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Old 10th March 2010, 08:49 AM   #121
khalsa is offline khalsa  India
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hi apex i want protection pcb layout and circuit for mosfet amp plz send me khalsaaudiocenter@yahoo.com
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Old 10th March 2010, 12:11 PM   #122
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Originally Posted by khalsa View Post
hi apex i want protection pcb layout and circuit for mosfet amp plz send me khalsaaudiocenter@yahoo.com
PSU for DIY with soft-start and DC protect. Transformer 1kVA sec: 2x55V 8A + 24V 1A.
PCB size: 200x75mm
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Old 10th March 2010, 12:34 PM   #123
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Originally Posted by homemodder View Post
Could you show schematic as a jpg image or other format that other users not having tina could see, Im interested in seeing this self biased cascoded.
You may look here Current Feedback IC input in a power amp
This thread concerns a design that is is embedding the self-biased cascode VAS. There are schematics JPGs. However I advise you to download and run Tina 7 Texas Instruments.
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Old 10th March 2010, 03:50 PM   #124
khalsa is offline khalsa  India
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hi apex thanks for send the power suplly pcb layout but i want the layout of your 20 no fourm kindly send me
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Old 10th March 2010, 04:48 PM   #125
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Originally Posted by homemodder View Post
Could you show schematic as a jpg image or other format that other users not having tina could see, Im interested in seeing this self biased cascoded.

I'm satisfied that simply adding 100uF to the original design pushes full output
single sine bandwidth to 91KHz, and sufficient slew to do that goes with. I'm
not sure its necessary or desirable to slew wider bandwidth than 96K???

Don't hold your breath, hoping I might translate the cascode variant to LTSpice.
Its a whole lot of extra part spaghetti, else requiring a new PCB layout. And I
simply feel it may be overkill fix for reasonable design compromises that aren't
causing any actual problems.
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Old 10th March 2010, 04:58 PM   #126
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I was planning to transfer the Tina circuit to LTSpice. I'll post it if / when I get around to it !
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Old 10th March 2010, 05:05 PM   #127
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Originally Posted by kenpeter View Post
I'm satisfied that simply adding 100uF to the original design pushes full output
single sine bandwidth to 91KHz, and sufficient slew to do that goes with. I'm
not sure its necessary or desirable to slew wider bandwidth than 96K???

Don't hold your breath, hoping I might translate the cascode variant to LTSpice.
Its a whole lot of extra part spaghetti, else requiring a new PCB layout. And I
simply feel it may be overkill fix for reasonable design compromises that aren't
causing any actual problems.
Ive seen it, I prefer simpler design myself, often I had found myself going off on complicated designs only to end up with a amp that does not sound any better and often worse, than a amp with half the parts.

BTW I did find the apex to oscilate in LTspice, at 20Khz, this is the frequency I always simulate or measure at.
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Old 10th March 2010, 05:11 PM   #128
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Originally Posted by JonHarrison View Post
I was planning to transfer the Tina circuit to LTSpice. I'll post it if / when I get around to it !
You can use mine as a shortcut to get started, if you wish.
Don't take my doubts about needing a cascode to mean you
should have to start the translation over again from scratch.
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Old 10th March 2010, 06:00 PM   #129
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Well, the 91kHz referred to the loop gain transition frequency, i.e. |LG(91kHz)|=1

This does not change with or without the 100F, as I said the whole loop gain curve doesn't change.
Quote:
Originally Posted by kenpeter
I'm satisfied that simply adding 100uF to the original design pushes full output
single sine bandwidth to 91KHz, and sufficient slew to do that goes with. I'm
not sure its necessary or desirable to slew wider bandwidth than 96K???
I don't think it is essentially necessary to have a slew rate greater than needed to follow a sine wave with maximum output amplitude and the highest frequency ever occuring in program material presented to the amp.
But i guess it can be nice to have a good margin for slewrate.

Is that what you mean with "to slew a bandwidth of 96K":
The amp has the slew rate that is needed to reproduce a 96kHz sine wave at full output amplitude?

would be nice to know, because it was a nice, short and efficient way of saying that
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Old 10th March 2010, 06:39 PM   #130
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I tried 2VPP@96K in, and it looked good. No triangles. Just slightly attenuated.
Jumped on your 91KHz figure as the better number without actually re-checking.
I also did not test the circuit quite as close to the limit of clipping as I probably
should have. Thats not (yet) to say the result would have been any different.

I gotta be more careful not to casually throw numbers without stating exactly
how I arrived at them. Or in this case, just fudge factored it, based upon a
few sim runs aimed at determining something else entirely...

At the time of the test, I was obsessing upon output currents and how they
crossed (or didn't) at the higher frequency. As push and pull get phase shifted
away from each other till they don't cross nice (without 100uF cap in place).
Wasn't attempting at that time to scientifically determine actual bandwidth.

As for why 96K instead of 20K for a single sine? Was something one of the
forum gurus (Cordell? or was it Pass?) I don't remember now... Transient
intermodulation when you got 18K and 19K into the amp at the same time.
That somehow that slew rate challenge was like a single sine 96K? I never
checked the truth of that math. It sounded plausible, I went with it.

I should probably just sum two sines, if I wanna test TIM, rather than fake it.

Last edited by kenpeter; 10th March 2010 at 06:48 PM.
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