Alex Hixon

Line Amplifier

Introduction

Pretty much just an implementation of the Application Note in the THAT1646 datasheet.

The hard part was getting down to such a small size, especially since it’s stereo. If you’re just using regular Eurorack, this means you get two modules in one!

As with the phono amplifier, as much as the module’s sockets are not included on the front. For my case, the signal you want to send to your speakers will always come from a particular module in my system, so there was no need to waste space on the front for two extra plugs (and another two on the thing that has to send it sound).

You can, of course, have access to as many or as little jacks as you need by plugging their outputs into a 1U jack tile – for instance, maybe you really do want access to both balanced TRS and XLR outputs, as well as having two audio input jacks. You can, if you so desire!

Photos

Front; with stereo XLR connectors.
Australian 10c piece for size reference (≈ size of a U.S. quarter)

Specifications

Size

1U, 12HP (60mm)

Inputs

Internal 4-pin header (L+R audio channels).

Both channels max 10v p-p.

Outputs

  • Stereo XLR connectors on front panel - datasheet says +27.5dBU maximum per channel, but probably less due to us not using the full power (±18V) range of the device.

  • Two 3-pin headers for stereo TRS connector (?? maximum per channel)

  • Outputs in either “true balanced” or “impedance balanced” mode (settable using S1).

Outputs are shunt protected against accidental plugging into mic preamp supplying phantom power.

Gain

  • +5.3dBU balanced, typical
  • +5.26dBU unbalanced, typical

  • +6dB balanced, typical, with 100k nominal load

Settings

S1 allows switching between “impedance balanced” (aka “balanced/unbalanced”) , and true balanced TRS outputs.

Current Draw

≈6mA unloaded, max.

≈25mA for 500 ft of Belden 8451 cable.

≈70mA typ with outputs shorted

Purchase

Not yet; though if you’re interested, please email me!

Schematic

Click for PDF version