The Vintage Direct Story

United's Chad Kelly discusses how the Vintage Direct came to be.

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The direct box story….

As I’m sure is the case with many electronics hobbyists and enthusiasts, the direct box (along with my hand-made cables) was the first thing I ever summoned the courage to put together on my own, probably almost 30 years ago. I remember the first time I heard the comparison between the built in active DI that is included on so many preamps and interfaces and the sound of a dedicated passive DI made with a high quality transformer. The added weight, headroom, depth, warmth, and clarity really left an impression on me. A great passive DI, coming into the mic input of a pre, can have a much better self noise and it becomes so much easier to control gain structure and avoid the all-too-common problem of instruments clipping on input with the onboard DI. This is especially true with bass, but quite often with guitar as well; and with extremely hot analog synth, it's a downright requirement. The direct signal sounds bigger, punchier, and seems to live in its own sonic space.

I also keenly remember buying my first high end active, transformer-less direct box and finding to my dismay that it was not actually as transparent as the passive ones I had built, not only adding a certain pillowy character to the sound, but also introducing a good amount of radio interference that I struggled to fully eliminate. It was refreshing to read Bruce Swedien’s first book, many years later, where he described the same problem and why he still relied on his trusty Bass Box passive DI built with a large, vintage transformer.

I have built hand-made direct boxes on occasion for the last 30 years, and many have found their way into major recording studios. Many of the early units were often in brightly-colored boxes, and made in mono or stereo versions.

Passive DIs often get a bad reputation as being the less transparent between active and passive, suffering from high frequency loss and compression of transients, etc.; but I feel this is not entirely true. Passive DI boxes can have those qualities; but they do not have to. I have made passive DIs that are absolutely neutral. I have also made some that have a good amount of deliberate color. Modern transformer design allows for parts that have exceedingly low loading loss and excellent high frequency response; many can even have a slight high frequency lift. To my way of thinking, the benefits of a transformer outweigh the negatives. The noise rejection, isolation, common mode rejection, and reliability are simply best with a well-made transformer design.

The custom US-made 5078 transformer

In the early days of direct boxes, there were no specially-made direct box transformers as we would know them today. Transformer makers had a much more limited catalog in those days, with most parts having a variety of applications and a sometimes wild number of taps available to configure in all sorts of ways, from unity gain to extreme step up to extreme step down… These early transformers were larger, more complex, and more expensive to build. Modern passive direct box transformers are usually very specialized parts made for a single application, and are usually much much smaller, often relying on outside semiconductors (pots, resistors, RC networks, filters, diodes, etc.) to pad and protect the transformer from clipping or from excessive levels and outside interference.

What we embarked to do with the Vintage Direct was to return to the beginning, with a part that was directly inspired by one of the vintage UTC parts manufactured in the 1960s that was used in some of the earliest direct boxes. We endeavored to maintain all of its original tap options as close to what was originally spec’d as possible, utilizing these additional taps to give us the output level range we desired. Because I am of the belief that having a lot of semiconductors (pads, pots, etc) in front of the transformer could contribute to some degree of parasitics (loss, and the dreaded tone suck’, we were adamant from the beginning that the incoming signal must hit the transformer directly, with nothing in between.

The transformer simply had to be made to such a quality level, size, and have such exceptional shielding that simply nothing else would be necessary. The transformer is simply so large and robust that it would be very difficult to clip. It has no pad, per say, and all of its level control is merely output control. To us, this ensures the maximum preservation of your instrument’s tone.

We spent years exploring many versions of this design, experimenting with different winding ratios and alloys; we ultimately settled on a high-nickel lamination and a winding ratio very close to the classics that inspired us. United’s US-made 5078 is one of the largest transformers you’ll find in a DI, delivering a pristine low-noise signal, wide frequency response, extraordinary headroom, and outstanding noise rejection.

Splitting the difference between color and transparency…

As anyone who knows me knows, the process of reamping is near and dear to my heart. To do reamping in a convincing way requires a direct box that faithfully retains the energy and sonics of the original captured performance. However, a vintage direct box is something that is known to have a certain character. We experimented with different core alloy materials and combinations, and different winding methods for years until finally coming to what we feel is the perfect compromise.

A transformer that measures almost perfectly linear in terms of frequency response; yet has an unmistakable hint of iron in the signal path that gives instruments just a slight heft and larger-than-life character. Tracked into a fairly neutral preamp, you will have a fairly clean and accurate reference DI track. Tracked into, say, a nice tube preamp and overdriven a bit, you can have a bigger, thicker sounding bass or keyboard or drum machine track.

Our Vintage Direct splits the difference about as closely as anything can, and allows the user to ultimately shape some aspects of tone via the preamp choice and gain structure.

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