Pricing is the same sekess. I estimate Christmas time. To get on the list email me at diyldr@gmail.com
Rakesh, yes I do. Please email me at diyldr@gmail.com.
Uriah
Rakesh, yes I do. Please email me at diyldr@gmail.com.
Uriah
LDRs are matched and can be purchased. If you emailed me for sets of LDRs and go on my Christmas list please check the store at Build An Amp
Uriah
Uriah
Hi,
I am getting ready to add an LDR volume control to a Mezmerize board in lieu of the standard pot allowed for.
The Mez already has a regulated +-10V supply.
I am thinking of tapping into the +10V & 0V, to power the LED side of the LDRs.
I plan to increase the current limiting resistors from 100r to 390r so that no LED can draw more than 20mA.
Any thoughts?
I am getting ready to add an LDR volume control to a Mezmerize board in lieu of the standard pot allowed for.
The Mez already has a regulated +-10V supply.
I am thinking of tapping into the +10V & 0V, to power the LED side of the LDRs.
I plan to increase the current limiting resistors from 100r to 390r so that no LED can draw more than 20mA.
Any thoughts?
I think 20mA is a great place to sit them at max. If its not max because of the uniqueness of each LDR then just increase the voltage a bit. What I have started doing is giving them around 160R and changing voltage til I get greater than 40R on the LDRs. Its my belief that less than 40R is in the danger zone for the LDRs. Some will hit lower than that with 20mA at 5V and some higher so I just give a very safe resistance and then slowly tweak voltage while watching the resistance of the LDR.
But you want to go from 10V. Then I think I would put trimmers on them and test them then measure the trimmer. Start with a 10k pot or trimmer and test it out. I remember one test at 10.6V through a 22k resistor was giving me around 200-500 on a bunch of LDRs.
Uriah
EDIT Let me rephrase that.. 20mA at 5V is good. 20mA at 10V is a dead LDR.
But you want to go from 10V. Then I think I would put trimmers on them and test them then measure the trimmer. Start with a 10k pot or trimmer and test it out. I remember one test at 10.6V through a 22k resistor was giving me around 200-500 on a bunch of LDRs.
Uriah
EDIT Let me rephrase that.. 20mA at 5V is good. 20mA at 10V is a dead LDR.
I don't understand where this comes from.
An LED passes current at near constant voltage, usually around 2V.
5V supply and 100r gives a maximum current through the LED of ~30mA, LDR dissipation ~60mW
10V supply and 390r gives a maximum current through the LED of ~20mA, LDR dissipation ~40mW.
Why should 10V & 20mA kill the LDR, when 5V & 30mA is the recommended standard set up?
On the Lightspeed I have here at home a 100R resistance in series with 5V gives me about 30R. Lower than I would recommend. An average LDR with 22k and 10.6V gives 200-500R. I have not been daring enough to put a 400R resistor in series with 10.6V as I am sure this would put the LDR where I consider dangerous. Once they go into that sub 40R region the matching starts to go bad with the LDRs. Sometimes you get one that can handle it without the resistance curve changing but most of them will forever change their resistance curve if left on for any significant amount of time at less than 40R. I wish I could predict what an LDR will do strictly based on voltage and series resistance. If I could do that then I would not need to match them. But they are in fact all different and act differently with changing voltage and series resistance. One thing that stays true for nearly all of them is that below 40R reading on the LDRs and you cant count on the resistance curve staying the same. I will get customers that drive them lower in resistance in an effort for lower volume on their efficient systems. What happens is that they will end up with a bad match or they will end up with an LDR that gets stuck somewhere around 75k as a minimum resistance and then they can go higher in resistance from there. So apparently the LED still works but the optoresistor does not.
So, no I have not tried 10V and 390R. They do suck current like mad and saturate down at low resistance so maybe 390 would be a minimum resistance to try but I would try on an LDR I dont care about. I am guessing it would kill it, but I think based on experience that its a good guess. Have I tested it? No.
Uriah
So, no I have not tried 10V and 390R. They do suck current like mad and saturate down at low resistance so maybe 390 would be a minimum resistance to try but I would try on an LDR I dont care about. I am guessing it would kill it, but I think based on experience that its a good guess. Have I tested it? No.
Uriah
I am going the same route. I am planing to tap the voltage directly from the mains capacitors of the DCB1, because I am afraid that at the turnoff the 12v regulator starts to behave incorrectly due to voltage being lower and lower.
I will place an LM338 regulator after that, taking it down to +5v.
What do you think of that?
you could add a 5V reg after the relay's 12Vdc reg.
I have 15Vdc here so that is clearly an option for me.
I have started testing my LDRs. The red pen that Uriah marked the pairs with is illegible.
A disadvantage of the higher LDR voltage (10V instead of 5V) is that the 100k does not turn down the LED brightness as far. This will result in a lower range of adjustment.
I have 15Vdc here so that is clearly an option for me.
I have started testing my LDRs. The red pen that Uriah marked the pairs with is illegible.
A disadvantage of the higher LDR voltage (10V instead of 5V) is that the 100k does not turn down the LED brightness as far. This will result in a lower range of adjustment.
yes a higher pot value will bring back the range of adjustment.
But, the track and wiper are not designed for these high currents and is likely to fail eventually. Even the 100k 1W has a current limit of just 3.1mA and should be run at less than this.
