> What importance is this the Transconductance figure (Siemens) , in relatition to hexfets in hi-fi amps?
In many cases, we apply a Voltage to the input, and get a Current at the output.
Transconductance (or Gm) tells how much current you get for how much voltage.
Transconductance can be seen as the opposite of Resistance (ratio of Voltage to Current).
In many cases, you can figure the voltage gain of an amplifier stage as (Load Resistance) times (Transconductance).
Clearly, a high transconductance can give a high voltage gain, which is generally good.
For a Source Follower, the output resistance tends to be 1/Gm.
High Gm means low output resistance, which is usually good.
Note that transconductance is not a constant. It always varies with current. In simple power amplifiers, Gm variation with signal current swing is the main cause of distortion.
When Gm is quoted on a spec-sheet, they usually pick an operating condition that gives an "impressive number", which may not be anywhere near an operating condition you can use in practice. When comparing different devices, don't go by the bold-print spec headlines. Dig into the graphs and compare both devices at your proposed operating current.
Emitter/cathode/source resistors act to reduce and linearize transconductance.
> Siemen sounds so... um... biological.
Get your mind out of your pants.
The Siemens family has dominated light-and heavy- electric systems in Europe for well over a century. A little like the US's Edison and Westinghouse, except with even broader interests and family participation through many generations. Siemens invented the practical electric generator (dynamo). Siemens played a major part in the transatlantic cable, in high-voltage AC power distribution, in underground/sea power cables, and became an industrial giant. They worked with radio and advanced electronics, computers, and their current product line ranges fron cellphones to drugs to really fancy ship propellers.
Siemens: the Company - the Family - the History
I am not sure which Siemens the mho was named for; but notice that we do not have any units called Edison or Westinghouse or Steinmetz. The Siemens' contribution to electricity is that large. We just don't like to know that in the USA.
In many cases, we apply a Voltage to the input, and get a Current at the output.
Transconductance (or Gm) tells how much current you get for how much voltage.
Transconductance can be seen as the opposite of Resistance (ratio of Voltage to Current).
In many cases, you can figure the voltage gain of an amplifier stage as (Load Resistance) times (Transconductance).
Clearly, a high transconductance can give a high voltage gain, which is generally good.
For a Source Follower, the output resistance tends to be 1/Gm.
High Gm means low output resistance, which is usually good.
Note that transconductance is not a constant. It always varies with current. In simple power amplifiers, Gm variation with signal current swing is the main cause of distortion.
When Gm is quoted on a spec-sheet, they usually pick an operating condition that gives an "impressive number", which may not be anywhere near an operating condition you can use in practice. When comparing different devices, don't go by the bold-print spec headlines. Dig into the graphs and compare both devices at your proposed operating current.
Emitter/cathode/source resistors act to reduce and linearize transconductance.
> Siemen sounds so... um... biological.
Get your mind out of your pants.
The Siemens family has dominated light-and heavy- electric systems in Europe for well over a century. A little like the US's Edison and Westinghouse, except with even broader interests and family participation through many generations. Siemens invented the practical electric generator (dynamo). Siemens played a major part in the transatlantic cable, in high-voltage AC power distribution, in underground/sea power cables, and became an industrial giant. They worked with radio and advanced electronics, computers, and their current product line ranges fron cellphones to drugs to really fancy ship propellers.
Siemens: the Company - the Family - the History
I am not sure which Siemens the mho was named for; but notice that we do not have any units called Edison or Westinghouse or Steinmetz. The Siemens' contribution to electricity is that large. We just don't like to know that in the USA.
Coin Flipping..........
NFB is not by definition sonically bad, but can very easily be so.
Zero loop feedback is not by definition perfect either.
Eric.
Yes that, and the additional multiple dependancy dynamic artifacts that NFB systems produce because of inadeqaucy of complete corrections due to multiple causes.fdegrove said:.....And that's about all that should be remembered....
Cheers,
NFB is not by definition sonically bad, but can very easily be so.
Zero loop feedback is not by definition perfect either.
Eric.
Hi,
How could you?
Let's look at it this way: NFB is a dog chasing it's own tail game when you look at it from a time domain perspective.
From that POV you'll realise that NFB will always suffer from time lag one way or another...
Whether it matters to our perception of sound remains to be seen, I think so but there's little we can do to minimise the effect other than use it wisely.
Cheers,
How could you?
Let's look at it this way: NFB is a dog chasing it's own tail game when you look at it from a time domain perspective.
From that POV you'll realise that NFB will always suffer from time lag one way or another...
Whether it matters to our perception of sound remains to be seen, I think so but there's little we can do to minimise the effect other than use it wisely.
Cheers,
>Should the feedback be adjusted for the Transconductance?
more like the xconductance adjusts the feedback
the primary reason for feedback is to be able to get a predictable gain using somewhat unpredictable active devices. i.e. the more (open loop) gm the more feedback thus making the closed loop gain dependent on the amount of feedback used.
more like the xconductance adjusts the feedback
the primary reason for feedback is to be able to get a predictable gain using somewhat unpredictable active devices. i.e. the more (open loop) gm the more feedback thus making the closed loop gain dependent on the amount of feedback used.
Hi,
Yes, Clevor Trevor, our mere being depends on feedback to survive...
We'll discuss Zeno and Franks' arguments whenever you do come over for a nice bottle of wine...
I just said, don't depend on feedback to make it work....make it work without and perfect it with a judicious amount of FB.
Cheers,
Yes, Clevor Trevor, our mere being depends on feedback to survive...
We'll discuss Zeno and Franks' arguments whenever you do come over for a nice bottle of wine...
I just said, don't depend on feedback to make it work....make it work without and perfect it with a judicious amount of FB.
Cheers,
>Ya mon...'splain that one to me, please....
I'm gonna use 'gm' loosely as the total open loop gain of an amp.
To set the closed loop gain we feed back (to the input (out of phase)) a certain fraction of the output. The more gm we have to begin with the larger the signal fed back thus balancing the system gain to the ratio of feedback ....... ? How 'bout that ?
I'm gonna use 'gm' loosely as the total open loop gain of an amp.
To set the closed loop gain we feed back (to the input (out of phase)) a certain fraction of the output. The more gm we have to begin with the larger the signal fed back thus balancing the system gain to the ratio of feedback ....... ? How 'bout that ?
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