berat23
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Which opamp are run a class.can ad797 runs a class
A class
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GASTAN
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this may be misleading, but I dont think u'd normally use opamps in class A design. u'd prolly use transistors or tubes
micesol@yahoo.co
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Sory for bed English. That's good. Thanks for that.
tomb
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Actually, the PPA has an option for specifically biasing the first stage opamps. I'm not aware of any other DIY amp that does that with the opamps, though.
steinchen
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there are quite some: PPA, PIMETA, M3, Meier-Audio Corda amps, the output stage of the AOS PICCOLO DAC, ...
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the comp output of AD744 runs class-A too
| Originally Posted by tomb /img/forum/go_quote.gif I'm not aware of any other DIY amp that does that with the opamps, though. |
there are quite some: PPA, PIMETA, M3, Meier-Audio Corda amps, the output stage of the AOS PICCOLO DAC, ...
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| Originally Posted by berat23 Which opamp are run a class.can ad797 runs a class |
the comp output of AD744 runs class-A too
tomb
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With respect, first stage opamps was what I addressed. The PIMETA and M3 do not bias the opamps, only the output buffers. I don't know about the others, but that's why I mentioned the PPA - it specifically has a feature for biasing the first stage opamps - completely separate from circuit and adjustment trimmers for the output buffers.
Perhaps I am mistaken in my understanding of this?
| Originally Posted by steinchen /img/forum/go_quote.gif there are quite some: PPA, PIMETA, M3, Meier-Audio Corda amps, the output stage of the AOS PICCOLO DAC, ... the comp output of AD744 runs class-A too |
With respect, first stage opamps was what I addressed. The PIMETA and M3 do not bias the opamps, only the output buffers. I don't know about the others, but that's why I mentioned the PPA - it specifically has a feature for biasing the first stage opamps - completely separate from circuit and adjustment trimmers for the output buffers.
Perhaps I am mistaken in my understanding of this?
amb
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Yes they do... The Pimeta has the option for you to put in a cascoded JFET pair to pull current out of the opamp for class A operation. The M³ also has a cascoded JFET pair to pull current out of the opamp for the same purpose, in this case not optional, because that current is pulled through the Vbe multiplier transistor and is also used for biasing the output stage.
| Originally Posted by tomb /img/forum/go_quote.gif With respect, first stage opamps was what I addressed. The PIMETA and M3 do not bias the opamps, only the output buffers. |
Yes they do... The Pimeta has the option for you to put in a cascoded JFET pair to pull current out of the opamp for class A operation. The M³ also has a cascoded JFET pair to pull current out of the opamp for the same purpose, in this case not optional, because that current is pulled through the Vbe multiplier transistor and is also used for biasing the output stage.
tomb
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OK, guess I've been working on Hybrids too long - where each stage is separately biased. I didn't realize that the buffer bias was a twofer in the PIMETA and M3. It also seems the PPA's stages are biased separately, but that may be wrapped up in some confusion between versions.
| Originally Posted by amb /img/forum/go_quote.gif Yes they do... The Pimeta has the option for you to put in a cascoded JFET pair to pull current out of the opamp for class A operation. The M³ also has a cascoded JFET pair to pull current out of the opamp for the same purpose, in this case not optional, because that current is pulled through the Vbe multiplier transistor and is also used for biasing the output stage. |
OK, guess I've been working on Hybrids too long - where each stage is separately biased. I didn't realize that the buffer bias was a twofer in the PIMETA and M3. It also seems the PPA's stages are biased separately, but that may be wrapped up in some confusion between versions.
pinkfloyd4ever
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umm I've been wondering for awhile now..what's biasing mean? sorry I'm a newb
tomb
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Amplifiers work by using an external power source and adding that power to a signal, thereby creating a stronger signal. However, if the power is not already flowing, the response is much slower and there is switching noise because the power actually has to be turned on within the circuit.
Biasing creates a false power demand so that the current is always flowing. This cuts down on the switching noise and allows the circuit to respond much more quickly: sound is noticeably superior. The downside is that a lot of energy is wasted. Not only does it cost more to burn the power all the time, but it usually means big heat sinks are needed, too.
An analogy might be your car - think how easy it is to respond to turns and obstacles in the road, versus coming to a complete stop every time and re-accelerating to a cruising speed.
| Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif umm I've been wondering for awhile now..what's biasing mean? sorry I'm a newb |
Amplifiers work by using an external power source and adding that power to a signal, thereby creating a stronger signal. However, if the power is not already flowing, the response is much slower and there is switching noise because the power actually has to be turned on within the circuit.
Biasing creates a false power demand so that the current is always flowing. This cuts down on the switching noise and allows the circuit to respond much more quickly: sound is noticeably superior. The downside is that a lot of energy is wasted. Not only does it cost more to burn the power all the time, but it usually means big heat sinks are needed, too.
An analogy might be your car - think how easy it is to respond to turns and obstacles in the road, versus coming to a complete stop every time and re-accelerating to a cruising speed.
amb
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It's the application of a voltage or current condition to allow an active device (transistor, tube, whatever) to operate in a certain manner. Biasing is a fundamental concept in electronics and I would advise you to do some web searches to get a feel of what it means by looking at some concrete examples.
| Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif umm I've been wondering for awhile now..what's biasing mean? sorry I'm a newb |
It's the application of a voltage or current condition to allow an active device (transistor, tube, whatever) to operate in a certain manner. Biasing is a fundamental concept in electronics and I would advise you to do some web searches to get a feel of what it means by looking at some concrete examples.
ryssen
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Is there any benefit in using in using j-fets over bjt´s when biasing an opamp?
amb
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Yes, due to its self-biasing nature, JFETs can be made into a constant current source with little or no extra parts. The simplest is a single JFET with its gate and source pins shorted together, and a cascoded JFET current source can be made with or without one extra resistor. These can be used to source or sink current, and can be excellent performers depending on the device used. By contrast, BJTs need several more external parts to bias it to become a current source and typically an opposite polarity device is needed to make it a current sink. With all those extra parts, the performance isn't any better than one made with JFETs.
The current issue of AudioXpress magazine has a good article by Walt Jung describing the performance of various current sources, with actual measured data.
| Originally Posted by ryssen /img/forum/go_quote.gif Is there any benefit in using in using j-fets over bjt´s when biasing an opamp? |
Yes, due to its self-biasing nature, JFETs can be made into a constant current source with little or no extra parts. The simplest is a single JFET with its gate and source pins shorted together, and a cascoded JFET current source can be made with or without one extra resistor. These can be used to source or sink current, and can be excellent performers depending on the device used. By contrast, BJTs need several more external parts to bias it to become a current source and typically an opposite polarity device is needed to make it a current sink. With all those extra parts, the performance isn't any better than one made with JFETs.
The current issue of AudioXpress magazine has a good article by Walt Jung describing the performance of various current sources, with actual measured data.
Nordic
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Do a search for poor man's zen, it is very simple, uses small heatsinks, dissipateing less than 4W. Buy a few mosfets to match them (or matched pair), unless you want to use seperate transformers for each channel...
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