Hi binspaul,
This will work. No doubt. The problem is twofold. Switching supplies, not all of them but the cheapies for sure, are noisy. It wont be particularly noisy since the LED is driven by the supply and the LED does NOT pass the signal, it just shines light. So you get big break this way if you have a somewhat noisy supply.
My first Lightspeed used a switching supply I built that operates at, I think, 52kHz. I can hear either it, or the LEDs. Maybe its both. But, when I turn the pot, if I put my ear right up to the Lightspeed, I hear a faint faint whine at some points along the pots rotation. I imagine its the LEDs because one set of them gets brighter and the other dimmer so I hear it at low rotation and high rotation but not so much in the middle. But why do they whine? I heard the same thing when I originally started matching LDRs when I was testing my setup with regular LEDs. So, is it the power supply I have been using or is it just LEDs? I am not sure but in both circumstances the supply was a switcher so the LEDs are turning on and off very fast. I also hear this noise in my speakers with my ear right up to them so the noise from either the supply or the LED DOES get to the speakers. Do I really care? No. I dont hear it when I am more than 4 or 5 inches from the speaker.
Now, the second problem is that you are considering a supply that has MAYBE the right voltage. You can use it. It will work. But if you match your LDRs with 5V it is my opinion that you should run them with 5V to get the LDRs to behave the same way they did when you matched them. If I run LDRs with 3V that were matched at 5V they are no longer matched until I return them to 5V. The same with constant current. If I match with voltage and then try to run with constant current I get mismatches.
If you want to use that supply until you can get something better.. by all means!! You will still reap the rewards of an incredible attenuator.
Uriah
Puffin,
I think your idea will work very well, plus you get to listen to music while you do it
It will be a very slow process unless you hit a match right away. Testing one at a time calls for some serious patience. I am going to suggest that you be able to swap in resistors as well as swap in LDRs. WHY? Because you will never turn the pot back to the same positions. Maybe this doesnt really matter in your situation if you are just looking for one LDR. But, if you are trying to get 4... man this is gonna really not be a lot of fun
Uriah
I think your idea will work very well, plus you get to listen to music while you do it
It will be a very slow process unless you hit a match right away. Testing one at a time calls for some serious patience. I am going to suggest that you be able to swap in resistors as well as swap in LDRs. WHY? Because you will never turn the pot back to the same positions. Maybe this doesnt really matter in your situation if you are just looking for one LDR. But, if you are trying to get 4... man this is gonna really not be a lot of fun
Uriah
Thanks for your suggestions. Having the Lightspeed near the amplifiers and separate input switching at the sources is an option I anticipated. I won't put it at the amps for several reasons. The amplifiers are Atma-Sphere M60s. Each one has 12 tubes and three power supply transformers. They run hot. They sit on a table between the speakers with no convenient place for a Lightspeed without unattractive clutter, and there is no extra outlet nearby for the Lightspeed supply. Having the Lightspeed PSU near the source and the LDRs at the amps would require a connecting wire as long as the interconnects, approx. 7 meters. The amplifier chassis is stainless steel, making any modifications difficult. Most importantly, the LDRs are temperature sensitive. The Lightspeed is left on for stability but anywhere near the amplifiers is subject to temperature changes and considerable heat when the amps are running. Last, I also use a headphone amplifier which has its own four-gang pot for volume control. Feeding it from the Lightspeed looks attractive and that's easier to do with the Lightspeed near the sources. The headphone amp also uses vacuum tubes. Putting LDRs inside it brings up the same considerations as with the power amps. Otherwise, a separate box for input switching is an attractive idea which I am still considering.
My main reason for posting was to assure people who haven't tried it, that the Lightspeed is a simple low-cost way to achieve superior audio. The line-stage it's replacing was worth about $1500 used, $4000 new. Again, thank you, George.
Never fear ya Barmy Codger! I am working at stabilizing the LDRs
Sometime this year I think I will have it fixed so that we can put them inside hot amps. I have had it work outside in 103 degree heat. An LDR set at 21k went from 21k to 25k in the heat. I tried a few different experiments. Some bombed one worked. Got it to stay withing 300-400 Ohms. I will be trying it in an amp soon.
Fun stuff!
Uriah
Sometime this year I think I will have it fixed so that we can put them inside hot amps. I have had it work outside in 103 degree heat. An LDR set at 21k went from 21k to 25k in the heat. I tried a few different experiments. Some bombed one worked. Got it to stay withing 300-400 Ohms. I will be trying it in an amp soon.
Fun stuff!
Uriah
Oh i'm already thereNo, I was thinking that if I rig something up which means I can swap them in and out without soldering that this would be a way to match them. What positions on the pot should I meaure at 9.00clock, 12, 3, fully on?
You need 5 precise mA readings say at 1 5 10 15 20 to measure all the LDR's 20odd (if you have the batch matched and s sorted ones then 10-15 will do) to get a 4 matched set, the 100k log pot will not allow you to do this accurately, you need a jig with precise mA feeds, a good dmm and lots of patience.
And once this is done do as I do in the production Lightspeed Attenuator pot the 4 matched set in hard wax after it is all built, this will keep them stable at different temps as they all rise and fall together because of the wax enviroment their in, they all touch each other this keeps them as one temperature wise within the wax potting.
Cheers George
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Never fear ya Barmy Codger! I am working at stabilizing the LDRs
Sometime this year I think I will have it fixed so that we can put them inside hot amps. I have had it work outside in 103 degree heat. An LDR set at 21k went from 21k to 25k in the heat. I tried a few different experiments. Some bombed one worked. Got it to stay withing 300-400 Ohms. I will be trying it in an amp soon.
Yea, I confirmed with Silonex that aging does occur with these LDRs, but they don't publish hard data. Makes me wonder why.
Not only that, but the temp issue above just compounds the problems. Without compensation, I personally wouldn't use this approach for volume control. To each his own.Lightspeed remote control
Hi folks,
If you are concerned about LDR aging use the VCCS, with or without the IR remote control section, as, not only are the volume steps small enough for volume control purposes, the balance control has equally small steps. In practice I have had no problems with level/balance adjustments even with unmatched LDRs.
I have plenty of boards left in stock for this project. If you are not comfortable with ground-up build I can supply the modules built and tested.
Regards
Paul
Hi folks,
If you are concerned about LDR aging use the VCCS, with or without the IR remote control section, as, not only are the volume steps small enough for volume control purposes, the balance control has equally small steps. In practice I have had no problems with level/balance adjustments even with unmatched LDRs.
I have plenty of boards left in stock for this project. If you are not comfortable with ground-up build I can supply the modules built and tested.
Regards
Paul
Hi Paul,
I done a full check on my modules, I think there is nothing wrong, just that the LDR start up and the respond is slow. I knew is was slow, but didn't realize that it was this slow. Now I understand why you guys leave it on 24/7.
And WOW, it beats my switches w dale resistors flat. Really transparent!!!
KK
I done a full check on my modules, I think there is nothing wrong, just that the LDR start up and the respond is slow.
I knew is was slow, but didn't realize that it was this slow. Now I understand why you guys leave it on 24/7. And WOW, it beats my switches w dale resistors flat. Really transparent!!!
KK
It will come on a bit sudden, esspecially if it's linear. You may be able to live with it, won't damage anything.
Cheers George
Hi Bins,
I have found my LDR.lbr for eagle. Attached below. I haven't used this as I went with a perfboard construction for my Lightspeed. There are two layouts: horizontal and vertical.
HTH
Jon