Use of unused windings on OPT

Design and use of the various types.
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Mrdean
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Joined: Sun Jul 19, 2020 7:12 pm

Use of unused windings on OPT

Post by Mrdean »

HI. I have 300B SET amps using Magnequest OPT (hey, I bought them 26 years ago) and right now I only use the 8 ohm taps. I want to experiment with supertweeters, and was wondering if I can use the 16 ohm taps with the 8 ohm taps as “grounds�- or negative returns. Will this cause Be some weird problems?
dave slagle
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Post by dave slagle »

How that works will depend on the how the drivers / crossover is wired.

It is unclear what you are trying to do but if you consider the 8Ω tap as ground and take signals from the 16Ω tap it will effectively be an 83Ω winding.

So... if your tweeter were 16Ω and needed around 16dB of attenuation you could put a 67Ω resistor in series with it and use the 16Ω tap with the 8Ω tap grounded. Then the original ground - 8Ω tap would still have the 8Ω impedance for the woofer.

Two important things to remember if you try this:

1: the phase of one of the drivers will need to be reversed.
2: there is no guarantee of how the transformer will behave in the frequency domain with this connection method so it would be wise to first do some frequency sweeps to confirm acceptable measured response.

dave
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