Other than the obvious, what really is the difference between positive and negative feedback, in terms of allowable amounts? My M2 works fine, is easy to zero offset, and usually floats around 1-5 millivolts or so, but after playing for a few weeks and I check it, occasionally it will be 1-5 negative.
Does this matter? Or is offset just offset negative or positive and don't worry about it...
My other First Watt clones seem to always drift positive, and I remember M2 discussion about resistor adjustment, but thought that only pertained to cases where zero could not be dialed in, right? Or no?
Russellc
Does this matter? Or is offset just offset negative or positive and don't worry about it...
My other First Watt clones seem to always drift positive, and I remember M2 discussion about resistor adjustment, but thought that only pertained to cases where zero could not be dialed in, right? Or no?
Russellc
Positive and negative offsets have no relation to positive and negative feedback.
Offsets can drift slightly either way due to a number of factors such as a dependence on absolute supply voltage and/or temperature change in semiconductors. Historically offsets of -/+100mv were acceptable although those limits have tightened with better understanding and design.
Feedback is a totally different mechanism and is something that is designed into a circuit to define its precise operating points and conditions. Positive feedback is used for example to make an oscillator.
Offsets can drift slightly either way due to a number of factors such as a dependence on absolute supply voltage and/or temperature change in semiconductors. Historically offsets of -/+100mv were acceptable although those limits have tightened with better understanding and design.
Feedback is a totally different mechanism and is something that is designed into a circuit to define its precise operating points and conditions. Positive feedback is used for example to make an oscillator.
Only wondered about the offset, just found it odd that it seemed to drift eventually to negative, where the others drifted positive. Then wondered if there was really a difference, sounds like offset is offset. My understanding is that the M2 has no feedback.
"The First Watt M2 is a two channel audio power amplifier delivering 25 watts per channel. It uses JFET and MOSFET transistors operating in Class A mode without negative feedback so as to produce a more musically life-like sound."
Russellc
"The First Watt M2 is a two channel audio power amplifier delivering 25 watts per channel. It uses JFET and MOSFET transistors operating in Class A mode without negative feedback so as to produce a more musically life-like sound."
Russellc
You need to understand the difference between 'global' feedback and 'local' feedback. All amplifiers use feedback of some kind, if they didn't they would be solely dependent on the devices used and totally unpredictable in operation.
A 'no feedback' amplifier is taken to mean an amplifier with no global feedback that wraps around several stages in the amplifier circuit. Instead it uses local feedback where the conditions of each stage are set independently.
A simple emitter follower or a simple one transistor common emitter amplifier are examples of local feedback.
Your offset voltages sound absolutely fine and very low. If you heat or cool one transistor quicker than the other then the offset will probably swing a little. It may also vary with supply voltage to some extent.
A 'no feedback' amplifier is taken to mean an amplifier with no global feedback that wraps around several stages in the amplifier circuit. Instead it uses local feedback where the conditions of each stage are set independently.
A simple emitter follower or a simple one transistor common emitter amplifier are examples of local feedback.
Your offset voltages sound absolutely fine and very low. If you heat or cool one transistor quicker than the other then the offset will probably swing a little. It may also vary with supply voltage to some extent.
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