JBL 705P Circuitry?

[mjgraves]

As mentioned elsewhere I've just upgraded to a pair of JBL 705Ps. To feed them I've assembled PiCorePlayer on a Pi4 with a HifiBerry SPDIF HAT. This feeds the AES input nicely. So it's an all-digital signal path.

Or is it?

Does anyone here have an insight into the internals of the 70x series? It has analog XLR inputs, so it has a DAC. I presume the EQ, crossover and timing correction are implemented in DSP.

The amplifiers are class D. Would the digital output of the DSP stage be rendered to analog for the power amp inputs? Or is that also a digital transformation? PCM to PWM?

I saw the electronics module offered on Ebay for around $500. I might be tempted to buy one, since they apparently fail on occasion.

 

[MachOne]

The amplifiers are class D. Would the digital output of the DSP stage be rendered to analog for the power amp inputs? Or is that also a digital transformation? PCM to PWM?

Just guessing, but given there's a PCM1795 DAC in there, I'd say it's analog going in to the power amp section. Pics here https://www.audiosciencereview.com/...s/jbl-705p-studio-monitor-review.11944/page-2

 

[dfuller]

If you feed digital, it will do SRC->DSP->D/A->Amp. If you feed analog, it will do A/D->DSP->D/A-Amp. Oddly enough, analog inputs tend to be lower latency.

 

[mjgraves]

It woud be nice have at least a block diagram. I presume the EQ and crossover are implemented in DSP. If the crossover is implemented digitally, that would require dual DACs.

 

[dfuller]

It woud be nice have at least a block diagram. I presume the EQ and crossover are implemented in DSP. If the crossover is implemented digitally, that would require dual DACs.

Yes, it is done via DSP. It does not require dual DACs, just a stereo one - which the PCM1795 is. Chip spec is 106dB THD+N, DN 123dB.

 

[mjgraves]

If you feed digital, it will do SRC->DSP->D/A->Amp. If you feed analog, it will do A/D->DSP->D/A-Amp. Oddly enough, analog inputs tend to be lower latency.

I've cetainly noticed the difference in latency. This is just one zone of a multi-zone installation. I have yet to do the work, but I need to assembled some tools are work our the various delays required to make it rational. All the analog zones need to be delayed.

 

[antcollinet]

Oddly enough, analog inputs tend to be lower latency.

No clock recovery or sample rate conversion needed for analogue, so one buffer eliminated.

 

[DVDdoug]

The amplifiers are class D. Would the digital output of the DSP stage be rendered to analog for the power amp inputs? Or is that also a digital transformation? PCM to PWM?

IMO Class D amplifiers should be considered. The input is analog and the signal is quantized in time (at a very high frequency) but not in amplitude. It's more like PWM than PCM, but it's neither. There are no digital "samples".

 

[dfuller]

IMO Class D amplifiers should be considered. The input is analog and the signal is quantized in time (at a very high frequency) but not in amplitude. It's more like PWM than PCM, but it's neither. There are no digital "samples".

They're rather like DSD - they're PDM. In fact, with the right setup you can feed a class D amp DSD directly and use the amp low pass as the filter for the digital.

 

[mjgraves]

IMO Class D amplifiers should be considered. The input is analog and the signal is quantized in time (at a very high frequency) but not in amplitude. It's more like PWM than PCM, but it's neither. There are no digital "samples".

If you search through AES papers or the patent office you'll find quite a lot of material referencing digital transformation from PCM to PWM. However, it's not clear that JBL would see the merit in paying for such in a product targeting this market & price point. As a manufacturer, they leverage existing silicon from other companies.

 

[NTK]

JBL (and Harman Kardon) is using the Axign digital class-D amplifier controller in some of its new active loudspeakers (e.g. 4305p and 4329p).

Axign Introduces Advanced Sound Processors and Power Stages for Class-D Audio Amplifier Solutions

Axign continues to expand on its mission to deliver better audio quality for connected home audio products, where the audio path is digital, making sense to stay in the digital domain all the way to the loudspeakers. At CES 2023, Axign's post-filter feedback loop technology for Class-D...

audioxpress.com

 

[GXAlan]

JBL (and Harman Kardon) is using the Axign digital class-D amplifier controller in some of its new active loudspeakers (e.g. 4305p and 4329p).

Axign Introduces Advanced Sound Processors and Power Stages for Class-D Audio Amplifier Solutions

Axign continues to expand on its mission to deliver better audio quality for connected home audio products, where the audio path is digital, making sense to stay in the digital domain all the way to the loudspeakers. At CES 2023, Axign's post-filter feedback loop technology for Class-D...

audioxpress.com

I didn’t know this! How interesting to hear of a new contender.

 

[mjgraves]

JBL (and Harman Kardon) is using the Axign digital class-D amplifier controller in some of its new active loudspeakers (e.g. 4305p and 4329p).

Axign Introduces Advanced Sound Processors and Power Stages for Class-D Audio Amplifier Solutions

Axign continues to expand on its mission to deliver better audio quality for connected home audio products, where the audio path is digital, making sense to stay in the digital domain all the way to the loudspeakers. At CES 2023, Axign's post-filter feedback loop technology for Class-D...

audioxpress.com

Indeed, that arrived long after the 70x series was introduced. So it seems that DAC post-crossover is the most likely flow, as you suggest.

 

[mjgraves]

Since these 705Ps don't have signal sensing power on/off, I'm using some smart outlets to toggle power based upon the reported state of the player. When the player indicates changing from power-off to any active state Home Assistant triggers the outlets, turning on the monitors.

I implemented this years ago for lesser M-Audio monitors. They make some nasty pops when they power on. The JBLs are quite civil, and take a moment to boot-up.

Does anyone here think that switching power to the 750Ps might cause any problems?

 

[Pearljam5000]

How do you like their sound

 

[BDWoody]

Does anyone here think that switching power to the 750Ps might cause any problems?

That's how I've had my 708Ps and 705Ps hooked up for years, and I've never had any issues, fwiw.

 

[mjgraves]

How do you like their sound

I'm very happy with their performance. They're vastly better than the devices they replaced. They're very impressive for the price and size.

In fact, so much so that I am planning to get some of the larger 708Ps eventually. I'm kinda waiting to see if the rumored 708P MK2 show up in the coming months.

 

[mjgraves]

JBL (and Harman Kardon) is using the Axign digital class-D amplifier controller in some of its new active loudspeakers (e.g. 4305p and 4329p).

Axign Introduces Advanced Sound Processors and Power Stages for Class-D Audio Amplifier Solutions

Axign continues to expand on its mission to deliver better audio quality for connected home audio products, where the audio path is digital, making sense to stay in the digital domain all the way to the loudspeakers. At CES 2023, Axign's post-filter feedback loop technology for Class-D...

audioxpress.com

Monolithic Power Systems Acquires Axign​

Monolithic Power Systems Acquires Axign

Monolithic Power Systems (MPS), a global company specializing in high-performance power solutions announced the acquisition of Axign B.V., the Netherlands-based fabless semiconductor startup that specializes in programmable multicore DSP (digital signal processors) and developed the innovative...

audioxpress.com

 

[GXAlan]

Monolithic Power Systems Acquires Axign​

I had never heard of MPS before, but it’s a $39B NASDAQ company!

Masimo is only 7.2B and AKM is 9.5B