Esperado,
Regarding 'speed', it's the gain-bandwidth product that matters and not the open loop bandwidth.
edit: See this paper: http://www.linearaudio.net/images/onlinearticlesPDF/volume1bp.pdf
(Thank you Jan for sharing)
Cheers, E.
Regarding 'speed', it's the gain-bandwidth product that matters and not the open loop bandwidth.
edit: See this paper: http://www.linearaudio.net/images/onlinearticlesPDF/volume1bp.pdf
(Thank you Jan for sharing)
Cheers, E.
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A speculation ? People who made high slew rate amplifiers did so because they wanted to give it a try . Listening to them , they liked them . In fact they liked them a lot . They then tried to say why and failed ?
I recently designed a valve amplifier that had minute ringing on square waves . I thought that's good I will keep that . I thought it might be slightly preferable to a rounded edge . Lets be clear I wasn't going to get it perfect whatever I did . I thought it would have a sound and it might even be preferable . Sounds very good . Measurements are good and triangle waves very good .
Can anyone say if high slew rate is a bad idea with harmful outcomes ? Or better still , a high slew rate amp with bandwidth limiting it supposedly doesn't need added ? Good or bad ? No politicians answers please .
I recently designed a valve amplifier that had minute ringing on square waves . I thought that's good I will keep that . I thought it might be slightly preferable to a rounded edge . Lets be clear I wasn't going to get it perfect whatever I did . I thought it would have a sound and it might even be preferable . Sounds very good . Measurements are good and triangle waves very good .
Can anyone say if high slew rate is a bad idea with harmful outcomes ? Or better still , a high slew rate amp with bandwidth limiting it supposedly doesn't need added ? Good or bad ? No politicians answers please .
It wasn't meant as one . I will buy my new copy ASAP . I then pass the old one on .
If it doesn't embarrass Mr Self it is the only book that gives us a standard to work from . It even gives us a common language . I use VAS as that's how the book says it . LTP is useful . My own CfbP for output stages I like .
The book is also something I would recommend as good plain English to someone trying to write text books . Before anyone says I could learn a lot from it in that alone .
If it doesn't embarrass Mr Self it is the only book that gives us a standard to work from . It even gives us a common language . I use VAS as that's how the book says it . LTP is useful . My own CfbP for output stages I like .
The book is also something I would recommend as good plain English to someone trying to write text books . Before anyone says I could learn a lot from it in that alone .
Only snag is it isn't a "VAS"; it is, in fact, a transimpedance stage (TIS).
Maybe you don't care what Mike called it, but also Bruno Putzeys calls it a transimpedance stage:
Attachments
Back to slew rate.
My rule of thumb is 1 V per microsecond per volt of peak to peak output voltage swing plus 20% for the road. So if the amp swings 150V pk to pk, I target 180V/us.
My e-Amp does not quite get there at 155V/us, but it's good enough.
However, if I build a CFA and it comes out at 250 V/us, what the hell, I'll go with it!
My rule of thumb is 1 V per microsecond per volt of peak to peak output voltage swing plus 20% for the road. So if the amp swings 150V pk to pk, I target 180V/us.
My e-Amp does not quite get there at 155V/us, but it's good enough.
However, if I build a CFA and it comes out at 250 V/us, what the hell, I'll go with it!
Hi Bob,
Indeed, it was flight AF 447 which I had in mind when I was fulminating on the training of French pilots.
I think it's unlikely that (in this case) failure/lost of the vertical stabilizer was the cause of the accident. Besides, this rudder controls the direction (left/right), thus not the height of the plane (as for the latter, the elevator, together with the amount of thrust, are used for this). Anyhow, please read this story and it becomes clear what has happened. In the meantime the procedures for how to recover from a stall has been changed. I've discussed this accident with several friends (who are pilots) and they not only blame faulty input from the instrument and software, but also the crew who, contrarily to old school pilots, can't handle such nasty situation any longer. The only thing they have learned today is how to push buttons (their words, not mine).
Cheers, E.
PS1: Did you have received my email about DTMC? edit: yes.
PS2: Last week, one of my flights back to Holland was in a Airbus. As you can see, I'm still alive.
PS3: Sorry guys for being so off-topic.[/QUOTE
OT//
Yes, it's clear the thing stalled. Loss of rudder and the plane would probably have flipped. The AA flight that went down near LA years before was because of aggressive over correction for turbulence that ripped the rudder off. I watched Air Crash Disaster ( I fly a lot) and its amazing how many accidents are due to pilot error, fatigue and ILS systems not working because they are being serviced or undergoing repair
Airbus is OK!
//OT
I call it VAS out of respect for the book and for it being universally understood . It is like centrifugal force is understood when often misapplied . It was very helpful when someone called it TIS .
I do suspect the VAS ( TIS ) is the Kingpin of the amp . It was very helpful to have cascodes questioned when a VAS . With good transistors becoming more difficult to find a cascode seems a good solution . I have had no problems with them . In fact they are the most obliging of arrangements . I will be cautious and check more carefully in future .
