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Please help me figure out how to solder an RCA connector to my DSP/Amplifier

2139 Views 31 Replies 8 Participants Last post by  siamnet, 
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Hello, this is the audio wiring diagram for my vehicle. I have to keep to the factory HU and this is the audio (line level output). I only need to grab three signals (front LEFT and front RIGHT and subwoofer) to run 3 way fronts.
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However, I've already tried to wire/solder to this RCA adapter but not seeing an input signal from the car HU to my DSP/Amp. I'm using a Helix DSP.3 (via software to see a signal and doesn't even show any signal from the car even when I'm running a test tone 20-20khz).

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For example, channel 1, I used wire 1 & 11 (Chan1+ with Chan11-) for the RCA and so on for channel 2 and 3. I don't think I did this properly because I used a continuity meter to test the inner RCA and outer conductor part of the RCA and seems to be "electrically connected to each other". I just assumed that RCA have separate wires for the inner pointy core and outer part?

Please let me know if that's the right way to make an RCA connect based on the above diagram. I don't know if I'm supposed to just use Chan1+ AND SGND or etc?

Thank you.
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gijoe said:
That DSP has high level inputs, why are you soldering on RCA plugs?
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Because the diagram shows Line level output from the factory HU and I don't know any better..lol.
I've tried using the Helix's high level input (from the factory diagram) and still it wasn't seeing any signal on the software and that's why I'm thinking that since it's a line level out not speaker level, I should be properly using an RCA connector into the Helix.
Honestly, I'm a bit lost/frustrated on why I'm not seeing any signal and trying to eliminate either the RCA vs high level input problem.

My other back up/last resort is to grab an actual speaker level output from the factory HU (might not be full range) and feed into the Helix. I was going to leave the factory rear doors intact since my daughter sits in back and I want to be able to play music back there as well.
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This is a brand new DSP that I bought from this forum. It's possibly that I'm an idiot since I haven't used PC DSP tool in 3-4 years. I did read these sections (KB from audiotec website) and the manual.
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I followed the manual where it asked me to play a test tone generator at 90% and keep sliding the input bar until it clips but it never did.
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I also watched this part of the screen to see if any signal (the blue bar never appears). Thus, I was thinking my input signal must be wrong.
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Cutaway said:
is this for the Tesla S in your signature?
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Yes, the diagram is for a Tesla model S (pre 2016.5)
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It's odd that my installer friend mentioned what @Cutaway stated above about seeing a speaker "load" (if it doesn't then it shuts down) but let me expand this diagram bigger so you can see that the "line level out" is going into the 2nd external OEM amp. I would think, this wouldn't require a "load" (impedance like from a speaker), right?
Otherwise, I might have to grab the speaker level signal after the 2nd OEM amp...again hope there is no load issue.
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SHAGGS said:
The line level inputs on the Helix should have the resistors built in, just for that.
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Well, then I'm doing something wrong.:cry:
Tomorrow, I'm going to try to grab some other speaker level output just to see if there's something wrong with the Helix DSP.3s.
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SSinstaller said:
Should be easy enough to test for ac voltage across those pins with a DMM.
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I can also do that (I assume, you mean the (+) and (-) pair before it goes into the OEM amplifier). For example, pin # 23 and pin # 28 which is for "LF Spkr", my fluke meter has an AC voltage measurement setting.
Thank you.
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dumdum said:
Ive just noticed that the signal from the hu to the amp looks to be balanced, you should be using the positive and the signal ground for the signal not the signal +ve and -ve

Speaker level will be fine, if you really want the best quality signal in, use the factory high level in and then a dap like a fiio M11 or an Smsl po100 from a phone via digital coax in to the dsp.3s
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Thank you, I will try that today (grabbing the signal ground in addition to positive !!!
And thank you for the tip on the DAP since I was thinking of using the coax input for some lossless audio.
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dumdum said:
I edited my post a little more…

it can still be balanced and use chassis ground as the ground, the Sheilds look like they are literally shields and not grounded at the amp end so won’t be part of the signal chain…

Use speaker outputs is easiest and then a dap or phone for critical listening
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Ok, it's easier to grab the vehicle/chassis ground but if I need to/have to grab the actual signal ground at connector (X427) then I will. I'll try the chassis ground first and then try at the connector.
If all else fails then I'll grab the speaker level. Thank you.
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So, I tried the chassis ground and that didn't work..Helix wasn't able to see the signal via RCA input nor speak level. I'm going to grab the speaker level and combine them...
I've been trying to figure out the signal input for the last 2 days on my car and I'm ready to chunk the Helix and just use a DSP/amp combo like JL Audio and call it a day.

