Ribbons and Impedance -- A clarification

The 1200/300 changes the winding configuration on the input transformer primary, which changes the reflected impedance as seen by the mic. This is the input impedance of the pre, and the load seen by the mic (same same).

Better is subjective.

As your literature noted, dynamic mics (ribbons, moving coil) tend to be more sensitive to changes in the load impedance, than a condenser or any active circuit mic would. So, "use your ears," is the advice, like the great sound you found. Seems like the experts have spoken so I just wanted to add this little tidbit of my own.

The same is true with active/passive instruments and active/passive direct boxes.

Ok, so it's fairly simple in layman's terms.

Matching a load to a source impedance will maximize *power* transfer and minimize reflections. However, it's relatively inefficient and you lose signal level. If something was designed to work best at this load, then we can assume that it's frequency response is also flattest at this load.

Using a load that's higher in numeric value (less loading) results in increased signal level from the source, but the possibility of reflections (probably not an issue at audio frequencies and normal cable lengths). It's more efficient, but it might change the frequency response of the signal from the source in favor of the low frequencies.

Using a load that's lower in numeric value (more loading) results in decreased signal level from the source and a changed frequency response. Lower frequencies take more energy from the driving components to generate and thus tend to fall in amplitude much more quickly than higher frequencies, which is why you have the reduction in lows. Quite inefficient and should result in increased distortion/harmonic generation.

30 ohm dynamic mics, of which there were many. 

The Jensen preamps have a setting for this too, and describe it as such.  

To add to the confusion there are dynamic mics like the SM57 that were introduced when impedance matching was “the thing” so it’s 150 ohm wants to see 150 ohms whereas some want to see 5X their impedance (Beyer for example recommends 1000 ohm impedance for the 88, 201 and 160) whereas others like Audio-Technica ATM250 have an impedance of 600 and want to see 6,000!

I did some messing around with high impedance preamp inputs (30,000) and found, for example, my Beyer M160’s never sounded better but I didn’t like either my 201 or 88 as much as I do through lower impedance pres

SM57 is sort of the Western Electric concept/model, expecting a matched load.  Almost all old multi-input remote mixers (and Altec 1567A's!) are matching input loads.  

As the Broadcast News article points out, the classic tube preamp has much higher input Z in most of the range than what you find in transformerless SS, for different reasons than described in 1957 though, now preamps tend to have load resistances in place to fix the relationship.   So as you say, my ribbons don't sound as good in my Sytek as they do through some pre-1960 tube pre, as the load is much lighter in the majority of the range than the Sytek, the Sytek kills some lows and highs.  If you changed it to a 300 ohm resistive load, it would get very telephon-y.  

The Sytek may be noisier at same gain for a couple reasons too, although that sounds crazy on the surface.   The loading effects on the mic knocks mic level down, requiring more preamp gain, and there's no 'free' transformer gain either.  

Then consider the pre-1960 thing with transformer taps for 30/150/600.  Those are the expected SOURCE impedance to excite the transformer winding for proper transformer response.  Besides the change in gain from varying transformer ratio, you change the loading and EQ outcome of the entire system by 'mismatching' the interface.  That may be bad, that may be good.  You may not actually experience a noticeable gain change, as the loading differences may wash out, and the EQ effect may be so dramatic as to obscure what's left.  

Doug knows his tube gear. The RCA manuals called for “unloaded” input transformer secondaries. This is one big reason why those old passive ribbons really shine with old tube preamps.

This is how I have to use my Altec 639a. It just sounds fuller at 300 ohms.  It’s a 50 ohm mic I think.