Inside a 360W digital amplifier

this ominous black box is a digital amplifier a stereo digital amplifier let me show you the back of this noting that I've already taken the lid off this and added an exploration so we have the inputs which is a combination it's the Jack and XLR and these are balanced inputs and we have an option of set it to stereo which is default or parallel or bridge when you get it in Stereo it just treats as two separate channels left and right in parallel it only looks at one of the inputs but approach it to both the channels so basically speaking you've got two channels but it is just one mono signal so to speak and you get the bridge option the bridge option uh inverse the phase of one of the waveforms and effectively means that you can connect a speaker across just the positive Terminals and it drives it at twice the power and this thing is a beefy little amplifier it's rated about 180 Watts RMS or 350 Watts if it's bridged the output is oh there's something else that's quite odd that they've actually put this here when this would have should actually belong there it's the ground lift and that is just basically the input signal it lets you choose if the screen is going to be connected to the chassis the Earth the chassis or if it's actually going to be left floating normally it would be a tighter ground but if you've got noisy ground introducing hum and noise into your audio you can use that lift function just have it purely balanced which is quite good uh the output gives you the option of using speak on connectors for a 428 ohm load or the classic pillars or banana plug type connectors here then we've got a little cooling fan which is quite small it's going to be quite nice this is only a one U unit which is quite a small unit that means it's basically one unit and a 19 inch rack we've got the IC connector and then we get the voltage selector switch here that can switch between European voltage and American or other voltage basically 230 or 120. on the front of the amplifier we've got uh this is a incident this is a pulse pla2180d that means two times 180 watt we've got the gain control on the front we've got the power indicator LED we've got the signal present LED it just basically flickers to show that you've got a signal there for Diagnostic purposes and then we get the clip LED which means the amplifier is close to its maximum output and it's potentially going to damage the speakers or damage that the amplifier but well it should protect it should over protect against overheating stuff the main thing is with clipping you don't want to go there you a brief pulse every so often if you're really pushing it hard is okay but not continuous because that puts a lot of strain the speakers run them DC they stop being uh impedance and become a resistance uh we've got the ventilation drills here very slick uh to allow the air from that fan to go somewhere and then we've got a power on off switch there is a bit of foam Behind These ventilation grills I think it's basically to stop bugs getting in or something like not really sure because uh there's not much uh space for the air to get in here is it quite odd anyway I've already had this open so I only put one screw in it to save time so I shall whip that screw out now I shall open it up and then refocus on the interior here is the interior look how minimalist that is right too well we'll focus down there super Sharp let me well actually you know what the pictures are almost I'll give you a brief thing but I've got some pictures printing off and then I'll show you in the pictures but the basic thing is we've got the power supply board a ribbon cable taking power across we've got the amplifier board very interesting way of clamping the transistors down here we've got the speaker board and then we've got this little bird here which is the incoming signal which is all just covered in op amps low noise op amps that deals with the balance signals and basically processing it for feeding over to the amplifier uh right now what I'm going to go and grab those pictures now and then we'll explore it in Greater detail one moment please and explore okay I kind of went a bit fur and I was expecting but this is good so let's take a look at the amplifier uh well the power supply for the amplifier section first so I have taken a picture of it such that we can zoom in a bit easier and I can point a bits and write numbers and things the incoming Supply goes via this big metal oxide Barista down here and there is some filtering circuitry on the bridge rectifier and then super duper big death beam capacitors there's two because it's using that thing whereby if we take a look at the voltage selector switch a couple of hours going to it can bridge out part of the bridge effectively and uh ultimately uh do a push-pull thing for 120 volts that it charges both capacitors up to get a decent voltage inside so um with 238 to 240 volts it charges up to say 330 volts but with the 120 volts it'll also charge up to that we have a common mode suppression choke we have class wide capacitors which I'd expect to be going down to the local ground pin and then rather oddly down here we have a ir2156 which is an electronic ballast controller for lamps but they've used it as a push-pull driver for the transformer in this that's odd and guessing they've just chosen it as a cheap mass-produced chip that's really rugged so it is using these two uh 26 nm60n by St mosfet to actually push-pill this Transformer by the look of it these things that I originally thought I thought this was a just a bank of diodes it's not these are the diodes there's a a Merwin 620ca and a CT one of them is the diodes point then the way one of them has the point out the way they're the main rectification because this is a dual real system and it's also he got here a 7812 for a positive 12 volt Rail and a 7912 for a negative uh Supply rail other