Reference Series · Integration
LOC vs A2B Interface on 2023.5+ Harley Touring: Which Integration Is Right?
Quick answer: A basic line output converter (LOC) is a fine way to feed an amplifier on older analogue Harleys, but on 2023.5+ Skyline OS bikes it is a poor foundation. Audio travels over a digital A2B bus, and the only analogue signal available to a LOC is the already-processed, already-amplified factory speaker output. If you are only swapping speakers and keeping the factory amplification, you do not need any interface. If you are adding or replacing amplification, the correct route is an A2B interface (NAV-TV ZEN-H or Volunteer Audio / SeirenHD HD-A2B) that replaces the factory amp and supplies predictable analogue outputs while retaining supported factory controls.
Line output converters work well on older Harley-Davidson Touring models. Tap the factory speaker wires, step the signal down, feed an aftermarket amplifier: a known approach used for years on 2014 to early-2023 bikes. On 2023.5+ Skyline OS models it is a weak foundation, not because LOCs are poor products, but because the signal they can reach is fundamentally different on these bikes.
What a Line Output Converter Actually Does
A LOC takes a speaker-level signal, the amplified output that normally drives the speakers, and steps it down to a line-level RCA signal for an aftermarket amplifier. On a conventional system this makes sense: the head unit outputs a speaker-level signal, the LOC converts it, and the aftermarket amp takes over.
The limitation is that by the time you are tapping a speaker-level signal, the audio has already been amplified once. Any processing, EQ or limiting upstream is baked in, and the aftermarket amp then amplifies it again, including whatever tonal shaping or distortion was in the original. On older Harleys the factory processing was manageable and a skilled installer could partly compensate with DSP downstream. It was a compromise, but it worked.
Why It's a Weak Foundation on 2023.5+ Skyline Bikes
On 2023.5+ Harley-Davidson Touring models, audio does not travel through conventional speaker wires between the head unit and amplifier. It travels over an A2B (Automotive Audio Bus): a digital network carrying audio and control data between the head unit, the factory audio processing and the factory amplifier. A conventional LOC cannot attach to that digital bus at all.
An analogue signal does exist downstream of the factory amplifier, at the factory speaker outputs, and a LOC could physically tap it. But by that point the signal has already passed through the factory processing and amplification: EQ for the factory speakers, dynamic limiting to protect OEM components, and volume-dependent processing. A LOC on those outputs receives a finished, already-amplified signal, not a clean starting point. The result can be made loud but not accurate, headroom is reduced, and no amount of downstream DSP fixes a compromised source.
The Three Realities on a Skyline Bike
| Approach | What it uses | When it fits |
|---|---|---|
| Speaker-only swap (keep factory amp) | Factory amplification retained | A confirmed direct-fit speaker upgrade; no interface needed |
| Passive LOC on factory speaker outputs | Already-processed, already-amplified analogue signal | A weak foundation for a high-output or precisely tuned system; not recommended |
| A2B interface (replaces factory amp) | The digital A2B bus, before the factory amplifier | The correct route for adding or replacing amplification and feeding external DSP or amps |
The Correct Approach: An A2B Interface in Place of the Factory Amp
To add or replace amplification on a Skyline bike, the signal is taken from the digital bus rather than tapped after the factory amplifier. An A2B interface installs in the factory amplifier location, physically replacing the OEM amp, and communicates directly with the A2B system. Instead of extracting an already-amplified analogue signal, it converts the digital audio to multiple channels of predictable analogue RCA output, while retaining supported factory functions such as volume, balance, fader, chimes and the factory EQ presets. Two interface ecosystems are commonly used, each with the correct Cicada amplifier harness:
- The NAV-TV ZEN-H, which supplies eight channels of 5V analogue RCA output.
- The Volunteer Audio (SeirenHD) HD-A2B, which similarly replaces the factory amplifier and supplies analogue outputs, and offers a preconfigured flat output on supported standard systems.
What this gives you compared with a LOC:
- Predictable line-level outputs taken before the factory amplifier, not a post-amp signal that has already been amplified and attenuated.
- Multi-channel RCA output configurable across front, rear and additional positions.
- Retained factory controls and infotainment, including supported volume, balance, fader, chime and EQ functions.
- A clean install in the factory amp location, compatible with the standard factory amplifier and, on some models, the larger Rockford Fosgate amplifier. Confirm compatibility for the exact model year and factory-audio package.
ZEN-H vs ZEN-H PRO: Which One
Two NAV-TV versions are available depending on your system architecture. The ZEN-H is the interface only: eight channels of analogue RCA output ready to feed an external amplifier or DSP. It is the right choice if you are running a DSP-equipped amplifier (such as the Cicada FLX PRO series) or a standalone DSP in the chain. The ZEN-H PRO adds a built-in 8-channel DSP (time alignment, crossover configuration, parametric EQ and phase) inside the one module, removing the need for a separate processor where space is limited or you want the DSP work handled at the interface stage. Both replace the factory amplifier in the same location with the same plug-and-play connection; the choice is where you want DSP to sit.
Why This Matters for the Rest of the System
Signal integrity at the source determines everything that follows. An aftermarket amplifier fed by predictable A2B-interface outputs can be gain-staged, crossed over and tuned with confidence. The same amplifier fed from a LOC on the factory speaker outputs is working from a compromised foundation, and the compromise does not disappear with better downstream components. For the full architecture explanation, see Why 2023.5+ Harley Audio Upgrades Need an A2B Interface.
Shop this setup
On a Skyline-equipped 2023.5 or newer bike, a conventional line-output converter cannot connect to the digital A2B bus, and a post-amplifier speaker signal has already passed through factory amplification and processing. For predictable low-level outputs when adding amplification, use an A2B interface confirmed for the exact model year and audio package.
Not sure what fits your bike? Contact Motorcycle Audio Australia with your year, exact model, factory radio, current speaker locations and whether the bike has a factory amplifier, and we'll confirm the right parts →
Related
- NAV-TV ZEN-H, 8-Channel A2B Interface for 2023.5+ Harley Touring
- NAV-TV ZEN-H PRO, A2B Interface with Built-In DSP
- Why 2023.5+ Harley Audio Upgrades Need an A2B Interface
- Cicada DSP Amps vs Standalone Processors for Harley Touring Audio
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