Banned
Joined 2002
Jasonl. The one thing i don't like about your amp Is the Bootstrap cap used in place of a current source for the upper output Devices. not only dose this allow Distortion to rise at low frequencies, But can leave the upper output device starved for Drive current. I would redesign usin a Constant current source at this location.
Banned
Joined 2002
more inductance
Have a look on the web for how to calculate the inductance of a circuit. An individual wire has some intrinsic inductance and like resistance is proportional to the wires length and is reduced with thickness. However, I would suggest in the amp circuit in the photo the inductance of concern is the much bigger loop inductance which is a consequence of the total area enclosed by a circuit of current.
A very practical and effective way of reducing loop inductance is to twist the wires of the circuit together to minimize the area enclosed between them. Shortening wires also reduces the area enclosed but may be physically restrictive.
Look at all current loops in your design and decide which need to have low inductance (not all will). Then build the thing (including PCB traces) to minimize the area enclosed of the circuits that matter.
You will see evidence of this in commercial designs - often the psu cables to the amp boards are twisted together or bound tightly using cable ties. This not only looks neat and mechanically robust but also serves a crucial electrical purpose.
BAM
Have a look on the web for how to calculate the inductance of a circuit. An individual wire has some intrinsic inductance and like resistance is proportional to the wires length and is reduced with thickness. However, I would suggest in the amp circuit in the photo the inductance of concern is the much bigger loop inductance which is a consequence of the total area enclosed by a circuit of current.
A very practical and effective way of reducing loop inductance is to twist the wires of the circuit together to minimize the area enclosed between them. Shortening wires also reduces the area enclosed but may be physically restrictive.
Look at all current loops in your design and decide which need to have low inductance (not all will). Then build the thing (including PCB traces) to minimize the area enclosed of the circuits that matter.
You will see evidence of this in commercial designs - often the psu cables to the amp boards are twisted together or bound tightly using cable ties. This not only looks neat and mechanically robust but also serves a crucial electrical purpose.
BAM
Banned
Joined 2002
2sj55/2sk175
Hi all people,
I wonder if anybody has built Holtons Lateral amp with Hitachi 2sj55/2sk175? Is it possible and if, do I have to make any changes? My problem is that I have tried byt it runs the positive power rail on the output and I can not find any fault in the circuit.
Any sugestions?
Regards from
Bengt Eriksson, Sweden
Hi all people,
I wonder if anybody has built Holtons Lateral amp with Hitachi 2sj55/2sk175? Is it possible and if, do I have to make any changes? My problem is that I have tried byt it runs the positive power rail on the output and I can not find any fault in the circuit.
Any sugestions?
Regards from
Bengt Eriksson, Sweden
caution: just hold on a minute there ...
I'd be a bit leery about building this circuit exactly as shown. A couple of warning signs jump out right away:
1. The bias arrangement as shown may work well for the Hitachi lateral FETs, but not those HEXFETs ....
2. No frequency compensation? Looking like a power oscillator !
I'm curious, what magazine was this in???
mlloyd1
I'd be a bit leery about building this circuit exactly as shown. A couple of warning signs jump out right away:
1. The bias arrangement as shown may work well for the Hitachi lateral FETs, but not those HEXFETs ....
2. No frequency compensation? Looking like a power oscillator !
I'm curious, what magazine was this in???
mlloyd1
topicreader said:
It may be that the f compensation is done by the input capacitance of the FET's.
The FET's are driven from a high impedance.
The Cresendo from Elektor has this kind of f compensation.
In this design short lead lengths are exremely critical.
For that reason in the Cresendo the power FET's were mounted on the pcb.
The FET's are driven from a high impedance.
The Cresendo from Elektor has this kind of f compensation.
In this design short lead lengths are exremely critical.
For that reason in the Cresendo the power FET's were mounted on the pcb.
Actually, the schematic in post #18 is very similar to no. 11.1 in
Slones power amp handbook. Slones design is slightly simpler
since it is the simplest of those in his book and intended as a
beginners project. However, Slone does address the issues
mlloyd1 has. He uses lateral MOSFETs, so themal compensation
is not necessary. While using a 6.8nF cap in the same way as
the schematic in post #18 he also has the usual comp. cap
between base and collector.
Slones power amp handbook. Slones design is slightly simpler
since it is the simplest of those in his book and intended as a
beginners project. However, Slone does address the issues
mlloyd1 has. He uses lateral MOSFETs, so themal compensation
is not necessary. While using a 6.8nF cap in the same way as
the schematic in post #18 he also has the usual comp. cap
between base and collector.
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