About my projects
The projects that I am going to present here can be categorized as follows:
1) Microphone circuit analysis (concept analysis, LTSpice simulations, measurements, etc.).
2) Microphone modifications, predominantly electronics-related.
3) Other Audio-related projects, e.g. my DIY Audio Analyzer and other DIY test equipment.
The microphones I have modified, or which I intend to modify in the future, are mainly popular budget and vintage microphones. I assume these categories are also the most attractive ones to modify for the average Do-It-Yourselfer. The microphones selected are generally fairly easy to open and modify.
Unfortunately, for you as a reader, at this moment I will not disclose every circuit I have designed because I still want to keep open the possibility of selling some of the circuits commercially as PCBs, as kits, or as complete PCBAs. However, I will present measurement data and recordings to prove the qualities of the circuits. Nevertheless, I hope you will find the content informative and inspiring.
Circuit analysis
The Schoeps/Dorsey transformerless circuit: this is by far the most popular transformerless phantom-powered impedance transformer circuit used in condenser microphones. There are many incarnations of this circuit around, with only minor differences. Is there anything that can be improved on this circuit? You bet! And I don’t mean replacing some capacitors and then hoping for Magic to happen. Read more here.
KM84 style charge amplifier circuit: admittedly, I have not spent too much time on this circuit yet. Something for the future.
Small Diaphragm Condenser mics
I have acquired several SDCs which I considered interesting modification subjects. These include:
T.bone SC140: this microphone is generally credited for its good value for money and versatility, which makes it a good starting point for further improvements. The SC140 comes with Cardioid and Omni capsules and has a switchable high-pass filter and pad circuit. Kind of a Swiss knife microphone. I’d like to make this microphone as transparent as possible with low-distortion circuits. But I also want to extend the versatility of this microphone by adding jumper-selectable top-end and bottom-end shelving EQs. January 2023 update: the narrow mic tube, the acquisition of the Takstar CM-60 and CM-63 mics made, and because I could not find alternative third-party capsules, I decided to put this project on the back burner. Or maybe I’ll decide to not modify it at all.
Gefell MV691/692 with M70 cardioid capsule: when I bought some studio gear several years ago, my son was delighted to find a vintage Gefell M70 capsule on an otherwise useless HH715 wireless microphone. Curious as we were about how this famous capsule with nickel diaphragm would sound, I then wanted to complement the M70 with an MV692 preamp. I was lucky to get one for a reasonable price, and we could start recording. On acoustical guitar, we appreciated the sound of this microphone so much that we decided to keep it. And I decided to acquire another two of them for modifications and direct comparison with an unmodified MV692/M70. My plan is to replace the rather crappy PCBA with old-fashioned, noisy electronics with something completely new. And at the same time, make them P48 compatible. I intend to try three different circuits: transformerless, with the stock transformer, and with a modern, high-quality Lundahl transformer.
AKG P170: The AKG P170 was chosen just because it is a popular budget SDCs from one of the major brands. AFAIK, this microphone is made by Takstar. It has well-designed and well-built electronics and is at a higher level than many other low-cost microphones.
MXL 603S and MXL 991: these are popular microphones among modders, so I decided to add these to the list as well. The 603S is probably popular because of the KM84 style capsule. At the time of writing, I had only acquired the 991, which might have a different capsule compared to the 603S. But I guess that their electronic circuits are quite similar, if not identical. January 2023 update: the crappy build quality and the acquisition of the allegedly much better and more versatile Takstar CM-60 and CM-63 mics made me decide to put this project on the back burner.
Takstar CM-60 and CM-63: As I mentioned above with the AKG P170, the build quality of the Takstar microphones is exceptionally good. And they are very cheap, making them attractive modding vehicles. 3U Audio sells three different capsules that allegedly sound very good and that will fit on the thread of these microphones. The CM-63 features a pad and HPF switch, which, together with the variety of available capsules, could make this an almost ideal Swiss-knife SDC.
The Schoeps-style electronics are probably very neutral-sounding. The idea I have regarding the electronics is to experiment with transformer-coupled circuits that might add some character.
Behringer B-5 and C-2: just like the MXL 603S and 991, these are popular budget SDCs, so from this point of view, they are perfect modding candidates. Actually, the B-5 was the first microphone I modded. However, after comparing it with the SC140, I lost interest in further developing electronics for the B-5. The frequency response was not as flat as the SC140, the smaller PCB limited design freedom and the combined pad/high-pass filter switch is less versatile than the separated switches of the SC140. I found the C-2 extremely difficult to take apart, so this one fell off too.
The t.bone EM 700: a popular, cheap electret SDC microphone from Thomann that is easy to modify. I want to try other capsules from e.g. Aliexpress or Primo in this microphone. The capsule seems quite similar, if not identical to the Behriger C-2. However, the EM 700 has switches for a pad and HPF, making it more versatile than the Behringer C-2.
Large Diaphragm Condenser mics
Although I first want to modify some SDCs and LDCs will come later, I already acquired some LDCs which I could not resist buying.
Behringer B-2 Pro (old version): The first edition of the Behringer B-2 Pro, the one with the striped Behringer “Ear logo”, is a popular modification candidate when you want to try different capsule types. The reason for this is the detachable head, which is rather unique and which the newer B-2 Pro does not have.
The t.bone SC400: I was just curious what one could expect from an LDC of less than €50. Even if it sounds disappointing, it still makes a cheap donor body for a new capsule and electronics.
AKG P120: For the same reason I chose the AKG P170, I chose this LDC.
Measurement Equipment
DIY Audio Analyzer: Every DIY audio enthusiast dreams of one day owning an Audio Precision or Rohde & Schwarz audio analyzer. But only very few can afford such an instrument. I decided to build one myself around a Behringer UMC202HD Audio Interface, a Home Theatre PC, and self-made front-end electronics. This instrument, or at the very least a soundcard with measurement software, is a true must-have if you want to do any serious microphone modding and building. When used properly, it will probably detect more flaws than your ears will ever be able to detect. It does not make listening tests obsolete, but it’s a great help in quantifying the qualities of your microphone builds, instead of just describing the qualities in subjective terms, which may mean something completely different for other people.