What happened with LDR preamplifiers?

[walpurgis]

LDR preamps were well discussed for a while, but not a word in the last few years. Why?

[struth]

possibly the ldr's, and their risks, and maybe they more transparent than the music was designed to be played on???

[walpurgis]

possibly the ldr's, and their risks, and maybe they more transparent than the music was designed to be played on???

Is that possible? Not sure I can see how.

[Macca]

reading round the forums I occasionally come across someone who is using one.

I have one but there's something up with the pot on it.

[walpurgis]

I think it's a fascinating idea and may look into building one. Surely there are non-toxic LDR types instead of the cadmium sort? Some LEDs are light sensitive as well as light emitting I gather, are they resistive? Or more to the point, of variable resistance? They are directional, but maybe out of phase pairs being bi-directional could be utilised as receptors, just a thought.

[Macca]

The LDRs are only toxic if you smash them with a hammer and eat the pieces. That was a lot of fuss about nothing.

[Puffin]

Blimey this is spooky! I have been using a DIY LS preamp for well over 10 years (Poss 15) being one of the first on DIY audio and other sites to put one together after the design was generously offered for free. It started to play up a couple of weeks ago and I suspected the LDRs were failing. I had bought a PCB at some stage and some matched LDRs and decided to change my effort with this. I tried it out yesterday and got no sound....so it is investigation time today.

https://www.diyaudio.com/community/threads/lightspeed-attenuator-a-new-passive-preamp.80194/
https://rockgrotto.proboards.com/thread/4066/lightspeed-passive-preamp


I have not heard any other preamp that does what this does and despite being passive behaves much more like an active pre. I would recommend that everyone try one.

[Puffin]

possibly the ldr's, and their risks, and maybe they more transparent than the music was designed to be played on???

I have read that the scare over Cadmium has been greatly exaggerated and the Silonex LDRs are completely sealed. I have not been affected by using them apart from the incessant twitching and jerking and uncontrollable Tourettes........

[struth]

I have read that the scare over Cadmium has been greatly exaggerated and the Silonex LDRs are completely sealed. I have not been affected by using them apart from the incessant twitching and jerking and uncontrollable Tourettes........

sure it is but its still an issue for many.

[Lawrence001]

I have read that the scare over Cadmium has been greatly exaggerated and the Silonex LDRs are completely sealed. I have not been affected by using them apart from the incessant twitching and jerking and uncontrollable Tourettes........But then you were like that at school [emoji23]

[CageyH]

Cadmium is pretty nasty stuff, but you would have to be seriously unlucky to breathe in the concentrated fumes upon failure of the LDR. The idea of an LDR preamp just seems wrong to me. I am sure that they work well, but it just seems like an overly complicated solution compared to a relay based preamp, such as a Topping Pre90, or a high quality stepped attenuator.

HiFi would be pretty boring if we all had the same gear and opinions though.

[Macca]

, but it just seems like an overly complicated solution compared to a relay based preamp, such as a Topping Pre90, or a high quality stepped attenuator.


I think you're right.

He says while using a 40 year old Philips active pre.

[Puffin]

But then you were like that at school [emoji23]

How did you know!

[walpurgis]

I wonder if a triac/thyristor dimmer could be utilised in a preamp? Bound to have been tried or considered.

[Barry]

Using LDRs seems to be an awfully complicated way to achieve a 'contactless' volume control.

Not only do all four LDRs have to be matched, the resistance as a function of illumination is non-linear and varies sample-to-sample, so you need a 'look up table' stored on a memory chip.
I believe this was provided in the Australian ready-made item.

[Lawrence001]

Using LDRs seems to be an awfully complicated way to achieve a 'contactless' volume control.

Not only do all four LDRs have to be matched, the resistance as a function of illumination is non-linear and varies sample-to-sample, so you need a 'look up table' stored on a memory chip.
I believe this was provided in the Australian ready-made item.This is what I've always thought and hence have never been tempted enough to buy one when I've seen them come up for sale, despite the positive comments from owners.

[Puffin]

Mission Accomplished. New LDRs and a fancy PCB and it sounds.....much like the old one.....Fab U Lous (nod to Craig Devil Bore-Would) Mrs Puffin HAS to watch Strictly!:doh: