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

2140 Views 31 Replies 8 Participants Last post by  siamnet
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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The line level inputs on the Helix should have the resistors built in, just for that.
Noooo, what if two cars require different load resistors, for example if it has 4ohm or 8ohm speakers? This will be an external thing you have to do per car
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.
Ive just noticed that the signal from the hu to the amp looks to be balanced potentially, you maybe should be using the positive and the signal ground for the signal not the signal +ve and -ve… it may also be a very low voltage signal, but the dsp should be able to amp it…

Is the amp plugged in when your testing the cables? The hu may shut the signal down if it doesn’t see the amp fully connected

Speaker level will be fine though and how I’d go for sure, 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
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.
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
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.
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 : 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.
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
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 ( 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.
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
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
The Smsl does also send 192khz via optical, I tried it on my denon av receiver and it took my go to Coldplay album

helix takes 192 from coax just fine though 🙈
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