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15 Posts
Discussion Starter · #1 · (Edited)
Current working through this installation and just documenting it, in case anyone else would like to do a similar installation as well!

This build is primarily for budget SQ(as far as budget can be concerned with a hobby like this... :worried:)

The Initial build starts with a 2DIN Joying Android Head Unit picked up from Aliexpress for about 230USD. Why?
  • Cheap
  • 2DIN
  • Runs Android (proper Maps, Waze, Spotify)

The Last Point is crucial to this build...
The ability to run USB Devices OTG via the headunit allows me to easily run high quality external DACs off the Android Headunit allowing me to bypass the internal DAC and Amps and essentially going 'Full Digital' all the way to the DSP.

So the System Layout is

Android 2DIN Headunit >(USB)> Powered USB Hub(crucial to get the power out for DAC/OTG Devices) >(USB)> PCM2704 >(S/PDIF)> miniDSP C-DSP 6x8>(RCA)>Alpine PDX-V9

Speakers Used
  • Polk db6501 2 Way Components
  • Standard Factory Coaxials
  • Rockford fosgate P1S4-12 in a generic sealed 1 cubic foot enclosure

very similar to this build I was inspired by, but less russian ;)

so as you can see the system is basically all digital up to the point of the DSP, also shortening the 'gain chain' down as well.

15 Posts
Discussion Starter · #2 · (Edited)
External DAC for Android Headunits (JY-UL135N2 and PCM2704)

So the key to running these DAC's is that as of Android 6.0, it supports USB DAC's naively.

Before this, you had to use an application that had built in drivers such as USB Audio Player etc, so it limited you to music playback (isn't that why we are here? :laugh:).

The unit i have which is a Joying JY-UL135N2 has a reasonably active development community over at XDA Forums, some of which have pursued this DAC > DSP route as well. Users over there have already developed a means to control the DAC Volume via the android unit, since naively it's just one set volume and you would have to use the DAC volume control instead, alongside modifying the system to allow DAC Usage pre Android 6.0.

The Benefit of this over say an Android Auto Headunit (which I recall also actually runs a closed source android system) like the XAV-100 by Sony is that you get to use the extra features of android but also run an external DAC.

the DAC I used was from eBay, "PCM2704 USB to S/PDIF USB Sound Card".
it has a SNR of 98DSB and THD of 0.006%, or so the specifications say.
it only supports 16bit 44.1 or 48khz audio but we're on a budget and honestly for a car, that is fine enough.

you can get any multitude of DAC's from ebay or other sources, but this was only about 15USD, is proven to work with windows without external drivers and also android phones/tablets and this head unit (assuming sufficiently new version of android). Newer DAC's than those based on the PCM2704 may output higher bitrates, but until someone tests and tries them on these platforms, the PCM2704 will do.
also the DSP I have chosen to use, so far only has a 48khz signal path, so any higher input and I would have to upgrade to maybe a Helix DSP Pro....:surprised:

as mentioned above, it also works natively with windows, which allows easy and direct output for tuning a DSP(USB DAC output for Sweeps and REW RTA etc)

I had to use a Powered USB Hub, which is powered by a hardwired USB Power supply on the HU harness so that it allows a decent signal to get to the back of the car, where the DAC is sitting.

The DAC is wired up with F Type Connectors and runs a custom RG6 Quad Shielded cable with the F Type on the DAC side and RCA on the DSP side to maximise signal shielding but also survive the vibration of a car (F type connectors can be threadlocked easily, unlike RCA connectors)

as of this post you can go get yourself a Android Headunit, run this DAC without any fuss!

Currently installed and works well and working on the Tuning!

15 Posts
Discussion Starter · #4 · (Edited)
working with the miniDSP C-DSP 6x8

so there really isn't much information on this DAC on here, so I guess I'll start!

so the miniDSP C-DSP 6x8 is a 'budget' (so far as you can use that word here...) DSP available from miniDSP and has 6 analog inputs and 8 analog outputs (hence the name 6x8).

they have quite a bit of experience working with DSP's and you can get a multitude of different ones from them for Home Theatre and other uses.

the C-DSP itself is quite new only a year or two old in their range and is built for car usage, as such it has the requisite inputs for most cars 6 being
  • Front Left
  • Centre Front
  • Front Right
  • Rear Left
  • Rear Right
  • Sub woofer
systems vary from car to car

in the case of no rear system, then you could effectively run a 3 way active front setup on both sides plus 2 subs for a total of 8 outputs.
or in my case I run an active 2 way front setup, Coax Rears and stereo sub output(required for the PDX-V9 see below)

in my case I am not using the analog input, and feeding it via the PCM2704 above with the S/PDIF inputs and the routing that as required to the 8 outputs i have with the required EQ, T/A and X-overs.

The best part about the CDSP is that it's quite tightly integrated with Room EQ Wizard, which can be used for measuring the response of your system.

if you chose to use the USB mic that miniDSP produces (UMIK-1) then it also is auto detected by REW and ask for a calibration file that miniDSP provides for you with the mic as well.

(ignore the actual filter, it's just for show ;) )
this integration allows for you to measure the frequency response of your system, auto EQ it to a house curve (see Jazzi's tuning companion for a start) and let REW do the heavy lifting with the EQ, save the EQ settings to a file and upload it to the C-DSP and you're done!

