Thanks juma, I had played with a simplified version of this back in post #10. Its a neat circuit, no question, the only downside is the need for a trimmer (or two!) to null the offset.
You're quite right juma - your circuit fulfils all the criteria at #1. Its an interesting circuit, thanks for sharing.
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Hi,
apart from the trimpot P1 the circuit in #7 fulfills all Your requirements a), b) and c), its even pushpull 😉
When using thermally coupled JFETs (or Duals) thermal stability -and thermally related offset drift- is also low.
You could then omit with the trimpot and install a fixed trimmer-R instead .... or a large output coupling cap 😉
jauu
Calvin
apart from the trimpot P1 the circuit in #7 fulfills all Your requirements a), b) and c), its even pushpull 😉
When using thermally coupled JFETs (or Duals) thermal stability -and thermally related offset drift- is also low.
You could then omit with the trimpot and install a fixed trimmer-R instead .... or a large output coupling cap 😉
jauu
Calvin
Hi,
yes, the current source towards the negative supply is modulated by the voltage drop over R15.
Its a SEPP (Single Ended Push Pull) topology.
As such Class-A biasing is required.
The current swings will not be perfectly symmetrical in amplitude, but the current source will supply for a considerable part of the load signal current.
The Buffer can drive lower impedances with lower distortions for the same set idle current than with a unmodulated ccs.
jauu
Calvin
yes, the current source towards the negative supply is modulated by the voltage drop over R15.
Its a SEPP (Single Ended Push Pull) topology.
As such Class-A biasing is required.
The current swings will not be perfectly symmetrical in amplitude, but the current source will supply for a considerable part of the load signal current.
The Buffer can drive lower impedances with lower distortions for the same set idle current than with a unmodulated ccs.
jauu
Calvin
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No, it's too simple and small for a "real" PCB. Perfboard and p2p are OK for such a simple circuit.
Not exactly related to this thread, but FWIW I've found a way to make a SEPP with much larger peak current than 2x the standing current (more like a 10:1 ratio) which still remains in Class-A operation (no turn-off). Useful for low power circuits, at some 100uA total consumption it can handle occasional 1mA peak currents with grace.
Conceptual schematic below, the sensing resistor is replaced by a diode which did the trick.
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Cheers, I'll just p2p it when I get around to doing it. What sort of input can it take before getting troubled?
Cheers George
George
3V into 1k and 2V into 600R is what I tested as OK. It is voltage/current/load dependent.
3V into 1k and 2V into 600R is what I tested as OK. It is voltage/current/load dependent.
Juma,
what is your experience with the gate leakage of the BF862?
If - in a similar, non CFP configuration - I wire the gate of the BF862 to a volume pot, it will drive the output DC up and down by some mV.
DC leakage in bf862 depends on Vds. Keep it as low as you can - the gate to GND resistor too. Cascoding keeps the Vds low and stable.
If you know what are you doing it's a non-issue.
If you know what are you doing it's a non-issue.
