I was reading through Cascode Amp Design art_cas_amp.pdf (Nelson Pass, Pass Labs) with interest.
Does anybody know if there is a full design based on this not just optional extras on here or on firstwatt.com?
The above papers is good but its just a simplified design not the full works and I'm not up to filling in the missing bits!
Does anybody know if there is a full design based on this not just optional extras on here or on firstwatt.com?
The above papers is good but its just a simplified design not the full works and I'm not up to filling in the missing bits!
Yes, but it's not called cascode amp, as it is basically a Supply Rail Bootstrap and the amps made by Nelson pass under Treshold (Treshold 400, 800 for example) were patented as STASIS (bias) technology as the Bootstraped amps were probably not invented by Nelson Pass.
Look up for Kenwood L-09m schematic too.
This technique was used for the first time(if i'm not wrong ) by Tektronix in vertical deflection preamplifiers of their oscilloscopes , first with nuvistors and valves, then with transistors.
https://www.davmar.org/TE/TekConcepts/TekVertAmpCircuits.pdf
page 374 and page 381
Look up for Kenwood L-09m schematic too.
This technique was used for the first time(if i'm not wrong ) by Tektronix in vertical deflection preamplifiers of their oscilloscopes , first with nuvistors and valves, then with transistors.
https://www.davmar.org/TE/TekConcepts/TekVertAmpCircuits.pdf
page 374 and page 381
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Also, the Pass Zen v9 amplifier is very close to the Pass Firstwatt F3 -
Zen Variations 9 | Pass DIY
Zen Variations 9 | Pass DIY
Something like these?
Papa amp.
http://www.firstwatt.com/pdf/art_diy_sony_vfet.pdf
Not Papa amp.
The β24 fully-differential power amplifier
Papa amp.
http://www.firstwatt.com/pdf/art_diy_sony_vfet.pdf
Not Papa amp.
The β24 fully-differential power amplifier
As I recall, the CAS1 and CAS2 from Threshold were cascoded everywhere,
as were the Stasis 1, 2, and 3.
The F3 is cascoded in the only gain stage it had.
Elsewhere, cascoding has been limited to front end input stage and Vas.
KENWOOD L-09M Service Manual download, schematics, eeprom, repair info for electronics expertsElsewhere, cascoding has been limited to front end input stage and Vas.
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The Kenwood is not cascoded everywhere; consider Qe7 and Qe8. In fact I wouldn't call its output stage "cascoded"; instead it is "stacked", two transistors are connected in series to split the 106 volt (!) power supply and use high current power transistors that aren't also rated for enormous voltages.
As I recall, the CAS1 and CAS2 from Threshold were cascoded everywhere,
as were the Stasis 1, 2, and 3.
The F3 is cascoded in the only gain stage it had.
Elsewhere, cascoding has been limited to front end input stage and Vas.
The 4000/400A appear to be fully cascoded everywhere.
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It's a judgement call. 400A and 4000 have series output devices.
You could call them a cascode, but there is a compromise in that
a cascode normally seeks to hold the main gain device at a relatively
constant voltage. In these output stages, as with designs like
Ampzilla, the voltage fluctuation on the output transistors is on the
order of 1/2 the output swing.
You could call them a cascode, but there is a compromise in that
a cascode normally seeks to hold the main gain device at a relatively
constant voltage. In these output stages, as with designs like
Ampzilla, the voltage fluctuation on the output transistors is on the
order of 1/2 the output swing.
Thank you for pointing out the difference. I will dig to see if I can understand the difference. I was around during the original Ampzilla craze. Never owned one but saw one in person at an acquaintence's digs. Do I recall correctly that they had a tendency to go up in flames?
It is wrongly called "cascoded"...a cascode has a fixed bias for the upper transistor.The schematic as per initial document in the first post is actually a Rail Bootstrap as the upper transistor is referenced to the amplifier's output.Most of the Stasis have the same rail bootstrap in a diverse variations of output stages which are stacked transistors too...
Kenwood has this bootstrap at the driver level which is a lot better design because this architecture has a potential for self oscillation because of the lower damping of the bootstrap transistor.
Stasis S1 has implemented it at the driver's level too , but there is a rail bootstrap driving a complementary transistor cascode in parallel with a conventional output stage AND bootstraping the conventional stage driver too.
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I always wondered why Treshold never claimed other than the variable bias in their Stasis designs ...
A subtle little thing I didn't see in the Tektronix paper linked above. Consider a cascode of two NPN transistors. Signal goes in the lower Base, the upper Base is held at a DC bias. Output comes from a resistor load from the Collector of the upper transistor to a power supply. You will almost always find in Tektronix circuits a resistor between the lower transistor's Collector and the upper transistor's Emitter.
This is done to reduce thermal distortion which would otherwise result if the lower Collector was connected directly to the upper Emitter. I think Nelson added this resistor in one of his designs where the lower 'gain' transistor didn't have sufficient breakdown Voltage.
This is done to reduce thermal distortion which would otherwise result if the lower Collector was connected directly to the upper Emitter. I think Nelson added this resistor in one of his designs where the lower 'gain' transistor didn't have sufficient breakdown Voltage.
page 413, fig 7-13...
even better, a zenner diode instead of a resistor, page 410, fig 7-12
the most interesting thing was though for me the reason for r13 , c11 in fig 6.80, page 381.
Anyway...we were comparing apples and oranges here.Rail bootstrap is not a cascode.
Zener diode won't do it. The idea is to reduce Voltage across the lower device as it reaches max current to equalize power dissipation relative to the case where current tends towards zero at max Voltage. The lower device runs at nearly a constant temperature. Important when you have to make big square waves with flat tops and bottoms, typically with no feedback !
Just a guess, but I think R13 equalizes power dissipation through the signal range and C11 holds the Voltage constant above the frequency where thermal distortion is most troublesome. This paper was written in 1969 before Tek really hit their stride with the 7000 series. The 7000 series were state of the art lab scopes discontinued in the 80's.
I have to agree with you there. The idea is to limit Voltage across the output devices to stay out of the Second Breakdown zone. One of Nelson's patents shows a triple stack.
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