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Old 1st June 2004, 05:10 PM   #21
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Could it be because this is current feedback? Just a wild guess.
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Old 1st June 2004, 05:13 PM   #22
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Hint: what is the formula for working out the output V in terms of input V and feedback V?

The effect of feedback is to reduce the open loop gain. The less feedback the less the open loop gain will be reduced. Under what special case do the feedback resistors set the closed loop gain exactly?
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Old 1st June 2004, 05:18 PM   #23
PMA is offline PMA  Europe
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When Aol is infinite.
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Old 1st June 2004, 05:21 PM   #24
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But closed loop gain can never be greater than that estimated by feedback resistors. If yes, then I have to give back my university diploma.
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Old 1st June 2004, 05:39 PM   #25
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Quote:
Originally posted by PMA
But closed loop gain can never be greater than that estimated by feedback resistors. If yes, then I have to give back my university diploma.
You don't need to give back your university diploma...you are right!

But maybe a new theory is coming around the corner...
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Old 1st June 2004, 06:05 PM   #26
mandat is offline mandat  Poland
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I think that input JFETs shoul have ID about 50 mA for driving output MOSFETs effectively. Does exist such a JFET on the market?
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Old 1st June 2004, 06:22 PM   #27
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Quote:
Originally posted by mandat
I think that input JFETs shoul have ID about 50 mA for driving output MOSFETs effectively. Does exist such a JFET on the market?

As the output Mosfets in this circuit have voltage gain they don't need to much voltage swing in his gate...so they are more easy to drive , than the usual source folower...
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Old 1st June 2004, 07:36 PM   #28
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Quote:
But maybe a new theory is coming around the corner...
Have you ever wished you hadn't said anything at all? The new theory is that I cannot do simple algebra. You guys are right. I have no explanation for the unexpected measurements.
Sorry for any frustration my diversion may have caused!

(PMA - how to I get one of those diploma things?)
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Old 1st June 2004, 08:17 PM   #29
Steven is offline Steven  Netherlands
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Quote:
Originally posted by argo
Maybe the Nobel Prize should go to this guy here:
http://www.ne.jp/asahi/evo/amp/J200K1529/report.htm

Click the image to open in full size.
Translation (Babelfish) of the Japanese text for that circuit:

This is the circuit which first is tried in taking of experiment. As for the first level in the complimentary differential circuit, as for the output step it made the complimentary push pull circuit of source ground operation, it made minimum 2 stage constitution as a power amplifier. The idling electric current of 2SJ200/2SK1529 is adjusted 0.5A with the variable resistor 100 Ohm. As for installed capacity by 8 Ohm loads approximately 50W, as for output resistance 0.8 Ohm about, it is the simple circuit by 8 Ohm loads, but even this way it becomes sufficient utility. If as for open loop gain of this amplifier in order the extent whose load impedance is low to decrease, being inversely proportional to load impedance, output resistance increases and output resistance 0.8 is Ohm by 8 Ohm loads, when by 4 Ohm loads as for output resistance 1.6 Ohm, becomes conversely by 16 Ohm loads as for output resistance 0.4 the extent damping whose load impedance is high in the condition which is called Ohm good, load impedance becomes low, becomes suddenly damping bad. As for MOS-FET of the output step because degree of curve of VGS-ID characteristic curve is large in the part whose drain electric current is little, idling electric current with 0.1A generates the big third distortion factor. MOS-FET being there is no necessity, does, drive electric current with the voltage input element, but when frequency becomes high, because electric current is consumed in the charging and of Ciss, electric current amplitude of the first level differential amplifier becomes large and the third distortion factor increases. In addition, because with 2SJ200 and 2SK1529 Ciss is different, the extent push pull balance whose frequency is high deteriorating, the secondary distortion factor increases.

No mentioning of supernatural closed loop gain, only that the output impedance is inversely proportional to the load impedance, resulting in bad loudspeaker damping for low impedance speakers.

Steven
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Old 1st June 2004, 08:25 PM   #30
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I see a potential follow up of the Gainclone
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