O.K., thank you.
This beeing put, i allow myself to insist:
What about my choice of devices? (they are under my hand)
- Five to six pairs of 2SC3264/2SA1295 Sankens as output devices
- 2sc5200/2sa1943 as drivers,
- 2sc5171 / 2sa1930 as pre drivers.
This beeing put, i allow myself to insist:
What about my choice of devices? (they are under my hand)
- Five to six pairs of 2SC3264/2SA1295 Sankens as output devices
- 2sc5200/2sa1943 as drivers,
- 2sc5171 / 2sa1930 as pre drivers.
klewis said:
Thank you Ken. What was the output level for THD simulation? If it was not high, the transistors were probably in Class A mode with higher bias levels. See Andrew's message above.
AndrewT said:
With drivers conducting non-zero current all the time, we avoid driver stage switching distortion. Switching distortion of driver (medimum power) might be insignificant.
Any comment?
Hi,
driver switching may give rise to increased distortion.
Modified versions of ClassAB in the output stage seem to give some distortion benefits in the performance.
I cannot see why applying similar modified ClassAB for the driver should not also offer some benefit.
What is quite clear is that the handover between pairs of halfwaves is currently not as clean as pure ClassA. It seems to be something to do with the sidebands.
But any stage that follows the sinewave or music signal for only one half of the wave form and becomes inoperative during the other half of the waveform will always be ClassAB and will always be in need of improvement.
Some methods will give rise to these much needed improvements, just don't believe the designer when he tries to convince us he has achieved ClassA when clearly this is not the case.
Some day someone might come up with a modified ClassAB scheme that betters a true ClassA stage, let's wait till that comes.
driver switching may give rise to increased distortion.
Modified versions of ClassAB in the output stage seem to give some distortion benefits in the performance.
I cannot see why applying similar modified ClassAB for the driver should not also offer some benefit.
What is quite clear is that the handover between pairs of halfwaves is currently not as clean as pure ClassA. It seems to be something to do with the sidebands.
But any stage that follows the sinewave or music signal for only one half of the wave form and becomes inoperative during the other half of the waveform will always be ClassAB and will always be in need of improvement.
Some methods will give rise to these much needed improvements, just don't believe the designer when he tries to convince us he has achieved ClassA when clearly this is not the case.
Some day someone might come up with a modified ClassAB scheme that betters a true ClassA stage, let's wait till that comes.
Aren't the drivers working in class A in the following scheme?
http://www.audiolabor.de/index.php?option=com_content&task=view&id=34&Itemid=51
Schaltplan = schematic
http://www.audiolabor.de/index.php?option=com_content&task=view&id=34&Itemid=51
Schaltplan = schematic
klewis said:
Hi Ken,
Thank you for your data. Do you have .option plotwinsize=0 in your simulations?
Re: Re: LME49830 on higher rails than output devices?
I built one of Borbely's designs many years ago and, to be honest, I think regulating the driver stage causes more problems than it solves. The feedback loops in the regulators introduce essentially another pole into the stability equation. Many authors and designers, such as Self, Slone, etc. have since mostly shunned driver regulation for stability reasons, and because it's very easy for the common mode rejection (CMRR) of a well designed input stage and VAS to reject the low frequency power supply variations created by the output stage.
Back when Borbely designed that amp, there were no high power driver IC's available (unless you count the LM391 but it was only good for 70 watts). It was more difficult to design high CMRR input and driver stages without the benefit of matched devices on a single piece of silicon and the other benefits of a monolithic design. Today, the LM4702/LME498xx make it easy to have extremely high CMRR.
My Borbely amp, with the regulators, would try to oscillate when clipped--especially into a real speaker load. With some creative compensation I got it to where it was stable on the bench with a resistive load only to have it later fry my tweeters in the listening room. A scope in the listening room showed huge bursts of HF into the speakers at clipping. The relatively sharp spikes on the rails at clipping apparently caused a high frequency transient response from the regulators, which in turn, apparently set up a positive feedback mechanism to the driver stage. Bad news! I removed the regulators and the amp was extremely stable with my tweeters having a long and healthy life from then on.
And even with lateral MOSFETs you can gain output power by having the driver stage run on a higher voltage. Power, of course, is the square of voltage. So even gaining a few volts on each rail makes a significant difference. With the much higher RDSon creating more Vds drop at full power, lateral MOSFETs need all the help they can get--especially into low impedance or reactive loads.
If the output devices can get closer to the rails, for the same power output, you can use lower rail voltages. That decreases the size of the heatsinks and also lets the amp run cooler at idle (especially with high bias lateral mosfets).
And, as an aside, for those who like to leave their amp on... In most areas, every single watt of 24/7 electrical consumption is at least $1 per year. A lateral MOSFET amp with 2 devices per side typically needs around 300ma bias. With 60 volt rails a 7 channel home theater amp would dissipate a toasty 252 watts at idle. With a higher voltage driver stage, and 55 volt output rails, it would produce about the same power and idle at 231 watts. Adding in power supply losses you might save $25/year in electricity. 😉
jackinnj said:
I built one of Borbely's designs many years ago and, to be honest, I think regulating the driver stage causes more problems than it solves. The feedback loops in the regulators introduce essentially another pole into the stability equation. Many authors and designers, such as Self, Slone, etc. have since mostly shunned driver regulation for stability reasons, and because it's very easy for the common mode rejection (CMRR) of a well designed input stage and VAS to reject the low frequency power supply variations created by the output stage.
Back when Borbely designed that amp, there were no high power driver IC's available (unless you count the LM391 but it was only good for 70 watts). It was more difficult to design high CMRR input and driver stages without the benefit of matched devices on a single piece of silicon and the other benefits of a monolithic design. Today, the LM4702/LME498xx make it easy to have extremely high CMRR.
