Modifying OEM head unit for un-eq’d line out

[SVXdc]

Great info (and nice, clear pics). Keep up the good work!

 

Is there any circuitry on the board that explains why Panasonic shows the output impedance as 10K ohms (instead of the typical 4 or 8 ohms with these kinds of amp ICs)?

 

Do the output pins on that IC connect directly to the pins on the 14-pin power/speaker harness, as they do on the previous non harman/kardon HUs?

[utc_pyro]

They are hooked up directly, this is literally the same PCB as the other radios. They just poped/depoped components. I presume the 10K is the input impedance of the HK amp. Based on the spec sheet and my testing the output impedance is actually around 1ohm.

 

I presume this will be the same for the newer head units but we'd probably need some internal pics.

 

Any idea on how to modify the board to kill the noise? My scope is too crappy to see it, so I cant tell where to start tweaking.

 

 

Edit: Tested the head unit with a 4ohm dummy load. Max output is 6.62 VRMS when fed with a 12V computer PSU, so ~11W before clipping. Output impedance is 0.12 ohms. So if anyone was wondering, you have a TRUE 48W head unit stock.

[SVXdc]

They [outputs from amp IC to 14-pin's speaker pins] are hooked up directly, this is literally the same PCB as the other radios. They just poped/depoped components. I presume the 10K is the input impedance of the HK amp. Based on the spec sheet and my testing the output impedance is actually around 1ohm.

 

Interesting. I was expecting there to be some kind of difference, because people who switched from the P-201/3/4 to the 206 remarked that they had to turn the volume knob up a little higher to get the same level they were accustomed to with their original HU. I'll bet nobody has done a scientific side-by-side A/B test, though.

 

Any idea on how to modify the board to kill the noise? My scope is too crappy to see it, so I cant tell where to start tweaking.

 

Sorry, I don't have any idea. I've never looked at the audio portion very closely (and you don't want to know how crappy my scope is). And I don't have service manuals for any of the Panasonic HUs. Just the older Matsushita P-201 and P-203 that were posted here years ago. Really wish I could find a source for the Panasonic SMs.

 

Given how much time you've spent on this and the helpful information you've posted, maybe we should do a GoFundMe to buy you a better scope. (1/2 )

[utc_pyro]

Interesting. I was expecting there to be some kind of difference, because people who switched from the P-201/3/4 to the 206 remarked that they had to turn the volume knob up a little higher to get the same level they were accustomed to with their original HU. I'll bet nobody has done a scientific side-by-side A/B test, though.

 

The output is actually lower on this unit. Based on the schematics of the old one and the levels I was seeing on the volume control chip you could send it almost 20db into clipping. This one MAYBE 3db.

 

Volume level should have been around 1.6 vrms when it hit the amp on the P-201 and we know the amp had a ~34db gain. I never measured the levels on the P-204 at the amp but it should have been the same. The P-206 is at ~0.16vrms going into the amp. So that comes out to ~10db in level difference.

 

Given how much time you've spent on this and the helpful information you've posted, maybe we should do a GoFundMe to buy you a better scope. (1/2 )

 

My current scope actually came from donations from this forum . I had extra left money over from the TCU reverse engineering fund to buy a scope to poke around on it. I didn't have the skill set to actually pull it off (obsolete MCU with no devkits available and most documentation in Japanese) so there would be a linch mob if I asked again.

 

Edit: Noise appears to be coming from in post volume control. The mute circuit tends to snub it as well. Need to investigate the signal path between the amp and the volume control chip.

[utc_pyro]

Alright, noise on these things is actually the crap-o bipolar output stage amp. New part of the thread: How to modify P-206 to have a TB2929HQ for a high quality balanced line level output!

 

I'm swapping the amp for one of these: http://www.hqelektronika.hu/datasheet/32/3253.pdf

 

Gain is 8db lower but with MUCH less THD and noise. Like an order of magnitude lower. That should put it close to the MS8's low level input voltage or I'll try to find the voltage dividers to up the gain.

 

Edit: ST TDA7560 actually looks better, ordering one of those as well. It's a 30w/chan@4ohms 55w/chan@2ohms amp if anyone wants a high output headunit.

 

Edit2: There is a V_in/.117 voltage divider between the volume control and amp (-18.6db). We'll need to tweak that for replacing the amp with a TDA7560 or TDA7801. The "beep" circuit in the old signal path is also gone, it's now driving the "aux in" on the amp directly.

[Guest]

utc_pyro, this is an awesome work. Many years later maybe it's time for me to upgrade the audio finally.

 

More updates on the mods to P-206 ?

[utc_pyro]

utc_pyro, this is an awesome work. Many years later maybe it's time for me to upgrade the audio finally.

 

More updates on the mods to P-206 ?

 

Um, truthfully it's been sitting in a box sence when the motor blew up two years ago. It's recently moved up the to-do list though to support the phone embedded in cubby door thing I'm working on.

 

Hopefully I'll have some updates next month after finishing the fueling and PCV work.

 

The P-206 more or less works for aftermarket use out of the box though with just a level converter or voltage divider. Much cleaner audio path than all of the other versions, and the only EQ crap is the loudness chip.