Why Use a Networked Preamp?

So you're upgrading the sound in your car. Why might you want to use a "network preamp" to bring audio signals out of your stock sound system? Because upgrading the sound system in a car is more complex than it used to be.

Back in the day, you got a new "head unit" installed in the dash, and that head unit had standard RCA connectors carrying a standard stereo signal. These RCA connectors supplied full-range stereo signals, flat in response, and aligned in time and phase., Connect those RCAs to your new amplifier, and you were ready to go!

Those days are gone. Now, many vehicles use dedicated infotainment digital networks, without standard connectors or standard audio signals. There are often 8, 10, 12 channels or more - and these signals are not flat in response, they aren't full-range, they aren't aligned in time or phase - and not one of them will deliver every note we need! To learn more about this complex topic, read on!

The Introduction of Fully-Networked Sound Systems

The first automotive sound system to combine program content, commands, and other data over a digital infotainment network used the Domestic Data Bus network technology, or D2B, back in the late 1990's. This network could have been implemented over either optical or coaxial cables, but only optical cables were used in actual production systems by Mercedes and Jaguar.

The original networks connected communication interfaces, optical disc players, amplifiers, tuners, and telematics devices on a common infotainment network. D2B used a ring networking configuration to do this.

In this diagram, you can see there were many devices on this network. The functioning preamp is located inside the “sound system”, which is the multichannel amplifier.

This amplifier contains a DSP sound processor chip, which the system designer programmed to alter the sound coming from the OEM speakers. Some speakers receive a signal without bass, some receive a signal without treble - and the sounds for some speakers are delayed relative to others. Sometimes the phase of individual notes has been manipulated.

The D2B Ring Infotainment Network

MOST

While this technology was groundbreaking, D2B was soon replaced by MOST fiber-optic technology (to be specific, this was “MOST 25’. Newer versions of MOST use higher numbers - MOST 50 and MOST 150 - and are not always fiber optic). MOST 25 was adopted by nearly every European premium manufacturer - Audi, BMW, Mercedes, Porsche, Land Rover, Volvo, etc.

MOST also uses a ring networking configuration. MOST amplifiers continued to alter the sound.

MOST 25 networking in a BMW

Other Network Technologies

In the years since, MOST 50 (unshielded twisted pair, or UTP), MOST 150 (optical or coaxial), Automotive Ethernet (UTP), and A2B (UTP) have been introduced by various OEMs. GM has switched from MOST 50, to Ethernet, and to A2B over the course of just a few years.

Here is a partial list of network types and the manufacturers using them.

D2B fiber-optic (obsolete) Mercedes, Jaguar

MOST 25 fiber-optic, (nearly obsolete) most European premium makes

MOST 50 (UTP) Lexus (in production), GM (obsolete)

MOST 150 (fiber-optic or coaxial) Mercedes (in production), VAG (transitioning away)

A2B V1.0 (UTP) Ford (in production), GM, Tesla

A2B V1.1 (UTP) Ford 2025+

Automotive Ethernet (UTP) BMW (in production), JLR (in production), GM (transitioning), VAG (transitioning)

Since all these amplifiers use DSP to alter the sound, the only place to derive pure, clean audio from the OEM infotainment is by connecting to this proprietary digital network before the amplifier.

Other Devices also on Infotainment Networks

In modern cars, Bluetooth handsfree calling interfaces, satellite tuners, HD radio tuners, and CD changers have either been combined into the in-dash receiver module or disappeared entirely. This means that there are far fewer devices on an infotainment network in a 2026 vehicle than there were in a 2006 vehicle. Sometimes there is just the source unit and the amplifier.

In the diagram below, the functional preamp is located inside the “ANC Audio Amplifier”. In this diagram below, ANC and handsfree microphones are shown on a dedicated A2B network, separate from the main infotainment network. Disabling the A2B network also disables the mics used for handsfree calls - we can't do that!

An example of an A2B V1 network in a vehicle (courtesy Analog Devices)

Today, many networks carry RPM data for “fake exhaust” features, often making these features difficult to defeat - although if they remain active, they degrade the sound significantly.

To prevent these features from affecting our sound, we need that signal from the network before these sounds are injected into them!

Why use a Networked Preamp?

A networked preamp is a device that installs to a vehicle’s OEM head unit, and provides similar RCA outputs as an aftermarket head unit - making upgrades simpler.

1. Audiophile Preamp Sections and D/A Converters for Great Sound

First off, Zen Audio networked preamps have much better sound than traditional passive Line Output Converters (LOC’s). Passive transformer-based LOC’s lose stereo separation, lose bass content at higher volumes and signal voltages, and risk picking up Electromagnetic Interference noise (EMI). And that's not even taking into account that LOCs take in signals intended for speakers, and those signals are what the OEM DSP amplifier has been altering.

Modern high-power OEM amps can reach three times the voltage passive LOCs were designed to handle - that means smoke, melted plastic, and bad sound.

LOCs also retain any deviations and nonlinearities that exist in the output stages of the OEM amplifier. Network preamps eliminate all those imperfections.

Zen Audio preamps include the sonic circuitry of a high-end head unit - but without the often-difficult task to try to integrate that high-end head unit into a modern vehicle. All limitations on OEM sound quality are removed when a ZEN Audio preamp is installed - the digital signal is converted and controlled by studio-grade D/A converters, op-amps, and digital processors.

