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Old 16th August 2007, 10:31 PM   #51
sandyK is offline sandyK  Australia
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Default Compensation Capacitor Cdom

The attached image should help to understand the differential circuit modifications for improving soundstage, as described in my previous post.Different amplifiers may require different methods.

If anybody wants a larger copy, please email me.
Sandyk
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Old 17th August 2007, 01:27 AM   #52
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Hi, SandyK,

Between those 3 methods, all using the same indicator (adjust for 0.0mV)?
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Old 17th August 2007, 01:50 AM   #53
sandyK is offline sandyK  Australia
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Default Compensation Capacitor Cdom

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Yes, assuming that the differential pair is closely matched for HFE and VBE, try to adjust to <5mV difference between their collectors when warm.Only use minor adjustment of the VAS emitter resistor so as to not affect it's correct operation. If unable to achieve with only a small variation of the VAS emitter resistor . try the diode and resistor method instead. Using the 2 series diode method, you may be able to get closer by selecting a suitable 1N4148, as their forward voltage does vary a little between diodes.
BTW, it is adviseable to use matched 1% resistors in the emitters of the differential pair and current mirror. The actual measured value of these 1% resistors isn't as important as them being close in value.
SandyK
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Old 17th August 2007, 03:49 AM   #54
Bonsai is offline Bonsai  Taiwan
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SandyK,

any possibility you could email me the orogonal Silicon chip article, or point to where I could find it?
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Old 17th August 2007, 04:02 AM   #55
sandyK is offline sandyK  Australia
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Default Compensation capacitor cdom

Bonsai
Silicon Chip now has a brand new 20W Class A which does not need an external PSU. If you like to email me, I will give you further information.
SandyK
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