After modding a number of cheap mics, some random observations may or may not help would-be modders.

Firstly, modding is far easier and cheaper than trying to build a microphone body yourself. For the hobbyist with a home metal shop, building the body may be the best part of the job, but for the amateur who may only have an electric drill and a set of files, making a mic chassis from pipe and stuff from Home Depot is near impossible. Cheap mics with decent bodies mass produced in Asia are available online and in music stores for anywhere from $15 to $50. You can’t buy the raw metal for a couple of mics at that price. They may even include shock mounts.

Some of the cheap mics are surprisingly good, and often can be improved considerably with a few inexpensive circuit changes. The major improvement in most of these, however, is a better capsule. Capsules aren’t as cheap as resistors and capacitors, but they are where the rubber meets the road, and there’s no electrical magic that can replace what a capsule didn’t capture. If you want a professional studio quality mic, figure on spending most of your budget here, $100 and up. There are some less expensive options, some better grade electrets, some cheaper large diaphragm capsules, but most of them aren’t in the same class as the big name studio mics. Beginning at around $100, DIY suppliers stock higher quality Chinese capsules which rival those used by the major US and European brands.

The most popular low cost mic circuit by far is based on the Schoeps CMC-5 “Colette” series introduced in the early 1970s. The circuit is cleverly designed with each part typically performing more than one function, and while it is somewhat tolerant of changes, performance usually suffers when the balance is disturbed. Some inexpensive Chinese mics have left out parts and most have used cheap parts to meet the low price point. Replacing capacitors and transistors with selected low noise types really can have measurable effects, but won’t generally make a “day and night” difference in the sound. Changes from the original design should be carefully thought through.

Other mic circuits which can be reasonably built by hobbyists are the early Neumann U-87a and the KM-84, but they require an output transformer, which is either a cheap “shot in the dark” purchase, or expensive if you buy from a name boutique supplier. You could also wind your own, but that’s akin to building your own capsule, something that requires years of study.

Fiddling with mics has reminded me that the closer a component is to the beginning of the chain, the more it influences the performance. In a Schoeps impedance converter ( it’s not an amplifier - it has no voltage gain) the input capacitor and FET are the most important. The coupling caps between FET and PNP outputs are next. The PNP transistors have little influence except on the output impedance of the mic. Higher beta (current gain) equals lower impedance.

As manufacturers have modernized from a factory of girls with soldering irons building circuit boards to robot assembled surface mount boards, the days of component swapping at the kitchen table have disappeared. Several people have filled the gap by offering kits of parts with new circuit boards for the DIY enthusiast. You can buy an upgrade kit now for almost any common Chinese mic from the $15 electret, to the MXL 990 and 991, to the low end tube mics.

The most important thing is to experiment. There’s a lot of information out on the internet, and some of it is even true and useful. But gurus make mistakes or educated guesses which turn out not to work in the real world. I’ve had a number of assumptions disproved by testing, such as the gain of a charge amp, which I assumed was the ratio of capsule capacitance to feedback capacitance. T’aint so. I’ll explain in another post.

I’ll add thoughts here as they occur to me.