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

(page 2)

Description and Design    As a kit, the Bent Audio Model 102s was an ideal candidate for a DIY project. It appeared to be within my soldering expertise (intermediate, but beginners should not shy away either), and it seemed complete, i.e., it did not require me to source parts from other vendors. So I contacted John Chapman, Mr. Bent Audio, and ordered the simplest version: One WBT RCA in, one WBT RCA out.   The core of the kit is a pair of high quality Stevens & Billington TX102 transformers, one for the right channel and one for the left. My kit is based on copper version: TX102 MK II.25 - basically the latest copper revision (OCC copper and OFC leadouts) but without the few additional taps recently added. The transformers are wrapped in a shield metal casing and look like cans with a bunch of wires sticking out. The wires are the different taps connecting the secondary windings and providing different attenuation levels. These transformers are quite hefty and account for most of the unit's weight. Also integral is a high quality volume switch, a Seiden Model 45SG. This is a 23-position shorting type two-deck/stereo switch, with copper shielding between the decks and gold plated contacts. A real beauty!   Bent Audio also offers, at a premium, an all-silver version of the transformers. The most recent addition to the options list is a remote controlled upgrade, allowing you to adjust volume from the comfort of your listening chair. Everything else is pretty much configurable. You may choose the number and the type of the unit's inputs and outputs. Depending on that number, your kit may also include the necessary input selector switches. The kit comes with an ample supply of high purity solid core silver wire for internal wiring and more silver solder than you will actually need for the project. The casework is all metal, well designed and well finished with enough of accompanying hardware to bolt and screw everything together. Thoughtfully there are spares a-plenty. You also get a comprehensive assembly instructions manual that ensures you get things done right. There are color pictures on-line depicting assembly steps and downloadable wiring schemas in Word or PDF format. If that's not enough, then you can also bug the ever helpful and patient John Chapman.   Depending on the transformer versions, the number of inputs and outputs and your choice of remote control or not, the price will vary. The simplest version will set you back about $750 US. Not having the need for may source inputs, the kit I ordered was very basic: One WBT RCA in and one WBT RCA out. Should I ever need more of one or the other, I only have to order additional supplies and heat up my soldering iron. Having said that, I did make a small change at the end: instead of completing the kit with RCA outputs I swapped in XLR ones. It was a simple matter of downloading the corresponding wiring schemas and adjusting accordingly. Putting It All Together   There's something about making your own "Hi-Fi" that makes it that much more sweeter. Obviously this assumes that the thing works at the end of your hard labor. Suffice it to say that mine does. In order to ensure success, you must be patient; don't rush things! The first thing you should do is to make sure you have all the required materials and tools; do a little cross check and mark the items off. Second, read the assembly instructions from beginning to end (all of it) before you start doing anything. This is important; you need to know where you're going and how it all fits together. If you have any questions after your initial review, make sure you get answers for them by either researching the topic or contacting customer support, in this case John. If you have never soldered before or even if you haven't done it in a while, it's a good idea to get a little practice prior to soldering these expensive parts. You want to do a good and clean job on every solder joint and not have to go back and fix it, possibly messing it up. I bought a very simple Velleman kit, a $5 flashing light thing and put it together just to get a feel for the solder. With blinking lights in the background and armed with confidence I moved on to the main job. I will not walk you through each step of the assembly process. The kit provides you with detailed instructions and there are assembly pics on-line too. I'll focus on things throughout the process that I think need additional attention. The following Parts are itemized as per the kit's assembly instructions.   Part 1 - Case Disassembly and Seiden Switch Installation   Everything arrives nicely packed and protected in layers of bubble wrap. When unpacking, be careful not to scratch things up, the metal case in particular is easily scratched. Also when unscrewing the bottom and top plates you may want to note their orientation. The top plate aligns only in a certain way. This is because the ground lug on the back plate offsets the top plate center screw hole by just a bit. I also found that the right angle mini brackets, the ones that hold the entire case together, have orientation: the longer part of each bracket should be mounted flush alongside the front and back plates. Installing the Seiden switch was a matter of just following the directions. One note though: before you screw and tighten the front plate together (it's made out in layers), use the supplied volume control knob to center the outermost layer of the front plate. Slide the knob on to the Seiden switch and then adjust the outer plate so that the knob and the plate hole are perfectly concentric.   next page: