Afaik, all volume controls, Alps, Noble, TVC etc have mechanical wipers, switches and mechanical contacts that the signal has to pass through. These things cause distortion and noise. Enter the LDR or Light Dependent Resistor. It's a variable resistor that changes in value according to the light shining on it. So, in a voltage divider volume control arrangement, by changing the power to the light, we change the resistance of the series and shunt and hence we change the volume. All the signal sees is one soldered resistor in its path! So how does it sound? Is this the ultimate volume control that at least one manufacturer used in some usd20k hi-end preamp?

To find out I built one.
The Lighter Note is more sophisticated than the better-known Lightspeed. It refines on that design.


The diy kit - all that to replace 1 pot, crazy?!!



Assembled and being calibrated. Yes it needs extensive tuning to select impedance, max and min resistance and even profile! Just the ticket for perfectly matching impedance between source and amp!
I use two boards for the LDRs instead of one so I have option to mount the LDR board into each one of my monoblocks. Torroid is mounted in external box that now also powers the B1 buffer.



In other thread I built the Pass B1 buffer. The Lighter Note was originally meant to replace its muddling early 20th Century pot. This is how they would look together - their red 'undies' totally match even to their thickness!



But no! the LN is really too good to be stuck with the B1 and deserves its own box
See those black blobs marked SR2 near the RCAs? That'll be the Silonex LDRs.
A little more complicated than the B1 preamp to build!



Still in the mood for sexy see-throughs, here's the LN with its own acrylic box
The B1 hasn't been forgotten, this box is designed for stacking with it, with matched footprints.



What's with that offbeat blue knob? It's the balance control, and happens to be the only knob I had on hand lah. Will look for something matching later.

So does it work? Yes. All those parts - two pots, 8 trimmers, 6 ICs, two power supplies, etc to replace just one pot, it better!

But how does it sound? Let me just say I'm still picking my jaw from the floor Seriously. But I'm going to listen over the next few days before trying to describe the sound for which I was not prepared. This way I'll avoid initial over-enthusiasm and report more objectively. It will be used as passive preamp and compared against the B1 and Yaqin CD3 buffer preamps.

This post has been edited by Bernie7: Oct 4 2010, 11:13 AM

I should add that the Lighter Note (LN) is connected between my DEQ2496 and monoblock power amps (UcD400HG HxR). Speakers are Swan F2.2.

The DEQ2496 has been modded so that its DAC chip plays directly to the output through banks of 0.47uF Dayton caps, bypassing all the stock opamps. The DAC chip has also been changed from AK4393 to the miracle dac AK4396

what it basically means is the rest of the gear should be good enough to assess the LN

cheers!

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Added on May 4, 2010, 10:21 amIt is 100% analog. And makes my whole setup sound more like it too

I have been using 24bit digital volume using the DEQ2496 gain control, and careful not to exceed my quota of digital attenuation. But this LDR thingee is at another level or three higher. Makes me wonder why.... how can a resistor sound so good???!!!

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Added on May 4, 2010, 10:22 amThanks bro.

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Added on May 4, 2010, 10:25 amWelcome to come hear next time you're in S'pore

Help me to confirm what my ears hear


This post has been edited by Bernie7: May 4 2010, 10:25 AM

Yeah LCR and impedance matching, but I suspect the sound of this thing is more than just that. It's just quite stunning! We know that resistors can sound different, so maybe this optico-type resistor has special audio qualities.

Impedance of the LN has been dialed in to 10k. The source O/P impedance is 1R (!!!) and the amps are 100K so all is cool.

But the LDRs are not very linear, so the impedance falls to 4.5K then rises back to 10K as vol goes up. Still cool as the lower Z is better for my power amps. It falls in my listening range.

Huge knowledge, nah, still trying and learning, and the LN kit is not exp lah

Thanks for compliments bros, but it really isn't that hard to diy this with the kit.
Gotta be v careful when soldering and tuning the LDRs though as they are delicate things that damage with too much heat or voltage.

jazzy939, the diyparadise project uses a different LDR part and it's nowhere near this design in maturity. I read it has problems with stability and channel balance which is obvious from the simple circuit. My LN has a measured balance variation of +-0.6% throughout the whole operating range! Noble pots go up to 10% imbalance, so a friend who measured them told me.

