AI-121 Audio Interface Transformer

This might just be the coolest product Bob's Devices has ever released. Designed to be used between line-level components, the AI-121 provides the same huge sonic benefits which their Sky models bring to MC phono cartridges. There are literally limitless uses for this device and the performance improvement is astonishing!

Featuring exceptional quality transformers and very high-level construction techniques, the AI-121 stabilizes the electrical connection between line-level components, simultaneously removing unwanted noise. This, in turn, provides a larger, clearer and better defined holographic image, superior focus, and a deep, wide and accurately sized soundstage. Tonal balance is also stabilized revealing greater purity top to bottom, excellent low-frequency extension and astonishing analog-like liquidity in the midrange.

Initially envisioned as a remedy for the "digititis" and inherent lack of smoothness of so many music streamers, rapidly it became apparent that the AI-121 also benefits a wide variety of sources; analog and digital alike: Disc players, DACs, Streamers, Preamps, Phono Preamps, Reel to Reels, Cassette Decks, even between high-end subwoofers and the preamp! Any analog source can be used with the AI-121 to jaw-dropping effect.

We first heard the AI-121 at AXPONA '25 and inserting this small box into the system was like opening a window in a stuffy room. The top end became airy and extended, better defined and vastly smoother. The midrange palpability was visceral, delivering spooky realism to voices and instruments. The bass became tighter, deeper, cleaner, with less overhang and bloat. And that was in an already great sounding system!

The AI-121 features gold plated hardware and a hand-polished black powder-coated cast-aluminum enclosure.
Optional Balanced unit uses high-quality XLR connectors in a larger custom chassis.

Premium construction using C&K Silver-contact toggle switches and Deluxe Gold Plated RCA jacks.

All connections are Resistance Soldered using the American Beauty system which eliminates heat damage which might occur on the delicate insulation on the hair-like wires of the transformers. Even the test equipment Bob's Devices uses is very-low current to avoid saturating the transformer cores.  This is your assurance of a premier state-of-the-art product.

The RCA version of the AI-121 features a ground switch which (if needed) allows the user to disconnect the chassis ground of the RCA, allowing only the signal to pass through. This can be enormously valuable in breaking ground loops or disrupting RFI or EMI interference on the ground plane. In general, we recommend running the AI-121 with the ground lifted, unless it is being used with a phono preamp, in which case grounding the AI-121 may result in a lower noise floor.

In "Lift" mode, the AI-121 disconnects the negative side of the RCAs from Chassis Ground, isolating both components from any potential noise on the ground plane. In most scenarios, this is the best option when implementing the AI-121.

In "Ground" mode, the negative connections on the RCA and the component are connected to the ground lug. This configuration operates just like a standard ground connection, but allows for greater ground potential to be generated, should the user require, such as when used with a phono preamp or certain other devices.

Note: Due to differences in configuration, the XLR variant (which is truly balanced) could not operate with the ground "lifted" and thus doesn't get a Ground Post or a Ground Lift switch.

The Output switch on the front of the AI-121 allows this unit to switch between Flat (0dB) and High (+6dB) gain. The Flat setting delivers the most neutral and natural presentation, this will be the setting most used with the AI-121. That being said, there are a few situations where having a few extra dB of gain might come in handy!

The High setting can be very useful in raising the output level of a vintage source to match higher output (aka modern) ones. Some older sources, such as Reel to Reel machines, some CD players, DACs, cassette decks, or even vintage phono preamps can have lower output than more modern devices, leading to unsatisfying listening conditions, inserting the AI-121 helps raise the output voltage of the source while improving overall sonic characteristics. 

This switch can also be useful when used on the output of a phono preamp which might not quite have sufficient gain for the cartridge being used. For instance, those with High-Output Moving Coil cartridges can't use one of Bob's SKY MC Step-up devices to raise the output of their cart, which means the phono preamp might not deliver sufficient output to fully drive the input of a line stage. Adding the AI-121 with the High switch engaged to the output of the phono preamp would bring overall system gain up to the perfect level.

Another use for the AI-121 High switch could be between an ARC phono preamp and any Line Stage preamp. Most ARC phono preamps simply don't have sufficient gain (~55dB) to drive a modern low-output MC phono cartridge, however, adding the AI-121 to the output of the phono preamp will raise the output voltage of the phono preamp to modern levels without increasing distortion or interfering with the signal path between cartridge and phono preamp.

Please note: the AI-121 is entirely passive. There are no active circuits within the unit. The extra gain is generated by accessing a different set of taps on the internal transformers.

Switch Function:
    Low/Flat: 0dB Gain
   High: +6dB Gain

Distortion (THD): 0.001% (@ 1kHz, +0.0dBu)
Freq Response:  (ref 1 kHz)
   -0.1dBu @ 10 Hz
   +0.05dBu @ 20 kHz
   +0.25dBu @ 50 kHz
Common Mode Noise Rejection:  >95dB @ 60 Hz