Now, I've got a USB to optical converter that I just ordered on Amazon (arriving this evening) for me to test a music SIGNAL into the HELIX. I was planning on using my laptop and play some music via USB port/optical out into the Helix's optical input just to make sure it works/etc. If that doesn't work then I'm going definitely going to chunk/sell the Helix eventhough I already ran the wire (from trunk to front) for the URC.3 knob and have WIFI controller installed.
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dumdum said:
I hope it’s an smsl po100, they are excellent and make a very nice job of it

the optical input works very well! I use coax from an iPad topping combo to get me digital into my ultra! 👍🏼
Not sure why you think a jl will do the job any differently to a helix… the helix is the best processor imo on the market for high level input and making it good 👍🏼
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USB optical adapter
It's a cheap thing (LiNKFOR USB DAC Audio Converter USB to Coaxial S/PDIF Converter USB Audio Sound Card with 3.5mm Headphone Jack USB DAC Optical Audio Adapter 1.5m USB Data Cable PCM/LPCM for Windows Mac PS4 PS3 : Amazon.ca: Electronics) that I could find on short notice in Canada. Now, your item, SMLS PO100, is a very interesting item, it seems you could almost use a phone (with USB-C) to play hi-res music via USB-C => Optical. I may send the Amazon item back and opt for the SMLS P0100 instead.

I'm kinda lazy and not sure if I ever want to put hi-res music on a DAP or just stream lossless via Tidal or Apple Music which I have a subscription for both.

Helix vs JL:
One famous installer in Maryland told me that I needed at least 8 channel input to combine midbass, midrange and tweeters to a full range signal (plus sub channel) from my Tesla. He suggested (based on his experience) for using either Helix V Twelve or JL Audio VX800/8i. However, I have read on the Tesla forums that it's possibly to just combine the rear doors 6.5 with the front midbass to get the full range. Thus, based on what people have done, I should be "ok" with DSP.3s since I should be using just 5 input channels. However, if not then I'm going to have sell the DSP.3 and get something with more inputs (like 8s). He was suggesting that I buy those DSP/Amp combo so that I can just run full active 3 way w/o needing a passive xover.
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SSinstaller said:
Before you give up, what was the peak ac voltage with your meter connected to pins 23 and 28? Those SGND wires are just shield grounds.

Looking at the diagrams the signal should be balanced differential, or single ended. Both of which should be ok for your dsp.
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AC Voltage was ~1.5 mV using my FLUKE 27 meter to measure. The plug was not connected to the secondary OEM amp. Thus, not sure if it needs to see a "load" at the 2nd OEM amp or not. I was using pink noise and 20-20khz track.

However, with the same plug back into the 2nd OEM amp, using high speaker input into the Helix (after the 1st OEM amp and 2nd OEM amp), I was able to see some signal (via DSP PC tool) when I run pink noise or test 20-20khz track.

Although the manual from Helix states that I'm supposed to see a blue bar for each channel that indicates a signal is presence and never saw that at all.
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dumdum said:
It specifically states you can’t use it from usb c to usb c, not sure why, so you need a charging otg lead with usb c charging input and also usb a out and then use the lead that comes with the Smsl 👍🏼 Cheap as chips for the adaptor, or use a charging hub and have an input for usb sticks and hard drives if required
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I'm trying to avoid spending $200 ish on USB HEC card for the HELIX when I can achieve "almost" the same optical from my phone/tablet/etc? I'm sure that HEC card can read a higher bit rate than optical but I highly doubt that I can tell the difference but might compare the specs later. I'm just a bit overbudget on my current build (still not finished lol).

Thnk you for the tip on the OTG charging.
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To summarize:
The "line out" was not usable by me at all per Tesla's wiring diagram. Now, I know why none of the experienced installers (e.g., Nick and Matt S) used that line out and instead chose to grab the speaker level signal for my car.

I had to grab 4 speaker level signal and combined them for full range...thank goodness for watching Nick (Skierz)'s video tutorial since the knowledge based webpage was not helpful for me to get started. Now, I can refer to those webpages for tuning and more next level stuff (RTA, etc). I was having trouble trying to connect/see a signal in the first place with my Helix.