What's the link to the diyparadise active volume circuit?

This post has been edited by Bernie7: May 5 2010, 08:23 AM

LSA = LST = Lightspeed? One person who has both says the LN is clearly better SQ wise on account of its better psu implementation which includes both voltage and current regulation.

I'd be interested to see how the Lightspeed + DCB1 fare against the LN alone. It already beats the B1 handily.

Yes agree absolutely especially when it comes to 'flavour' type of differences

To me and a few others who have heard so far, the LN is clearly better than the B1, but then your DCB1 should be better than the B1 without caps in the signal path.

From the diy forums, the most popular LDR to use now is by Silonex, and it comes with LED built-in, no need to bother abt LED color.

http://www.silonex.com/audiohm/index.html

The Silonex LDR has a sound signature that is different from the simpler types, you really need to listen for yourself. Not all LDRs may sound alike. I don't know any active volume control that does not use mechanical pots or digital control, can you give an example or tell us what you use? Or are you comparing passive preamps with active preamps?

Passives lack 'life' because often there is impedance mismatch between it, the source and the power amp. So people use buffers with it which helps with matching. You may also have an impedance mismatch issue with your LDR project. What are the impedance values of your source, LDR vol control and your power amp?

The LN power boards are dang complicated with voltage and current regs, but they help to 'tame' the non-linear LDRs. If LDRs behave better, yeah a simple psu should suffice. The power boards allow max, min resistances, and slope of profile to be fixed. This gives flexibility for impedance matching between source and power amp. According to the designer, psu plays a big part on the SQ. Anyway, you can try and build the Lightspeed version with Silonex LDRs and a simple psu. Only point-to-point wiring is needed, it's a simple circuit with less flexibility. For only usd50 more I opted to build the LN. No regrets!

This post has been edited by Bernie7: May 7 2010, 01:28 PM

Being aware of it and actually using it are two different things bro. Anyway, good luck with your tube preamp.
Happy listening!

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Added on June 4, 2010, 2:53 pmFinally, LDR attenuators or passive preamps are getting the recognition they deserve from the main stream media

Stereophile reviewed one version, the "Lightspeed Attenuator" in the April issue and awarded it Best of the Best Recommended Components with highest $ rating for value.

Maybe now more audiophiles will come to enjoy this remarkable device!

This post has been edited by Bernie7: Jun 4 2010, 02:57 PM

Update: I have moved the LDRs right into the monoblocks, so it's now 0cm distance between LDR volume control and monoblock amp module!

The Itch
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The LN is a keeper. SQ has gone up several notches since it came, altogether a huge leap in overall sonics as many who use LDRs attest in the Net. It's been the best mod since I removed the analog stages in my DEQ2496's DAC and linked the AK4396's output through decoupling caps to my power amps. The impedances of my DAC, LN and power amps all match, being 1R, 7K and 100K respectively. So there shouldn't be any impedance loss issues.

Now the LDRs work like a volume control pot, so what if I place the LDRs directly at my power amp modules and eliminate the interconnect and any other niggling issues between LN and amp entirely? This would be ideal. But if I do so, my LN cannot be used with other amps. A dilemma! Easily solved by having a second set of LDRs that allows me to switch between the two using the same power controller boards as central console.


The Plan
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In addition to building two remote LDR boards one for each monoblock, I have to add one more balance board at the central LN console (seen at the initial post), put in a second balance pot and add RCA sockets to my all-XLR monoblocks. So I'm going back to the dark side of unbalanced, but hey my leads are er short (less than 2m) and I don't detect emi/rf issues. Besides It's twice the work and many times the expense to implement a balanced LN (costly to get 4 matched pairs of LDRs).


The Build
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Here's the remote LDR board cut to fit the tight space in my monoblocks. LDR signal lines are soldered to pins inside the Molex connector that plug directly into the UCD signal and control inputs. Why the long LDR legs acting as antennas for rf Class D radiation? Well I just plonked them in without trimming for initial trial. Will cut them for custom fit later. See the voltage-divider in the setup?




