LDR (Light Dependent Resistor) Volume Control

[Tachikoma]

I was browsing diyparadise.com today and found this:

diyparadise - all about volume control...

Is there a reason it should sound good?

[Beefy]

SKA Audio sells LDR volume controls here.

I have never personally used one, but quite a few DIY'ers have used them in their Millett Maxes, and many report good results.

[utilisateur]

There is a long thread somewhere on DIYaudio about a volume controls with LED/LDR arrangements i think if you search for Lightspeed attenuator you should find it.

I have not heard one but to my understanding, in theory it should have the shortest signal path and least parts in there.You'd have to watch the impendances and the measured distortion may be higher than with other approaches.

With seperate LEDs and LDRs you'd have to match everything quite carefully and make sure there are no leaks.With LEDs/LDRs in one package matching is probably more difficult.

I don't have a clue about a shunt configuration..

[moray james]

a bud of mine has oe of George's Mk 2 units with a buffer and it is the best Passive pre that I have heard. The Passion unit built by a British company who's name I have forgotten is the same thing as is the Melos unit. George's unit sounds superb. You will most likely need a buffer and a battery supply enhances the quality of the sound. One resistor (variable in the signal path) how can you beat that? Gregs unit is just too inexpensive not to try I plan to as soon as they are back in stock.

diyAudio Forums - Lightspeed Attenuator a new passive preamp - Page 1

[luvdunhill]

no offense to George, but the one Choky is selling should sound a lot better. I'd recommend trying that out one.. includes a nice integrated buffer to boot:

diyAudio Forums - Poor Serbian Man Lightspeed packages - Page 1

[Smeggy]

I'm gonna make one

A little clarity needed first, this needs Two of the LDR circuits shown in the drawing, one per channel with one LED circuit, is that correct? Looks that way in the photo.

Parts list...

Four Light Dependent Resistors (LDR)

One 250k linear pot.

Two 24-100 ohm resistors (is this an actual rating or just a range to work from?)

One 5V supply. Any 5v supply? Even batteries?

two input and two output jacks.

I can fix any channel balance by adding screw adjusters for fine tuning.

Did I miss anything? I'm notoriously bad at circuit diagrams.

[luvdunhill]

Four Light Dependent Resistors (LDR)

well, depends on how important channel matching is to you. I'm betting you'll need around 20 or so LDRs to get good matches, and perhaps a few more to get a decent price break.

[manaox2]

I have two of the SKA audio kits that I want to use with the Aikido.

[Smeggy]

well, depends on how important channel matching is to you. I'm betting you'll need around 20 or so LDRs to get good matches, and perhaps a few more to get a decent price break.

Eh? Why would I need more than the four if they're screw adjustable?

[luvdunhill]

Eh? Why would I need more than the four if they're screw adjustable?

eh x 2? What's screw adjustable?

I'm talking about the Silonex devices, here's a datasheet:

http://www.alliedelec.com/Images/Products/Datasheets/BM/SILONEX_INC/SILONEX-INC_ACTIVES-AND-PASSIVES_6993012.PDF

[Smeggy]

Well the plan is to fix the LEDs in place with a baffle between them to stop light bleed, and the LDRs on adjuster screws so their distance from the LEDs can be adjusted individually on the fly to match volume and any time drift that may occur. Hope that makes sense.

I just has a brainwave... or brainfart. wonder if the LDRs can be used to rig a subtle crossfeed circuit adjusted by LED brightness. Hmm, need to think about how to rig this. It would also be completely cut out of the circuit by turning off the LED.

Thoughts? I'm looking at two LDRs crossing the signals and mixing by light input. Is this completely insane?

[luvdunhill]

Well the plan is to fix the LEDs in place with a baffle between them to stop light bleed

heh, look at the datasheet I posted... it's a bit more sophisticated approach.

[Smeggy]

I didn't understand any of it

I need simple paint-by-numbers DIY

On my simple setup based on the first post and my crossfeed idea, will it still be workable as I have a radio shack nearby with cheap parts and I can test on my next Starving student

[luvdunhill]

I didn't understand any of it

I need simple paint-by-numbers DIY

On my simple setup based on the first post and my crossfeed idea, will it still be workable as I have a radio shack nearby with cheap parts and I can test on my next Starving student

basically, the Silonex optocoupler is what you're trying to do, all one one neat package. It's a extra, extra dark black box with a photocell and a LED inside.

[Smeggy]

Ah, I sees. I was more looking to tinker and have fun doing daft stuff myself

[luvdunhill]

Ah, I sees. I was more looking to tinker and have fun doing daft stuff myself

well, by all means then. Maybe find a way to use "light pipes"

[Smeggy]

Oooh, light pipes.... sexy

BTW, can the standard led types from rat shack or similar work with a 6v battery?

[Dusty Chalk]

Well the plan is to fix the LEDs in place with a baffle between them to stop light bleed, and the LDRs on adjuster screws so their distance from the LEDs can be adjusted individually on the fly to match volume and any time drift that may occur. Hope that makes sense.

I just has a brainwave... or brainfart. wonder if the LDRs can be used to rig a subtle crossfeed circuit adjusted by LED brightness. Hmm, need to think about how to rig this. It would also be completely cut out of the circuit by turning off the LED.

Thoughts? I'm looking at two LDRs crossing the signals and mixing by light input. Is this completely insane?

On a theoretical basis, I could see this as being possible. You could have prisms (or mirrors with very clean edges) split the light into its associated receptor and the alternate channels receptor, and adjust the levels of each by how much into the lightbeam you edged the mirror in. You could also make other more fine-tuned adjustments by filling the intermediate volume with gas suspensions with different opacities.

Smoke, perhaps.

[Smeggy]

Hmm, crossfeed with incense burner, yeah, I can do that...

[luvdunhill]

Oooh, light pipes.... sexy

BTW, can the standard led types from rat shack or similar work with a 6v battery?

yup, as long as you can provide enough current and handle the voltage drop (~1.7V) you'll be good.

[Smeggy]

Heh, well I'm assuming my rat shack even carries these things. If they do I'm gonna play with the crossfeed idea first to see if/how that works. I may rig it as an external box from the phones out as a post process unless you think it'd be better on the input side.

I'll try a pair of LDRs in a box with one LED and a linear pot with a battery holder in a small project box with a signal splitter so I can mix it.

Wish me luck!

[Smeggy]

Oh well, so much for getting them at rat shack...

I did get led's, batt housing and pot. Just need to find LDRs now and I'm in business.

[Dusty Chalk]

I may be talking out of my ass (again), but I would think it would be easier on the line-level side -- you could make the input and output impedances more friendly to gear that isn't, as an added benefit of the device.

[Smeggy]

Yeah, would prolly be better on the input I guess. It seems I do have all the parts, I bought a photocell assortment pack hoping they may do the job and it appears they might. The name seems to be interchangable with LDR.

[mypasswordis]

I laughed when I first saw these "LDRs" because they are indeed just photocells, with some LEDs in front. I never would have thought such a crude way of having variable resistance would be good sounding. You can't have too much ventilation in your casing, for obvious reasons.