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Inside the JBL305P MkII

PaperBoat

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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.
It's blew up my mind! Before reading your statement I knew that JBL 305p MKii has all analogue circuitry... And now I know it's a kind of digital product! Thanks! Thanks! Thanks! for this great insider view... My both JBL 305p MKii are connected to an IFI Zen V2 and the DAC has an Analogue volume control knob on it... I just want to know that what is the best practice to control those JBL's sound volume? Settle the volume at 100% on both JBL and control them from the DAC OR fixed the DAC volume at 100% and control it on monitors individual pot? (I know the latter will be quite inconvenient but I can manage it if there's a possibility of better sound quality achivement) Please tell me which method would be better for this scenario?
 
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Berwhale

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It's blew up my mind! Before reading your statement I knew JBL 305p MKii has all analogue circuitry... And now I know it's a kind of digital product! Thanks! Thanks! Thanks! for this great insider view... My both JBL 305p MKii are connected to an IFI Zen V2 and the DAC has an Analogue volume control knob on it... I just want to know that what is the best practice to control those JBL's sound volume? Settle the volume at 100% on both JBL and control them from the DAC OR fixed the DAC volume at 100% and control it on monitors individual pot? (I know the latter will be quite inconvenient but I can manage it if there's a possibility of better sound quality achivement) Please tell me which method would be better for this scenario?

You should use the volume control on your IFI Zen V2. The controls on the back of monitors are for setting input gain, not volume control. You use these controls to set the gain optimally for your setup (see Gain Structure) and sometimes like a balance control between the monitors.

In your case, make sure that you do not set the gain so high that any channel imbalance with your analogue volume control becomes apparent (i.e. make sure the IFI Zen V2's volume control doesn't have to be set close to zero at your minimum listening volume)
 

RayDunzl

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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.

The LSR 308 gets a little heat sink on the amp chip,

Here are the mounting holes:

1687043054574.png
 

PaperBoat

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You should use the volume control on your IFI Zen V2.
That's what I'm currently doing now... JBLs are connected to the IFI using high quality RCA to TRS cables and they are already sounds good to me...


make sure that you do not set the gain so high that any channel imbalance with your analogue volume control becomes apparent (i.e. make sure the IFI Zen V2's volume control doesn't have to be set close to zero at your minimum listening volume)
IFI Zen V2 has slight channel imbalance at its lowest volume. I've maxed out JBL gain knobs... Input sensitivity switches are set to -10dBv. IFI Zen V2 also has a gain switch and I'm occasionally using it.
 
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FrantzM

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Hi

One of my LSR 305 MKII refuses to turn on. It had developed this issue and I sent it to a tech, it worked for about 3 months.. Now it would not turn on, no matter what I do. This seems to be a common issue with the LSR 305 MKII, rarely so with the 308. The LSR 305 are surrounds in my set-up .. I listen to music in 2-channel + subs .. for Movies, 305 are necessary.

My pair has served me for more than 4 years. I have ordered one on Amazon, not being in the USA, it will take up to 8 weeks to reach my doorsteps... In the meantime, I'd like to try to repair the malfunctioning one.. I can measure, solder and can understand schematics... EE after all but not in circuits.. IT person :(, that is about it ..
How can you people help? Where do I start?

Peace
 
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computer-audiophile

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My pair has served me for more than 4 years.
Oh my, this is not very long. My wife has her 305p II since 3 years now. And mine are from the last year. Hopefully I will have more luck.
Now I am curious to see the problems what yours have and if you will be able to repair it.

Good luck!
Where do I start?
Opening it up and make close up pictures. :)
 

FrantzM

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Oh my, this is not very long. My wife has her 305p II since 3 years now. And mine are from the last year. Hopefully I will have more luck.
Now I am curious to see the problems what yours have and if you will be able to repair it.

Good luck!

Opening it up and make close up pictures. :)
:)

I will.

Peace.
 

