for 600 Ω sources and loads, but cost about 4 times what a good input transformer would to achieve the same high noise rejection.
 

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