Yes yes yes, inside. But for the moment, we can have a look outside.
This is the JBL305P MkII
reviewed by Amir here.
From the outside, we have this picture from JBL :
View attachment 91992
And some information from the User Manual. The JBL305P MkII is the smallest member of a serie:
View attachment 91993
And I cannot resist to show some figures from the same document:
View attachment 91994
Before we open, just have a look on some controls:
View attachment 91995
Ok ok, we want to see inside, remember the tittle of this thread!
Ok, so let's open the box:
Two speakers connected to the motherboard (yes yes, wait a minute) with ultra audiophile grade cable and some damping foam.
View attachment 91997
And the rear port (looks like 2 same parts glued altogether):
View attachment 91998
So... We you open the open, you have two parts, the box, and the more interesting back plate.
(I was not able to upload the whole pic so I splitted it into few parts) :
View attachment 92001
View attachment 92002
View attachment 92003
View attachment 92004
So I've noted few parts:
- switching power supply
- voltage regulator from 25V to 3.3V
- another one from 25V to 5V
- one little MCU from ST Microelectronics code name STM8S005K6
- one ADC Cirrus Logic CS5341
- a quartz, do not know the values, why just one ?
- an amplifier again from STM, the STA350
- the decoupling capacitors and outputs of the amp
Because I really would like another capacitor war on ASR, here is for you guys,
View attachment 92005
So with this components:
- one have a switching power supply with 25V
- two voltage regulators, one 3.3V et one 5V
- one micro controller managing the logic, switches, volume pot, front LED and Amplifier
- one ADC: grab the sound from XLR in analog domain and convert it into digital domain
- one amplifier with settings for stereo mode in the aim to power the woofer and tweeter speaker
Here is what I have understood (not the truth, just what I believe I've understood):
- the input from XLR connector is converted from analog to digital by the ADC
- the digital signal is send from the ADC to the power amp via I2S protocol
- the power amp chipset is receiving the digital signal, proceed some DSP in his first stage
- then signal is send to the output stage, one output to the woofer and the other output to the tweeter
Let's check the components.
Micro Controller STM8S005K6
Datasheet here
View attachment 92007
On the picture we cans see the STM and also the voltage regulator in 3.3V for this component. This is a little micro-controller 8-bit line from STM @ 16MHz, something comparable to the Atmel 328P and brothers used with the Arduino cards. There is some input and output on it, especially an ADC on 10 bits, not used for the sound (you cans top to cry), but I am pretty sure the ADC is used to read the volume pot on the back of the speaker to translate it after to some command on the amp side.
On the table below we can understand there are some GPIO (General Purpose Input Output), it means input and output to communicate with the physical world. So, it means four our purpose that Boundary EQ, HF Trim, Input Sensitivity and volume are connected to the GPIO.
The volume level is connected to the ADC in order to calculate the volume for the amp. Using 10 bits 2^10 = 1024 step from the volume control, from 0V to 3.3V... Anyway the JBL has a kind of notch (not sure of the word).
View attachment 92008
Also we have the information of an I2C (not I2S, no sound!): this is a serial protocol communication to transmit bit by bit information. Using this the STM is able to control, depending on the settings on the back plate, the amplifier parameters.
Here is an example on how to use the Tone Control boost/cutwith the SMT with this table (from the amp documentation):
View attachment 92009
Another point: the amplifier has pinouts (20 & 32) for "thermal warning" or "fault interrupt" : I am pretty sure some GPIOs are connected to the amp, to grab default information and light the front LED in RED.
View attachment 92010
And finally, this circuit is certainly managing the switch off of the speaker after a delay. Ok, let's continue, I start to like it!
Cirrus Logic CS5341 ADC
Datasheet here
Really difficult to take a picture...
View attachment 92013
So here we are. The ADC grab power from the second voltage regulator in 5V (this chip is able to run with max 5V) and takes anolag signal from XLR.
Here is the functional schematic.
View attachment 92014
And some words from the ds : "
It performs sampling, analogto-digital conversion, and anti-alias filtering, generating 24-bit values for both left and right inputs in serial form at sample rates up to 200 kHz per channel. The CS5341 uses a 5th-order, multi-bit Delta-Sigma modulator followed by digital filtering and decimation, which removes the need for an external anti-alias filter. "
If we have a look on some specs, we can read some (bad?) informations:
View attachment 92015
So THD+N is -98dB is the best you can grab from this component. On the good side, with 5V power, you have the best the chip can do:
View attachment 92016
So, as
@daftcombo explained to me, why to use a 120dB SINAD dac to power this speaker?
Well, well, well, after the ADC, we have the amp (I guess).
ST Microelectronics digital amp STA350BW
Datasheet
View attachment 92017
In the Focal Alpha 50, you have two mono (class A/B) amp, one for the woofer, and a second one, less powerful, for the tweeter. In the JBL, you have one stereo Class D amp used in stereo. This is why the power for each speaker is the same... Another point is this photo below:
View attachment 92020
it lets me believe the same board is used for the 305, 306 and 308 (I know, for the 308 it's just what I suppose).
If JBL produces more watt with the board and the same amp, I think they just adjust the output of the switching power supply. From 41W to 56W.
View attachment 92021
Ok, let's grab some information from STM about this amp:
View attachment 92022View attachment 92027
So we can confirm some points:
- this amp is used in stereo,
- it's feed from the ADC using I2S interface
- it's controled from the micro controller using the I2C interface
- gain is independent for each channel
- there is a digital DSP...
Reading few more pages from the datasheet, we found this figure:
View attachment 92028
I let you think about it.
I want to add few points.
From the outside, this is a pair of speakers. Usually a speaker is a box, a filter, a boomer and a tweeter. More or less. Here, we have something very different. This is a kind of digital product, even if from the outside it looks like traditional speaker.
Another point is the price. There is a lot of engineering into the JBL. I believe only a big company can produce this kind of toys. And the price is so loooow.
But recently on ASR
@TomJ, in the thread of the NAD, wrote: "
I wonder what we'd find if we measured the electronics of active monitors the way we measure external components..."
Don't know, but now we have some datasheets.