From now 8 years developing Light Dependant Resistor audio circuits:
Better audio result I perceive is achieved with LDR's when there is no resistance or capacitance in parallel with the LED side cathode. This also includes prior power supply
capacitance and pot resistance if arranged in parallel. The cathode when arranged
to be the only grounding element which is not impossible, creates the best ability
for LDR's to excel as audio optocouplers.
Cheers / Chris
Better audio result I perceive is achieved with LDR's when there is no resistance or capacitance in parallel with the LED side cathode. This also includes prior power supply
capacitance and pot resistance if arranged in parallel. The cathode when arranged
to be the only grounding element which is not impossible, creates the best ability
for LDR's to excel as audio optocouplers.
Cheers / Chris
Hi Andrew
No still V+ ground, the attached schematic shows, how R is solved not grounding,
and in the process solves the LDR turn off issue due to high value of 500k on the pot.
but C is more difficult, solved partially with respect to rectifier switching
separated by an h11f1m ground lifting.
Updated schematic to show diode lift on 7812
Cheers / Chris
No still V+ ground, the attached schematic shows, how R is solved not grounding,
and in the process solves the LDR turn off issue due to high value of 500k on the pot.
but C is more difficult, solved partially with respect to rectifier switching
separated by an h11f1m ground lifting.
Updated schematic to show diode lift on 7812
Cheers / Chris
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No it's the other way around. I have never got used to this valve/tube jargon.
The cathode of the LED goes to - and the anode goes to +.
Thus all normal LED driven by a +ve supply use a grounded cathode.
i.e. nothing different.
Referring to Silonex data, now Advanced Photonix, there are no examples where
the cathode is given direct access to ground, to be at the same point as power
supply capacitance, rather it is always either transistor or diode lifted.
The anode with respect to the supply, is given similar even better separation.
See figure 10 and 12, where diode lift occurs and figure 16 where a transistor lifts the cathode
Their purpose would appear to have been to arrive at a best circuit for measurement
purpose, not necessarily listening with a audio system, although they might have
done that too.
Cheers / Chris
the cathode is given direct access to ground, to be at the same point as power
supply capacitance, rather it is always either transistor or diode lifted.
The anode with respect to the supply, is given similar even better separation.
See figure 10 and 12, where diode lift occurs and figure 16 where a transistor lifts the cathode
Their purpose would appear to have been to arrive at a best circuit for measurement
purpose, not necessarily listening with a audio system, although they might have
done that too.
Cheers / Chris
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But this is not only an LED, it is in tandem with coupling via varying luminessence
to a photocell, that then is matched for best achievable characteristics.
from each.
A Resistive Capacitive circuit has time constants- tau , when wrongly placed the
photocell responds, similarly when better placed the photocell also responds.
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I'm having a little trouble understanding that schematic. Why are C2 and C3 in series? C4 is sort of in parallel with C2-C3, except the negative side of C3 isn't at "ground". Is anything attached to the gate of the JFET? What is D6, is it related to the LDR in any way? What i the purpose of D8 and D1?
Hi
Series caps or a singular cap can be used, series are shown.
An h11f1m opto fet coupler is used, which is on one half a LED
shown by D6, its purpose is to resistively distance psu ground switching from
cathode and signal grounds related to the LDR's, in use it forms
a set resistance between psu and LDR ground. So the gate is
optocoupled; see https://www.fairchildsemi.com/datasheets/H1/H11F3M.pdf
The purpose of D8 is to lift the 7812 ground, and corrected for voltage
by D1, and to reduce noise from rectifier switching disturbing
7812 vout.
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Yes all fine, and quite acceptable to do, if you are very careful with
RCA plugs, if you are not careful ie pulling out plugs transition noise will occur
that can damage loudspeakers, This is why it is usually
best to star ground cathode returns and signal ground to chassis.
Emitter of Q2 is an input, and collector its output, its a common base
transistor. it ensures R2 defines current.
Q2's base is grounded. For its emitter to act as an input it must be negative. The emitter is connected to ground via resistors and LEDs, which can only conduct if the emitter is positive. The emitter also has a feed via R2, which appears to come from a positive supply. Hence if Q2 is an NPN transistor, as marked, then it can't conduct.
Would you like to revise your circuit? At present, parts of it look like they were produced by a random circuit drawing algorithm.
Would you like to revise your circuit? At present, parts of it look like they were produced by a random circuit drawing algorithm.
Why not use a resistor? You have a 7805 configured as a constant current source, producing a fixed resistance across the h11fm1. I think a resistor would have less noise and accomplish the same thing.
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