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Old 15th July 2010, 12:59 PM   #3411
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Originally Posted by AndrewT View Post
This Member has his head screwed on correctly.
He measures and checks.
He allows the arithmetic to remove the need for guessing.
I take that as a high compliment, thank you.
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Old 15th July 2010, 02:42 PM   #3412
udailey is offline udailey  United States
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I like around 150R as well. In the little board I sell that is basically the Lightspeed backend I use a 200R pot for the Shunt LDRs. They reference ground through it with the wiper going to ground and each shunt tied to one of the other legs. Then between the outer legs and the LDR is a series 68R resistor. So approx 168R for each shunt. Works well and no burnt LDRs.
Uriah
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Old 15th July 2010, 04:42 PM   #3413
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Quote:
Originally Posted by udailey View Post
I like around 150R as well. In the little board I sell that is basically the Lightspeed backend I use a 200R pot for the Shunt LDRs. They reference ground through it with the wiper going to ground and each shunt tied to one of the other legs. Then between the outer legs and the LDR is a series 68R resistor. So approx 168R for each shunt. Works well and no burnt LDRs.
Uriah
Uriah, could you explain the purpose of this setup -- is it intended as a control to balance the two channels? What about the series device?
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Old 16th July 2010, 03:14 AM   #3414
udailey is offline udailey  United States
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Yep, its for balance. Series you need two pots. This way only one. Also when I match I cant match under about 200-250R so the 200R pot allows matching that last little bit without effecting the matching at higher resistances. If you match several hundred of them at high mA then you end up drawing a serious amount of current and not having a super accurate power supply. If I match at that level then I dont have to draw a huge amount of current and I have a super precise supply.
Uriah
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Old 17th July 2010, 05:27 PM   #3415
udailey is offline udailey  United States
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Default Varying Ground to each LDR for balance.

Here is a drawing further illustrating my grounding technique that allows balance with one pot. This is what's on the tiny board I sell on my site. Anyone can feel free to use it for their own uses as long as youre not selling my exact representation of it. Meaning, go build your own boards if you like.
Attached Images
File Type: gif LightspeedJuly10.GIF (22.8 KB, 476 views)
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Old 17th July 2010, 08:59 PM   #3416
tinitus is offline tinitus  Europe
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wapo54001 has started his own thread

A precision LED/LDR-based Attenuator

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Old 18th July 2010, 01:37 AM   #3417
udailey is offline udailey  United States
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That board I just showed the schematic for is part of whats available on my site. There is a sale on a small kit right now. Includes 4 matched LDRs, the board, all parts that are mounted on the board plus the 5k pot. You will need to source a dual log 100k pot and a 5V supply. One member is trying Teddy Pardo's regulator and I think this is a fantastic idea that will provide excellent sound. For a while I will have the board/parts/LDRs for sale for $30. I think thats a fine deal. I hope you guys will write about the sound you hear and help get others interested in LDRs.
http://www.buildanamp.com/LDRs-for-L...RsBOARDKIT.htm
Uriah
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Last edited by udailey; 18th July 2010 at 02:01 AM.
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Old 18th July 2010, 12:14 PM   #3418
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I hope you guys will write about the sound you hear and help get others interested in LDRs.

Happy to. I recently finished building UD's version of the basic Lightspeed circuit using a decent PSU and have been listening to it now for a day or two.

First, thanks to Uriah for making matched LDRs and a PCB available at very fair prices. They make what is otherwise an esoteric project pretty easy.

Second, very hearty thanks indeed to George for making his design available to the audio DIY community and for his on-going help to constructors. His generosity is unusual and should be acknowledged more than perhaps it is. He and UD have the patience of a brace of saints. (Yup, I think I've read every page of this looooong thread . . .)

Third, sound quality. I replaced a pretty good stepped attenuator which was itself a significant step up from an elderly Alps pot. Simply put, the Lightspeed circuit blows it away.

My experience is that almost everything the designers and others claim for LDR-based attenuation seems to be true, especially the razor-sharp detail, well-defined bass and almost tactile vocals. The effect is particularly marked on complex orchestral music where it is now much easier to follow what is going on. That alone makes it a worthwhile upgrade.

On the technical side, my source is a highly-resolving audio PC (cMP^2), the Lightspeed's PSU is a step up from run-of-the-mill LM317 circuits but nothing overly exotic, the driving DAC's Z(out) is 90R and the power amp's Z(in) 20K. This last is of course significantly lower than George and others recommend but it's working just fine. (I'd anticipated having to modify the amp's input or even to buffer it but it really seems unnecessary.)

In short, a super upgrade and extraordinary value for money (as BTW I assume George's production unit is even if it's out of my reach). Anyone dithering about whether to proceed should just go for it.

In a world where folk happily pay $1,000 for a piece of wire, they'd be daft not to.
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Old 19th July 2010, 10:47 PM   #3419
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Quote:
Originally Posted by Ryelands View Post
I hope you guys will write about the sound you hear and help get others interested in LDRs.


Second, very hearty thanks indeed to George for making his design available to the audio DIY community and for his on-going help to constructors. His generosity is unusual and should be acknowledged more than perhaps it is. He and UD have the patience of a brace of saints. (Yup, I think I've read every page of this looooong thread . . .)

Third, sound quality. I replaced a pretty good stepped attenuator which was itself a significant step up from an elderly Alps pot. Simply put, the Lightspeed circuit blows it away.

My experience is that almost everything the designers and others claim for LDR-based attenuation seems to be true, especially the razor-sharp detail, well-defined bass and almost tactile vocals. The effect is particularly marked on complex orchestral music where it is now much easier to follow what is going on. That alone makes it a worthwhile upgrade.


In short, a super upgrade and extraordinary value for money (as BTW I assume George's production unit is even if it's out of my reach). Anyone dithering about whether to proceed should just go for it.

In a world where folk happily pay $1,000 for a piece of wire, they'd be daft not to.
Thanks for the pat on the back Ryelands, makes me feel good people appreciate it.
Just so people don't think the production Lightspeed Attenuator is the same price as the above piece of wire, it's not, it's $450 posted worldwide.

Cheers George
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Old 23rd July 2010, 06:24 PM   #3420
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Hi

I've recently completed Uriah's LDR mount & board. I'm finding I have to rotate the 5K series balance pot fully clockwise to achieve a near central image. If I start to rotate counter clockwise it starts to shift to the right speaker and the volume increases. I thought I had calibrated the shunt LDRs correctly prior to testing...maybe not?
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