I'd like to present a design for a power amplifier, the main features of which are as follows:
The principle on which the design is based is that of a current (high-impedance) amplifier, using feedback to reduce the output impedance.
Full details, including a practical design example, can be found at: https://robinet.co.uk/amplifier-design.
I have attached RTA spectra plots taken using REW, showing the performance of this design at 1 Watt into 8 Ohms, and at 100 Watts into 4 Ohms.
Comments will be welcome.
- The output impedance can be varied from a fraction of an Ohm, to several Kilo-ohms, by selecting two resistors.
- The amplifier is stable with virtually any load.
- It is very robust, and can survive accidental short-circuits.
- Total harmonic distortion is below 0.02% at 1 watt into 8 Ohms, up to 40kHz (This is a real measurement, not a simulation).
The principle on which the design is based is that of a current (high-impedance) amplifier, using feedback to reduce the output impedance.
Full details, including a practical design example, can be found at: https://robinet.co.uk/amplifier-design.
I have attached RTA spectra plots taken using REW, showing the performance of this design at 1 Watt into 8 Ohms, and at 100 Watts into 4 Ohms.
Comments will be welcome.
t's nice to see something different around here, for a moment I thought you were describing my amp.
Very nice and a different approach to amplification.
And a triple Sziklai as an output stage - daring!
Work for serious study.
And a triple Sziklai as an output stage - daring!
Work for serious study.
Congratulations! While there's a bunch of us who tackled this class b current mirror drive output mainly through voltage feedback, it's not the overall current feedback that draw my attention. I have to say it didn't cross my mind using that secondary shunt current feedback path through the
current mirror to controll the output impedance through the power transfer ,but then I remembered Marcel VDG design from 1996 which looks like using the same concept with a mosfet output : https://www.diyaudio.com/community/threads/margan-non-switching-class-b.122007/page-3#post-6999038
current mirror to controll the output impedance through the power transfer ,but then I remembered Marcel VDG design from 1996 which looks like using the same concept with a mosfet output : https://www.diyaudio.com/community/threads/margan-non-switching-class-b.122007/page-3#post-6999038
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Excellent. I heard 2 of Duo’s trans amps , one based on a diskrete electron gun and one based on LM3875. They had a bit more Rout range and are continues range set by a pot
Very good sonics, every loudspeaker best with a different setting
dave
You may need to constantly controll the output impedance in a current conveyor output as you always know the voltage drive , the current drive being the unknown, so I'd say it's a topology dependent type of controll which in a well known emitter follower design still goes down to making the output being seen as purely resistive as the distortions are related to a voltage function instead of a current function so a classical voltage feedback still does what it needs to do if it can monitor all the voltage variations .
Reading a purely resistive output can be done both in a classical way or as in KCP current feedback way where the load impedance is controlled with a voltage function within a classical emitter follower topology and the double current feedback is used to null the current variations
https://www.edn.com/the-class-i-low-distortion-audio-output-stage-part-2/
If we're looking into a very high slew rate feedback design as in LM6172 we see it's a voltage controlling the current nonlinearities of the drive and output stage while preserving the pure voltage drive develloped over the input Re, but that Re is purely conceptual , it's actually the final stage Re that's deemed to be maintained in a pure resistive form with the aid of a classical VFB.
Do we still have a case for high slew rates amplifiers in VFB designs if we can convert the output current over output impedance into pure voltage feedback?
Reading a purely resistive output can be done both in a classical way or as in KCP current feedback way where the load impedance is controlled with a voltage function within a classical emitter follower topology and the double current feedback is used to null the current variations
https://www.edn.com/the-class-i-low-distortion-audio-output-stage-part-2/
If we're looking into a very high slew rate feedback design as in LM6172 we see it's a voltage controlling the current nonlinearities of the drive and output stage while preserving the pure voltage drive develloped over the input Re, but that Re is purely conceptual , it's actually the final stage Re that's deemed to be maintained in a pure resistive form with the aid of a classical VFB.
Do we still have a case for high slew rates amplifiers in VFB designs if we can convert the output current over output impedance into pure voltage feedback?
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Well...I know Sziklay output pairs behave better on low output loads and there's ton of proof on that, so I'm not trying to get a forced equality between different topologies, I quite like the OP's design, I just anxiously wait to have my arguments completely destroyed by people more knowledgeable than me 🙂
Aren't you then basically -artificially- boosting bass, making up for speaker LF imperfections? Same could be achieved with a proper LF equalizer i.m.o..
Sorta, sometimes. More taking advantage of the current drive & the loudspeakers impedance to extend up & down.
For instance the FExx6 horns this is baked in so one can be married with a highish Rout SET.
dave
For instance the FExx6 horns this is baked in so one can be married with a highish Rout SET.
dave
I posted this a while back. Copy the comments to a csv spread sheet to find resistor values for other gain and/or output impedance. Select values for the desired gain (A=23.5), the sense resistor (R=0.39), the output impedance (Z=4) and resistors Pa (=10K) and Na (=10K).
And if you want a bridged amp, ie both inverting and non-inverting:
Note the inverting values are not the same as non-inverting. Note the comment spread sheet values are not for this schematic (oops).
Note the inverting values are not the same as non-inverting. Note the comment spread sheet values are not for this schematic (oops).
Thread split of Kendall Castor-Perry's Class I output stage is now here:
https://www.diyaudio.com/community/...rys-class-i-output-stage.427174/#post-8000899