Try paralleling shunt and/or series with a LDR that does NOT move. It actually sets the max resistance for that LDR and it tames the curve. If you can tame two curves it might look much nicer.
So lets imagine an LDR that does not move set at 10k. Lets imagine you have an LDR paralleled with it that moves that goes up to 20k. Remember how sharply they increase in resistance? Imagine the curve as it tries to raise sharply in resistance. Maybe this would be beneficial for you.
Also think about this: Recently tried 100uf//.47uf caps on the LDR LED legs and I like it a lot. Smooooooth.
So lets imagine an LDR that does not move set at 10k. Lets imagine you have an LDR paralleled with it that moves that goes up to 20k. Remember how sharply they increase in resistance? Imagine the curve as it tries to raise sharply in resistance. Maybe this would be beneficial for you.
Also think about this: Recently tried 100uf//.47uf caps on the LDR LED legs and I like it a lot. Smooooooth.
Go with number 2: as it is so easy to change the 10k7 resistor to ground on the input for say 82k as when the Lightspeed is connected to it it is loaded back down to around 7k again so it doesn't matter.
Just be carefull when you switch it on without the Lightspeed attached as you may get hum if the amp is bi-polar input, if fet input there is usually no hum. "But then who switches their amp on with no input attached."
And remember the best buffer is no buffer, no matter how good. I've tried many and none sound as good as NO buffer.
Cheers George
.
Potting Wax for thermal stability-How?
Have been enjoying my ldr's. They have lived up to the reputation. Thanks to George and everyone who has contributed. I understand that drift will be less with a "potted" circuit. My question is has anyone but George done this. Search of the forum- haven't found a good how to guide. What type of wax? Any specific precautions etc. What to use for the form for the wax. Am I asking for a big mess? Thanks.
Jack C
Have been enjoying my ldr's. They have lived up to the reputation. Thanks to George and everyone who has contributed. I understand that drift will be less with a "potted" circuit. My question is has anyone but George done this. Search of the forum- haven't found a good how to guide. What type of wax? Any specific precautions etc. What to use for the form for the wax. Am I asking for a big mess? Thanks.
Jack C
Just a hard ski base wax, mount all the LDR's so they touch each other get a plastic former that fits over them and pour in the melted (just before setting heat) wax, wait to properly cool and remove the plastic former, then check calibration again.
Cheers George
no volume control on one channel
I am trying to build the lightspeed. I am having a problem with one of the channels where the volume does not adjust. Also, the one channel that does not adjust is at full volume.
When I follow the Blues Method of measuring the resistance amongst the shunt and series ldr, the resistances are matched after letting the lightspeed warm up for 15 minutesl. Also, the one channel that does not adjust is at full volume. The channel that is working goes from near silence to full volume very quickly.
Any tips would be appreciated. I tried switching the wiring on the pot but that did not help.
I am trying to build the lightspeed. I am having a problem with one of the channels where the volume does not adjust. Also, the one channel that does not adjust is at full volume.
When I follow the Blues Method of measuring the resistance amongst the shunt and series ldr, the resistances are matched after letting the lightspeed warm up for 15 minutesl. Also, the one channel that does not adjust is at full volume. The channel that is working goes from near silence to full volume very quickly.
Any tips would be appreciated. I tried switching the wiring on the pot but that did not help.
I second Georges assumption that you soldered to long on that one. When you solder use lots of flux and a hot iron. Put solder on the iron so you have a good drop on the iron. Then touch the iron to whatever pad you will be soldering the LDR to. When the solder wicks over to the pad then roll quickly to the LED leg of the LDR and as soon as solder wicks to the leg you are done. Dont mess with it even if it looks messy. As long as it conducts this is the last time you want to heat it. This should take literally 3 seconds in all.
Uriah
Uriah
Yeah, Uriah -
I got a bit paranoid about killing off any of your perfectly matched ldr, so used some of those little metal spring clips - thin little clothes pegs things - and just "clamped the leads" at the ldr body, bove the pcb and quick soldered the tracks - it's a bit awkward, but "better to be safe than ...."
