As a minor comment / suggestion on the source follower design shown in W3DSP's earlier post (attached schematic):
As shown, the back-to-back capacitors C3 and C4 appear to have been selected to enable this circuit to feed a very low load impedance, while blocking DC of either polarity. For example, if the load impedance were 100 ohms, the 3dB rolloff frequency associated with C3 and C4 in series (50uF net capacitance) would be 31Hz.
On the other hand, not being a fan of using electrolytic capacitors back-to-back in this way (for a variety of reasons... particularly in this kind of application), and taking into account that in many (but not all) applications, the load impedance that this circuit will look into will be 10k ohms or more... I suggest that C3 and C4 be replaced by a single 1uF or a 0.47UF non-polar capacitor.
In cases where this circuit will be feeding a 600 ohm load (a microphone input specified to have a 600 ohm input impedance), I suggest using a small 10,000 ohm: 600ohm matching transformer (the impedance values are not critical) between the output of this circuit and the 600ohm load.
As an aside, the Thevenin equivalent circuit of a typical vintage D104 microphone cartridge is a voltage source in series with a .001uF capacitor*. Many people are not familiar with the properties of a signal source that behaves like a voltage source in series with a capacitor (not a resistor).
To keep the .001uF series capacitance, that is intrinsic to the microphone, from rolling off low frequencies (down to a maximum 3dB low cut frequency of 30Hz, for example), it is necessary that the resistive load that the microphone is looking into have an impedance that is greater than the impedance of this .001uF capacitor at 30Hz (in this example). The impedance of the .001uF capacitor at 30Hz is 5.3M ohms.
That is why one needs to have a 5M ohm or larger resistive load on the microphone. [There are other ways to deal with this requirement... but using a 5M ohm or larger resistive load works fine]
If one uses a 1M ohm resistive load (like the grid leak resistor used in the microphone preamplfier in many boat anchor transmitters), the low cut 3dB roll off frequency will be 159Hz.
*I have measured newer D-104 cartridges that have a significantly higher equivalent series capacitance (around 0.01uF). With those cartridges, the minimum load resistance value will be lower. With 0.01uF of equivalent series capacitance, a 500k ohm (or higher) value of load resistance should be fine ... to achieve a low cut 3dB rolloff frequency of 30Hz.
Stu
As Joe said it is a simple matter to match a D104 to any rig. I use the attached circuit to drive all of my HF rigs, low or high impedance and it works very well. This is built into the base of the microphone. Most all modern rigs supply +8V at the mic connector. If not you can create it externally or use a 9V battery if you have contacts in the mic to disconnect it with PTT.
I built a mic switch box to switch between my various rigs that switches power also and when older rigs are connected I supply an external 8V. When I restored my Ranger I changed the rear panel mic connector to an 8 pin wired Kenwood standard and added an 8 volt regulator in the Ranger to supply the voltage to the mic.
