[jrebman]

And my Tap-x arrived late yesterday.  Put it in the system today along with a pair of custom KCI Silkworm ICs, and so far I'm more than happy.  A proper report will have to wait until all the new gear fully breaks-in, but as of right now there has simply never been any better sound in my home -- no exxagerration.

And the TAP is just a way cool thing!

-- Jim

[richidoo]

The LDR VC is the subject of a long thread on diyaudio called "Lightspeed Attenuator"
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=lightspeed

It uses Silonex LDRs and is said to be extremely good sounding. Several posters compare it favorably to various other attenuation techniques. The main problem with the simple Lightspeed circuit was powering the LDRs in a way that matched their attenuation channel to channel. As LEDs the brightness is current dependent but the lightspeed designer is driving them with voltage, thus the LDRs need to be precisely matched. Maybe your EE buddy uses current source to control the LEDs accurately. I have been waiting for such a VC, thinking I would have to build it myself, which would be painful process to use LED drivers and logic controller.

With Zo of 3 ohms it must have buffer, something the Lightspeed does not have, it is pure passive. I'm looking forward to learning more about it, anubisgrau. I volunteer to host a tour stop here in NC to show it off to our local gang.

DartZeel uses LDR for source switching and attenuator.
Rich

[dweekie]

The LDR VC is the subject of a long thread on diyaudio called "Lightspeed Attenuator"
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=lightspeed

It uses Silonex LDRs and is said to be extremely good sounding. Several posters compare it favorably to various other attenuation techniques. The main problem with the simple Lightspeed circuit was powering the LDRs in a way that matched their attenuation channel to channel. As LEDs the brightness is current dependent but the lightspeed designer is driving them with voltage, thus the LDRs need to be precisely matched. Maybe your EE buddy uses current source to control the LEDs accurately. I have been waiting for such a VC, thinking I would have to build it myself, which would be painful process to use LED drivers and logic controller.

With Zo of 3 ohms it must have buffer, something the Lightspeed does not have, it is pure passive. I'm looking forward to learning more about it, anubisgrau. I volunteer to host a tour stop here in NC to show it off to our local gang.

DartZeel uses LDR for source switching and attenuator.
Rich

I wish I had a clue about building one of these.  I've been trying to follow that thread, but my diy skills are not quite up to the level of any sensible understanding in that thread.  I do know Nelson Pass released a buffer schematic for the lightspeed attenuator for people to add, so it will have a bit more universal compatibility.  You can order the original from Australia; I'm unsure of the current exchange rates, but if it's anything like it has been recently with the USD compared to other currency, it may be a great time to buy one. 

[gongos]

EVS Ultimate Attenuators for me. If you have a passive friendly system, you're not going to do any better. Compared to a $5000 Lamm and other high end tube preamps. The EVS sounded better every time. And they're cheap.

[miklorsmith]

In your setup Tyson . . .    I agree, there no preamplifier will help.  In other setups, different.  Not a knock, it's all just preferences y'all.

[anubisgrau]

The LDR VC is the subject of a long thread on diyaudio called "Lightspeed Attenuator"
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=lightspeed

It uses Silonex LDRs and is said to be extremely good sounding. Several posters compare it favorably to various other attenuation techniques. The main problem with the simple Lightspeed circuit was powering the LDRs in a way that matched their attenuation channel to channel. As LEDs the brightness is current dependent but the lightspeed designer is driving them with voltage, thus the LDRs need to be precisely matched. Maybe your EE buddy uses current source to control the LEDs accurately. I have been waiting for such a VC, thinking I would have to build it myself, which would be painful process to use LED drivers and logic controller.

With Zo of 3 ohms it must have buffer, something the Lightspeed does not have, it is pure passive. I'm looking forward to learning more about it, anubisgrau. I volunteer to host a tour stop here in NC to show it off to our local gang.

DartZeel uses LDR for source switching and attenuator.
Rich

i didn't follow a diy thread - it's too long for me and i'm not that good with more complex DIY things so i tend to skip lots of posts.

i've had a session with the mentioned LDR (the official name is "myth") yesterday again. the designer has improved the earthing of the unit since last demo i had and now i really can't hear anything i can complain about it. the first time i wasn't 100% sure if there was a slight artefice in the upper mids or lower treble, but now i'm confident it was due to something else in the system. it's stunningly transparent, as i said a big step ahead of mf audio copper TVC which sits in my shelf, plus thanks to the buffers it has a drive of an unstoppable train, something i haven't heard from a passive device yet. so far it seems it just works with everything you try it with - my F3 just loves it.

as i said, strictly speaking it's not a passive device - it's just a zero gain preamp. it uses power not only for buffers (yes 3 ohm output imp is thanks to the buffers) but also for controlling the LDRs which is done in a completely new way compared to anything seen on the net, as i said the guy behind the design is an extremely talented industrial engineer so it seems he's exposed to much higher level of electronic knowledge than one can usually find on a DIY forum. it's funny you mentioned tolerances between the channels as he explained me yesterday that the way he's controlling the light secures such a tight tolerances that the differences are almost impossible to measure.

i'm trying to persuede him to get a demo unit for those who are interested here, the only problem is that he's coming every week with another upgrades not only in the way it sounds but also in the ergonomics - so far the unit will be armed with touch screen display, jog dial that will be able to control all the functions plus a remote control. i believe he's a controller freak and that's so obvious from such a sophisticated set of controls. could be i'm extremely frustrated (i have no single RC-ed unit in my system, even my old CD160 i use as a transport doesn't have it:)), but it's such a revelation to be able to do everything you want from your chair!

