jkeny said:
It depends on the curve of the led controller pot (100kdual pot) itself. In my production Lightspeed Attenuator's case if you use a log all follows close to an audio taper, slow to begin with then increasing faster around the mid position and after. If you use a linear dual pot it starts way too fast for my and others liking.
So in my production Lightspeed Attenuator it is as my circuit I posted up a few times:
"NSL32rs2s all matched, 100ohm resistors on the positive leg fed positive voltage by a 100k dual Logarithmic pot in push/pull arrangement from a 5vdc regulated supply".
If any of the above are changed the ideal audio taper volume curve will be effected.
I tried a single log 100k and the results were not to my liking, as it ended up crackling, I think because the single track was asked to control all 4 led's, where the dual only had to service 2 led's on each track.
Cheers George
Aha thanks soongsc - should have looked before posting Q! - you mean this: http://www1.silonex.com/audiohm/pdf/levelcontrol.pdf
Edit: Thanks George
Edit: Thanks George
Hi Thomas,
This thread is so long now that gems of info like yours are hard to find - I read forward from your link & saw that you had temp drift issues but you eventually solved them. Also I see that you're using a DAC & remote control. I'll PM you to pick your brains, if that's OK?
Edit: Ah I see that you're not accepting emails - please email me - I'm working on a uC remote controlled multichannel preamp using unmatched LDRs & I wished to confer with you!
This thread is so long now that gems of info like yours are hard to find - I read forward from your link & saw that you had temp drift issues but you eventually solved them. Also I see that you're using a DAC & remote control. I'll PM you to pick your brains, if that's OK?
Edit: Ah I see that you're not accepting emails - please email me - I'm working on a uC remote controlled multichannel preamp using unmatched LDRs & I wished to confer with you!
Maybe this helps:
An externally hosted image should be here but it was not working when we last tested it.
I'm building a preamp which uses a ATMega uC & unmatched LDRs with a calibration function to bring the LDRs into alignment with each other - I figured matching to the ideal slope for the particular LDR type would be the best option.
Jackiinj, your graph is most helpful - do you have different K constants for the NSL-32SR3 which enabled you to plot the expected resistance for this device? My plot for NSL-32SR2 might be slightly different to your graph for NSL-32SR3 with R at a value of 1250 when crossing the 1mA.
Jackiinj, your graph is most helpful - do you have different K constants for the NSL-32SR3 which enabled you to plot the expected resistance for this device? My plot for NSL-32SR2 might be slightly different to your graph for NSL-32SR3 with R at a value of 1250 when crossing the 1mA.
Odd question here. I've built a few of my own LDRs and they work fine. Now I'm looking at a minimalist push-pull tube amp fed directly by a transformer connected to a DAC. The DAC is a Cirrus Logic with differential voltage outputs, about 5v peak to peak. I'm looking at driving the grids of the tubes from the output of the transformer. I was noodling around in my head for a volume control and came around to LDRs. Does anyone have any opinions on the attached schematic? Back of the envelope calculations using the NSL-32SR3 datasheet says that I should get about 15v out of the transformer (good for driving an EL-34) and keep the input impedance at a minimum of 840 ohms.
Attachments
Straight voltage output according to the datasheet:
http://www.cirrus.com/en/pubs/proDatasheet/CS4398_F1.pdf
Output swings up to about 96% or 134% of the 5v analog voltage input (depending on mode). Also, there's a limit on how low the output impedance can be (1000 ohms), which would seem to indicate a current limited voltage out. See page 9 of the datasheet. The application note for a lowpass filter and balanced to unbalanced converter:
http://www.cirrus.com/en/pubs/appNote/AN048Rev2.pdf
treats the outputs like pure voltage outputs rather than the usual current to voltage conversion.
http://www.cirrus.com/en/pubs/proDatasheet/CS4398_F1.pdf
Output swings up to about 96% or 134% of the 5v analog voltage input (depending on mode). Also, there's a limit on how low the output impedance can be (1000 ohms), which would seem to indicate a current limited voltage out. See page 9 of the datasheet. The application note for a lowpass filter and balanced to unbalanced converter:
http://www.cirrus.com/en/pubs/appNote/AN048Rev2.pdf
treats the outputs like pure voltage outputs rather than the usual current to voltage conversion.
Fenris said:
Hello Fenris
you can expect about 1.7 to 2.5 V rms from your dac, output resistance will be 118 Ohms (datasheet), loaded with 210 Ohm (180 series, 30 must be the "on" resistance of the cell). This impedance will be transformed 1:16, will be 3360, not 840.
This is just the loudest setting, with a lower setting impedance is getting too high to handle for the transformer. I would go with a second (series) cell, without transformer. Definitely not possible to drive the grids of an EL34. If the cells would be on the secondary side, impedances would be okay, but the cells have high distorsion at higher voltages.
regards
Andre
Lightspeed remote control
Hi Folks,
Just thought you might like to know that I will be shipping the Lightspeed remote control circuit boards out from Tuesday next, and I should be able to start shipping the modules the following week.
I have not finished the website revision yet so I will send the parts list with the boards. The application notes should be on the website by the time you are ready to build.
Regards
Paul
Hi Folks,
Just thought you might like to know that I will be shipping the Lightspeed remote control circuit boards out from Tuesday next, and I should be able to start shipping the modules the following week.
I have not finished the website revision yet so I will send the parts list with the boards. The application notes should be on the website by the time you are ready to build.
Regards
Paul