D!sco

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This specific product has driven my minor obsession with finding or building a decent stereo 50W DSP plate amp. It has been completely impossible so far. Either the THD or noise is pathetic, or the price ends up being too high. Is there an input for programming the DSP on the JBL? I once pretended to be a company to ask Platin how to program their amps (they make the amps for Buchardt). Platin's engineers do them all in-house. I suspect building a platform usable by DIY'ers or enthusiasts who want to bi-amp existing projects while bypassing analog crossovers is very expensive and time consuming. I've never seen promising reviews for Dayton's stuff, but it's as close as we get to a turnkey solution. I don't think Amir will ever test it, at this rate.
 

DavidMcRoy

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This specific product has driven my minor obsession with finding or building a decent stereo 50W DSP plate amp. It has been completely impossible so far. Either the THD or noise is pathetic, or the price ends up being too high. Is there an input for programming the DSP on the JBL? I once pretended to be a company to ask Platin how to program their amps (they make the amps for Buchardt). Platin's engineers do them all in-house. I suspect building a platform usable by DIY'ers or enthusiasts who want to bi-amp existing projects while bypassing analog crossovers is very expensive and time consuming. I've never seen promising reviews for Dayton's stuff, but it's as close as we get to a turnkey solution. I don't think Amir will ever test it, at this rate.
I've built 6 custom DSP/active dipole (open baffle) speakers for my surround system, and I ended up using multiple Aiyima and Fosi amplifiers, a channel per driver. If your speakers are big enough (mine all are) you can just strap the tine amps to the back panel. Their outboard power supply bricks end up cluttering the floor behind each speaker, though.

I've been using Dayton Audio DSP-408s for years (five of them in this system) and I love them.
 

D!sco

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I've built 6 custom DSP/active dipole (open baffle) speakers for my surround system, and I ended up using multiple Aiyima and Fosi amplifiers, a channel per driver. If your speakers are big enough (mine all are) you can just strap the tine amps to the back panel. Their outboard power supply bricks end up cluttering the floor behind each speaker, though.
But look at how small and well integrated the JBL board is. And think of where the bar really starts for the kind of feature set hobbyists end up cobbling together (no offense). The FA122 is $500 a piece, won't fit in my nearfield monitors, and will make them explode. Your route is totally the practical one, I'm just bemoaning the size and power bricks and boxes. Some of the existing plate amp options also bind you to stereo and all run through a single plate.
 

DavidMcRoy

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I'll be the first to admit that my route is cumbersome and really isn't practical unless you really know what you're doing, but the performance is great. My goal was a system with highend performance and doing it myself was the only affordable way for me. With slightly lower expectations, a mass-produced commercial product probably makes more sense. This is a Dolby Atmos system, and my four height speakers: JBL LSR305s.
 

D!sco

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My DIYs just barely scraped the value mark over the JBLs once upon a time. In fact, my roommate’s 308’s were the bar I used to hold my DIY standard to. Now I think the LSR 30X line is an unbeatable value. I’m not sure what it would take to move that bar back. The 306p in particular screams “perfect compromise” to me, though I keep thinking the woofers could use an update. Just look at that distortion!
1698501458097.png
 

computer-audiophile

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I have listened to the 305p II and the 306p II in direct comparison and only find the 305 well tuned. The 306p II doesn't sound as good in the bass to midrange, imo. That's why I opted for the 305. The price doesn't really matter with these speakers. They are both ridiculously cheap.
 

RayDunzl

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Here is the 308P mkII PCB

View attachment 340567

Yes, with the heat sink over the amplifier chip...

And I notice this:

1704754334979.png


Same board for all three versions.

Different progarmming for the amp chip, voltage setting on the power rails, heat sink for the 308, I wonder what else?

More white goo?
 

afico

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From what o understand the Adc will be bypassed if I don’t use XLR input ?
 

FrantzM

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From what o understand the Adc will be bypassed if I don’t use XLR input ?
No.
the jack and XLR share the same connections, thus signal path. Everything goes through ADC.

Peace.
 
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