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Lightspeed Attenuator a new passive preamp
Lightspeed Attenuator a new passive preamp
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Old 6th April 2012, 08:29 PM   #4501
udailey is offline udailey  United States
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yes, great place for it.
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purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
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Old 6th April 2012, 09:27 PM   #4502
BFNY is offline BFNY  United States
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Quote:
Originally Posted by kumori View Post
Hallo,

I just finished and installed my lightspeed kit. It sounds wonderfull.

I have a problem though. The minimum level is just too loud to be acceptable.
also see messages here

http://www.diyaudio.com/forums/analo...ml#post2847577

Make sure to put the lightspeed in front of, not after, the gain element.
Until you get the buffer built, you can try a fixed 20k to 40K resistor in front of the series LED/LDR. This can also be a LDR with a pot to fix the R.
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Old 6th April 2012, 09:30 PM   #4503
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by kumori View Post
Hallo,

I just finished and installed my lightspeed kit. It sounds wonderfull.

I have a problem though. The minimum level is just too loud to be acceptable.
I read in this thread, that it would be possible to add an additional series LDR to increase attenuation. How does one best manage this? Can someone give a short hint?

I guess the possible attenuation with second series LDR will be also "not so much different" than it is now, isnīt it?
Iīm testing the lightspeed with a 1.8x-gain-preamp at the moment, an it is too loud (for quiet). Finally I would like to install it in my main system with 6x-gain-preamp.Thanks,
Florian
Hi Florian, first off an additional series LDR will add more distortions and reduce the amount of transparency of sound, it is detectable in the circuit when doing an A/B with a single series one.
I don't know why you are using an active preamp after the Lightspeed maybe for better impedance matching, is it because you have a low input impedance poweramp? If so and you want to keep it, then make it unity gain this also will reduce your min volume problem.
The other way you could reduce the gain is to use LDR's with a lower "on" impedance, the NSL32SR2S quad matched that I use in the production Lightspeed Attenuator has this, at 40ohms "on" value this is far lower than you may be getting now without pushing them to their mA limit and cooking them.

Cheers George
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Last edited by georgehifi; 6th April 2012 at 09:34 PM.
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Old 6th April 2012, 09:46 PM   #4504
kumori is offline kumori  Europe
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Hey George,

To keep things in perspective, I didnīt use a high gain pre after the lightspeed. It is just that I wanted to use the lightspeed in my preamp because it is known to be a good volume control. I know now, that this is maybe a bad combination, and consequently plan to use it with a unity gain buffer, where it is apparently better suited. I have been listening today with my low gain alternative preamp, and it is definitely better sounding than the alps blue fitted before.

Thanks for the tip with the alternative LDRs, but I guess it wonīt be needed.
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Old 20th April 2012, 04:49 PM   #4505
Audio68 is offline Audio68
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I'm interested to know if anyone has used a Burson case to build their kit. I have a Burson AB-160 buffer and would like to have my lightspeed kit in a case that matches. Burson is willing sell me a case.
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Old 21st April 2012, 12:06 AM   #4506
Chris Daly is offline Chris Daly  Australia
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Quote:
Originally Posted by kumori View Post
Hey George,

To keep things in perspective, I didnīt use a high gain pre after the lightspeed. It is just that I wanted to use the lightspeed in my preamp because it is known to be a good volume control. I know now, that this is maybe a bad combination, and consequently plan to use it with a unity gain buffer, where it is apparently better suited. I have been listening today with my low gain alternative preamp, and it is definitely better sounding than the alps blue fitted before.

Thanks for the tip with the alternative LDRs, but I guess it wonīt be needed.
Hi kumori and anyone similarly interested in actually measuring equipment rather than guessing

Can you measure with the product switched on, but unloaded ie without input or output cables Shunt and Series resistance for each channel ideally at 27 or more settings, so we can see the Left and Right channel resistance figures please.

Now write down each measurement and add each Left figure this provides an aggregate for the left - a true indication of the products resistance on the Left ,without the volume control moving at all .do the same for the Right Now very slowly move the attenuator and measure each channel Shunt and series to show Left and Right channels for each of the settings ( starting L Shunt ) suggested below. Its painstaking work but will really show us if it is a good volume control, or something else.

If you publish the figures for each volume setting i have provided suggested left start point ohms for each below and publish back here in this format;

L Shunt =
L Series =
aggregate= Ohms

R Shunt =
R Series =
aggregate= Ohms

Result for each volume setting ie Difference Left to Right = OHMS

Can I suggest (Reference Start point Shunt L ) At beginning then 75R then 165R followed by 350R 421R 532R 645R 748R 853R 959R 1K 1.19k, 148K 2k 2.5k 3K, 3.5k 4K, 4.5K 5k 6K 7.5K 9K 10K 12K 15K 40K 105K and at end

I look forward to those figures.

Cheers / Chris

Last edited by Chris Daly; 21st April 2012 at 12:32 AM.
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Old 21st April 2012, 10:09 AM   #4507
Ryelands is offline Ryelands  United Kingdom
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Quote:
Originally Posted by Chris Daly View Post
. . . anyone similarly interested in actually measuring equipment rather than guessing . . . [It] will really show us if it is a good volume control or something else
You have me confused here. Are you suggesting that linearity is the sole criterion of attenuator quality?

If so, it seems you're the one who's guessing. If not, what is the purpose of the 'painstaking' work you want people to do? IOW, what are you trying to prove?

One of those Ģ20 Valab devices (good value BTW) will outperform any LDR design in that regard. Sound quality? Hmmmm.
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Old 21st April 2012, 10:12 AM   #4508
DF96 is offline DF96  England
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As we explained elsewhere, it is the ratios which matter not the absolute values. Are you still struggling to understand how a volume control works?
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Old 21st April 2012, 11:15 AM   #4509
Chris Daly is offline Chris Daly  Australia
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Quote:
Originally Posted by Ryelands View Post
You have me confused here. Are you suggesting that linearity is the sole criterion of attenuator quality?

If so, it seems you're the one who's guessing. If not, what is the purpose of the 'painstaking' work you want people to do? IOW, what are you trying to prove?

One of those Ģ20 Valab devices (good value BTW) will outperform any LDR design in that regard. Sound quality? Hmmmm.
When you get a LDR design also managing good channel balance within approx 400 ohms each channel through the range where normal listening is done, you will not want any other attenuator. Accurate channel balance is amazing to listen to, and is an extremely good indicator of valid design with LDR's My post encourages someone to measure this product as it is supplied with channel balance, If no one can, I rest my case and will be happy to continue my life believing that it is very inaccurate,

Cheers / Chris

Last edited by Chris Daly; 21st April 2012 at 11:19 AM.
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Old 21st April 2012, 11:19 AM   #4510
AndrewT is offline AndrewT  Scotland
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Chris,
I shall repeat DF's comment.

You don't understand what you are posting.
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