The Bent Audio Model 102s Kit
Transformer-Based Passive Volume Control

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Performance    For the reference: my Bent Audio 102s Kit is based on a pair of copper Stevens & Billington transformers, TX102 MK II.25 versions to be precise. The source component is an Ah! Njoe Tjoeb 4000 CD player and the amplifier a PS Audio HCA-2. The speakers are a pair of Magnepan MG 1.6QR and the cabling by Nordost: Red Dawn interconnect and Blue Heaven RevII loudspeakers cables in bi-wire configuration. I've set the input grounding on the Bent Audio 102s to the middle position, effectively isolating the input ground from the output ground. This is because both my source component and my amplifier are grounded. For comparison purposes I will be using my resident EVS Ultimate Attenuators; one of the best resistive type passive volume controls out there.   The EVS Ultimate Attenuators represent excellent value and I have been very pleased with their performance. The transformer based Bent Audio 102s volume control, however, significantly bettered the already excellent EVS UAs. The improvement was apparent in the first few minutes of the audition, even before the transformers had a chance to break-in properly.   I believe all audio equipment benefits from break-in, also known as burn-in. The TX102s, according to John Chapman of Bent Audio, require about 100 hours of standard use to fully break-in. "Standard use" means connected to an amplifier that is exhibiting a typical load. To expedite the break-in process John provides a little Break'n Box you can assemble and connect to the unit instead of an amp. The little box effectively works as a tougher load for the transformers; this translates into more current passing through the transformer wires, consequently "exercising" them more. The recommended break-in period then comes down to about a third of the standard time, or just about 30 hours. After a quick first listen and favorable first impressions, I allowed the unit to burn-in with the kit's break-in box for a continuous 48 hours.   The first thing I noticed about the sound of the Bent Audio Model 102s was a wonderful increase in sound stage width. The EVS attenuators have very good depth but the sound stage, as compared to the Bent Audio unit, is more cone-shaped. It starts out wide but then narrows as depth increases. The Bent Audio Model 102s on the other hand opens up with clear instrument and vocal localization behind and beyond the speaker boundaries. The added width in the depth plane translates into a more natural and believable spread of musical information. Along with this increase in special resolution came an increase in vocal and instrument focus, presence, and palpability. Wow! What I noticed next was an improvement in dynamics and control at volume extremes. The passages did not pale at lower settings or congest at higher ones. Not that the EVS UAs had a major problem with this, just that the Bent Audio TX102s seemed equally alluring at all volume settings. The EVS UAs in contrast tended to work optimum in the neighborhood of the 12 o'clock setting. The bass was initially a bit dry and shy, but after the break-in period it came back with a vengeance. There was no bloating mind you, just a full, earthy quality. The low frequencies were deep, tactile and firm. Just the way they should be. The midrange was fresh, open and wonderfully communicative, and the highs sweet, detailed and transparent. Passive volume controls are prized for their dark background and lack of noise or hum. Here too the Bent Audio excelled, offering a vibrant and rich musical landscape on a pitch-dark canvas. Some passive solutions are accused of sounding un-dynamic, slow and restrained. The Bent Audio transformer based unit is the opposite case in point. It is thrillingly dynamic, fast, expressive and wonderfully involving. For all those who believe passive preamps to be lacking in these departments I strongly recommend they audition a Bent Audio transformer unit. Conclusion   The Bent Audio Model 102s kit is one of the most rewarding DIY projects I have put together. Though easy enough to assemble, it does require from you patience and thoroughness. Once completed the reward is twofold: one of accomplishment and the other of sonic delight. The kit is available in many input and output variations, it offers optional remote control and is also sold pre-assembled for those who prefer not to build the kits themselves. The Bent Audio Model 102s delivers in spades on the promises of transformer-based passive volume controls. I applaud the concept and the design and believe it to be superior to its resistive type alternatives. The kit is versatile, outfitted with high-quality parts, reasonably priced and has excellent sound quality to match. This all adds up to a wining combination. I have made the Bent Audio 102s my current reference and a permanent system member. Highly Recommended!     If you would like to comment on this project or suggest improvements to it, please click here.

Comments (add)   Ivan Hi Boris, I'm thinking about buying the Bent Audio Passive Attenuator Kit. Thanks for your great review--it's one of the main reasons I'm considering it. I also saw a picture of their newest model, featuring input/outputs that you'd hard-wired into the unit. Can you provide the details of what you used for the strain relief connections at the chassis? If I bulid this kit I would like to try hard-wiring like this. Thanks, Ivan     Boris Hi Ivan, I used a very basic technique to provide some strain relief and also protect the wires from being tugged out. I cut out a rectangular piece of wooden board; large enough to cover the two unused XLR holes in the back. I then drilled two holes in the wooden board in such a way that they center on the unused XLR holes, the hard-wired interconnect cable is to pass through these. The holes were just a bit larger than the cable. I then wrapped the cable in some Teflon tape for a snug fit. Before screwing on the wooden board to the back of the unit, I attached two wooden dowels (with screws) to the wooden board and secured the cables to them, one for each channel, with cable ties and tape. This entire assembly resides inside the unit, it's not pretty but it's out of sight and it works. Here's an illustration:   Ivan Hi Boris, Well, here's the picture that they have at the Bent Audio website: This was for the NOH preamp. It doesn't seem to be the same thing as what you show on your review of building the earlier Bent 102s. But maybe it's because the strain relievers are hidden inside the chassis, so you can't really see what he's talking about? From the way it's written, I assumed that what we were looking at here shows the strain relievers. Thanks again, Ivan