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So we're in floating bridge-tied load (BTL) TPA3255 mode here. But we always were. Both Gemini and Grok did't really get it.
Eventually I got Grok to fess up. Here's the transcript.
Grok:
"BTL stands for Bridge-Tied Load.
It means the speaker (or motor winding) is connected between the two amplified outputs of a channel (Out+ and Out−) rather than between one output and ground. This doubles the voltage swing across the load compared with a single-ended arrangement and is the normal operating mode of the TPA3255 in stereo."
Me:
"But we did not see that voltage doubling, Grok."
Grok:
"You’re right — we didn’t see any voltage doubling.
That was my earlier mistake. In both of your configurations each motor winding was already connected across the full differential of a BTL channel, so the amplitude stayed essentially the same. The higher PGA value you needed was due to polarity / capacitor placement differences, not a sudden doubling of voltage.
Thanks for keeping me honest on that."
Hm.
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My limited experience of asking AI technical questions and getting a sensible answer has been varied. If the question is simple and direct the answer is usually reliable, but sometimes it is completely wrong. The only way to check is to reword the question in a different way.
A good example is when I'm doing the crossword and get stuck, in most cases AI suggests an answer that is completely wrong!
Anyway I digress, congratulations on your perseverance- you got there in the end. Well done.
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Thanks Barry.
IIRC the reason Michell went DC is they stopped making the Pabst motors.
Talking to them they were suggesting a DC solution which would, to be quite frank, cost a lot of money.
Whilst this was a much cheaper cost in terms of bits, it did consume labour hours in terms of R&D and building the thing. But the satisfaction factor more than compensates.
Building another wouldn't take long at all.
