Small board...
Hi, made a small board for this charming little LDR attenuator measures 1 4/8” x 1 5/8” (1.5" x 1.6250). Pot would be on the chassis panel. Kept the audio and PSU ground separated and tied them together at one point with a jumper. Also increased the smoothing caps to 10uf and 100uF. If anyone wants the gerbers or Eagle file let me know, haven’t tested it yet.
Stan
Hi, made a small board for this charming little LDR attenuator measures 1 4/8” x 1 5/8” (1.5" x 1.6250). Pot would be on the chassis panel. Kept the audio and PSU ground separated and tied them together at one point with a jumper. Also increased the smoothing caps to 10uf and 100uF. If anyone wants the gerbers or Eagle file let me know, haven’t tested it yet.
Stan
I did p2p at first to see how the Lightspeed worked in my system. Tinned the tips of the LDR leads. Later, as mentioned earlier I soldered the LDRs directly to the input and output XLR sockets. That'd be eight LDRs. The LED leads I soldered all to a board made for the DC supply. Painted the traces with nail polish and etched.
Banned
Joined 2002
I wonder if i'm ever going to get some parts / kit / package / board etc etc what ever needed to build one ?
Jase,
I dont have the boards yet. Chinese New Year coming up and they are on DHL right now. What can I do? You have my email address, you and I communicate on PM, I am sure you could contact me that way. However if you want some of my prototype boards that do not have plated through hole I am happy to send those to you in exchange for the packet of parts that you sent me. Recently you said you did not want to build a Lightspeed or other complicated LDR passive pre so I could send you some cash for those parts you sent me as well if you would rather that. Up to you but we can do this on email of PM or give me a call. I would be happy to finally talk to you.
Uriah
I dont have the boards yet. Chinese New Year coming up and they are on DHL right now. What can I do? You have my email address, you and I communicate on PM, I am sure you could contact me that way. However if you want some of my prototype boards that do not have plated through hole I am happy to send those to you in exchange for the packet of parts that you sent me. Recently you said you did not want to build a Lightspeed or other complicated LDR passive pre so I could send you some cash for those parts you sent me as well if you would rather that. Up to you but we can do this on email of PM or give me a call. I would be happy to finally talk to you.
Uriah
Hi udailey, I have not built it yet and that may take some time (time is rare for me these days). It's pretty straight forward with the exception of the C1 which is a 100uF smd cap, but this could easily be replaced with a standard radial through hole cap.
Stan
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Referring to:
http://diyaudioprojects.com/Solid/D...r/Lightspeed-Passive-Attenuator-Schematic.png
Are you saying that its viable to simply dispense with the 7805 entirely, and supply 17V (or similar) to the potentiometer --- taking care not to exceed the power rating of the device ?
No. I experimented with using higher voltages on the LDRs. They are not rated for only 5V applied to the LEDs. They can handle a lot more. However I would not use that higher voltage in the Lightspeed circuit in light of things we learned about potentiometers and their wiper weaknesses.
I was using an LM334 controlled by a trimmer. The trimmer sees much less than a volt. Its basically a set resistor. The LM334 can handle about 40V. If we dont give the LDR more than 100mW things still seem to be fine.
So what I am saying is that if you want to experiment dont be scared to go over 5V just keep the current in check.
Uriah
I see.
What is the typical observed forward voltage drop (V_f) of the LED ?
(The NSL-32SR2 data sheet only gives V_f max of 2.5V.)
Yes, that's the calculation I want to do. I was looking for the V_f so that I could finish the computation. I believe you are referring to this post. The little snippet in there gives a "typical" V_f of an arbitrary LED as 2V which is close to the 2.5V maximum in the data sheet.
I was wondering what values folks have observed in practice for V_f.
Using my 12V supply, a "typical" V_f of 2V and a 20mA target limit yields a value of about 470R.
Dragon,
I have never done a study on how close they all are to each other as far as their Vf. I have often wondered if its the LED that I am matching rather than the resistive surface. We know that both resistors and LEDs change values when heated so perhaps its a combo of the two, but I do wonder if I put the LDRs on a curve tracer and compared the LEDs reaction to different voltages and currents if I could match them that way.
The only one I have had explode did so at 20V but I frankly dont remember the current going to it at the time. I was turning a pot and waiting for it to break but never recorded the resistance of the pot as it was more of a 'huh, lets see how far I can push this" than information I planned on using later. It split right in half and you could see the LED and resistive surface. Kind of neat. I know it was under 1k Ohm as it was in the last turn of a 20k 20turn pot.
I have never done a study on how close they all are to each other as far as their Vf. I have often wondered if its the LED that I am matching rather than the resistive surface. We know that both resistors and LEDs change values when heated so perhaps its a combo of the two, but I do wonder if I put the LDRs on a curve tracer and compared the LEDs reaction to different voltages and currents if I could match them that way.
The only one I have had explode did so at 20V but I frankly dont remember the current going to it at the time. I was turning a pot and waiting for it to break but never recorded the resistance of the pot as it was more of a 'huh, lets see how far I can push this" than information I planned on using later. It split right in half and you could see the LED and resistive surface. Kind of neat. I know it was under 1k Ohm as it was in the last turn of a 20k 20turn pot.
I know this is way off topic but I found something really cool today from one of the ads at the header of the home page here at DIYaudio. Check this out MiniDSP
Its a little board that has a usb connection to your computer. Music does not go through the USB, it uses the rca's. Anyway with a program on your computer you can control the DSP. You can create a 31 band equalizer, several crossovers, etc. etc. Its really really cool.
Uriah
Its a little board that has a usb connection to your computer. Music does not go through the USB, it uses the rca's. Anyway with a program on your computer you can control the DSP. You can create a 31 band equalizer, several crossovers, etc. etc. Its really really cool.
Uriah
Very interesting. Maybe spin off another discussion topic.
Placing another ADC/DAC combination in the signal path might be problematic for some folks.
I would find SPDIF (digital) input with four output RCAs more interesting (electronic cross over, etc).
I think you're right in surmising that it would be a combination of the two. The LED/LDR combination work together as a system with each of the subparts (LED vs LDR) having its own behaviours but you are observing the result of the two combined (signal path resistance).
Has this spun off to another thread yet? If so where?
And the minidsp DOES have I2S inputs too.. I had to write them for that answer.
