By the way, a regularity can be a coincidence in the relation of cause and effect. Currents do not control currents, voltages do.
Although it is highly beneficial to take a quick look at the ideal port impedances regarding voltage, current and power transfer, in audio things are more complicated.
WuYit`s first law states that linearity and efficiency are inversely related.
WuYit`s second law states that distortions increase with the magnitude of power transfer.
By definition, a cascode comprises a transconductance amplifier and a common base/gate transimpedance amplifier. A common emitter/source amplifier amplifies both voltage and current, which is not advantageous from a linearity point of view. JFETs are far superior to BJTs for current amplification, but do not excel in voltage amplification, so the latter has to be kept at a minimum level. This is done by the very low input impedance of the common base amplifier setting the JFETs` output impedance. Additionally, we limit the voltage operating area (Vds) of the JFET for the same reason (and for some other reasons).
The JFET/ bipolar cascode is a great compound.
WuYit`s first law states that linearity and efficiency are inversely related.
WuYit`s second law states that distortions increase with the magnitude of power transfer.
By definition, a cascode comprises a transconductance amplifier and a common base/gate transimpedance amplifier. A common emitter/source amplifier amplifies both voltage and current, which is not advantageous from a linearity point of view. JFETs are far superior to BJTs for current amplification, but do not excel in voltage amplification, so the latter has to be kept at a minimum level. This is done by the very low input impedance of the common base amplifier setting the JFETs` output impedance. Additionally, we limit the voltage operating area (Vds) of the JFET for the same reason (and for some other reasons).
The JFET/ bipolar cascode is a great compound.
Hi sumaudioguy,
Sorry, I missed your post #110. I cannot agree with that description.
Look, we cannot do much about the time delay.
Emitter degeneration resistors reduce the voltage gain and thereby widen the bandwidth, not using any will leave vital parameters undefined and is a very, very bad idea. A constant Vce significantly prevents the intrinsic capacitances from varying.
Also, since the Vbe-Ice relationship is pretty nonlinear (much more than the casual Ibe-Ice relationship), even a small reduction in the Vbe signal excursion can mean a considerable improvement.
To avoid the phase errors of the differential pair I recommend single-ended input stage and low power amplification in general.
Sorry, I missed your post #110. I cannot agree with that description.
Look, we cannot do much about the time delay.
Emitter degeneration resistors reduce the voltage gain and thereby widen the bandwidth, not using any will leave vital parameters undefined and is a very, very bad idea. A constant Vce significantly prevents the intrinsic capacitances from varying.
Also, since the Vbe-Ice relationship is pretty nonlinear (much more than the casual Ibe-Ice relationship), even a small reduction in the Vbe signal excursion can mean a considerable improvement.
To avoid the phase errors of the differential pair I recommend single-ended input stage and low power amplification in general.
Believe it depends on the goal. If the amplifier is strictly for audio then whatever causes "audible distortion" is what is important. For instrumentation then emitter resistors on a diff pair are called for. I use a voltage to current converter as the input which solved most of my troubles. In phase voltage/current is pretty available for a preamp for audio purposes which allows for V to C conversion at the input. This is likewise available for instrumentation if delay is not an issue using a buffer in front of the V to C input.
My point is very much goal dependent. What I hear turns into figuring out a way to measure what is heard or at least find some aspect which seems to correlate to what is heard. From there amplifier design becomes the challenge of not having to much of the common distortion (THD & IM <.1% at any test level where such a value has meaning) and to likewise reduce whatever it is that damages the sound cause by the amplifier. After 35 years others say creamy, dynamic, crystal clear and fast while never bright or harsh.
Just various design philosophies targeted toward different specific applications. The VAS transistor is a very important part of any of these so this is a great thread!
My point is very much goal dependent. What I hear turns into figuring out a way to measure what is heard or at least find some aspect which seems to correlate to what is heard. From there amplifier design becomes the challenge of not having to much of the common distortion (THD & IM <.1% at any test level where such a value has meaning) and to likewise reduce whatever it is that damages the sound cause by the amplifier. After 35 years others say creamy, dynamic, crystal clear and fast while never bright or harsh.