My Borbely amp, with the regulators, would try to oscillate when clipped--especially into a real speaker load. With some creative compensation I got it to where it was stable on the bench with a resistive load only to have it later fry my tweeters in the listening room. A scope in the listening room showed huge bursts of HF into the speakers at clipping. The relatively sharp spikes on the rails at clipping apparently caused a high frequency transient response from the regulators, which in turn, apparently set up a positive feedback mechanism to the driver stage. Bad news! I removed the regulators and the amp was extremely stable with my tweeters having a long and healthy life from then on.
And even with lateral MOSFETs you can gain output power by having the driver stage run on a higher voltage. Power, of course, is the square of voltage. So even gaining a few volts on each rail makes a significant difference. With the much higher RDSon creating more Vds drop at full power, lateral MOSFETs need all the help they can get--especially into low impedance or reactive loads.
If the output devices can get closer to the rails, for the same power output, you can use lower rail voltages. That decreases the size of the heatsinks and also lets the amp run cooler at idle (especially with high bias lateral mosfets).
And, as an aside, for those who like to leave their amp on... In most areas, every single watt of 24/7 electrical consumption is at least $1 per year. A lateral MOSFET amp with 2 devices per side typically needs around 300ma bias. With 60 volt rails a 7 channel home theater amp would dissipate a toasty 252 watts at idle. With a higher voltage driver stage, and 55 volt output rails, it would produce about the same power and idle at 231 watts. Adding in power supply losses you might save $25/year in electricity. 😉
Hi,
In ClassA by definition, current flows thru the device for the full 360 degrees of the musical cycle...
it is by this definition that Leach and others term their topologies as being in classA...
i do not know that the definitions have changed or who changed them...
i am eager to find out whether there are other links that says otherwise...
all amps for that matter will have this classA window no matter how small...
a classic example is the "Halo" amps by John Curl... it operates classA for the first 7 watts, then switch to class AB at higher powers....
In ClassA by definition, current flows thru the device for the full 360 degrees of the musical cycle...
it is by this definition that Leach and others term their topologies as being in classA...
i do not know that the definitions have changed or who changed them...
i am eager to find out whether there are other links that says otherwise...
all amps for that matter will have this classA window no matter how small...
a classic example is the "Halo" amps by John Curl... it operates classA for the first 7 watts, then switch to class AB at higher powers....
Re: Re: Re: LME49830 on higher rails than output devices?
Thanks -- I have not built the Borbely amps -- at the time I couldn't find the driver transistors!
WRT idle expenses -- is that "before" or "after" Waxman-Markey?
RocketScientist said:
Thanks -- I have not built the Borbely amps -- at the time I couldn't find the driver transistors!
WRT idle expenses -- is that "before" or "after" Waxman-Markey?
Re: LME49830 on higher rails than output devices?
Well you get a $100 credit but you have to pay a tax accountant $400 to file the paperwork... 😉
As to my original post, apparently even Audioman54 (ex National employee working on the LME498xx series) hasn't tried the higher-rail scenario. So I might have to venture into bold new territory on my own. I can always bring any popcorn'd parts to Burning Amp for Show And Tell.
jackinnj said:
Well you get a $100 credit but you have to pay a tax accountant $400 to file the paperwork... 😉
As to my original post, apparently even Audioman54 (ex National employee working on the LME498xx series) hasn't tried the higher-rail scenario. So I might have to venture into bold new territory on my own. I can always bring any popcorn'd parts to Burning Amp for Show And Tell.
bobodioulasso said:
Yes, the devices you have will work very well for a triple Darlington EF or CFP output stage. If you use five to six pairs of those 2SC3264/2SA1295 devices, you couple probably deliver 1KW into 2 ohms with the right power supply and design.
The 2sc5171/2sa1930 devices are only 180Vceo devices, so you should keep the rail voltages at or below about +/-75VDC.
The 2sc5200/2sa1943 devices are only 30MHz devices while the others are faster, so watch for parasitics.
All said, you have all the devices for a monster power amp, and with any of the three LME49810, LME49811, or LME49830 devices it should sound great.
DCPreamp said:
You reckon LME49811 can drive CFP directly (no 3rd transistor stage)? I have used this output topology in a Blameless amp before, and I am tempted to do so again...
that's where you and others fail to understand what the definition of ClassA mean by "for the full 360degrees of the cycle".Tony said:
DCPreamp said:
Thank you for your answer.
My rails are 90v no load (1,2 kVA 2x63v transformers)
I want to keep the Sankens output devices.
Which higher voltage pre-drivers and faster drivers would you suggest, please?
and how much higher will they rise if mains goes up to maximum tolerance?bobodioulasso said:
Have you looked at the SOAR of the 1943/5200?
It is atrocious at higher voltages.
@ 90Vce it is down to 500mA (45W) when Tc<=25degC
Re: Re: Re: LME49830 on higher rails than output devices?
I think you are actually referring to PSRR instead of CMRR.
I wonder that feedback loop introducing poles in amp's loop equation is a proper statement. The amp will act as a reactive load to the regulator. The regulator loop characteristic will be affected by the load condition. It should be designed to operate under all expected conditions.
Have you tried another regulator to supply the Borbely amp's driver stage?
I agree that designing an amp with sufficient PSRR should be attemped before considering a regulated supply (for input and VAS).
RocketScientist said:
I think you are actually referring to PSRR instead of CMRR.
I wonder that feedback loop introducing poles in amp's loop equation is a proper statement. The amp will act as a reactive load to the regulator. The regulator loop characteristic will be affected by the load condition. It should be designed to operate under all expected conditions.
Have you tried another regulator to supply the Borbely amp's driver stage?
I agree that designing an amp with sufficient PSRR should be attemped before considering a regulated supply (for input and VAS).