Zapco Z-OTG-BT C — Hi-Res USB OTG and Bluetooth Audio Converter

Zapco Z-OTG-BT C — Hi-Res USB OTG and Bluetooth Audio Converter

The Z-OTG-BT C takes audio out of a phone — over USB OTG or over Bluetooth — and delivers it to a car audio system as optical, coaxial, or analog RCA. The USB input handles 192 kHz / 32-bit and charges the connected device at the same time. Bluetooth is Qualcomm 5.2 at 192 kHz / 24-bit with aptX, aptX HD, and aptX Adaptive.

It is a source converter, not a processor. It does not equalize, cross over, or delay anything.

Getting Past the Phone's Own Output

A phone connected by its headphone jack or a factory USB port has already converted the file to analog using whatever converter is inside the phone, and whatever level it chose to output.

Over USB OTG, the Z-OTG-BT C takes the digital bitstream directly instead. The file leaves the phone as data and is converted here, on a TI PCM5102A running to 384 kHz / 32-bit, with a JRC 5532 low-noise dual op-amp on the analog output. Or it is not converted at all — the optical and coaxial outputs pass digital straight to a processor's digital input, which is the better path when the system already has a DSP with a converter you would rather use.

Bluetooth Worth Using

The Bluetooth side is Qualcomm 5.2 carrying aptX, aptX HD, and aptX Adaptive. aptX HD supports 24-bit transmission, and aptX Adaptive varies its bit rate with the connection quality rather than holding a fixed rate and dropping out.

Both endpoints have to support the codec. A phone that only speaks SBC or AAC will connect and work, but will not deliver what the aptX HD path is capable of — that is a property of the phone, not of this converter.

Outputs

Three ways out, and the right one depends on what it is feeding:

• Optical: digital, into a processor's optical input at 48, 96, or 192 kHz
• Coaxial: digital, same rates, where the processor has an SPDIF coaxial input
• RCA: left and right analog at 1.5 V RMS, using the internal DAC

If the system has a Zapco processor with a digital input, use it. Passing the signal digitally means one conversion in the chain instead of two.

System Application

A build where the phone is the source and the factory head unit is either gone or bypassed. It also suits a system that has kept the OEM display for its vehicle functions and needs a separate high-quality audio path around it.

Because it can output digitally, it works cleanly ahead of a DSP-Z8 IV, an ST-X DSP, or an HDSP-V — the converter handles the source, the processor handles the tune.

Installation Considerations

The unit is 140 × 23 × 96 mm and runs on 9–16 V DC. It needs main power at +12V B, a solid ground to bare chassis metal, and a +12 V turn-on at REM — taken from a head unit remote output, or from an accessory (ACC) terminal if none is available.

Mount it where the USB connection is reachable from the driving position, since a phone plugged into a converter buried behind a panel is a converter that will not get used.

Zapco recommends a fuse or circuit breaker within 18 inches of the battery on the main power run.

Specifications

• Type: audio converter
• OTG input: 192kHz / 32-bit, with device charging
• Bluetooth: Qualcomm 5.2, 192kHz / 24-bit · aptX, aptX HD, aptX Adaptive
• Op-amp: JRC 5532 high-performance low-noise dual
• DAC: TI PCM5102A, 384kHz / 32-bit
• Digital outputs: optical and coaxial · 48 / 96 / 192kHz
• RCA outputs: left + right, 1.5V RMS
• Power supply: DC 9–16V
• Dimensions: 140 × 23 × 96 mm

HF Audio Perspective

Most systems are limited at the source and the owner does not realize it.

A build can have a good processor, good amplifiers, and good drivers, and still be fed by a phone's headphone output or a factory USB port that resamples everything to something convenient. The signal never recovers from that, and no amount of tuning downstream fixes it.

What the Z-OTG-BT C does is take the digital data off the phone before the phone has had a chance to compromise it, and either convert it properly or hand it to a processor still in the digital domain. For a system built around a phone as its source — which is most systems now — that is a more meaningful change than another upgrade further down the chain.

Two honest limits. The Bluetooth path is only as good as the phone's codec support. And if the vehicle's factory head unit has to stay in the signal path for other reasons, this converter cannot route around it.