LDR attenuator, the passive preamp update.

This is actually version one of the project! I was using a multitude of LEDs with different colors and burnt several due to overvoltage! I had a bunch of light green colored ones and it works without much noticeable difference! This version 1 prototype did not last long enough... ;)

This is the two excellent DC voltage controllers(using MOSFET) that I acquired. Working voltage is from 6VDC to 15VDC.. I see a multtude of applications here ;) Suffice to say, it works beautifully in this project!


This is my second prototype I have built to investigate the performance of the LDR preamp. Suffice to say, the initial sound quality that I got was really promising! It had all the SQ that was mentioned. The only quirks that I encountered was the non-linearity of the LDR itself. Evenhough I managed to control the intensity of the light proper but the LDR did not response as linear as I want it to be.. something for me to look into.. The shroud used to isolate the LDRs is not shown here for clarity of the unit.

As earlier mentioned, I was thinking of using alternate source of light instead of the LED which I think did not give linear light control as per original circuit.
After much thinking and hunting.. I found a DC controller based on PWM(Pulse Width Modulation) which would work better than linear control eg. variable voltage control.

Conclusion?
The LDR preamp works great. No wonder diyparadise resorted to digital volume control on their LDR volume control to properly managed the attenuation.
If you don't have any preamp and itching to build one.. go for this one. It is cheap and simple!

LDR volume control - A passive preamp aka Lightspeed Attenuator.

I am aware of the above for quite sometime now.. Have read with interest and somehow it (the interest) 'flame out' for no reason.. maybe I'm 'not in the mood' as usual..
The thread at diyaudio.com can be found here.
It so happened that I read the same project at diyparadise.com this evening and somehow it striked me that the circuit is sinfully simple and cheap to do.. why the heck didn't I do it?
Details are here.

There were some problems with channel imbalance and diyparadise solved it by using a digital volume control. Handy of course with remote control.. ;)

What really hit me on the face is that this LDR (passive) volume control is far better than, (read this) : "We found the Light Dependent Resistor (LDR) solution to be much much better than ALL passive preamps we could lay our hands on. This includes transformer volume control, autoformer volume control, shunt/series resistive stepped attenuators, marque volume pots like Black Beauty... "

Damned! I gotta find out! So I have somewhat set my mind that this weekend will be LDR volume control week!

While reading the write up, I was thinking,
1. instead of using LEDs as the light source, why not use a proper bulb? Depending on voltage and wattage, I can certainly get the LDR to drop to a very low resistance.. better than the LEDs, right?
2. instead of using a pot for LED brightness control, why not use a variable voltage PSU? More precise control here.
3. instead of adjusting voltage to control the LED brightness why not keep the LED at a fixed brightness but control the amount of light to the LDR by other means? I have an idea like using something like a camera's variable aperture.. and some other contraption which I have in mind that need to be evaluate... all mechanical means..

Let me 'play' with the idea for a while.. will update this on my final version.
Could this be 'better' than my current buffer preamp? We'll find out soon..!

Cheers.