Most OEM systems degrade the sound once the user goes above 75% on the volume knob - but Zen Audio preamps maintain clean sound across the entire volume range! If you like the idea of upgrading your OEM source unit’s sound with advanced digital-to-analog converters, audiophile op-amps, and higher-voltage signals, then you will love the sound of a Zen Audio preamp!

2. Eliminating OEM audio processing

Secondly, Zen Audio networked preamps eliminate OEM processing!

We can think of this processing as the OEM sound tuning of the sound system’s output. OEM tuning has different goals than aftermarket tuning - the OEM tune is often focusing on limiting what’s asked of the factory speakers.

In premium sound systems, the list below is processing performed inside the OEM amplifier:

Active Crossover Filters
Dynamic Subsonic Filters
Fixed Equalization
Dynamic Equalization (varying with volume)
Sub-bass Compressors and Limiters
Phase Manipulation (All-Pass Filters)
Automatic Loudness Compensation
Source Dependent Tone Controls
Seat-Optimized Processing
3-D or Surround Processing (DTS, Centerpoint, Logic 7, Dolby PLII, etc.)
Frequency-Slicing Surround (such as Quantum Logic)

A “flat”, unprocessed signal on the left, and a processed signal on the right

In the analog days, an unprocessed “pre-amplified” signal traveled from the OEM in-dash receiver to the OEM premium amplifier. It was flat in response, and aligned in time and phase. These analog preamp signals were preferred for aftermarket audio upgrades, because they sounded so good.

OEM amplified outputs are heavily processed!

Today most premium vehicles use a proprietary digital network to connect the in-dash receiver to the amplifier. There are various types of network used - MOST 25, 50, or 150; A2B 1.0, 1.1 (and soon, 2.0); and Automotive Ethernet.

Why do OEMs use networks? One reason is so they maintain the highest-fidelity source signal, free from noise or distortion that affect analog preamp signals.

ZEN audio outputs eliminate all processing!

When upgrading the sound in these digitally-networked vehicles, there is no clean, unprocessed analog signal for an installer to use.

The only analog signals are speaker wires out of the OEM amplifier, and they make great sound very difficult to achieve. It is rare to even find full-range signals, much less unprocessed signals without equalization, delay, limiting, etc. The OEM processing is not based just on the acoustics of the cabin, but the limited performance of the OEM speakers. Once the speakers are upgraded and the power is increased, this OEM processing hurts more than it helps.

If some channels (such as subwoofers) are limited by compression at some point in the OEM volume knob’s progression, a Zen preamp restores full-volume operation. In fact, Zen Audio preamps eliminate all OEM audio processing!

3. Eliminating Automatic Noise Cancelling feedback

Automatic Noise Cancelling systems have a reference sound level they expect. If ANC “hears” more sound than expected, the system attempts to cancel it out using the vehicle’s speakers. When we upgrade the sound system, we change the measured sonic result (that’s the point, of course!) The ANC system then attempts to cancel out the new subwoofer - with the new subwoofer! The result is bad acoustic feedback which “sounds like a jet engine”.

First-generation ANC feedback was defeated by disconnecting the mic wires:

Defeating first-generation ANC:

Next-gen ANC uses networked microphones for both ANC and handsfree calls. These mic networks can't be taken offline without also disabling the handsfree-calling mics - and that’s a deal-breaker for almost every vehicle owner.

No wires can be cut with next-generation ANC!

Zen Audio preamps eliminate ANC feedback - without cutting wires!

4. Eliminating “Fake Exhaust Note”

This "fake exhaust" is disliked by many enthusiasts - and becomes really obectionable in high-performance audio systems. With early examples, “fake exhaust note” generators used analog tach wires for RPM data - simply cutting this wire at the OEM amplifier disabled the fake exhaust generator.

Disabling first-generation “fake exhaust” sounds:

Modern implementations supply RPM data over the digital network, without a straightforward way to remove it.

Zen Audio preamps eliminate“fake exhaust” note - without cutting wires!

5. Retaining high-quality handsfree-calling audio

OEM handsfree systems generally function really well - but aftermarket audio sometimes reduces call quality by adding echoes to one side of the call.

To explain this, let’s introduce the concept of latency. In a network, latency refers to the time required for the transfer of data between two points.

All handsfree systems use a technology called automatic echo cancellation. It synchronizes the sound from the speakers to the sound of the microphone, similar to the way that many televisions allow the audio to be adjusted so it can be synchronized with the image on the TV screen. This essentially corrects for the latency in the system.

OEM Echo Cancellation

To do this, the digital information must be temporarily stored in a digital memory buffer. Since the automakers know the size of the vehicle and the design of the system, they know how much data might need to be stored temporarily in the buffer - they know how much memory to build into the system.

Once we change the system by adding new DSP processing, we change the total end-to-end latency of the system. If we add too much latency, the OEM echo-cancellation buffer is overwhelmed - there’s just more information than the buffer can store. The result is audible echo at the other end of a handsfree call.

OEM Echo Cancellation Can’t Always Handle Added Latency

Zen DSP can address this differently from other aftermarket processors, because - since we live on the infotainment network - Zen DSP devices know when a phone call is in progress!

Zen DSP dynamically adjusts the end-to-end latency of the system during a handsfree call, allowing OEM echo-cancellation to function as designed. The difference is dramatic - crystal-clear call quality and uncompromising sound.

In Conclusion:

Nav-TV solves all these integration problems with the Zen Audio family of networked preamps and amplifiers. These devices provide unprocessed digital audio and supply pure analog or digital signals for your upgraded sound system.