... Regards, and thanks to George, too.
I got a bit paranoid about killing off any of your perfectly matched ldr, so used some of those little metal spring clips - thin little clothes pegs things - and just "clamped the leads" at the ldr body, bove the pcb and quick soldered the tracks - it's a bit awkward, but "better to be safe than ...."
... Regards, and thanks to George, too.
Good point James. I dont use them but I definitely endorse them!!. I have used pliers to grab onto them before when I knew I would be soldering a few extra seconds, like when removing the resistor leads from a board. I dont know if pliers will transfer heat fast enough but it makes me feel better. Even soldering on the resistor side can be damaging.
soldering
...just thought if I can easily avoid burning the LDRs, when I solder them as long as they are in ice-cold water.
I would provisonally fix them on an empty pcb, turn the pcb upside down, put the pcb (LDRs then on the downside) on a cup, that´s filled with ice-cooled water. The soldering side of the PCB remains out of the ware and dry. Leave them in the cold water for some minutes to allow the inner part of the LDRs to be "precooled" to 2C or so.
Some developing heat on the part between soldering point and LDR would be taken by the water. Nevertheless, still keep the soldering process as short as possible.
Afterwards, dry it to avoid corrosion.
Cheers , Frank
...just thought if I can easily avoid burning the LDRs, when I solder them as long as they are in ice-cold water.
I would provisonally fix them on an empty pcb, turn the pcb upside down, put the pcb (LDRs then on the downside) on a cup, that´s filled with ice-cooled water. The soldering side of the PCB remains out of the ware and dry. Leave them in the cold water for some minutes to allow the inner part of the LDRs to be "precooled" to 2C or so.
Some developing heat on the part between soldering point and LDR would be taken by the water. Nevertheless, still keep the soldering process as short as possible.
Afterwards, dry it to avoid corrosion.
Cheers , Frank
Jeez, don't go psycho over these little things - they are a bit sensitive but if you're fairly quick, no problems at all - those heatsink clips are available everywhere, or make your own and are perfect for "nervous Nellies" like me - just do one leg of each device at a time and go onto the next one, then the next, etc and then come back to the first one, etc - it gives each one max cooling time - clean solder it, don't hesitate and don't go over it to make a perfect joint unless absolutely necessary - I understand that the lead free solder is a bit more difficult to use until you get used to it (I prefer the bad ol' lead stuff with a dash o' silver).
- great little devices.
- great little devices.
Hi,
I am using dvb-projects board and I have fitted the matched LDR pair to input and shunt instead of to the 2 inputs.
With the pot turned fully clockwise I read 83ohm across the LDR and
full anticlockwise I read 9.8Kohm and have managed to roughly balance the 2 channels.
Connecting to a chipamp and a portable cd via headphone outputs I get very little change in volume. Fully counterclockwise is about listening level and full clocwise a bit louder.
Would swapping the LDR's fix the problem? I feel I would probably destroy the LDR when I remove them. Also, would the higher resistance pair be used for the input or shunt. I had to remove the paper stuck to the legs so don't even know what the readings were anyway so this has turned into a bit of a stuffup. Knowing the above might help my next attempt.
Thanks,
kffern
I am using dvb-projects board and I have fitted the matched LDR pair to input and shunt instead of to the 2 inputs.
With the pot turned fully clockwise I read 83ohm across the LDR and
full anticlockwise I read 9.8Kohm and have managed to roughly balance the 2 channels.
Connecting to a chipamp and a portable cd via headphone outputs I get very little change in volume. Fully counterclockwise is about listening level and full clocwise a bit louder.
Would swapping the LDR's fix the problem? I feel I would probably destroy the LDR when I remove them. Also, would the higher resistance pair be used for the input or shunt. I had to remove the paper stuck to the legs so don't even know what the readings were anyway so this has turned into a bit of a stuffup. Knowing the above might help my next attempt.
