Doubling down

May 12, 2022
 by Paul McGowan

It is often difficult for people to grasp how balanced audio cables are 6dB louder than single-ended cables or how two channels of a stereo power amplifier can have double the output voltage and 4 times the power output when in bridged mode.

It is difficult to understand because, in each case, only one output level is available. Put another way, if we have only 1 volt of signal available to us, how do we create a 2-volt signal?

The answer is easiest understood with an analogy using cars or trains. It’s somewhat the same thought process Albert Einstein used as he was figuring out the theory of relativity.

Motion and distance are relative to each other. You and a friend traveling in a car together at 60 mph are moving at the same speed so it appears as if you’re stationary. To an outside observer, you both whiz past at 60 mph.

In the case of a single-ended cable, the hot wire with the signal is moving away from ground (zero). For this thought experiment let us specify the maximum “distance” the signal travels as 1 volt.

How to double that voltage if we are restricted to only 1-volt.

Now, imagine two hot wires each with a maximum 1-volt signal. If we invert the direction of one signal we can double the voltage between the two signals. Signal 1 is moving away from ground in a positive direction while, at the same time, signal 2 is moving away from ground in the opposite direction.

Each is only moving a maximum of 1-volt. But measure between them and we get 2-volts (6dB louder or twice the voltage).

It’s very much like a train moving away from the station. If the train is moving at 60 mph, then we can say that in 1 hour that train will have traveled 60 miles. Now, add a second train leaving the station in the opposite direction and at the same speed.

Measure the distance between the two trains and we discover a 120-mile difference. One train would have had to travel at twice the speed to get that far, but two trains traveling the same speed in the opposite direction give us twice the distance.

The same is true for a bridged amplifier. One amp channel goes positive while the second amp channel goes negative. If you place the speaker terminals between the two outputs you get double the voltage resulting in up to (depending on the amp’s available power supply current) a 4X increase in output power.

Hope that helps.

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20 comments on “Doubling down”

  1. My Musical Fidelity – ‘M6si500 ‘integrated amplifier is bridged & balanced with the option of SE.
    Because my Marantz – ‘SA12 SE’ is less than 1 metre away from said ‘M6si500’, I’m ok with using my high quality Furukawa – ‘FA-11S’ (PCOCC 7N) RCA interconnects, as the difference in SQ between them & something of similar cost in an XLR interconnect of 1m length is negligible, imo.

    RCA: 2volts
    XLR: 4volts
    Inputs are matched for voltage outputs.

  2. This technical stuff is not my thing. I am glad someone understands it, but I read this twice and am still glazed over. If I want my stuff to play louder I just crank the volume knob higher, and do not give any specific thought to balanced/unbalanced. Thank you to those that do grasp these concepts and turn them into products that I can use however.

  3. Thanks for the attempt, but there are fundamental principles I’m still missing. I thought everything through an interconnect traveled from source to destination. The fact that signals travel both ways, but can increase the output voltage of the source… it “short circuits” my brain.

    Is there any advantage to the doubled voltage, or is it simply a by-product of a balanced design?

  4. Understanding the difference between XLR and SE and also the ability to bridge an amplifier is second nature to some and pure voodoo to others. Some of the terminology… “true balanced” “versus fully balanced” versus “balanced” can lead to confusion and and require investigation.

    In the case of my mono blocks there’s is a very noticeable difference in sound quality – for the better – when feeding them balanced versus SE. (same cable model no external adaptors). I attribute that fact to circuit design, not necessarily the cable.

        1. Just to add to the “nerd” factor…When Paul started on Einstein and GR I was hoping to read something like voltage contracts while current dilates.

  5. While I’m a home-made electrical “engineer”, I get this…
    As to the trains and cars, I think Paul was on one train, and the audience was on the other. This is called “out of phase” 😉

    The analogies are fun, however.

    Now, I’m phasing out … … …

  6. Maybe this description helps.
    Draw 3 parallel lines an inch (or 25.4mm) apart horizontally across a paper.
    Call the middle line zero or ground – Call the top line plus 1 – call the bottom line minus 1
    Measure the distance between zero and one of the lines – you get “one” (or 25.4mmm) Single ended.
    Measure the distance between the two outer lines you get “two” or (50.8mm) XLR

    Then to push many over the edge study this table 😀

    https://www.canford.co.uk/TechZone/Article/dBComparison

    or do like Larry said, just turn the volume up or down.

  7. And silly me. I had thought balanced circuits were double the voltage because there were two identical parallel amplification circuits, or a single circuit with output that is duplicated and inverted to create a second signal, creating a “faux balanced” output. In other words, I just thought the voltage doubled because there were more amplifying components to provide more juice. LOL

    Paul’s explanation never even occurred to me. It would take me weeks to grasp the physics. At any rate, I’m glad the train speed virtually doubles. My balanced amplifiers perform better and sound better with balanced sources and balanced interconnects in which a train moves in two directions. 🙂

  8. Paul’s had me sold on an all “True Balanced” rig from input to output a few years ago with the arrival of my SGCD/M700’s (now long gone but they were great). Yes there is a difference in sonic’s not just a 6dB gain. I’ve had so many arguments on this topic with friends. Some don’t understand it. Some think it’s more of Paul’s Snake Oil Salesman tactics (it’s not of course).

    I like XLR because it’s easy to solder over RCA mainly. The sonic benefit is a plus of course.

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