I appreciate everyone in this thread that responded since you all have been very helpful since I've been beating my head for the last week on this matter.
Next step for me is to finish the install one last midbass component (i.e., waiting for the correct 8inch midbass to fit my front doors properly since the brand new AD W800 Neos didn't fit) and tune the sound.

Thank you !!!
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ckirocz28 said:
If you can't get a measurable signal, a different dsp won't help.
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Yes, agreed.

At the time, I assume incorrectly (based on the manufacturer's audio wiring diagram) that the line level out was working and was thinking that there was something wrong with the brand new DSP. Hence, I was trying by process of elimination.
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dumdum said:
I hope it’s an smsl po100, they are excellent and make a very nice job of it

the optical input works very well! I use coax from an iPad topping combo to get me digital into my ultra! 👍🏼
Not sure why you think a jl will do the job any differently to a helix… the helix is the best processor imo on the market for high level input and making it good 👍🏼
Click to expand...
I just purchased the SMSL P100 USB adapter as you suggested and I can't seem to get a signal from the optical or coax to work from my Android phones. I've tried using my Samsung S21 and Google Pixel 3 phones. I've tried different optical and coax cables directly (instead of using the original optical cable that I ran from the front of the car to the trunk where my Helix resides) to my Helix and no sound.

I followed your suggestions of using OTG (USB A to USB C) from the phone to the SMSL P100 and no luck. This is what I bought (Amazon.com: USB C OTG Adapter with Power, 2 in 1 USB C to USB Female with 60W PD Charging Adapter Compatible with iPad Pro, Samsung Galaxy S22/S21/S20/Note10, Google Pixel 4/4XL Google Chromecast with Google TV : Cell Phones & Accessories). I've tried using a USB A to USB C adapter that I use in my wife's car in case that Amazon adapter doesn't work.

I've tried hooking up both phones via SMSL P100 USB adapter to my home receiver's optical and coaxial input and still no sound from my home theater speakers. I don't have any apple product at the moment and could wait on an Ipad Mini 3 that I ordered for my daughter to test (but that's a week from now).

I'm almost to the point of scraping this optical setup and buying a HEC USB interface card that this guy is selling on Ebay but it's for a Helix mini. I know the rear faceplate doesn't have enough holes and won't fit but I am ok with the backside wide open until I source the correct faceplate. He is offering me $75 USD for it which is a good deal in my opinion since these optical/coax adapters are already around $30 USD.
If it work then it's worth $75 but I have no idea if it will work or not and I'll have to run a USB cable from the trunk to the front which is going to be a pain since I just finished putting all the interior panels back into my car.

Any thoughts? Thank you.
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dumdum said:
Does the phone recognise the smsl po100 as a device, whenever I’ve plugged a topping into my android tablet it recognised it as an output device straight away
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Short answer is "NO".
Both Android phones "sees" the SMSL device as "something" that either requires the phone to charge it or transfers files, MIDI, etc.
Both phones does not recognize it as an audio output (like it recognizes the USB-C Samsung headphones that came with the phone).
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SiW80 said:
What Helix is it being connected to? Some only take 96kHz but the SMSL outputs 192kHz so the Helix won’t be able to use it.

You can request the UAC1 firmware to fix the output to 96kHz.


Sent from my iPhone using Tapatalk
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I have a the Helix DSP.3s but I tested the output from the SMSL (coax/optical) to my home theater receiver just to eliminate 1) optical/coax cable, 2)Helix DSP optical input (this worked when I had a different USB DAC to optical that I was testing via my Windows laptop). It seems both of my Android phones do not like/recognize this SMSL as a USB audio device.

Either, I try another SMSL P100 (maybe this one is a dud) or try another USB DAC (I just ordered this one from Amazon (arrive this Sunday): Amazon.com: Cubilux USB Type C to TOSLINK Optical Audio Adapter [192KHz/24bit DAC] Thunderbolt 4/3 to SPDIF Converter Compatible with MacBook Pro/Air Mac Pro/Mini iMac Samsung Note 20/10 S22/S21/S20/S10 Intel NUC : Industrial & Scientific

I do know that this USB DAC worked on my laptop to test my Helix's optical input: LiNKFOR USB DAC Audio Converter USB to Coaxial S/PDIF Converter USB Audio Sound Card with 3.5mm Headphone Jack USB DAC Optical Audio Adapter 1.5m USB Data Cable PCM/LPCM for Windows Mac PS4 PS3 : Amazon.ca: Electronics
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