I just finished the DD33 center gear replacement, and the sound coming out of it is pretty good. But then the question came up, could I possibly swap the permalloy head of the DD33 with a better amorphous head of another walkman, like the D3? It seems the model number differs by one letter. DD33: TC-D3:
From what I see in the schematics there is a difference in the compensation circuit in parallel with the head: - WM-DD33 uses C=1000pF and R=47k; - WM-D3 uses C=680pF and R=27K; What I would do is measure the resistance and inductance of the 2 heads. If they're pretty much the same, you can interchange without changing that compensation circuit. That RC circuit, combined with the inductance of the head is what will determine the treble response. Typical values on 35711 head are: - 100mH of inductance at 1kHz; - 260 ohms resistance at DC/low frequency; What are you expecting to see exactly by replacing the head ? Apart from less wear on the amorphous head.
Hypotetically it is possible, but it my opinion not worth it unless you already have the replacement one. The original one is more than good enough in my opinion and there are other limitations, like some capacitor values limiting the bass response and the relatively high noise floor of the BA3304F preamp. If you want to do something, I suggest starting with this: https://fixyouraudio.com/product/sony-wm-dd33-capacitor-upgrade-kit/ This will make an audible difference in the frequency response, unlike some tiny things noticed after replacing head which can just be placebo effect.