Thanks,
kffern
If you got your LDRs from me then, more recently, all 4 are near matches. 2 pair that are close to identical. I tend to think something more is wrong than just the LDRs in the wrong spots. I feel you may hurt the LDRs when removing them as well, but if you use a lot of flux, a very clean iron, a hot iron ~30W or so.. I think you can remove and swap the two you need to switch. Still, it seems something else is wrong.
Uriah
Uriah
Here is a picture of my board. The only thing I can think of are the 1k pots being the right way round and the 100k pot wired correctly. The 100k pot is wired so that it would fit onto the board pins. Its from Jaycar in Aus.
The pot is getting 5 volts and varying it changes the voltage from 0 to 5.
I was very carefull with soldering the LDRs. Used a crocodile clip on the legs and very little heat.
Thanks,
kffern
The pot is getting 5 volts and varying it changes the voltage from 0 to 5.
I was very carefull with soldering the LDRs. Used a crocodile clip on the legs and very little heat.
Thanks,
kffern
I received my shipment of (unmatched) LDRs, but haven't started playing with them yet.
Is the differences between devices best characterized mostly by different slopes, or does the 20ma/40ohm relationship and temperature coefficient vary between devices as well?
Looking at the Silonex PDF, it says that 40 ohms is the MAX resistance at 20ma. Does that, at least, hold true? What is the most typical resistance at 20ma?
I dont run them at 5V anymore so my current is different but I also dont run them lower than 40Ohms. George and I differ on opinion here if I recall but my experience has been that they WILL go lower than 40Ohms but that when driven lower the resistance curve permanently changes. I have had an LDR explode at 25Ohms but I also have a Lightspeed I built that sits at 25/27 Ohms for shunt at min volume with no problem. LDRs are funny things that are each unique. Some can handle more than others. 40Ohms is my rule of thumb.
The difference between each LDR is the curve. This is what we try to match. Dont worry about temp. Yeah it might be slightly different between devices but it doesnt matter til high resistance and at high resistance the difference made by temp wont move your stereo image a bit.
20mA at 5V if I recall will give around 30Ohms. Fine for some LDRs, not fine for others. Dont try to typify the LDRs. Thats the problem.. none of them are typical. If they were no one would have to match them. Been a long time since I tested at that level. But here is an example. Recently on a test at 11V with .5mA I got measurements from 200R to 1500R. LDRs cant be pinned down to a 'typical' operating characteristic.
So anyway in matching yours why dont you just use a pot and take one down to 100Ohms or so, then measure the resistance of the pot and use that resistor value for your lowest measurement in matching. This way you know how they act at near lowest resistance and yet you dont fool with their resistance curve. Trust your own measurements and experiments. Silonex removes more crap from their website every few months. I expect they remove it as people show them how their datasheets are full of you know what. I have sent them literally thousands of measurements and a handful of junk LDRs to prove my point that their datasheets are not sound and that their manufacturing suffered when they changed manufacturing plants but they just try to steer me to using other optoresistors they make.
Uriah
The difference between each LDR is the curve. This is what we try to match. Dont worry about temp. Yeah it might be slightly different between devices but it doesnt matter til high resistance and at high resistance the difference made by temp wont move your stereo image a bit.
20mA at 5V if I recall will give around 30Ohms. Fine for some LDRs, not fine for others. Dont try to typify the LDRs. Thats the problem.. none of them are typical. If they were no one would have to match them. Been a long time since I tested at that level. But here is an example. Recently on a test at 11V with .5mA I got measurements from 200R to 1500R. LDRs cant be pinned down to a 'typical' operating characteristic.
So anyway in matching yours why dont you just use a pot and take one down to 100Ohms or so, then measure the resistance of the pot and use that resistor value for your lowest measurement in matching. This way you know how they act at near lowest resistance and yet you dont fool with their resistance curve. Trust your own measurements and experiments. Silonex removes more crap from their website every few months. I expect they remove it as people show them how their datasheets are full of you know what. I have sent them literally thousands of measurements and a handful of junk LDRs to prove my point that their datasheets are not sound and that their manufacturing suffered when they changed manufacturing plants but they just try to steer me to using other optoresistors they make.
Uriah