I'll make a tuning guide later specifically for this purpose.

however the simplicity of this is also the downside of the 6x8 as you only get 6 PEQ's for each channel, being 6 on each of the 6 analog inputs, 6 on both of the S/PDIF channels(Left and Right) and 6 on each of the 8 analog outputs.
this is far less than what's available on competing DSPs such as the mosconi, and the Helix but hey, this is a 'budget' build so far as you can reasonably use that word here :p

this limitation also extends to the Time Alignment Restrictions, it only supports basic time alignment via ms input in afaik 0.02ms steps, no phase adjustments like the Helix and it's limited to 15ms so isn't overly useful for differential rear fill setups.

all in all the DSP is great, does a good job of what it says it does, however is limited compared to say the Helix units, both a good and bad thing depending on the user.

The unit also only currently allows for summation routing, which means you can't do L-R or R-L you can only do R+L and L+R and so on, which means differential rear fill is difficult without daisy chaining a miniDSP 2x4 which they have produced an easy to use rear fill interface for, to allow for differential signal processing and enough Time delay to achieve rear fill.

another less documented feature of this unit is that I'm fairly certain it uses canbus signalling for it's remote, so since we're using an android head unit, an entrepreneurial soul could theoretically develop an android app that runs off the head unit, allowing you to control the volume but also profiles you are currently running (the 6x8 supports 4 saved profiles onboard), someone has achieved something along those lines already and has documented it on the miniDSP forums, however it was translated from Russian and the source code isn't available. this alleviates the need for an external remote like most DSPs.

I'm currently working through tuning this system and will have a thread over in the Technical sub.

15 Posts
Discussion Starter · #6 · (Edited)
The Rest of the system

The Rest of the System is nothing special,
I'm running a PDX-V9, which wasn't originally in the plan, since i had some older A/B class Amplifiers i could use for this however I did the initial headunit install, and DSP install and didn't like the idea of having to wire up 3x amplifiers (4ch for active fronts, 2ch for rears and a monoblock for the sub)

I managed to find a PDX-V9 for less than half retail here in Australia(Used Unit) and that's how a high end Class D amplifier ended up in this 'budget' build :laugh:

the PDX seems to like a 2ch Subwoofer input, so thats why above I have a dual input / output for the Subwoofer on the DSP. another way around it would be a RCA splitter, but that isn't as neat :laugh:

I also built a custom 6 way shielded RCA Multicore snake to run between the PDX and the miniDSP using locally sourced shielded multicore cable for Live Audio purposes and NYS373 Connectors from Rean (Neutrik subsidiary), it's shielded and the correct length required., I found using unshielded or untwisted RCA cables introduced significant noise into the system (it was tried before I ordered the parts to make the custom cable)

all the speakers currently used are either recycled from previous installs, (ala the P1 Sub) or picked up for dirt cheap from Wreckers or Gumtree(Australia's Craigslist essentially). I figured with a DSP in the mix, it's better to make this work and upgrade later, than go all out to begin with.

I plan to make a custom fabbed box at some point to get some trunk space back, at which point i may upgrade the sub woofer. Also might upgrade the coaxials to something branded and of known specification.

15 Posts
Discussion Starter · #8 ·
Addressing the other Audio Outputs not via USB DAC

As i noted above, the USB DAC only handles what is internally processed by the Android Headunit, this is basically any output of any application running directly on the android system.

This affects this installation because the way that these android head units are made is roughly like this

Modified Android System + Micro controller + Video/Audio Processor/Router

Android handles
  • App Audio
  • Android System Audio

the MCU handles
  • Amplifier Signalling (Remote on)
  • Steering Wheel Control Interface
  • External Bluetooth Unit (which routes audio directly to the Audio sub system)
  • FM Radio/DAB/Radio in general
  • GPS/Wifi
  • any other features or systems not commonly found in android devices

the Video/Audio Processor/Router handles
  • FM Radio Output
  • Android System Output
  • Bluetooth Output (external)
  • Video/Audio Output for Reversing Cameras or other video feeds
  • any other audio routing or processing work

I could go into more technical detail but
as you can see, the USB DAC is only really able to access the audio streams
available to the android system directly, and not anything else.

So for this install we still need to make use of the Analog audio system within the joying unit via the amplifier Pre-Outs routed to the analog inputs in the miniDSP.

this presents us with another issue of where to route this audio, I haven't tested it yet, but I suspect the analog outs are still active when we use the USB DAC, so I can't just route the signal to the main audio outs or we'll get duplicated output(ostensibly also at a much lower signal quality than the USB DAC). If it somehow does just route anything BUT the usb dac audio then GREAT we're good to go otherwise I'm probably going to route it to a separate centre speaker already in my dash for the purposes of say BT calling, that leaves me without a FM Radio...

which brings me to another solution made possible by Android™ :laugh::laugh::laugh:

android phone running OTG FM Radio

since we're running an Android headunit, we can solve the FM Radio problem with an SDR, otherwise known as a Software Defined Radio, essentially we plug in a FM Tuner via USB(with the installed hub I have already) and use an android application to tune in to the FM radio, and tada! we have a FM radio within the android system and able to be routed via the USB DAC. (also possible to watch TV from most dongles...)

I should also note currently I am already running a DAB+ dongle, and Reversing Camera from the USB inputs of the headunit... The flexibility of this head unit cannot be stated enough :surprised:

the Amplifier chips in this headunit can also be upgraded by soldering in a new one with better specifications as well, a few have done it already, to further improve the audio output of the analog system we are forced to use to an extent.
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