things on this circuit board it's got the outlet to the fan and it's also got a temperature sensor that is going from here onto the heatsink plate for the amplifier so presumably if that gets too hot at signaling back now there is a ribbon cable going from this section to the amplifier board that's not just carrying power it's carrying signals but these pins are clustered as sets of six we've got the plus Supply on six the main Supply in six the ground on six and then we've got the six controls and Signal pins for basically indicating when this is paradox stabilized and over temperature and loads of other things uh the amplifier board itself oh it's worth mentioning look here in here there's something I don't actually like that much and it's a soldering at the back of these uh pillars for connecting the speakers they've sorted that side relatively but this side's fairly dry if you have a problem with any of these amplifiers and it's crackling when you wiggle those connections check these solder joints the other option is to switch over to the speakons uh the input board has a fair amount of circuitry on it I'm not going to reverse engineer that there's tons that's a very big schematic and it deals with processing that analog signal I'm not sure where this switching I think that happens on that Triumph fire board but that also has the volume control board notes the indication of like clipping and stuff like that going over here the board that I have removed from here the reason I've removed it was to see how they've mounted the transistors so they've got these transistors just folded flat on the back and uh they have a plate that goes through here and the transistors are physically pressed onto that heatsink by the plate now let me show you and this is it it's a metal plate with four screws through it and a little plastic spacer covers it's actually a spacious along in the screws but it basically goes through and it's a bit that pushes the transistor and then they tighten a single screw in the middle down and they've tightened it really tight to the point the plate is deformed slightly just to actually make sure all those transistors are pressed firmly into contact with this insulating pad on the heatsink that's very good and if we take a look at this circuit board we have what's the best way to put this there's a speaker output connections that relay is the anti-thump really it's designed to only come in once the circuitry is stabilized and it's at between the inductors these inductors and capacitor networks are the filters on the output of the amplifier just to reduce remove this of high frequency switching noise we've got local decoupling capacitors or smoothing capacitors just local to the amplifier two of the plus Rail and two of the negative reel and there's the ribbon cable coming on we've got this massive array effectively a program delivery of resistors somehow tied into the four to one C I think that's to do with either sensing or a power supply but it's kind of hard working out what it's doing um it looks as though it may be for a local power supply particularly given these zener diodes that seems to be detecting a threshold in some way that's a standard npn transistor we have lm3 I think the mlm319 hold on let me just double check that there's two chips on here I couldn't identify that's quite annoying uh lm319 M we've got two of those which are comparators I think which are possibly dealing with the analog to uh digital output and then we get these two chips here which I'll try and read it it's very very small text Mega Mega something hold on Mega semi that did not come up with anything that came up with an AliExpress seller but not thing and their number is me98-1036 under that is what looks like a date code e2106 I do a blanken that I did not find those chips but I do get the feeling that they are driving those transistors on the other side so in this h-bridge type format well not the H Bridge ultimately they're just push-pull either side but it is effectively kind of any well it is when it's in uh in a particular mode in the amplifier when it's doing this abridged uh but there we go is there anything else about saying about this we have the beefy power supply we've got the fan only blowing across that power supply it's really just what they're doing with this fan is they're basically just stirring here in this box um and that's more or less it signal processing output the amplifier section with this slab of metal here not thinned heat sinks this chunk of hair aluminum here for the uh switchboard power supply with the diodes and output and the mosfetch then putting some voltage regulation filtering the voltage selection the transformer for isolation and then just power and signals going across that is it so it's quite neat quite a neat amplifier indeed I am already zoomed out okay right uh but there we go that is the pulse pla what is it again pla2180 d which is rated 180 Watts RMS per channel it's pretty good isn't it for something that's so minimalist inside but that's the magic of digital amplifiers there are fantastic things they make life a lot easier in the entertainment industry because they just uh make things lighter oh there is one thing worth mentioning they've put a nice smear of silicone up the bus bar on the uh positive connect the live connection let's see down to the fuse that's quite a nice feature and it is Earth which is also a nice feature and that Earth is snug this is good but there we go the pulse digital amplifier very minimalist very functional

Channel: bigclivedotcom

Views: 74,528

Keywords: cpc, pulse, digital, amplifier, 180W, 350w, 360w, pla2180d, class d

Id: dAM882I6u7g

Length: 12min 44sec (764 seconds)

Published: Sun Aug 06 2023

Reddit Comments

[u/nemom]

From the description:

"""

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.

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