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/pla2180d/19-1u-amplifier-class-d-2x-180w/dp/DP36607
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
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/pla2180d/19-1u-amplifier-class-d-2x-180w/dp/DP36607
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
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.
Clive the "D" doesn't stand for "digital". There isn't a such thing.
Good video.
Question…🎉
If I connect 80w 6 ohm speakers to a 30w 8ohm stereo could it blow the LCD display chip?
Coz I did lol
I would love you to do a guitar valve amp teardown
digital amplifier amplifies digits.
How can we have high current in that ribbon cable?
Not bad. But i love my iron pigs. Qsc usa amps
I must admit I expected to see 2 relays, one on each channel that switched when each corresponding amp had powered up OK and was stable. I guess they use a double pole relay and combine the 'ready' signal and only switch the speakers on when both amps are ready.
Class-D isn't "digital".
In a class D amplifier, there will be a modulator that compares the input signal to a triangle wave and sends its output to drive the gate of the output transistors, but if the output transistors are large, this gate can become very capacitive so an additional "gate driver" IC is needed between the modulator output and the gate of the output transistors.
Loudspeakers are a linear motor connected to a diaphragm that moves to produce sound. They don't have any other power source or electronics built inside them, so in order to operate, they require an amplifier to send them a high voltage, high-current signal that can drive them. An amplifier is a big power supply that drives the linear motor inside the speaker to push and pull on the diaphragm. There is always a power supply section that rectifies the incoming AC power, into DC and there is always an output stage that acts like a valve for that power which modulates the DC voltage to an AC voltage in proportion to the incoming electrical signal, which is the musical signal. The output from the amplifier is just like the input waveform, only much higher voltage, and capable of much larger current. This amplifier makes it very easy to see the different parts of the unit that serve different functions; sometimes the circuit boards get very dense and it becomes difficult to see what is going on.
Something to get straight … Class D amplification is not digital. The "D" designation was simply the next available letter in the alphabet when listing amplifier classes. This odd coincidence has been the source of huge confusion. These amplifiers are an analog process, but not like the usual brute force process used in A AB or B class amplifiers.
Class D operates rather like an FM Transmitter. What they are doing is encoding audio onto a high powered carrier signal. In FM this is done by changing the carrier frequency. In Class D it is done by changing the width of square wave pulses in step with the audio input, hence Pulse Width Modulation.
In an FM receiver you would lock onto the carrier frequency then filter it to recover the audio signals. In a PWM amplifier you do the same thing… filter out the high powered PWM carrier in order to recover the much amplified audio signals, for your speakers.
This entire string of events is an analog function… the audio signal is never digitzed, the pulse widths are governed by an analog comparator, the output filters are simple analog coil and cap filters. Nothing digital about it.
I haven't used any Pulse PLA series amplifiers, but the Pulse APB2100 and Citronic PLX2800 (both the same amplifier as each other) are junk that fail.
Unless it has a SPDIF in or a TOSLINK in it is just a class D amplifier using a Pulse Width Modulation.
letter D used to designate this amplifier class is simply the next letter after C and, although occasionally used as such, does not stand for digital. Class-D and class-E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of digital symbols, but a class-D amplifier merely converts an input waveform into a continuously pulse-width modulated analog signal. (A digital waveform would be pulse-code modulated.)
The D in Class D amplifier does not in fact stand for Digital
Its just the logical next step coming from class A, class B, class AB and class C amp
Maybe there’s something on the other side of that input board that we’re not seeing, but I don’t see how this amplifier is digital. It has analog inputs, analog outputs, and from the looks of it, no digital components. I could be mistaken, but I’m wondering if this is one of the sellers that mistakenly assumed that “class D” means “digital”
Nice teardown Clive. I love class D amps, so simple yet ingenious. I built one many years ago, from memory it generated a pure triangle wave using a pair of comparators, a flip flop and a pair of matching current sources/sinks, then fed that into a simple comparator as the A/D converter, and a full bridge output. It worked surprisingly well and sounded quite good though I never got round the issue of high quiescent current and ended up losing interest. I was going to build a car sub amp using the design one day but never got round to it. Think the schematics are still out there on diyaudio.