Hi All. I have been following the thread on the “Light Speed” and other LDR controls. There are a few issues of note.
1/ Source impedance is relatively low especially around the mid range.
2/ Output impedance is too low for some high impedance input amplifiers.
3/ Despite the “No Pot’ in the signal path, there are at least two in the LED illumination circuit.
The following design has no Pots at all, minimum source impedance of 27K and output of around 21K which may still be too low in some cases.
I’ m calling it a Shutter light for want of a better name. A shutter is moved across four 25mm long tubes housing the LDRs via a 270 deg cam. The four LEDs are not in line with the LDRs but offset toward the centre point. If they were in line, the source impedance would drop into the 100’s of ohms area in the centre of travel (135 deg). At the centre point both shunt and series LDRs are relatively shaded and both have 13K or so of resistance. As the shutter moves from the centre; move light falls on one and less on the other increasing the source impedance.
Alignment and channel matching is done simply by shoving the LED’s one way or another. Response can also be altered by moving them closer to the centre, or just the series one to create a log response. I’m still messing about with this and have yet to do any listening test. You thoughts?
1/ Source impedance is relatively low especially around the mid range.
2/ Output impedance is too low for some high impedance input amplifiers.
3/ Despite the “No Pot’ in the signal path, there are at least two in the LED illumination circuit.
The following design has no Pots at all, minimum source impedance of 27K and output of around 21K which may still be too low in some cases.
I’ m calling it a Shutter light for want of a better name. A shutter is moved across four 25mm long tubes housing the LDRs via a 270 deg cam. The four LEDs are not in line with the LDRs but offset toward the centre point. If they were in line, the source impedance would drop into the 100’s of ohms area in the centre of travel (135 deg). At the centre point both shunt and series LDRs are relatively shaded and both have 13K or so of resistance. As the shutter moves from the centre; move light falls on one and less on the other increasing the source impedance.
Alignment and channel matching is done simply by shoving the LED’s one way or another. Response can also be altered by moving them closer to the centre, or just the series one to create a log response. I’m still messing about with this and have yet to do any listening test. You thoughts?
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Interesting, how is this project coming? Any listing impressions yet compared to standard lightspeed? I'd love to see some more pics of the insides of this device as well as a schematic?
thanks
MC
thanks
MC
Hi,
I am confused with the way you describe the impedances.
The Source impedance is the output impedance of the Source as seen by the Receiver.
The output impedance is that seen by the Receiver.
The Source has an output impedance
The receiver has an input impedance
The LDRs have a source impedance and an input impedance.
The Source sees the input impedance of the LDRs.
The Receiver sees the output impedance of the LDRs.
I am confused with the way you describe the impedances.
The Source impedance is the output impedance of the Source as seen by the Receiver.
The output impedance is that seen by the Receiver.
The Source has an output impedance
The receiver has an input impedance
The LDRs have a source impedance and an input impedance.
The Source sees the input impedance of the LDRs.
The Receiver sees the output impedance of the LDRs.
Hi Andrew. To avoid confusion just consider the LDR network as a standard pot. The plot on the left is the resistance through 270 deg of rotation Across the pot. i.e. top to bottom (the connection to the source, CD etc)
The plot on the right is of the resistance through 270 degs of the wiper to the bottom or earth of the pot ( connects to the amplifier)
The plot on the right is of the resistance through 270 degs of the wiper to the bottom or earth of the pot ( connects to the amplifier)
Hi MC. Sorry for the delay. Have been away working and haven't got around to doing some serious listening as yet. Will post some more images of the unit apart to give you an idea. I also have CAD drawings I used to construct it, if you are interested.
Cheers,
Simon
Cheers,
Simon
I understand the concept of your design, but if I'm seeing it correctly, it looks like both LDRs are operating exactly the same way, that is it appears they increase and decrease resistance together, whereas one should increase awhile the other decreases. Am I seeing it right?
Mike
Mike
Hi Mike. In the photo you are seeing the bottom half of both channel LDR tunnels. The other two are hidden under the shutter. Would a pic of the shutter half way help. If so I can post one.
Cheers,
Simon
Cheers,
Simon
It's always fun to view different solutions.
I do however wonder if this isn't making it more difficult than it has to be?
A MPU can be programmed to control a LDR in any way you like.
I like fancy solutions as much as the next guy but simplicity has it's virtues too.
Cool idea though.
I do however wonder if this isn't making it more difficult than it has to be?
A MPU can be programmed to control a LDR in any way you like.
I like fancy solutions as much as the next guy but simplicity has it's virtues too.
Cool idea though.
Hi Tade. Glad you see the plot. Have got side tracked making up a UHF remote controlled stepper motor and driver board with power supply for the LEDs. Have done some listening tests with the shutter in series with the existing amp. Sounds "warm" and likable. The amp is very different and requires a lot of mechanical fitting of the shutter. The mechanical is much harder and therefore more fun for me to do being an electronics type.
Cheers,
Simon.
Cheers,
Simon.
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