IC Pin sockets are used so I can simply plug in the LDRs without having to solder them (LDRs are easily killed by heat). More sockets to allow for cap rolling. Here I use 0.1uF Wima caps as snubbers. When my russian K73-16 caps arrive, they'll be plugged in next, followed by my Panasonic FC caps.


My unsuspecting UCD400HGv2 module before it's piggybacked.



LDR module added to UCD. Plug and play!

Notice the signal lines from the RCA plug into the sockets. Helps in removal of LDR board as I want my monoblocks to easily revert back to XLR days.


Proof of the Pudding is in the Eating
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Put everything together and turned on the set to warm up. No BOOM no sparks, no hiss, nothing, just black silence. So good so far. Went for a shower, came back and put on the first playlist, a selection of unplugged audiophile tracks from China divas. So how does it sound? Zounds!!! Within secs I can tell there's been another leap in sonics from before. Big WOW factor. Instruments/voices stand out even more, bass is fuller, voices acquire more emotion, clarity is way up there, there's more prat and dynamics. Did I say instruments and voices are clearly more pacy and palpable? Finally, the life and dynamics I felt somewhat lacking in my setup is here! Downsides? Haven't detected any yet, the change is not to make the setup sound more analytical, but more musical and true to life.

Or is this due to a change of room acoustics on account of one sofa set being sent out for refurb? Or that solid copper RCA I just put in? Nahhh...can't be all that. Dang, that kick-drum never sounded so good...

Just sharing and hoping bros here will be poisoned, er inspired to give LDRs a try. YMMV, but the betting is once you taste them, you won't live without them in your audio

Just added my Yaqin SD-CD3 tube buffer into the chain

Music server > AK4396 > Yaqin > LDRs > UCD400HG.

The Yaqin is actually serving as my DAC's analog stage since I bypassed its op-amps. The result is ....very nice. Tube sound in spades without losing bottom end control.

Haven't decided yet whether to give the Yaqin a permanent place in the setup. Need to listen more to hear if the setup sounds better or more accurate with or without the Yaqin's euphonic sound. All I can say is this tube buffer is dang good for the price, and it works a treat with LDR volume control. Like adding caramel topping to creamy ice-cream



This post has been edited by Bernie7: Jul 9 2010, 11:02 AM

Too much caramel on ice-cream may tire after a while

For now, my goal is neutral, highly resolved and natural sound with good PRaT and imaging. The Yaqin's specs says <0.3% distortion and 10-100KHz (-0.1dB) FR which looks great on paper, but it will take time to hear if it veers anywhere from my goal. And I hope to do some tube rolling later to try out Shuguang CV181 in place of the stock 6n8p tubes. I've already tried Sylvania 6SN8WGTB tubes which raised the SQ.

Yes, shortest connection is best, and the LDRs inside the monos make my setup sound better than ever. The Lampizator guy built his tube stage into his DAC (Behringer SRC2496). With digital signals we shouldn't have to worry about connection distance unless it's very long.

When your LN kit arrives, I suggest you leave the option open of planting your LDRs inside your power amp as I did. Try it let us know

This post has been edited by Bernie7: Jul 10 2010, 10:51 AM

Hi bro

Thanks for the feedback

Update:

The latest Lighter Note design is now all on one board. Here's one I built recently



Plenty of space to put in some Class D amp modules too



Dark Horse?

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Added on October 4, 2010, 7:05 pmAlso, bro why not replace your active preamp volume control with the Lightspeed? That way you should have the best of both worlds - the Lightspeed's transparency and your preamp's flavour? It's volume control is likely a bottleneck as it is.


This post has been edited by Bernie7: Oct 4 2010, 07:05 PM

You mean the full aluminum box with 7mm thick panels? <drool>

The bro that I built this for got it from Shenzhen.

Those are high grade audio components, eg caps by Panasonic FM, Nichicon Muse. Part of the audiophile makeup of the Lighter Note kit.

You can order the complete kit from http://www.buildanamp.com/Lighter-Note-Kit...tm?productId=15

Price is only usd145 incl shipping, imo a terrific bargain for the SQ you're getting.