[Brown]

played the passive game for a while. clarity beyond belief, detail but for my system just not enough weight or slam compared to the actives. To date the most affective was the TAP followed by the S&B. The Promitheus was promising but the build quality and customer service is lacking.
   At first the amazment of the clarity and silence was addictive. After listening to my favorites for a while the love affair grew old. just missed the air, decay body of the active. To each their own I guess.
 By all means listen to as many as you can. The TAP is a great place to start. My bet is you'll be back to your active. Whats a few tubes anyway.
  Would be interested in hearing the "Myth". Nothing to loose.

[JoshK]

FWIW, Ska-audio provides an LDR VC stuffed and tested for ~$35.  You need to put it into your preamp and provide it with the appropriate voltage, but this is peanuts compared to the lightspeed solution.

[richidoo]

Thanks Josh, looks cool.
http://www.ska-audio.com/diy/optivol.html

anubisgrau, I hope you will keep us posted on the "myth" I am very interested in that. Thanks! Will it have any balanced ins/outs? Maybe he can make a simple version to help launch his brand quickly.

Rich

[anubisgrau]

Thanks Josh, looks cool.
http://www.ska-audio.com/diy/optivol.html

anubisgrau, I hope you will keep us posted on the "myth" I am very interested in that. Thanks! Will it have any balanced ins/outs? Maybe he can make a simple version to help launch his brand quickly.

Rich

yes, the ska audio price is fantastic. shame i'm unable to change a bulb otherwise i would solder it direct into my F3....

rich, no worries, i take this as my duty to audiocircle who tremendously influenced my listening habits and choice to organize a demo unit. i'm only worried the LRD VC can get stuck half way - it's easy for me to imagine someone not wanting to pass the demo unit on to the next listener:)

regarding the inputs, the version i've heard has only SE - i mentioned this to the designer and he said that the balanced outputs demand circuit to be doubled but he said he would be willed to make a special version.

however as i said before, there's lots of work to be done in terms of testing, de-bugging etc and let's give the guy some peace to do it proper. i will keep you posted once things are ready.

[TomW16]

I'd love to try out the LDR volume control and with a price of $35, it seems like pretty easy thing to try.  The new Bent AVC looks pretty interesting too but is at a little higher price point.

I used to use a ladder attenuator with Holco resistors but then went to a Welborne Labs attenuator (http://www.welbornelabs.com/remote.htm) for the convenience of the remote control.  Both passive preamps sound impressive in my system. 

Passive preamps have to the potential to be the best sounding preamp but require the following to work well:

1.  A source with sufficient drive
2.  A source with low output impedence
3.  An amp with high input impedence
4.  Everything connected with low capicitance interconnects

Cheers,
Tom

[platoo168]

anubisgru

can you post picture of the unit. also who can i contact about it?

[anubisgrau]

anubisgru

can you post picture of the unit. also who can i contact about it?

i have no pics, sorry, my camera was broken when i tried it at my home.

anyway it's still a prototype unit, there will be no commercial units ready before late winter, early spring - i will keep you posted, including a contact with a manufacturer

[platoo168]

thanks.. i am currently using MF copper version as well, what i am looking for is more weight and bandwidth.  may be this will give me what i am looking for .

cheers

[anubisgrau]

i have mf copper and i have to say it's a bit painful to listen to it after this LDR, however in some systems it may be too revealing of the imperfections either upstream or in the recording. anyway, there's quite some information missing with mf compared to this...

[JoshK]

I haven't read through that big thread in some time, nor kept up with that last few hundred pages.  Is the Myth just a passive unit or does it have a buffer built in?  If buffer, do you know any details on what kind of buffer? 

P.S.  I ordered one of the optivol LDRs from ska.  I will try it out in my Aikido against a 100k ladder attenuator.  The input Z of the Aikido is appropriately high for the LDR. 

[anubisgrau]

I haven't read through that big thread in some time, nor kept up with that last few hundred pages.  Is the Myth just a passive unit or does it have a buffer built in?  If buffer, do you know any details on what kind of buffer? 

P.S.  I ordered one of the optivol LDRs from ska.  I will try it out in my Aikido against a 100k ladder attenuator.  The input Z of the Aikido is appropriately high for the LDR. 

it has buffers but i have no clue what kind. i didn't open the unit....

[Brown]

Imo and experience with passives weight is one thing that is elusive to this format. When using a passive the key to great sound is in the source. The passive will reveal what its truley capable of. If you cannot achieve your goal with the source change the amp. Passives are tricky and system dependant.
  To date the Bent units have been to my ears and system the most affective all around. His new units are even better. Give it a try.

[doug s.]

FWIW, Ska-audio provides an LDR VC stuffed and tested for ~$35.  You need to put it into your preamp and provide it with the appropriate voltage, but this is peanuts compared to the lightspeed solution.

this sounds a lot like the photentiomter wolume pot that was used in some melos preamps.  fantastically transparent, but shipping the preamps meant they would go out of adjustment and fail, as often as not.  my melos pre has had the pots replace w/a tubed wolume pot; designer mark porzilli sez they are even better than the photentiometers, which he also designed.  since my melos awreddy had the photentiometer pots replaced w/alps pots prior to my purchase, i can't say...  i am yust glad to hear that mark porzilli is going to re-open melos next year, for service and even further upgrades, and perhaps even new product...  my melos has been a mainstay in my system for many years, and i don't see it going anywhere soon.  can't say that for most of my other gear.   

doug s.

[JoshK]

Now there are LDR/LED packages that are one unit, so you don't have to worry about coupling them.