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Lightspeed Attenuator a new passive preamp
Lightspeed Attenuator a new passive preamp
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Old 16th August 2011, 06:28 AM   #4221
georgehifi is offline georgehifi  Australia
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Maybe it's the SR3, because they have such a high 25mohm dark resistance, that's 5x higher than the SR2's. Or your load resistance was too low making them hot. Also do it at the normal cd level 1-2v

Cheers George
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Old 16th August 2011, 11:59 AM   #4222
AndrewT is offline AndrewT  Scotland
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2Vac from a CDP is ~5.6Vpp.

6Vpp is ~2.12Vac which many CDP can put out (and more).
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Old 19th August 2011, 06:02 PM   #4223
udailey is offline udailey  United States
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Default Audio Precision Testing

I will test the Lightspeed but I am sure its the same. I just tested the Lighter Note on my Audio Precision. Bought one a short time ago and just hooked it up. My camera wont take pics of the screen because its bright vs the darker background. I will see if another camera in the house will do better. Most tests were done at 1V and 1kHz. There was a certain spot in attenuation that produced the least distortion. Interestingly its my favorite listening position on the dial. As long as the test is a sweep type test I went from 20-20kHz.
Anyway
Noise is 16uV no matter what voltage I am putting through it and is just a straight line.
THD+N has a few results
- at .5V=.007%
- at 1V = .0055%
- at 2.5V= .0154%
- at 10V=.146% which surprised me. I expected much higher as in several percent. It certainly sounds bad with high voltage through it even if not measuring bad.
I have a balance function on my remote and was curious how precise I could dial it in.
With 1V in at a bit less than half volume I dialed in 430.3mV on Left and 430.2mV on the right. Dead center if you ask me.
XTalk varies a lot. The best I got was -103.4db @782.5mV output, thats with 1V in. I have my volume limted so the kids cant screw it up plus the balance pot limits the volume. It seems that the higher in volume the lower the crosstalk.
Worst crosstalk was -64.27dB at 76.7mV which is limted by the 40Ohm rule of the shunt LDR. If it would go lower then the crosstalk would get worse.
IMD or intermodulation distortion is something I am not very familiar with at all. Reading the AP manual I am guessing that its supposed to give me a ratio of the low to the high frequency as it sends two frequencies through at once and I suppose measures distortion where they intermingle or something. Will read up on it. Anyway, I dont see a way to read or set the ratio yet. The settings are 1V in and with attenuation I am getting 365mV out. The low frequency was 250Hz for this reading and the high was 7k. IMD reading was .0108%.
Well, thats all I have got for now. This is with NSL32SR2. I think those of you wondering about SR3 at least can rest easy that SR2 is a good device.
Uriah
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Last edited by udailey; 19th August 2011 at 06:05 PM.
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Old 30th August 2011, 11:49 PM   #4224
georgehifi is offline georgehifi  Australia
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An interesting little snippet for those of you who own or have built a Lightspeed Attenuator, this will give you maybe some bragging rights.
Not only does the $28k DarTZeel NHB 18-NS preamp have a form of Lightspeed Attenuator controlling the volume (which they tried to patent).
But now there is a new player on the block, Constellation Audio with their $60k fet line stage preamp, the Altair which also uses a Lightspeed Attenuator form of volume control. (at least they didn't try to patent it)
Altair

Cheers George
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Old 31st August 2011, 03:05 AM   #4225
udailey is offline udailey  United States
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I keep wanting to build a multi ldr unit. I guess I just have a hard time believing the sound gets better that way. I could see channel matching being better though. Simple law of averages.
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Old 31st August 2011, 10:18 AM   #4226
Earfanatic is offline Earfanatic  Hungary
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Quote:
Originally Posted by georgehifi View Post
Constellation Audio with their $60k fet line stage preamp, the Altair which also uses a Lightspeed Attenuator form of volume control.
But why does it have 48 of them in the circuit?
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Old 31st August 2011, 10:33 AM   #4227
georgehifi is offline georgehifi  Australia
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Could be 48 1% trimming resistors to go with the quad unmatched ldr's, which in my opinion would detract from just a quad matched set, as the i/o impedances for both channels would not remain constant, and there would be another component in the signal path.
Or it could be 48 x ldr's in some paralleled setup for series and shunt ldr's, again this would definitely detract from a simple matched quad set.

Or it could be just a 48 position switched volume control instead of continuous rotary pot with a quad matched set, this would then sound the same no different than my production Lightspeed Attenuator.(this is the most logical explanation)

Cheers George
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Old 31st August 2011, 11:26 AM   #4228
udailey is offline udailey  United States
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My bet is that they use 48 because they parallel the heck out of them. The advantage is zero volume. Using one we can only go to 40 ohms on shunt so volume goes real low but not zero. Hard to sell a 60k device that won't go to zero.
Uriah
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Old 31st August 2011, 03:49 PM   #4229
AndrewT is offline AndrewT  Scotland
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a series pair of series LDRs can easily be set up to give 50k each for a total 100k of series resistance.
A parallel pair of shunt LDRs can be set up for 40r each for an effective 20r of shunt resistance.

This set requires 8 LED/LDR for a stereo control.
-0.1dB to -74dB is within reach as the range from this doubled quantity of LED/LDR.

A few mores series and paralleling can be used to avoid the need to match and to give an even wider range of control. Avoiding matching releases a lot of cash to buy extra LED/LDRs.
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Old 31st August 2011, 07:03 PM   #4230
Earfanatic is offline Earfanatic  Hungary
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Quote:
Originally Posted by georgehifi View Post
Or it could be 48 x ldr's in some paralleled setup for series and shunt ldr's, again this would definitely detract from a simple matched quad set.
Paralleling LDR-s could average its characteristics... in this case we would get an LDR (array) that has lower impedance and characteristic that reflects more the average of a lot. But will paralleling resistors mean more distortion? They could use 12 LDRs paralleled and have 4 arrays ar for a SE setup is needed. If it is Balanced then 6 of them / array.
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