Hi
I've just swapped out the two suspect LDRs, adjusted the other two using the 1K trim pot and I now have controllable volume!
It looks like I am going to require a resistor on the 100k pot as the volume control is very sensitive. When I adjust the pot to the off position I can still faintly hear music from the speakers. How do I correct this?
Thanks a lot for all your help, especially Fred 🙂
Richard
I've just swapped out the two suspect LDRs, adjusted the other two using the 1K trim pot and I now have controllable volume!
It looks like I am going to require a resistor on the 100k pot as the volume control is very sensitive. When I adjust the pot to the off position I can still faintly hear music from the speakers. How do I correct this?
Thanks a lot for all your help, especially Fred 🙂
Richard
the range of resistance of the LDRs is limited. They cannot go to infinity and they cannot go to zero.
This inherent characteristic of the LED driven LDRs restricts the range of adjustability of the volume control.
If you want to switch to zero sound output, find another way.
This inherent characteristic of the LED driven LDRs restricts the range of adjustability of the volume control.
If you want to switch to zero sound output, find another way.
Congratulation, Richard.
Others helped me in the past, I just tried to do the same for others. This is the communty spirit.
A couple things that you can try to improve the attenuation and range:
1. Add a small resistor like 22R in between the 5VDC and the pot.
2. Change the pot to a higher impedance one, e.g. 200K or 250K.
Independent of the above, I recommend to replace the 100R's with something
like 220R to protect the LDR's from over current.
Cheers,
Others helped me in the past, I just tried to do the same for others. This is the communty spirit.
A couple things that you can try to improve the attenuation and range:
1. Add a small resistor like 22R in between the 5VDC and the pot.
2. Change the pot to a higher impedance one, e.g. 200K or 250K.
Independent of the above, I recommend to replace the 100R's with something
like 220R to protect the LDR's from over current.
Cheers,
Hi Richard
Good to hear you got it working
I sure dont hope I have go through this
Any idea what triggered the failure ?
Good to hear you got it working
I sure dont hope I have go through this
Any idea what triggered the failure ?
When the pot is at full counter-clockwise, there is only a 100R between the 5VDC and the LDR's. While the 100R can protect the LDR from over voltage, it doesn't lower the current enough to below 25ma. I have seen LDR's drawing 30+ ma in this situation. Since both shunt LDR's exhibited same symptom, it is logical to have a common cause. I suspect over current.
Hi
I'm not sure what cause these particular LDRs to fail. The circuit was really simple to put together and haven't changed anything since.
Richard
I'm not sure what cause these particular LDRs to fail. The circuit was really simple to put together and haven't changed anything since.
Richard
Hi Tinitus
If you are about to build your attenuator and are not using a PCB, I would recommend constructing your circuit using the point to point method with perf board. Try also leaving the LDR anode and cathode legs a reasonable length, this will simplify testing when attaching your DMM probes for calibration.
I hope this helps
Richard
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Perhaps this is a good place to add a timely reminder about taking some care with soldering those LDRs - they just don't like too much of it - suggest you use a couple of those small metal heatsink clips, especially if the resistor leads are short.
It's good to see the "George" Lightspeed, the "Alekzander" (ZenMod) version, and the DC-B1 (with the Salas shunt reg) all coming together at the same time.
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Perhaps this is a good place to add a timely reminder about taking some care with soldering those LDRs - they just don't like too much of it - suggest you use a couple of those small metal heatsink clips, especially if the resistor leads are short.
It's good to see the "George" Lightspeed, the "Alekzander" (ZenMod) version, and the DC-B1 (with the Salas shunt reg) all coming together at the same time.
It was asked why there was still sound when pot turned down at full attenuation
Maybe we should remind that George recommends not to leave pot fully turned down, as this will put wear on the LDR
Maybe we should pay more attention to the power up situation
Probably also best not to have pot fully turned at power up
Maybe this could a worst case situation
Maybe we should consider to have a "mute" switch between supply and pot
Im sure I will
Maybe we should remind that George recommends not to leave pot fully turned down, as this will put wear on the LDR
Maybe we should pay more attention to the power up situation
Probably also best not to have pot fully turned at power up
Maybe this could a worst case situation
Maybe we should consider to have a "mute" switch between supply and pot
Im sure I will
good idea.
Without the "mute" switch there is a temptation to forget the attenuator is turned fully down and leave it that way.
The mute switch could also add in a resistor to reduce the LED currents just as if it were a standby that can be left "ON" for extended periods.
Hi
I am really impressed with my attenuator. It has such a clean, crisp sound and a really expansive sound stage. I was surprised by the amount my previous pre-amp degraded the sound.
If you are considering one of these...do it! 🙂
Thanks again
I am really impressed with my attenuator. It has such a clean, crisp sound and a really expansive sound stage. I was surprised by the amount my previous pre-amp degraded the sound.
If you are considering one of these...do it! 🙂
Thanks again
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I suppose the resistor would also lower "inrush current"(not a joke 🙂)
How big would this resistor be ?
I don't believe "inrush" current to the LEDs actually happens. The regulator will bring up the 5V supply relatively slowly and any overshoot should be tiny.
If the pot were centred, then the resistance feeding the LEDs would be ~200k.
If the pot is accidentally left all to one end, then the LEDs could be fed from ~120r to 200r. This could be augmented by having a permanent resistor of >=1k0 in the feed line that is bypassed by a switch contact that closes when "standby/mute" is turned OFF.
If the pot were centred, then the resistance feeding the LEDs would be ~200k.
If the pot is accidentally left all to one end, then the LEDs could be fed from ~120r to 200r. This could be augmented by having a permanent resistor of >=1k0 in the feed line that is bypassed by a switch contact that closes when "standby/mute" is turned OFF.
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I have tried reducing the gain by adding a resistor in series with the +5v line. I am getting no effect at all. The gain remains the same. Should this not be used with another resistor tied to ground?
what gain have you tried to reduce?
The 5V line supplies the LEDs.
The LDRs are in the audio signal line.