I wanted to share a little bit about the story behind the tube microphone I designed (term used loosely) and the process that went into it.
My microphone is essentially a clone of a clone of a clone. It started with a pair of microphones owned by Ken Goerres that I was fortunate enough to get to use in LA. These were built by Howard Gale under the brand Sonic Integrity Labs. I know very little Howard other than that he was known for building very nice power supplies. I believe only a handful of these mics were made. Howard passed away a few years ago.
After taking a look inside one of these microphones, I figured the circuit was simple enough for me to build on my own but I couldn’t see everything going on and don’t know enough about electronics to fill in the gaps. A few years later, I came across an article written by David Royer which described a microphone he designed and sold a DIY kit for many years ago. This microphone eventually became the Mojave MA200 which Mojave was founded on. Royer’s microphone is essentially a modified U47 circuit with a 67 style capsule.
As I later learned, Howard took the original Royer kit and modified it to improve it. My goal was to clone (get close to? improve?) Howard’s mic which was a slightly modified version of the MA200 which is the modified U47 circuit. A clone of a clone of a clone.
My “design” work didn’t involve modifying the circuit in any way other than changing some transformer and capacitor values. I was mainly “voicing” the microphone. Considering that I don’t have access to a Howard mic in Canada, I bought an MA200 to be able to compare to and make sure that my microphone was a step ahead of it.
There were 4 elements that I voiced - the capsule, microphone transformer, tube, and capacitors. It was done in the order mention so that the elements that make the bigger differences were established first and I then focused on smaller and smaller details.
Starting with the capsule, I had 4 choices ranging from about $50 to $300. The cheaper Chinese ones had a less extended top end and more closed sound. The higher end ones brought a more open sound which more closely matched the MA200.
For the microphone transformer I once again got 4 different transformers to test, 2 of which were custom made. Some had a very transient and aggressive sound while others had a darker and more liquid sound. I chose to go with the later.
With the tubes, there are only so many 5840 tubes that I can repeatedly buy so I ended up with only 2 choices. both of which were NOS parts. The differences here were starting to get very subtle but one tube offered a more open sound.
The last element which I focused on testing and which involved the most extensive testing were the capacitors. Royer’s circuit uses only 2 capacitors in the microphone. While this may not seem like much, I had over 150 possible combinations of capacitors to try out. Theoretically changing the values of these capacitors should have essentially no effect on the sound but I found that not to be true. Some of the capacitors I tried out were Solen, RTX, AudioCap, Axon, NOS Russian, Mundorf, and Sonicap. Although the differences they made were subtle, getting the right combination was key to having an excellent sounding microphone. Ultimately I ended up with 3 top choices for one of the capacitors and 5 for the others. This led to 15 combinations which I picked a winner from. I chose a combination which was a little fast and transient as well as open which worked well with the transformer that I chose to use.
The result is an excellent versatile microphone. with some very high end components that have been meticulously voiced. I am offering them for sale for $850 USD (discount on pairs). Compared to the MA200 which sells for $1200 USD, I can say that mine uses much higher end components. Whether or not it sounds better is subjective. I’m also offering a version for $550 as a way to use up the parts that didn’t make it into the final design. These are still parts which are at least on par with what is in the MA200 and gets you a sound that’s still in the ballpark of the MA200. Arguably better.
Getting the design to where it is today took countless hours but I’m happy with the end result and look forward to using these microphones in future sessions.