Just various design philosophies targeted toward different specific applications. The VAS transistor is a very important part of any of these so this is a great thread!
The inspired circuit works.
Got to thank you all again! Just built up a really "lame" version (proto board) of the circuit you guys are largely responsible for inspiration of from parts on hand. It passes signal and with a diff pair input showing 100 nanoseconds delay from the input signal applied until the output appears on the VAS collector. Not bad at all! Is plenty low enough distortion for audio. All good.
If I remember and do not die and ever build another power amp am going to build it up proper. It would be replacing the one in the power amp now with 90dB gain and 85kHz at -3dB from diff input to VAS output which takes like 2.3µS. More loop stability for sure.
Many thanks!😀
=SUM
Got to thank you all again! Just built up a really "lame" version (proto board) of the circuit you guys are largely responsible for inspiration of from parts on hand. It passes signal and with a diff pair input showing 100 nanoseconds delay from the input signal applied until the output appears on the VAS collector. Not bad at all! Is plenty low enough distortion for audio. All good.
If I remember and do not die and ever build another power amp am going to build it up proper. It would be replacing the one in the power amp now with 90dB gain and 85kHz at -3dB from diff input to VAS output which takes like 2.3µS. More loop stability for sure.
Many thanks!😀
=SUM
I wonder what WuYit means?
Does WuYit have a differential input and VAS stage with less delay suitable for audio? Would like to see that.
Does WuYit have a differential input and VAS stage with less delay suitable for audio? Would like to see that.
sumaudioguy,
There is one objective reality that is the truth of the physical universe and how it works. However, we are never directly aware of the external world, only knowledge of our own subjective states is direct. All things we can experience are product of mind, subjective impressions correspond to nothing in the object. Objective knowledge can be obtained through science. The sound as we perceive it is not in the object itself. The idea of employing standards for quantifying physical parameters to express objectively undefinable subjective values is patently absurd.
Last edited:
Scientific method - Wikipedia, the free encyclopedia
Some people just do not believe this is possible. WuYit is one of them.
Some people just do not believe this is possible. WuYit is one of them.
Kanwar,
I secretly counted on your support in this relevant matter.
😀
Tell us about the development of your VAS.
I secretly counted on your support in this relevant matter.
😀
Tell us about the development of your VAS.
Maybe Wu You think IT ?
Odd words and what to associate them with is fun.
Over the last week in this thread i keep thinking of a male Dolphin, that adores both Water and Beer, resides in Stockholm with a chick called Ran.
(good thing certifiable nuts don't count as reliable sources)
Attachments
Last edited:
Thanks to all again for all these great VAS devices. If it was not for many here, the new circuit would never occur. In my circuit design have found the VAS transistor needs to be highest gain, hfe, more important than being really linear. Highest gain give best overall open loop performance, lower distortion (THD) than using the most linear transistor in that position. The higher gain allows for more feedback also.
I already gave conceptual schematic of that thing.
Try simulating it, since you love to simulate circuits more than making in real life.😀
Maybe Wu You think IT ?
Odd words and what to associate them with is fun.
Over the last week in this thread i keep thinking of a male Dolphin, that adores both Water and Beer, resides in Stockholm with a chick called Ran.
(good thing certifiable nuts don't count as reliable sources)
Keep it real.😀
Hi there,
have you ever experienced listening fatigue and other discrepancies due to massive time errors?
have you ever experienced listening fatigue and other discrepancies due to massive time errors?
Kanwar,
what I`m saying is that the common base amplifier is best suited for voltage amplification, the large difference between output and input impedance does not necessitate a buffer, and base currents do not cause slope distortion. Did you see any holes in the arguments?
what I`m saying is that the common base amplifier is best suited for voltage amplification, the large difference between output and input impedance does not necessitate a buffer, and base currents do not cause slope distortion. Did you see any holes in the arguments?
In common base amplifier, the signal is injected into emitter which is low impedance node and it certainly requires a source with matched impedance, since there is no current gain in CB stage , you only have a voltage gain at collector.
My favorite VAS transistor is 2SC5200
I don't accept "voltage only" or "current only" conception; the power amp amplifiers POWER.
I don't accept "voltage only" or "current only" conception; the power amp amplifiers POWER.