Heider 312 vs 312 Platinum

Hmm. I think the 312’s might be a little more refined on the top? Not quite as punchy. Really can’t go wrong with the 312’s.

The Heider is a matching input impedance instead of the typical bridging input impedance, so the loading on the mic signal will do different things to different mics. Actual input Z is 167 or 300 (or is it 334?) ohms as opposed to typical 1500+, or even well above 10K with things like the AEA ribbon preamps.  Even with the pad on, it's 765 ohms input.  The sort of change you expect when moving from a dynamic to a condenser on the same source may vary more greatly than on a typical preamp because of the loading difference. The heavier loading will to varying degrees lower the output level of the mics, so it's possible if recording very quiet sounds at high gains that another preamp type would win the S/N contest; there you might prefer the standard 312. With dynamic mics a 6 dB/oct LPF at some frequency is created with matching loading, so you may find a more mid-centric air-lean result with some mics. Steve Dove writes about matching loads with microphones in the Handbook for Sound Engineers : The New Audio Cyclopedia.

Now, the obvious major difference is the Heider is structured like a VP28, more gain stages, extra transformer.  

Both of those use the different input transformer which I believe has some nickel content, unlike the standard line.  Less transformer distortion at both low and high signal levels.  

"Yeah, but what's it sound like?"   For you to decide.....