Magic Dynaudio Amp Signal

[nermal]

I've upgraded my factory Dynaudio system (B6 R36 Passat) to add a 12" sub and am having some odd issues with the Factory Amp rejecting input signals...

Here's a diagram of my system:


The aftermarket DSP is added between the RNS510 head unit and the factory Dynaudio amp (3C0 035 456 J). The design is for the DSP to create the new sub channels and apply frequency filtering and time delays to the existing signals before the Dynaudio amp/DSP applies it's own passat-specific tune. The DSP pre-processing brings the sub 'forward' more (by delaying the existing signals) and allows the sub to take over the lower frequencies - so I can push the bass harder without bottoming out the factory speakers.

For some reason, the Dynaudio amp only accepts the signal if the Front-Left speaker input is either connected directly the the RNS510 head unit (RCA joiner F-F), or indirectly via a y-split (RCA 1M-2F)...

I've used multimeters to test the head unit and dsp output voltages and to ensure the connections on my (custom) wiring harness go to the right pinouts (also tested the harness by bypassing the DSP altogether). The aftermarket (Helix) DSP software is showing input signals and outputs to the sub amp fine... I even resorted to using headphones via an RCA adapter to listen to the input/output signals.

Everything tests fine, accept for the Dynaudio amp rejecting the DSP signal if the Front-Left signal isn't connected directly to the amp. It seems a though there's some magical signal being sent to the Dynaudio amp from the RNS510 head unit that is being filtered out by the aftermarket DSP...

Here's a graphical summary of what the Dynaudio amp accepts/rejects:



Does anyone have any knowledge/experience with this and ideally know how to get it working?

[nermal]

In case anyone is having a similar issue, I was able to solve the problem by adding a bypass on the front left channel with a 100kHz high-pass filter.

An oscilloscope showed that there was indeed a hidden ~1MHz signal (approx 2.5mV sine waves) on the front-left channel.. This is what it looks like:



Here are some photos and diagrams of the prototype (if the magic smoke stays inside, I'll replace with something more elegant):





I designed the filter using the following website, and below are the details: (Sample) 2nd order CR Low-pass Filter Design Tool - Result -

[nermal]

More details available in the following thread: VW Dynaudio amp signal issues - please help | DiyMobileAudio.com Car Stereo Forum

[ope126]

Some very useful information there!
Glad yo got it all sorted.
How is the sound with the 12" sub now?
I assume you do all the install / wiring etc. yourself?
Very handy to know your in Brisbane too!!!

[nermal]

Some very useful information there!
Glad yo got it all sorted.
How is the sound with the 12" sub now?
I assume you do all the install / wiring etc. yourself?
Very handy to know your in Brisbane too!!!

Sounds pretty amazing - thanks

The wiring was mostly done by TBass (Straphpine): Tbass Audio - Custom Audio Installations. - I built the custom quadlock harness and put together some silver plated cabling.
The Esotar 1200, Helix P One and Helix DSP were acquired from FHRX, along with loads of helpful advice: Fhrx Studios Pty Ltd - Audio / Visual Connoisseurs. Free Shipping Australia Wide.

I'm also working on a simpler enclosure for the sub. The old one sounds great, but is a bit awkward when trying to use my boot space. Nearly done:

[ope126]

Impressive, keen to see the end result!

[kamold]

Great sleuthing!

[nermal]

Ended up making a custom printed circuit board and case (fuse holder + RCA sockets). Just waiting on some piggyback RCA leads before replacing the current prototype circuit.

Accidentally printed the first batch back-to-front (used KiCad and forgot to mirror when printing). Some of the soldering was a bit rough too - will use a smaller drill bit next time...

[NinetySix]

Little bit late to the party... But I just had to say, bloody ripper job getting to the bottom of that

I actually saw it on diyma a while back, and was quite unimpressed at the general negativity in most of the replies, just "nah, too hard, just buy all new hardware and amps."

Don't get me wrong, there's lots of good info over there, but they really ought to ditch the "diy" part of the forums name 😁


Once again... Nice work slaying the beast 😎


PS, stop playing with boxes, there's a ski port there and it ain't for skis 😂

[nermal]

Little bit late to the party... But I just had to say, bloody ripper job getting to the bottom of that

I actually saw it on diyma a while back, and was quite unimpressed at the general negativity in most of the replies, just "nah, too hard, just buy all new hardware and amps."

Don't get me wrong, there's lots of good info over there, but they really ought to ditch the "diy" part of the forums name 


Once again... Nice work slaying the beast 


PS, stop playing with boxes, there's a ski port there and it ain't for skis 

Thanks!

Yeah, admittedly it would have been quicker/cheaper to have just bought a DSP amp to begin with... but the engineer in me had to solve the problem. That and I wanted a stock + sub system - what it could have been if VW offered a sub with the Dynaudio system.

I don't know about your car, but my ski pass backing (the part that folds down) generally rattles like a freight train with any moderate bass... The enclosure worked out great (only adds ~50mm to the height of my boot floor), fully removable, provides spare wheel access and sounds great. Here's how it turned out: