Bottlehead Forum
General Category => Technical topics => Topic started by: Deke609 on October 12, 2020, 03:48:11 PM
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@PJ: I just came across the following statement by 6A3sUMMER on diyAudio that alarmed me:
"If the speaker impedance is high at the same frequency as the resonance of the combination of choke, cap, primary, the voltage can go higher than 2X B+ volts."
Here is a link to his post: https://www.diyaudio.com/forums/tubes-valves/361496-parafeed-se-300b-amp-cheap-2.html#post6373792 (https://www.diyaudio.com/forums/tubes-valves/361496-parafeed-se-300b-amp-cheap-2.html#post6373792)
Should I or others be worried about this? I use my parafeed amps with 200R headphones connected to nominal 16R, 32R or 64R secondaries, often without a parallel resistor load to hit the nominal secondary impedance.
cheers and MTIA, Derek
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If you play a 60Hz tone through your amp into your heapdhones, at what AC voltage on the speaker terminals are your headphones painful to listen to?
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1) That resonance is about 8Hz in the Kaiju, very unlikely to match a speaker resonance.
2) This happens with pentodes, not with triodes.
3) The choke/PF cap resonance is well-damped by real-world chokes and/or OPTs
In 20 years of making and selling SET parafeed amps at ~ 400volts power using 600v-rated caps, this issue has never come up. I added that in case you are like me, and don't trust the theory until it's confirmed by experience.
:^)
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Awesome. Many thanks.
cheers, Derek