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Vox AC15 EF86 with one power tube
Vox AC15 EF86 with one power tube
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Old 19th July 2019, 03:21 AM   #81
PRR is offline PRR  United States
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You could patent that.
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Old 20th July 2019, 12:26 AM   #82
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by PRR View Post
You could patent that.
I don't think I could even afford the $1000 - $2000 preliminary "Patentability Search and Opinion": Patent Fees - Canadian Patent Lawyer and Trademark Agent Intellectual Property and Business Law Commercial Contracts and Litigation

Thanks for the implied compliment, anyway!

But how did Kevin O'Connor implement his power scaling solution? Did he come up with the same circuit idea, I wonder? Or did he find some other way to implement it?


-Gnobuddy
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Old 20th July 2019, 01:01 AM   #83
stephen_keller is offline stephen_keller  United States
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Originally Posted by Gnobuddy View Post
But how did Kevin O'Connor implement his power scaling solution? Did he come up with the same circuit idea, I wonder?
Given that O'Conner's fixed-bias kit contains three power and a half-dozen small-signal transistors, I reckon he does something a little different.

Stph
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Old 20th July 2019, 01:19 AM   #84
Bigun is offline Bigun  Canada
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Vox AC15 EF86 with one power tube
i’m not convinced that a fancy circuit is worth the trouble given that our ears change their sensitivity to different volume levels I think it’s chasing ghosts plus the speaker cone will behave differently at lower and higher powers

I think the simpler system is adequate
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Old 20th July 2019, 02:24 AM   #85
stephen_keller is offline stephen_keller  United States
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I would agree. I was not suggesting Kevin O'Conner's circuit was better, just different.
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Old 20th July 2019, 04:12 AM   #86
PRR is offline PRR  United States
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> I don't think I could even afford

I actually don't think you could ever recover the *postage* for a patent application. (Except it may be all on-line now?) Audio is tough. Either you write I Claims so general they appear to cover too much (which should be rejected), or so narrowly that any clever monkey could figure a different way to do the same thing.

And it is all on YOU to defend your patent against infringers.

But I do think your circuit is sufficiently useful and novel in this specific application to be patentable, maybe. Which may only be a clue to some evil copycat to swap a few parts around. Or, noting you are not a Big Company, simply copy knowing their lawyers are bigger than any you could fund.

I have doubts that "working to the knee" is such an exact thing that compensation will really change the user experience, but only doubts, not conviction.
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Old 20th July 2019, 11:14 PM   #87
Gnobuddy is offline Gnobuddy  Canada
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...swap a few parts around.
I'll save them the trouble. Here is an improved version, achieved by swapping the position of the voltage reference. This time there is no interaction at all between the slope of the Vg2 line and the offset (the amount by which Vg2 is less than Va).

As the three Vg2 lines show, one pot (R2+R4) lets you make Vg2 track Va exactly, or not at all, or anywhere in between those two extremes.

If V1 is an adjustable voltage reference, twiddling the knob that changes V1 will adjust the offset between Va and Vg2 without changing their relative tracking. Using one zener diode and one transistor wired as a Vbe multiplier would be easy and should do the trick.

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I have doubts that "working to the knee" is such an exact thing that compensation will really change the user experience, but only doubts, not conviction.
I have no evidence one way or the other right now. I'd have to build it and try it out to find out.
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Originally Posted by Bigun View Post
our ears change their sensitivity to different volume levels
They do indeed, but IMO that is a separate issue, and suggests that the inclusion of a loudness control or switchable loudness compensation EQ in a power-scaled guitar amp might be a good thing.

I find I have to turn down both bass and treble when I move my Katana 50 from my living room (where it's set to 0.5W) to a jam or stage situation (where it's set to 25W or 50W). I'd like a single loudness knob instead, it would be less fiddly.

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Originally Posted by Bigun View Post
I think the simpler system is adequate

And it's certainly possible that you're right, but AFAIK you have no data either, which means you, I, and PRR are all merely guessing at this point. None of us have any data to back up our guesses.

I've fiddled with tweaking the screen voltage in small signal pentodes operating in class A, and to my ears and oscilloscope, that causes tremendous changes in overdriven timbre and output waveform. I've also fiddled with bigger-value screen resistors in my little 2W push-pull pentode amp, and that too changed the overdriven timbre dramatically. That's why I'm pretty convinced that twiddling the screen voltage can indeed make dramatic differences to the sound of a guitar amp. The logical corollary is that you have to get the screen voltage just right if you want to keep the sound consistent while power scaling, but as mentioned, I have no data on that at the moment. Just a hunch.

But that's the beautiful thing about DIY. You can choose to build exactly what you want, to please your own personal tastes, and not have to worry about what will sell best to the hoi polloi.


-Gnobuddy
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Last edited by Gnobuddy; 20th July 2019 at 11:16 PM. Reason: Fix a typo
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