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Inside the JBL305P MkII

renaudrenaud

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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 :
1604745000367.png


And some information from the User Manual. The JBL305P MkII is the smallest member of a serie:
1604745256535.png


And I cannot resist to show some figures from the same document:

1604745296370.png



Before we open, just have a look on some controls:
1604745340585.png



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.
1604745617543.png


And the rear port (looks like 2 same parts glued altogether):

1604745767562.png


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) :
1604746882064.png

1604746945027.png

1604747020020.png

1604747077173.png


So I've noted few parts:
  1. switching power supply
  2. voltage regulator from 25V to 3.3V
  3. another one from 25V to 5V
  4. one little MCU from ST Microelectronics code name STM8S005K6
  5. one ADC Cirrus Logic CS5341
  6. a quartz, do not know the values, why just one ?
  7. an amplifier again from STM, the STA350
  8. the decoupling capacitors and outputs of the amp

Because I really would like another capacitor war on ASR, here is for you guys,

1604747643086.png



So with this components:
  1. one have a switching power supply with 25V
  2. two voltage regulators, one 3.3V et one 5V
  3. one micro controller managing the logic, switches, volume pot, front LED and Amplifier
  4. one ADC: grab the sound from XLR in analog domain and convert it into digital domain
  5. 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):
  1. the input from XLR connector is converted from analog to digital by the ADC
  2. the digital signal is send from the ADC to the power amp via I2S protocol
  3. the power amp chipset is receiving the digital signal, proceed some DSP in his first stage
  4. 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

1604751571366.png


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).

1604752166793.png


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):

1604753090727.png


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.

1604754110376.png



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...

1604754297028.png



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.

1604754326491.png


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:

1604754765698.png


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:

1604754951866.png


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

1604755248941.png



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:

1604755580726.png


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.

1604755769565.png



Ok, let's grab some information from STM about this amp:
1604755949952.png
1604756089648.png


So we can confirm some points:
  1. this amp is used in stereo,
  2. it's feed from the ADC using I2S interface
  3. it's controled from the micro controller using the I2C interface
  4. gain is independent for each channel
  5. there is a digital DSP...

Reading few more pages from the datasheet, we found this figure:

1604756375799.png


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.
 

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TomJ

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Awesome. Would love to see a similar analysis of a KEF LS50 Wireless II when available
 

Dmitri

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“Because I really would like another capacitor war on ASR, here is for you guys”

Sarcasm, right? Please say it’s sarcasm.
Thanks for the tear down images and info.
Can’t say I understand most of it, but that’s my impetus to learn! :)
 

daftcombo

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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:
  1. switching power supply
  2. voltage regulator from 25V to 3.3V
  3. another one from 25V to 5V
  4. one little MCU from ST Microelectronics code name STM8S005K6
  5. one ADC Cirrus Logic CS5341
  6. a quartz, do not know the values, why just one ?
  7. an amplifier again from STM, the STA350
  8. 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:
  1. one have a switching power supply with 25V
  2. two voltage regulators, one 3.3V et one 5V
  3. one micro controller managing the logic, switches, volume pot, front LED and Amplifier
  4. one ADC: grab the sound from XLR in analog domain and convert it into digital domain
  5. 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):
  1. the input from XLR connector is converted from analog to digital by the ADC
  2. the digital signal is send from the ADC to the power amp via I2S protocol
  3. the power amp chipset is receiving the digital signal, proceed some DSP in his first stage
  4. 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:
  1. this amp is used in stereo,
  2. it's feed from the ADC using I2S interface
  3. it's controled from the micro controller using the I2C interface
  4. gain is independent for each channel
  5. 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.
Great work Renaud.

French version of the teardown available also, right?
 
OP
R

renaudrenaud

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“Because I really would like another capacitor war on ASR, here is for you guys”

Sarcasm, right? Please say it’s sarcasm.
Thanks for the tear down images and info.
Can’t say I understand most of it, but that’s my impetus to learn! :)

Not sarcastic. A bit ironic maybe, but with great respect to the ASR community.
 

DavidMcRoy

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Great job. This confirms everything I ever knew (or suspected) about the nature of the circuit, and pushes forward my plans to build a hotrod (Frankenstein?) LSR305 and/or 305P MkII with outboard DSP and Class-D amplifiers sporting higher specs.
 
OP
R

renaudrenaud

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Great job. This confirms everything I ever knew (or suspected) about the nature of the circuit, and pushes forward my plans to build a hotrod (Frankenstein?) LSR305 and/or 305P MkII with outboard DSP and Class-D amplifiers sporting higher specs.
I was thinking about that few days ago. With no ADC, better amp and DSP. But I am not sure it's worth the effort / money.
 

thewas

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This confirms everything I ever knew (or suspected) about the nature of the circuit, and pushes forward my plans to build a hotrod (Frankenstein?) LSR305 and/or 305P MkII with outboard DSP and Class-D amplifiers sporting higher specs.
I would also stiffen and damp internally the enclosure or build a better/stiffer one (except the front baffle of course which I would also reinforce from the inner side).
 

somebodyelse

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I would also stiffen and damp internally the enclosure or build a better/stiffer one (except the front baffle of course which I would also reinforce from the inner side).
That would be my initial reaction too. @NoAudiophile did at least part of that to the LSR308 and measured the change - scroll down to the Modifications section. Maybe it would show a bigger difference on some other measurements.
 

thewas

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That would be my initial reaction too. @NoAudiophile did at least part of that to the LSR308 and measured the change - scroll down to the Modifications section. Maybe it would show a bigger difference on some other measurements.
Yes I know the review, as you say in other measurements like waterfall the difference would be probably larger, although I don't even find the FR differences small, especially at the tweeter position at below the mids where it shows significant more silence due to less enclosure vibrations (blue vs pink curves):

1606913856741.png
 

Berwhale

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There is a lot of engineering into the JBL

I wish they had expended some effort to remove the hiss from the tweeters. I had to send my pair back as I found it intolerable.
 

Count Arthur

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I wish they had expended some effort to remove the hiss from the tweeters. I had to send my pair back as I found it intolerable.

Did you try adjusting the input sensitivity?

On my active speakers you can adjust the input sensitivity and the maximum output volume. On the highest settings the hiss is quite noticeable, on the lower settings, it's inaudible from ~60cm, 2 feet away.
 

Berwhale

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Did you try adjusting the input sensitivity?

On my active speakers you can adjust the input sensitivity and the maximum output volume. On the highest settings the hiss is quite noticeable, on the lower settings, it's inaudible from ~60cm, 2 feet away.

I set the input sensitivity as advised in the manual for an unbalanced input. I don't recall if I tried the other setting. The hiss did not appear to be dependent on the volume set on the rear of the speaker and was present even with the speakers disconnected.

I have a pair of iLoud MTMs on back-order with Bax - I paid £527 after a CyberMonday discount :) - so I hope I don't get the same issue.
 

x-dfo

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I often wonder if this would actually sell for 1000 a pair from a non-jbl company, probably much more tbh.
 

x-dfo

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I would also stiffen and damp internally the enclosure or build a better/stiffer one (except the front baffle of course which I would also reinforce from the inner side).
would a fibreglass/epoxy layer work for that?
 

dfuller

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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.
You wouldn't by chance be interested in tearing one of those down, would you? This is fascinating stuff.

Because I really would like another capacitor war on ASR, here is for you guys,

Haha, no - but I think at this price point a more budget option can be forgiven. ;) It's a 105C part too, which is a nice touch. Koshin brand apparently which is from what I can tell generally decent quality.
 
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