I have 250k, 500k, 1M, 1M2, 2M2 pots but they are all single track.
As one decreases the current, by using a higher resistance pot, the LED brightness goes down and the resistor element increases in resistance.
A higher value pot will give a higher input impedance and a higher output impedance.
A higher voltage combined with the higher pot value will restore the input and output impedances, if selected correctly.
I am now wondering what benefit could come from using 4V or even 3.5V with either a 50k pot or 100k pot. Obviously lower input and output impedances. But a greater range of adjustment would also follow.
The voltage across the pot is [Vsupply - Vled]. 10V would give ~ 8Vr
3.5V would give ~1.6Vr. A difference in current (and brightness) of 5times.This could give the same maximum brightness by using a selected current limiting resistor to protect the LDR but 5times less current at the other end and so a lower pair of impedances and a wider range of adjustment.
I suspect the balancing of the two channels will be more pernickety at this reduced Vr
Need to add that the muting relay in the DCB1 avoids any problems with LDR peculiarities at power off.
But, the track and wiper are not designed for these high currents and is likely to fail eventually. Even the 100k 1W has a current limit of just 3.1mA and should be run at less than this.
I have 250k, 500k, 1M, 1M2, 2M2 pots but they are all single track.
As one decreases the current, by using a higher resistance pot, the LED brightness goes down and the resistor element increases in resistance.
A higher value pot will give a higher input impedance and a higher output impedance.
A higher voltage combined with the higher pot value will restore the input and output impedances, if selected correctly.
I am now wondering what benefit could come from using 4V or even 3.5V with either a 50k pot or 100k pot. Obviously lower input and output impedances. But a greater range of adjustment would also follow.
The voltage across the pot is [Vsupply - Vled]. 10V would give ~ 8Vr
3.5V would give ~1.6Vr. A difference in current (and brightness) of 5times.This could give the same maximum brightness by using a selected current limiting resistor to protect the LDR but 5times less current at the other end and so a lower pair of impedances and a wider range of adjustment.
I suspect the balancing of the two channels will be more pernickety at this reduced Vr
Need to add that the muting relay in the DCB1 avoids any problems with LDR peculiarities at power off.
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I have what maybe is a newbie question in LDR matters. Based on Georgehifi schematics, turning the adjustment trimmers to 0 plus the 100r limiting resistor, will add a total of 100r. Ohm's law tells me that if you supply it with 5v, you will get a maximum of 50mA going through each LED when you turn the 100k por all the way.
But if you look at the datasheet, it clearly sais that LED max forward current is 25mA. Are we allowing to pass double the maximum current supported by the devices? What am I missing here? Maybe that fact has been treated before...
Here the direct links to the datasheet and schematics:
http://diyaudioprojects.com/Solid/D...-Attenuator/Silonex-NSL-32SR2-Optocoupler.pdf
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)
But if you look at the datasheet, it clearly sais that LED max forward current is 25mA. Are we allowing to pass double the maximum current supported by the devices? What am I missing here? Maybe that fact has been treated before...
Here the direct links to the datasheet and schematics:
http://diyaudioprojects.com/Solid/D...-Attenuator/Silonex-NSL-32SR2-Optocoupler.pdf
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)
Regi,
you have misread the schematic.
The LED part of the LDR drops a voltage when current is passed through it.
No current and no voltage drop.
If sufficient current is passed through the LED then VLED is as specified in the datasheet. Expect this to be about 1.9Vled
Now subtract the back emf of the LED from the forward emf of the PSU and you are left with about 3.1V driving current through the resistances in that circuit. The worst case current if VR is set to zero ohms is ~31mA if 100r is used as the protection resistor. I think that you should measure the actual voltages in your assembled LDR and select a protection resistor that does limit the current to somewhere in the range 20mA to 25mA. 120r to 150r will provide a lower current limit than 100r.
you have misread the schematic.
The LED part of the LDR drops a voltage when current is passed through it.
No current and no voltage drop.
If sufficient current is passed through the LED then VLED is as specified in the datasheet. Expect this to be about 1.9Vled
Now subtract the back emf of the LED from the forward emf of the PSU and you are left with about 3.1V driving current through the resistances in that circuit. The worst case current if VR is set to zero ohms is ~31mA if 100r is used as the protection resistor. I think that you should measure the actual voltages in your assembled LDR and select a protection resistor that does limit the current to somewhere in the range 20mA to 25mA. 120r to 150r will provide a lower current limit than 100r.
Red pen? Wow its been a long time AndrewT. If you have any trouble with those let me know and I will replace. Its been a long time and my methods and understanding have both improved since you bought those. The pairs should match but at the time I was only matching pairs and not concerned at all with quads. That said I still use the Lightspeed I built back then. Sounds and works great.
Uriah
Uriah
Hi there guys i have just decided to make the lightspeed attenuator and i would like a set of LDR's to make one, i have bought 5 of them alredy and will be buying another 10 later on
question is can some one please explain how to match them up? im new to electronics but do have access to electronic test engineers and equipment at my work
Also i have bought an alps 100k x2 pot is this ok??
any info on the above would be great
Mat
question is can some one please explain how to match them up? im new to electronics but do have access to electronic test engineers and equipment at my work
Also i have bought an alps 100k x2 pot is this ok??
any info on the above would be great
Mat
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