75µS to 50uS Pre-Emp

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folkeu08
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75µS to 50uS Pre-Emp

Post by folkeu08 » Sat Oct 23, 2021 9:47 pm

Hi,
What change to adapt this pre-emp 75µS to 50µS :

Image

Thanks

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reverend
no manz can test innit
no manz can test innit
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Re: 75µS to 50uS Pre-Emp

Post by reverend » Mon Oct 25, 2021 1:56 pm

cir_rfv007.jpg
In theory (though I haven't tested this), changing the 330pF capacitors circled in red with 220pF ones should do the job.

Rev
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Albert H
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Re: 75µS to 50uS Pre-Emp

Post by Albert H » Mon Oct 25, 2021 10:40 pm

The Rev is exactly right. Use accurate 220pF capacitors (not cheap ceramic ones), and be careful in setting up the HF clipper - it's easy to overdo it! It's also worth using slightly lower frequency filters (16 kHz is getting a bit too close to the 19 kHz stereo pilot). My filters use "gyrator" networks (to emulate inductors), and go over like a cliff at 15.15 kHz. By 19 kHz, they're around 74 dB down.
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