Differences between this two kind of input stages??? - diyAudio
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Old 31st October 2007, 02:15 AM   #1
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Arrow Differences between this two kind of input stages???

Any big differences between this two???
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Old 31st October 2007, 12:28 PM   #2
ilimzn is offline ilimzn  Croatia
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Well, yes, your diagram B is not drawn correctly (wrong polarity of input Qs makes for their B-E junctions being in series across the power supply).
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Old 1st November 2007, 01:18 AM   #3
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VERY VERY SORRY !

Making a big mistake of the schematic.Here is the corrected one:
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Old 1st November 2007, 02:11 AM   #4
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I don't think either on them will work very well. The circuit is too dependent on the Vbe drops of the various transistors. It could be that with a zero input the transistor currents will be too large and the devices overheat and burn up.
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Old 2nd November 2007, 01:44 AM   #5
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I don't think either on them will work very well. The circuit is too dependent on the Vbe drops of the various transistors. It could be that with a zero input the transistor currents will be too large and the devices overheat and burn up.
If so,why certain manufacturer still using them,such as Accuphase???
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Old 2nd November 2007, 04:37 AM   #6
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I can't see why both shouldn't work, however it must be in a very low Current mode for both circuits.
Do you have a scan of actual the Accuphace circuit?
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Old 2nd November 2007, 02:08 PM   #7
wg_ski is offline wg_ski  United States
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Default current-mode feedback stage

It will work, but you really need all 4 transistors inside the same package or it can go into thermal runaway. Or, more correctly, force the VAS that follows it to go into runaway. Transistor arrays are a solution, but what really works is the old LH0002 current buffer. The one in the "N" package is required, because the collectors of the second pair are brought out individually rather than tied to the first stage emitters. It really wasn't meant to be used for that, but it can. Elantec used to make a whole family of current-mode op amps with both input and output stages based on that topology.
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