Inside a 360W digital amplifier

I bought this amplifier purely so we could open it and take a look inside. It's a modern class-D amplifier that uses pulse width modulation and filtering to achieve high power audio amplification efficiently with low heat and size.

One slight correction. The incoming supply comes in via an NTC inrush current limiter which I inadvertently called a MOV (Metal Oxide Varistor).

Initially I thought it might have a dedicated chip or module for the amplification, but it seems to use discrete transistors on the output with a couple of mystery chips. The power supply is notable for using a discharge lamp ballast control chip, presumably because it is a dual rail power supply with the zero volt output referenced to mains ground, and the two-MOSFET push-pull drive circuit makes it better suited to that.
The way the four output transistors are pinned down onto the aluminium backplate is quite interesting.

The areas of most concern for reliability are the ribbon cables and the solder joints on the speaker pillar terminals I'd rather the power had been linked across with a beefier dedicated wiring loom and auxiliary low current control cable. The IDC (Insulation Displacement Connectors) used with ribbon cable are alway problematic with high current.

The unit has three operational modes:-
Stereo - independent left and right channels.
Parallel - One input fed to both channels (mono)
Bridged - One input fed to both channels in antiphase to drive one speaker at higher power.

The stereo and parallel modes have one speaker connection connected to zero volt/chassis level and the other connection is pulled between the positive and negative rails by two transistors.
In the bridged mode both ends of the speaker can be driven to either supply rail by a full H-bridge transistor arrangement.

The "ground lift" option just isolates the incoming signal cable's screen from the chassis. Do not ever disconnect the mains earth/ground. There's a rather unpleasant culture within the audio industry to "avoid ground problems" by cutting the earth/ground wires in the mains plugs of equipment. That is absolutely the WRONG thing to do, but is perpetuated by the vague word-of-mouth training prevalent in showbiz. Removing the safety earth/ground means that in the event of a fault full mains voltage can be present on audio cables, resulting in a serious shock risk and equipment damage.

Professional audio equipment uses a balanced pair of audio signal wires which are twisted along their length to ensure that any external electrical noise influence is coupled onto both, cancelling it out. The audio signal is purely derived from the difference between those two wires and not with reference to ground. To reduce ground-borne electrical noise between equipment, the cable screen may be "lifted" at one end. On large scale shows the audio is often buffered locally and may be sent to the desk via a fiber optic link.

This amplifier was bought from CPC in the UK.
https://cpc.farnell.com/pulse/pla2180...
Note that I've not tested the audio performance of this amplifier.


If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- https://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's algorithm quirks, allowing it to be a bit more dangerous and naughty.


#ElectronicsCreators