Factory HU sound mods with JBL amp

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Captain Jack
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Factory HU sound mods with JBL amp

Post by Captain Jack » 14 Aug 2019, 08:39

Hi all,

I have a Pug 407 with an RT4 unit and a JBL amp. It all works well enough and the sound is good.

However. Has anyone found that as the volume is increased, the bass drops off dramatically? It's almost as if the volume increase is not linear across all frequencies. I have found the exact same thing in my old 406 with the JBL system. I am pretty sure this is limited by the HU itself as if I connect the amp to another HU (with a lot of rewiring) then the problem isn't there. Likewise, it does not seem to do it in cars without the JBL system - volume increase is linear across the frequencies. Perhaps there dance between the HU and the amp. I suspect this might be controlled by the wire running to pin 15 on the amp from pin 11 on the HU (on C connector).

Is there any way to stop this behaviour?

Also has anyone done any mods to the HU amp side itself to improve sound?

Thanks
CJ

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GiveMeABreak
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Re: Factory HU sound mods with JBL amp

Post by GiveMeABreak » 14 Aug 2019, 09:13

What's your VIN - I'll need that to check year and specs.

Captain Jack
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Re: Factory HU sound mods with JBL amp

Post by Captain Jack » 14 Aug 2019, 13:30

Well, the VIN won't tell you much as I retrofitted the JBL amp. RT4 was from the factory, though.

My question is around these units (RTx) in general - since they are all very similar from the audio side and seem to behave the same way.

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GiveMeABreak
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Re: Factory HU sound mods with JBL amp

Post by GiveMeABreak » 14 Aug 2019, 13:49

Well that tells me a lot.

Did you configure the Head Unit ECU & BSI correctly after fitting?

Captain Jack
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Re: Factory HU sound mods with JBL amp

Post by Captain Jack » 14 Aug 2019, 14:13

Yes, configured it all via PP2000. BSI (and HU) is set to "amplifier present". I can still give you my VIN if you want :)

The reason I didn't post this in RT4/5 area is because I know this issue (that only I can probably hear) exists on other units installed with JBL amp, including RD4 in 407 and whatever was used in the 406. Hence, the general nature of the question of whether there are any known a) sound upgrades and b) potentially any settings that I can set with something like Mirascripts or RT4 settings editor - though there's nothing that stood out.

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GiveMeABreak
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Re: Factory HU sound mods with JBL amp

Post by GiveMeABreak » 14 Aug 2019, 16:22

Not sure where you're going with that.. Pin 11 on the Head unit is for the Hands Free Audio. Pin 15 on the Amp is to the Bass Unit.

Did you also replace all the speakers and install the bass unit in the boot when you retrofitted?

Captain Jack
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Re: Factory HU sound mods with JBL amp

Post by Captain Jack » 15 Aug 2019, 11:46

All speakers replaced including addition of the subwoofer in the boot.

I was wrong re pins (in text, not in actual connection). The wire from HU in block C pin 9 (not 11) to pin 15 on the amp on the input plug. This, as I've found out, is a mute wire.

Anyway, sounds like what I am asking is too much. This has been in operation for many years now - I've just always found the system a bit lacking. And to get the best bass, I have to have either the ski hatch open or seats down, else it gets muted...

Xantippa
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Re: Factory HU sound mods with JBL amp

Post by Xantippa » 24 Aug 2019, 08:07

Could it be so that the rather pathetic stock "subwoofer" is protected on higher volumes, and it´s level is dropped in the additional amp.

I would scrap that JBL-soundsystem and install aftermarket amp and at least sub after original HU. Then you have to remove that JBL-amp with diagbox, after that I think you wouldn´t suffer this problem.