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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 28th December 2017, 01:05 AM   #1
hellokitty123 is offline hellokitty123  United States
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Default Tubelab Solid State OPT design

I was looking around for inspiration for my next amplifier build and I decided to skim through various tubecad and tubelab articles for ideas.

I haven't checked the Tubelab site in a couple of years but it seems it still hasn't been updated since I last checked . Not quite sure what he's been up to lately.
I did come across an article I couldn't understand a few years ago but now I can comprehend conceptually at least, that being the solid state transformer idea of his Solid State OPT | Tubelab.

My understanding is that it is supposed to splice up the amplitude of the signal from the output triode at a constant frequency outside the audio-band and then transfer it via a small transformer and do a reverse splice.

I haven't done any extensive dabbling in theory involving high frequency switching circuits so I find myself a bit confused by the schematic he posted, it looks as if that circuit would act as a high frequency source follower load to the triode.
How exactly is it meant to function?
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Old 29th December 2017, 11:36 AM   #2
hellokitty123 is offline hellokitty123  United States
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Anyone there? (echo echo echo)
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Old 30th December 2017, 12:41 AM   #3
Tubelab_com is offline Tubelab_com  United States
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Anyone there? (echo echo echo)
Here, but out of town on a cell phone browser.

The circuit acts as a chopper, or modulator to impose the audio on a carrier signal at about 200 KHz. This creates an AM signal with a suppressed 200 KHz carrier. The resulting signal occupies the frequency band from 180 KHz to 220 KHz with about 40 Hz missing out of the middle, assuming 20 Hz to 20 KHz audio. This is similar in action to a double sideband radio transmitter.

I experimented with this concept about 10 years ago and never got it to work right. I believe that the recovery circuit has too much resistive loss which caused some distortion at low volumes. I have not revisited this idea since then, and don't plan to any time soon.
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Old 30th December 2017, 12:35 PM   #4
hellokitty123 is offline hellokitty123  United States
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Why did you use P channel fets on the top? It seems like it would make the timing easier using all N channel.
Paralelling the output transistors and/or using very low rdson transistors should solve the resistive loss issue if that is indeed the problem.
Although of course I'm not sure how that would pan out at 200khz if they are unmatched.
Maybe increase the frequency and increase the dead time to compensate.
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