Preview: Soul Drive Unbalanced to Balanced Converter

A few months ago, I talked to Psychaudio who is a local amplifier designer, about building a device that will take an unbalanced signal, and create a balanced signal to feed to balanced amplifiers. This will make it easier for people who wants to have balanced drive on their headphones, but not owning a true balanced source.

Although a lot of people would object to this method, after the release of the Protector, we can definitely see that the improvements gained from having balanced drive is very noticeable even from if you have an unbalanced source.

Enter the Soul Drive, which utilizes a Burr Brown DRV134 chip to do the unbalanced to balanced conversion. As quoted from the DRV134 datasheet page:

The DRV134 and DRV135 are differential output amplifiers that convert a single-ended input to a balanced output pair. These balanced audio drivers consist of high performance op amps with on-chip precision resistors. They are fully specified for high performance audio applications and have excellent ac specifications, including low distortion (0.0005% at 1kHz) and high slew rate (15V/ยตs).

These are some pre-launch photos of the Soul Drive:

The capacitors are for the power supply, and there is no capacitors used in the signal path. Since the Soul Drive is an active device, it requires a 12V wallwart for operational.

I personally haven’t tested the Soul Drive, but a prototype unit is out and the early testers have been saying good things about it.

Stay in tune!


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12 Comments

  • Reply May 26, 2010

    direcow

    wow, any chance this will be available for purchase?

  • Reply May 26, 2010

    Earfonia

    Besides for acting as buffer for impedance matching, or when ground loop problem occur, I don't see the need of active component for connecting unbalance output to balance input.

    Can anyone hear any improvement using this active component compared to the normal passive way of connecting unbalance output to balance input?

    Usually this is how I connect unbalance output to balance input:

    Source Left output (+) –> Amp Left + input (hot)

    Source ground –> Amp Left – input (cold)

    Source Right output (+) –> Amp Right + input (hot)

    Source ground –> Amp Right – input (cold)

    I normally don't connect the source ground to the balanced input ground.

  • Reply May 26, 2010

    psychaudio

    Well sir, those connections will surely work, but it will defeat the benefits of balanced signal itself, where in a balanced signal the – (inverting) signal is an exact opposite of the + (non-inverting) signal, the electromagnetic fields are canceled out by the equal and opposite currents, thus removing any noise picked up along the way ๐Ÿ˜‰

    • Reply May 26, 2010

      Earfonia

      Yes, that's right, especially if the length of the connection is significant, then placing Soul Drive near to the source would reduced a lot of interference ๐Ÿ˜€

      • Reply May 26, 2010

        psychaudio

        True ๐Ÿ˜‰

        And since we talk about balanced driven headphones…

        Putting a ground signal at the amplifier's inverting input, will make the headphones driven by a non-inverting signal and an active ground signal (since the inverting amplifier only acts as a ground follower this way), so the headphones is actually not driven by a balanced signal ๐Ÿ˜‰

  • Reply November 1, 2010

    Juan

    • Reply November 1, 2010

      Mike

      Thanks for the links, Juan!

  • Reply August 15, 2011

    Andy

    Where would this fit in the signal path? DAC -> Converter -> Amp, or DAC -> Amp -> Converter?

    • Reply August 15, 2011

      Anonymous

      DAC > Converter > Amp.

      • Reply August 15, 2011

        Andy

        That’s kind of a shame, it’d mean that if you only have a DAC/Amp combo box you couldn’t use it.

        • Reply August 15, 2011

          Anonymous

          That’s true.

          I don’t think it’s absolutely necessary though. I’m not so big on balanced drive as I was before.

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