Hi minek
i just looka t your schematic and think about wasting the voltage for the LT1056 U1. your rail is 45V and if you use 2k7 with 7mA i just got 18,9V and additionally 0,7 volt for the diode D3 1n4148 --nearly 20V waste. the LT1056 is driven with 25V?
what did i wrong?
thx
chris
i just looka t your schematic and think about wasting the voltage for the LT1056 U1. your rail is 45V and if you use 2k7 with 7mA i just got 18,9V and additionally 0,7 volt for the diode D3 1n4148 --nearly 20V waste. the LT1056 is driven with 25V?
what did i wrong?
thx
chris
U1 is powered with 30V. Nothing is wasted.
BUT - Its rails are referenced not to the ground, but to the output - look at D7 controlling max voltage for U1.
D7, via C4/C5/R9 is connected to the output of the amp.
U1 is NOT powered by fixed/constant regulated DC.
Zeners D1/D2 are not used by U1, they are there only for U2 (which is powered in conventional 'non-floating' way).
That's why everywhere in this thread U1 is called as 'floating'. While DC voltage across U1 rails remains constant (30V),
the actual voltages (if measured against the GND) are 'floating' up and down along with output wave.
This way, U2 can provide actual voltage swing much higher than +/- 18V if its rails were powered by traditional +/- 18V.
Elvee designed it this way, because most of op-amps can't be used with rails over +/- 18V or so.
The 1st version of his design was 'active' - using transistors like in the article attached below.
The last version - was called 'passive' as he managed to simplify it, and got rid of the transistors driving op-amp rails.
So this amp is unique in (at least) 2 ways - a) current dumping b) floating op-amp VAS.
Just run the sim, and plot voltages on the rails of U1. The difference between them is always around 30V.
Perhaps Elvee can explain it better...
BUT - Its rails are referenced not to the ground, but to the output - look at D7 controlling max voltage for U1.
D7, via C4/C5/R9 is connected to the output of the amp.
U1 is NOT powered by fixed/constant regulated DC.
Zeners D1/D2 are not used by U1, they are there only for U2 (which is powered in conventional 'non-floating' way).
That's why everywhere in this thread U1 is called as 'floating'. While DC voltage across U1 rails remains constant (30V),
the actual voltages (if measured against the GND) are 'floating' up and down along with output wave.
This way, U2 can provide actual voltage swing much higher than +/- 18V if its rails were powered by traditional +/- 18V.
Elvee designed it this way, because most of op-amps can't be used with rails over +/- 18V or so.
The 1st version of his design was 'active' - using transistors like in the article attached below.
The last version - was called 'passive' as he managed to simplify it, and got rid of the transistors driving op-amp rails.
So this amp is unique in (at least) 2 ways - a) current dumping b) floating op-amp VAS.
Just run the sim, and plot voltages on the rails of U1. The difference between them is always around 30V.
Perhaps Elvee can explain it better...
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