The Story of the Analog Bridge

So, what is an Analog Bridge https://www.modwright.com/products/analog-bridge/, and where did it come from?

The Analog bridge provides a unity gain tube circuit, with three modes of adjustment, allowing you to tailor the tone of the sound to suit your system and taste. It has a high input impedance and extremely low output impedance, allowing it to create the ideal impedance relationship between source and preamp, source and amp or preamp and amp. It is available as RCA only, or RCA and fully balanced XLR in and out.

The original purpose of this product was to provide an Analog ‘bridge’ from harsh solid state Digital to true musical enjoyment.

As many of you, but not all, may know, I started out in 2000 offering mods to digital gear. We really hit our stride with the replacement of solid state output stages in digital gear, with tube circuits. I found that we could make a good digital source, great this way.

Oppo Digital was a company that made some of the most popular Universal Players in the market for some time. We designed and offered mods for a range of Oppo Universal players, culminating in the Oppo 205, the last unit they produced. An Oppo 205 with ModWright Truth mod was a sought after product and we modified A LOT of them.

When Oppo closed its doors, a void was left. I could not find a source to replace the Oppo players, and people were moving onto DACs and streaming much more at this time. So, the idea came to me, what could we offer as an ‘add-on’ product that would produce the same quality sound as the modified Oppos.

The name Analog Bridge came from reference to a ‘digital bridge’, in Roon’s nomenclature. I decided what digital needed, was an ‘Analog bridge’…

The first prototype used 6922 tubes and was solid state rectified. We added it the output of the cheapest CD players and DACs we could find. We were surprised at the good result. When I played a $300 Pro-Ject DAC (with upgraded linear power supply of my design) into the Analog Bridge, all of us at ModWright were surprised at how close the sound was to that of a modified Oppo 205.

I decided that if we were going to do this, then we needed to do it Wright, with a high level of user adjustability and flexibility. The addition of a parallel 6SN7 circuit, in addition to the 6922 circuit, allowed for two very different tube tones. I consider the 6922 to be neutral and beautiful sounding with just a touch of tube warmth. The 6SN7 on the other hand has what I consider a Fat Tone. It sounds like Tubes!

A circuit was designed that allowed for a brief mute when switching between tube circuits. This allowed for on-the-fly switching with no clicks, ticks or pops.

The addition of tube rectification came next as I decided that we needed a third variable to truly make the product complete. As many of you know, tube rectifiers all sound different. While 5AR4/GZ34 is the basis of design, compatible rectifiers include 274B, 5R4GY, 5U4G, 5U4GB, 5V4G, 5V4GB and virtually all 5AR4 equivalents.

The initial design was RCA only. I decided that if we were going to offer it as a balanced product, it had to be done Wright. There are different ways to create truly balanced circuits. One of which involves twice the circuitry, including both (+) and (-) circuits, closely balanced. This is fine if both polarities are very closely matched, and it adds a lot of needless complexity. Other manufacturers use opamps to split and integrate phase, but I don’t like feedback. I am a big fan of transformer coupling and have used Lundahl transformers for years in similar applications. A quad of Lundahl transformers was selected then, to ideally split and integrate phase, allowing for truly balanced XLR inputs and XLR outputs.

The most important part, of the Analog Bridge design, was ‘Do No Harm’ to the audio signal. If we are going to add a product to the signal chain, it cannot add noise, distortion or limit frequency response. A special unity gain circuit was selected that would provide very low output impedance, very wide bandwidth (20Hz – 150Khz), very low distortion (THD < .003%) and very low noise. I am pleased to say that we have achieved this with the Analog Bridge.

So, the Analog Bridge https://www.modwright.com/products/analog-bridge/ was born out of what I considered necessity. I wanted a way to include tube sound in any system, without requiring the modification of anything, or the replacement of any part of your existing system.

As I like to say, ‘No Tubes, No Magic!’