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Old 12th January 2012, 02:29 PM   #4391
udailey is offline udailey  United States
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Quote:
Originally Posted by BFNY View Post
My understanding is you recommend a constant fixed value for the LDR then, set by a trimpot? From your experience, can this be set to say, in the range of 20k to 40k ohms?

Again, comments appreciated as to why this approach would be preferred over, say, a fixed high quality tantalum or other boutique resistor of the same value.
You could use a single LDR or two set up as a voltage divider. You can set them at those high values but they dont stay stable at those high values. Even at 10k you can see a single LDR fluctuate by 400R or so when you blow on it. The higher in value the less stable. So a voltage divider will do the trick at lower values. Its not the best ever solution, but it will work and will sound better and likely cost less than boutique resistors or at least cost about the same.
OOOH, you could also throw a switch in there that enables the shunt LDRs in your static resistance circuit to go to 40R so when you want very low volume just throw that switch. Its admittedly a kludge but hey it WILL work and its not even special magic.
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Last edited by udailey; 12th January 2012 at 02:39 PM.
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Old 12th January 2012, 03:11 PM   #4392
udailey is offline udailey  United States
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I think its time for me to release boards so guys can do their own matching. This way we can avoid all this crazy conjecture and everyone will see for themselves.
Plus I am pretty tired of matching. It truly gets boring. I prefer working on circuits and finding something new.
Anybody thats interested shoot me an email. Will throw in free Lightspeed boards.
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Last edited by udailey; 12th January 2012 at 03:17 PM.
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Old 12th January 2012, 08:30 PM   #4393
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The specs on the data sheets don't lie
Lightspeed Attenuator a new passive preamp
and this was backed up to me by Fred P. Rohrbacher V.P. & General Manager of Silonex a Casco Company and I have done thousands of these now and I can verify it's fact, that the NSL32SR2S goes far lower in impedance at the same given led mA current than the NSL32SR2 can without stressing by over driving the led with more than 20mA.

Cheers George
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Old 3rd February 2012, 09:06 PM   #4394
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All you proud Lightspeed Attenuator owners and builders, look out for the upcoming Stereophile issue (I think April issue which comes out in March) with Recommended Components listing, as they just emailed me for any changes (pricing, design etc) to be included in the write up on it.
This will be the 5th time your Lightspeed Attenuator has made it into Recommended Components since 2009 when Sam Telling first bought his from me. I have a feeling it may set some sort of record for Recommended Component longevity.

Cheers George
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Old 14th February 2012, 07:37 PM   #4395
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Hi All, I am building a passive pre and heard the lightspeed and was VERY impressed. I am a good and creative builder, but a little lame on the workings of electronics....please forgive. I have heard that the lightspeed needs a certain range of impedance both coming and going. SO, it will be going into a Pete Millete Low Mu preamp then on to 3 amps. For inputs, I have a CD player that goes into a tube DAC, an octal phono pre, music server that goes into the same DAC as my CD, and FM tuner (at some point in time) The tube DAC is the Maverick D1.

So, will the lightspeed work with these inputs and the tube preamp?
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Old 14th February 2012, 08:11 PM   #4396
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Hi djn, the Lightspeed Attenuator in it's purest form, with no buffers or extra series or shunt components, as I have attached, using quad matched NSL32SR2S led/ldr packages.
1: like to have sources (cdp,tuners,dacs, phono stages etc) of less than 200ohms output impedance (which most are theses days)
2: The input impedance of the poweramp should be higher than 47k (which most are) as 47kohms is the industry standard, tube amps are generally higher which is great. Many customers of mine have still had great results down to 33k poweramp inputs.
3: interconnects from the Lightspeed Attenuator to the poweramp should be 1.5mts or shorter and of low capacitance 100pf per foot or less which most good quality one's are.

And you can use one of these led testers (attached) and your DMM on the ldr to do the quad matching, $5 at your local Rat Shack or similar.

Cheers George
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File Type: jpg Lightspeed Attenuator MkII Circuit.JPG (41.8 KB, 266 views)
File Type: jpg LDR tester.jpg (60.5 KB, 265 views)
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Old 14th February 2012, 11:12 PM   #4397
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Quote:
Originally Posted by georgehifi View Post
This will be the 5th time your Lightspeed Attenuator has made it into Recommended Components since 2009 when Sam Telling first bought his from me. I have a feeling it may set some sort of record for Recommended Component longevity.

Cheers George
With all due respect, the Linn Sondek was in the recommended products for 20 to 30 years and may still be there today.
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Old 15th February 2012, 01:34 PM   #4398
djn is offline djn  United States
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Thanks George. I think this will work out well. I'd like to have a semi professional look about it. Does anyone sell boards and bits? Also, since I am getting or have gotten old, I want remote controlls on the V-pot. The only ones I can find have circuits of some sort attached to them. Is there anywhere I can get just a V-pot with a remote motor and controll board attached?
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Old 15th February 2012, 01:51 PM   #4399
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check ebay...here's one.

MV02 4way input Motorized Remote Volume Control Kit | eBay
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Old 15th February 2012, 03:16 PM   #4400
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If all you are looking for is a motorized pot, then there are lots of them available online. Google search.
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