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OSD BK-100W70T

70V commercial transformer

Item # 452BK1HW70

This transformer lets you convert an 8-ohm speaker for use in an indoor 70-volt distributed audio system.

This transformer lets you convert an 8-ohm speaker for use in an indoor 70-volt distributed audio system.

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Item # 452BK1HW70

In stock
$39.99 each

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About the OSD BK-100W70T

Eric A.

Convert 8-ohm speakers to 70-volt use

The OSD BK-100W70T indoor transformer allows you to convert standard 8-ohm speakers into 70V speakers for use in a commercial-style custom-installed sound system. With taps at 20, 40, 60, 80, and 100 watts, it allows you to daisy-chain the 8-ohm speaker together with multiple additional 70V speakers, all driven by a single amp. It is rated for indoor use only.

Product highlights:

  • lets you convert a standard 8-ohm speaker for use in a 70-volt distributed audio system
  • selector for choosing 20, 40, 60, 80, and 100-watt taps
  • color-coded, in-wall rated 18-gauge wire leads included
  • 4"W x 2-3/4"H x 2-1/2"D
  • weight: 1.8 lbs.
  • warranty: 2 years
  • Our 60-day money-back guarantee
  • MFR # BK-100W70T

What's in the box:

  • 70V Transformer with 7.5" wire leads and attached mounting bracket (adhesive backed)
  • Wiring & Specification sheet

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More details on the OSD BK-100W70T

Stacey B.

Product Research


Overview: The OSD BK-100W70T line-matching audio transformer lets you power 4- or 8-ohm speakers from a commercial 70V amplifier, letting you deliver high wattage over long speaker wire runs. Featuring taps at 20, 40, 60, 80, and 100 Watts, the BK-100W70T lets you connect speakers up to 2000' away using 14 AWG wire, making it an ideal solution for commercial installations where distance is an issue. The transformer has a frequency response of 20Hz-20kHz with little insertion loss and no effect on sound quality.

Mounting: The OSD line-matching audio transformer is pre-attached to an angled mounting plate for installing it on the back of a speaker magnet. An adhesive pad on the the mounting plate allows it to be attached to the speaker without the need for mounting hardware.

Wiring: The BK-100W70T features six input wires for connection to a 70V commercial amplifier, offering five wattage options for your connected speaker. Each wattage can be selected by using a color-coded input wire. Three output wires are used for connection to either a 4- or 8-ohm speaker.

  • 70V Amplifier Input (Primary):
    • Black: Common negative
    • Brown: 100W (50Ω)
    • Red: 80W (62.5Ω)
    • Yellow: 60W (83Ω)
    • Blue: 40W (125Ω)
    • Green: 20W (250Ω)
  • Speaker Output (Secondary):
    • Black: Common negative
    • White: 4Ω
    • Red: 8Ω


  • Primary Voltage: 70V
  • Power Rating: 100W
  • Primary Taps: 100W, 80W, 60W, 40W, 20W
  • Secondary Impedance: 4- and 8-ohms
  • Insertion Loss: 1dB
  • Frequency Response: 20Hz-20kHz (± 1dB)
  • Dimensions: Width = 3.91", Height = 2.71", Depth = 2.48"
  • Weight: 1.8 lbs.

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Customer Q&A

1 question already asked

this article, "Convert 8-ohm speakers to 70-volt use". Will these transformers also convert a 8ohm amp signal to 70v for running 70v speakers?
[ Reynold  Jan 31, 2023 ]
1 answer
These transformers will not allow allow you to use 70V speakers on an 8-ohm compatible amplifier.
[ ZACHARY  Feb 01, 2023 ]  Staff

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