Colour Design Pt. 4: Big Time Interface and Circuit Overhaul August 09, 2013 17:40 16 Comments

Wow, it's been nine months since the last Colour update. But, believe it or not, the project has not been shelved or even dormant during that time. Since December's update, Link has (understandably) left the project to focus on other things, and I've had to quickly learn a ton about circuit design and manufacturing to get this thing off the ground. Add to this the fact that Colour is a completely new piece of gear with no established circuit, sound, or interface to reference and you've got a pretty clear picture of what I've been doing for the past nine months. The good news is that all of this studying, designing, prototyping, and testing has resulted in a much more solid, well thought out piece of gear. In the video below, I clarify my design philosophy going forward and detail the newly overhauled interface and circuit.

In summary, after doing some mixes with the most recent prototype pictured below, I became dissatisfied with the current approach of feeding the dry signal to the colours in parallel and controlling how much of each is mixed in with the dry signal. I found that in almost every application, I was keeping the colours cranked all the way up and turning the dry signal all the way down. In retrospect, this makes sense, as the colours themselves are tuned to impart only subtle distortion, the way a colored preamp or compressor might.

The most recent physical prototype (#4) with JFET, tape, and Cinemag colours installed.

The most recent physical prototype (#4) with JFET, tape, and Cinemag colours installed.[/caption] So I went back to the drawing board, this time with some real mixing experience in hand. One of the first things I knew I wanted to do was simplify the interface. While the idea of having control over the amount of each colour is tempting on paper, in practice I found that I didn't want to be bothered. What I did find myself doing was turning individual colours up and down quickly to hear what the signal sounded like with them bypassed. So I decided to substitute the individual colour volume controls for simple in/out switches. This interface trades a little control for a lot of ease and simplicity. This jives with my original intuitions about Colour: that, like a preamp or tape machine, a harmonics generator is not a piece of gear people want to spend significant time tweaking. Rather, it's something that we should be able to switch into the signal chain with a press of a button, nod with satisfaction, and move on.

Colour 500-series harmonics generator

A mockup of the current interface with bypass switches instead of individual volume controls for each colour.[/caption] I've also reworked the circuit from the ground up, putting the colours in series rather than parallel and adding a master input drive control. This approach is taken directly from real-word recording practice. When a microphone signal travels through a preamp, and compressor to a tape machine, the coloration from those devices is not applied in parallel. Rather the harmonics generated by the preamp are modified by the compressor, which are then further tempered by the tape. Indeed, part of the art of being a tracking engineer is combining complementary pieces of gear into a signal path. Putting the modules in series makes Colour sound and behave more like a true recording chain.Colour Schematic

The new working schematic , with colour modules placed in series with a single input drive control.[/caption] So, that's where are as of now. Circuit boards are already on order for the new design outlined above. If all goes well with this round of prototyping, hopefully I'll have a kit to offer very soon. As always, I welcome and appreciate your thoughts on this project. It's come as far as it has in no small part thanks to your feedback!

Need some Colour in your recording chain? Colour is now available from DIYRE Store.