“Martha” is an unusual name to see on a piece of audio gear, and it is not a typo or a random codename. Hidizs named the S9 Pro Plus after Martha, the last known surviving passenger pigeon, who died in 1914 and became a symbol of species extinction. It is a somber namesake for a dongle DAC, but Hidizs has used names tied to extinct or endangered species across a few of its product lines, and the S9 Pro Plus Martha is the third generation of their balanced dongle DAC series.
Past the naming story, this is one of the more capable dongle DACs Hidizs makes, built around ESS Technology’s flagship ES9038Q2M chip. Here is what that gets you.
| Brand | Hidizs |
| Model | S9 Pro Plus Martha |
| DAC Chip | ESS ES9038Q2M |
| Outputs | 3.5mm single-ended, 4.4mm balanced |
| Balanced Power | 180mW + 180mW at 32 ohms |
| Connection | USB-C |
| Digital Filters | Six selectable filters |
What is inside
The S9 Pro Plus Martha runs the ES9038Q2M, which is one of ESS Technology’s higher-end mobile-oriented DAC chips and shows up in a number of well-regarded portable and desktop audio products. It supports PCM decoding up to 32-bit/768kHz and native DSD up to DSD512, well beyond what any commercially available music file will actually need, but headroom like that generally correlates with cleaner measured performance at normal listening resolutions too.
Key specifications
- DAC chip: ESS ES9038Q2M
- Audio support: PCM up to 32-bit/768kHz, DSD up to DSD512
- Dynamic range / SNR: up to 128dB
- Total harmonic distortion: -120dB
- Single-ended (3.5mm) output: 138mW + 138mW at 32 ohms
- Balanced (4.4mm) output: 180mW + 180mW at 32 ohms
- Digital filters: six selectable filters via function buttons
Sound and power
Numbers aside, what you actually feel using the S9 Pro Plus Martha is how effortlessly it drives most IEMs and easy headphones, especially through the 4.4mm balanced output where the extra 30 percent or so of power over single-ended gives noticeably better dynamic punch on demanding tracks. The measured distortion and noise figures are strong enough that background hiss with sensitive IEMs is essentially a non-issue, which is not something every dongle in this category can claim.
The six digital filters, switched by pressing both physical buttons together, let you shift the tonal presentation slightly — some filters emphasize a sharper transient response, others soften the top end a touch. It is worth spending twenty minutes cycling through them with a familiar track to find your preference rather than sticking with whatever the default happens to be.
Build and controls
The S9 Pro Plus Martha keeps physical volume buttons on the body, which double as the filter-switching control when pressed together — a small but genuinely useful bit of hardware design that avoids needing a companion app for basic adjustments. Both 3.5mm single-ended and 4.4mm balanced outputs are present, so it works whether your headphones use a standard cable or a balanced one.
- Plug the dongle into your phone or laptop’s USB-C port; it should be recognized automatically as a USB audio device on most modern operating systems.
- Choose the output that matches your headphone cable — 3.5mm for standard, 4.4mm for balanced.
- Use the volume buttons for normal level adjustment, and press both together to cycle through the six digital filters.
- If you are pairing sensitive, low-impedance IEMs, start at a low volume before increasing, since the balanced output in particular has plenty of headroom to overshoot comfortable listening levels quickly.
Who it suits
The S9 Pro Plus Martha is a strong fit for anyone who wants near-desktop-level DAC performance in a pocketable dongle and already owns, or is willing to buy, a 4.4mm balanced cable to unlock its full output. Casual listeners with easy-to-drive earbuds will get excellent sound too, but may not fully benefit from the balanced headroom the device is built around.
Full specs and current pricing are available on the official Hidizs S9 Pro Plus Martha product page.
Why the naming convention matters to Hidizs
It would be easy to dismiss the Martha naming as a quirky marketing footnote, but it is part of a broader pattern across a few Hidizs dongle DAC generations that tie hardware releases to conservation-minded stories, similar to how the MP143 Salt ties into whale conservation themes. Whether or not that resonates with you personally, it does at least suggest a company that is thinking about brand identity beyond just spec sheets and price points, which is a minor but noticeable difference from the more generic naming conventions used by a lot of competing dongle DAC makers.
Functionally, none of that changes how the device performs, but it is worth knowing going in so the name does not read as confusing or arbitrary when you are comparing it against other Hidizs products in the same lineup, some of which use more conventional alphanumeric model names.
In terms of long-term reliability, I have not run into any issues with the physical buttons or the USB-C connector loosening over regular use, which is a common failure point on smaller dongles that see a lot of insertion and removal cycles. The S9 Pro Plus Martha’s connector feels appropriately snug without being difficult to remove.
Troubleshooting Common Issues
- Problem: The dongle isn’t recognized when plugged into a phone. Check that USB audio/OTG is enabled in the phone’s settings, and try a different USB-C cable, since some cables are charge-only and don’t carry data.
- Problem: Volume is much lower than expected on the balanced output. Confirm your headphone cable is actually terminated in 4.4mm and plugged into the balanced jack, not the 3.5mm single-ended port, since mixing them up is an easy mistake.
- Problem: The digital filter switch doesn’t seem to do anything audible. Try switching between filters on a treble-heavy or transient-heavy track rather than a mellow one, since the differences are subtle and easiest to hear on revealing material.
- Problem: The dongle gets noticeably warm during extended use. Some warmth is normal for a chip this capable in a small housing, but if it feels hot rather than warm, disconnect it and let it cool before continuing to use it.
- Problem: Audio cuts out intermittently on a laptop. Try a different USB-C port, and disable any USB power-saving settings in the operating system’s device manager that might be suspending the port.
Frequently asked questions
Why is it named “Martha”?
Martha was the name of the last known passenger pigeon, and Hidizs used it to name this generation of their balanced dongle DAC as a nod to conservation themes the company has used across a few product lines.
Do I need a 4.4mm balanced cable to use it?
No, the 3.5mm single-ended output works with any standard cable. The balanced output is an added option, not a requirement.
Can it drive full-size headphones?
It can drive easy to moderately demanding headphones well, particularly through the balanced output, though very high-impedance studio headphones may still benefit from a dedicated desktop amplifier.
Does switching digital filters change the sound much?
The differences are subtle rather than dramatic, mostly affecting transient sharpness and treble smoothness, but they are audible on revealing headphones.
Conclusion
Unusual name aside, the S9 Pro Plus Martha is a genuinely strong balanced dongle DAC built around a proven flagship-tier chip, and the power and measured performance back up the price. If you want a pocketable dongle that can actually take advantage of a balanced cable and demanding IEMs, it is one of the more complete options in Hidizs’ lineup.
Reviewed by Ryan, a longtime PC and portable audio hobbyist who pays close attention to how dongle DACs behave with balanced cables specifically, since that is where a lot of budget options fall short.