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Old 9th October 2012, 07:35 AM   #1271
sonnya is offline sonnya  Denmark
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IGBT with mosfet only!? Try add gate stoppers.
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Old 9th October 2012, 07:48 AM   #1272
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No problems in reality, 100 kHz square waves sharp with no ringing on 4 ohm resistor.
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Old 9th October 2012, 11:13 AM   #1273
Jay is offline Jay  Indonesia
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With the driving topology, I think the BIGBT with HEXFET+BJT is a logical contender for competition with all-BJT output. But for HEXFET+LATFET, I prefer BJT driving LATFET because in the original circuit, the HEXFET is not really enjoying much current.

For very high power low distortion SSA LATFET, my plan has been to drive the LATFET with emitter driver (2N5401 or MPSA92), with cascoded VAS or non-cascoded VAS. That is what I think is more feasible to create the best sound at high power.
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Old 9th October 2012, 01:12 PM   #1274
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Quote:
Originally Posted by Lazy Cat View Post
At which frequency?
6/ 10Mhz depending of comps or gate stoppers. Gates stoppers or not. But just a quick run, adding it in a existing schematic. It has not worked out of the virtual box. Murphy was there.
I need to look at this as stand alone to explore it more deeply.
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No problems in reality, 100 kHz square waves sharp with no ringing on 4 ohm resistor.
Did-you tested-it in real (I'm exited :-)? How do you feel -it?
HEXFET-> LATFETs ?
Is-it faster than without driver ?
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Last edited by Esperado; 9th October 2012 at 01:19 PM.
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Old 10th October 2012, 02:31 AM   #1275
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Some times with LTSpice (i don't like this beast), and i managed to make-it stable. But at the price of increased compensation, and, so reduced bandwidth.
With no reduced distortion, no visible advantage, so far, and on a pure virtual point of view.
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Old 10th October 2012, 04:45 AM   #1276
Jay is offline Jay  Indonesia
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Some times with LTSpice (i don't like this beast), and i managed to make-it stable.
I like that it exaggerates problems. When it is not stable in simulation, it may work in practice. If it is stable in simulation, it will usually work in practice.
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Old 10th October 2012, 02:39 PM   #1277
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I thing it was definitively a bad idea.
MOSFET driving complementary BJT can have a x10 FT than the BJT, so it do not add a pole.
We are not in this situation with MOSFET driving MOSFETs.
This added pole divide by 2 the Open loop bandwidth where we wanted the reduced Drain/gate capacitance to increase-it :-(
The added non linear GMs add distortion.
We do not need any current gain at low frequencies, where power MOSFETs are near infinite.
The low transconductance introduce a peak to peak of -10v on each rail with my parts, as L.C said..
I feel stupid, as a simple reasoning was able to bring-me to those conclusions. I was upset by the aesthetic symmetry of the schematic and by the disparity of the N and P gates capacitances of the power units.

Nice looking schematic, poor results.
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Old 15th October 2012, 03:29 AM   #1278
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The low transconductance introduce a peak to peak of -10v on each rail with my parts, as L.C said...
..Due to the power FETS, not the MOS driver, to be precise. No difference with or without.
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Old 24th October 2012, 08:15 AM   #1279
Harry3 is offline Harry3  Australia
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Any ideas from the amp gurus on this thread on how to increase the number of output devices on the TSSA circuit on page 16, post 159 as my load will be 4 ohms or less?
Also I am not sure what typology to use on the output after reading Christophe’s informative posts.
Perhaps I should be using the SSA Low Impedance circuit from the Simple Symetrical Amplifier thread??
Simple Symetrical Amplifier
Comments are welcomed as I am not an expert.
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Old 24th October 2012, 09:19 PM   #1280
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Any ideas from the amp gurus on this thread on how to increase the number of output devices on the TSSA circuit on page 16, post 159 as my load will be 4 ohms or less?
You can always do it like this or to be moderate and reduce the number of outputs a bit.
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