When I say Kingpin I mean far more than the obvious . I do wonder if some of the TID debate was describing the difficulties in driving the VAS base correctly ? I have no evidence to support this . My hunch is the rather distorted waveform we see into the VAS base is not 100 % a ghost in the machine . I have seen a series resistor placed there by some . As said I have no evidence , just a hunch it matters more than is suspected . I do understand how the base input is current if TIS . I just question if that is ideal ? Myself I try to make the driving impedance very low . I have zero interest in slew rates . If above 6 V/uS 100 watts then it should be OK for music . No, I just feel trans-conductance is not practiced in other areas of hi fi so why here ? It is a very poor argument I know and I have as many reasons as anyone to reject it . All I am saying is how do we know ? I 100 % accept it works very well , that is not the question . If you look carefully at solutions like the Darlington VAS it solves these problems if they exist ? It also gives a useful lift in base voltage to help the current mirror that usually precedes it . The high gain , high voltage , low Cob transistors like 2SD756 and 2SB716 seem to echo my thoughts . These were if you like audiophile 2N 5551/5401 .
Although again I can offer no evidence I always felt a single transistor for the VAS to be best ( I like twin VAS very much if asking , sorry to confuse the meaning ) . One with high gain . There have been measurements to support that . However the slightest change in Cdom will fix it . To say there will be no trade off if a Darlington is daft . I accept it is a statement of the obvious . The bigger statement is the days of ideal VAS transistors is nearly at an end .
I do suspect the VAS ( TIS ) is the Kingpin of the amp . It was very helpful to have cascodes questioned when a VAS . With good transistors becoming more difficult to find a cascode seems a good solution . I have had no problems with them . In fact they are the most obliging of arrangements . I will be cautious and check more carefully in future .
When I say Kingpin I mean far more than the obvious . I do wonder if some of the TID debate was describing the difficulties in driving the VAS base correctly ? I have no evidence to support this . My hunch is the rather distorted waveform we see into the VAS base is not 100 % a ghost in the machine . I have seen a series resistor placed there by some . As said I have no evidence , just a hunch it matters more than is suspected . I do understand how the base input is current if TIS . I just question if that is ideal ? Myself I try to make the driving impedance very low . I have zero interest in slew rates . If above 6 V/uS 100 watts then it should be OK for music . No, I just feel trans-conductance is not practiced in other areas of hi fi so why here ? It is a very poor argument I know and I have as many reasons as anyone to reject it . All I am saying is how do we know ? I 100 % accept it works very well , that is not the question . If you look carefully at solutions like the Darlington VAS it solves these problems if they exist ? It also gives a useful lift in base voltage to help the current mirror that usually precedes it . The high gain , high voltage , low Cob transistors like 2SD756 and 2SB716 seem to echo my thoughts . These were if you like audiophile 2N 5551/5401 .
Although again I can offer no evidence I always felt a single transistor for the VAS to be best ( I like twin VAS very much if asking , sorry to confuse the meaning ) . One with high gain . There have been measurements to support that . However the slightest change in Cdom will fix it . To say there will be no trade off if a Darlington is daft . I accept it is a statement of the obvious . The bigger statement is the days of ideal VAS transistors is nearly at an end .
The issue with the KSC/KSA is that, yes, they are in production but have different Hfe grades.
Things move on and you have to adapt. May be we'll see new ideas and solutions.
Or risk the grey market....
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I'm a beginner at this, but how did a VAS become a TIS ?
In the LIN (spelling ?) topology the LTP produces a changing current at the collector of both devices. The collector of interest has a resistor in series with it. This resistor converts the current signal to a voltage signal. The voltage signal drives the VAS transistor and the VAS transistor produces a fluctuating current at it's collector. The VAS load is a high impedance and it converts the current to a voltage. So from my understanding - transistors/FETs/Valves take a voltage at their control inputs and produce a changing current at their outputs. But when you include the load, their outputs become voltages again. I always include a load in my definition of the 'stage'. A VAS is a VAS is a VAS.
Just to further complicate things .
Audio amplifier topology with push-pull transimpedance stage - Part 3: Experimental verification
Audio amplifier topology with push-pull transimpedance stage - Part 3: Experimental verification
Hi Guys
Nigel, I believe the benefits of Groen's "novel" push-pull VAS are shared by all push-pull VAS, the traditional forms of which are much simpler and do not invoke some of the pitfalls displayed in that article's plots.
Bigun: "TIS" is the traditional term for "transimpedance stage", and precedes the use of "VAS". However, I have older texts that refer to the stage as the voltage amplifier, it was just not formalised that way until later.
"VAS" is as far as I know Doug Self's invention, and it does describe what the stage does overall inasmuch as it produces the full voltage swing required by the output stage (at least in LIN and similar designs).
I use VAS in my books just because it colloquially implies what the stage does better than TIS does. My opinion only, and as respect to Doug who's influence is far more reaching than many here may wish to recognise.
Have fun
Kevin O'Connor
Nigel, I believe the benefits of Groen's "novel" push-pull VAS are shared by all push-pull VAS, the traditional forms of which are much simpler and do not invoke some of the pitfalls displayed in that article's plots.
Bigun: "TIS" is the traditional term for "transimpedance stage", and precedes the use of "VAS". However, I have older texts that refer to the stage as the voltage amplifier, it was just not formalised that way until later.
"VAS" is as far as I know Doug Self's invention, and it does describe what the stage does overall inasmuch as it produces the full voltage swing required by the output stage (at least in LIN and similar designs).
I use VAS in my books just because it colloquially implies what the stage does better than TIS does. My opinion only, and as respect to Doug who's influence is far more reaching than many here may wish to recognise.
Have fun
Kevin O'Connor
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