Crown XLS Class D - Speaker Output Ground Referenced or Not?
Ted_B
Posts: 2
I'm looking to connect the outputs of a Crown XLS series amplifier (running in 2-channel mode) to the high-level inputs of powered subwoofers in a 2.1 home audio system. Some Class D amp designs are such that the (+) and (-) outputs are offset from ground by a large DC voltage (e.g. 24 VDC). This does not pose an issue for conventional enclosures, but it can pose an issue for a powered enclosure when using the high-level (speaker level) inputs. I believe this may be an issue mostly with older designs, but I would like to know for certain if the output of the Crown XLS series is referenced to ground or not before moving forward.
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Comments
Q1. Reference to ground : Use your ohmmeter! Check for continuity between the negative speaker output and chassis ground.
Q2. Note on output offset voltages: Usually designers will insert a cap between the 24V and the output terminal to eliminate any large DC offset at the output. If the 24V were present, assuming a speaker as the load, the speaker would be seen as a low resistance and can be fried by the DC current available at the output. (I = V/R => 24V/6R = 4A!)
Q3. Alternate connection : However, if memory serves, there are two different input connectors (XLR and TRS) for each channel. These connectors are parallel connected. Connect the sub inputs to the XLS extra inputs. If XLS has a single connector per channel, use a 'Y' patch wire with appropriate jacks.
Thanks for the response! I agree on all points and was thinking a DC blocking cap on the sub amp high-level input would be an intelligent design feature, but I didn't want to make assumptions and wanted word from Crown prior to purchasing the XLS 2502. I contacted Crown tech support via telephone, and had a good chat with a knowledgeable engineer who confirmed that the XLS series amps are indeed referenced to ground, so there should not be any positive offset DC voltage on the (-) speaker terminals when the amp is in stereo operation. After buying the amp, I did verify this with the power on and no signal applied prior to making any connections. The system is now installed, calibrated (REW), and sounds great.