I think there might be a few things to add to the previous discussion about transformer versus transformerless mics. Since we make both kinds, and it took quite some years to find suitable components, maybe I should share some of the things we found out in this process. In my own recording I use both types and I think I know the causes of the various other problems that people report with each type of design. As with everything in audio transducers, you have a choice of tradeoffs to make.
Some of the most revered microphones have some of the most awful transformers, and people seem to like them just the same. I am specifically thinking of the Haufe T14/1 in the AKG C12, C24, Telefunken ELA-M 251 series, and so on. These are almost as bad as the Beyer peanut transformers at high levels and low frequencies. Like the Beyers, however, they can work just fine when you design the circuit around them correctly (which obviously has been done in a lot of equipment that people like). There are some choices that designers have used to get around the problems, that I don't think anyone in this thread has noticed.
First, the output transformer in a microphone is almost always a step-down transformer, with voltage ratios of 4:1 to 10:1. This allows the amount of power being transferred through the core, and thus the distortion at low frequencies, to be greatly reduced. The C12's T14/1 is normally wired for a 10:1 ratio. This gives 1/10 the voltage (and ten times the current) to drive the cable. This avoids a lot of problems! The transformer in the Neumann KM80 series has a 7:1 ratio. The transformer we use in the C609 is of a more modern design (amorphous tape core from Lundahl in Sweden, rather than stacked nickel or steel alloy plates) than either of these, so we can get away with a 4:1 ratio, preserving a fairly high output level. One thing to try with a transformer output mic that seems to have poor bass handling is to wire it for 50 ohm output instead of 200. This puts the output windings in parallel rather than in series and reduces the amount of work that it has to do (and the voltage output it produces). The sound is entirely different in most cases. Sorry, you can't do that with the C609, we wanted to nail the sound to a particular characteristic and that's what you get.
David Satz's comment that transformer-based mics are unable to handle high signal levels, is simply not correct. Our e22S microphone, which is our C609 body with a KA22S capsule, was designed in cooperation with Steve Albini. He's very picky about distortion and coloration, and was looking for a spot mic for drums. This is now the one mic that he uses on every session -- for drums, mostly -- and it has a transformer output. It played much better with his collection of preamps than the transformerless C606A. For what it's worth, this transformer will produce 0 dBm (0.78 volts) into a typical mic preamp at 20 Hz with about 1% THD. In the e22S that's about 142 dB SPL.
Another critical thing, that's responsible for much of the bad sound reported by people using transformerless mics with older preamps, is that the actual output impedance of transformerless mics is much lower (on the order of 20-40 ohms, versus several hundred ohms for most transformer mics). Many mic preamps are very sensitive to source impedance. Transformer-based mic preamps, particularly older ones, often have tuning components on the secondary of the transformer to make it behave properly with a given source impedance. Lowering this by a factor of 10 or so throws all those design choices out the window. Some designs even have negative feedback applied to the input transformer windings, in an effort to reduce the distortion of the whole input stage. We are used to thinking of loading in terms of output transformers, but it's the same here -- any negative feedback into the input transformer sees the mic's impedance as a load. Neumann addressed this in some of their designs by putting resistors in series with the output -- 50 ohms each side for the TLM170 for instance.
*If* you are using modern transformerless preamps that can handle very low source impedances, it's possible to get much improved distortion and phase response performance with transformerless mics. Not all transformerless mics, of course, but it is possible. But if your sound recipe includes the characteristics of a certain piece of gear, it might not play well with transformerless mics.
The effect of the mic pre on the microphone is also generally ignored. Often, the dominant impedance is the resistance of the phantom power resistors. But depending on the input circuit, the mic cam see a very different load from one preamp to the next. In transformerless mics this is generally not an issue but with transformer output mics, different loading can make a big difference.
Now as a designer and manufacturer of microphones, I run into another whole range of choices, that also get omitted from any of these discussions. I don't modify other companies' mics, we try to make the very best we can given the technology of today. Some aspects of this technology are an improvement over the old style, others are not. 40 years ago one could buy quiet tubes to use in microphones; today you can't. 30 years ago it was impossible to get quiet, linear JFETs; now they are cheap, if you can get the factory to pay attention. For a while it looked like we would get low noise MOSFET-like devices that behaved a little more like tubes, but it never happened (good idea, no funding). Today we can use circuit topologies that would be impractical with tubes or early FETs. Every design is a compromise, and the parameters you choose determine what kind of compromise it is. People judge microphones without the knowledge of these choices, and tend to make comparisons based on what they can see -- transformer or not -- regardless of the other implications of this choice. For instance, a transformerless design typically produces a higher output level. This means I can choose a less sensitive capsule for a given perceived output level, which might sound a lot better in some other way.
So please, can we avoid the simple comparison between transformer and transformerless mics as if they were two of a kind? Each mic has its own personality, and within this personality there are a lot of different aspects. Contrary to Georg Neumann's wisdom, the electronics do greatly affect the sound of the pickup -- particularly, as David Satz points out, at high signal levels. There are also the issues of how a given design handles high RF noise environments, cable lengths and interaction with various preamps. Remember that your own experiences are exactly what they are, and will probably help you to make better choices in the next session. But if you want to remain open to still better choices in the future, it would be a good idea to skip the connection between the design differences that you can only know a little bit about, and the performance differences that you can hear.
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Topic: What sounds better: transfomers or transformerless? (Read 44702 times)