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Old 23rd April 2012, 10:50 AM   #4531
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Chris, with respect, I feel it is time for you to stop posting in this thread. It seems that you are here for one reason only, and that is to try and convince people that your offering is better. That is something you can do to your hearts content in your own thread, but is inappropriate here.

As has been pointed out by a number of people, this is not a commercially oriented thread, however it seems it is your intention to make it such.

The purpose of this thread is for those that want to diy their own lightspeed, it is not a sales vehicle.

Consider this a warning
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Old 23rd April 2012, 09:04 PM   #4532
atupi is offline atupi  Romania
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Today i've tested the LDR and with potentiometre @minimum still have some music, is not totally quiet. What i did wrong ?
I followed this article to build it DIY Lightspeed Attenuator - Passive LDR Volume Control (optocouplers)
Still is an audible enhancement over previous Alps pot.
The amplifier is a MyRef C also fresh finished project.
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Old 23rd April 2012, 09:26 PM   #4533
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Quote:
Originally Posted by atupi View Post
Today i've tested the LDR and with potentiometre @minimum still have some music, is not totally quiet. What i did wrong ?
I followed this article to build it DIY Lightspeed Attenuator - Passive LDR Volume Control (optocouplers)
Still is an audible enhancement over previous Alps pot.
The amplifier is a MyRef C also fresh finished project.
Hi Autpi, glad you've also discovered the magic the Lightspeed can give.
As the circuit is posted by me, it is correct, the Lightspeed Attenuator will not go to complete silence it does have a very small amount of sound at min volume that can be just heard.
As the series LDR cannot go complete open circuit when no led light present and the shunt LDR cannot go complete close circuit when the led light is at it's brightest.
You could use your source pause or stop button if you need complete silence. Or you could make a mute switching arrangement that's be done somewhere in these pages.

Cheers George
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Old 24th April 2012, 08:46 AM   #4534
atupi is offline atupi  Romania
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I have two another issues and will try to solve it. First is that i have in a short movement of the potentiometre a huge increase of sound level.
Second i think i need a buffer as my freq response seems a bit changed. I will try a B1 buffer from Pass Labs.
If you have any sugestions i'm listening.
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Old 24th April 2012, 10:34 AM   #4535
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Short movement can be caused by
1: Not having matched series/shunt (quad) sets of LDR's
2: Or way too much system gain.
3: Also this has the same effect, and I have had this done by careless customers, the source has been put into the output of the Lightspeed and the input of the Lightspeed to the amp/s.
As for the buffer question, it is defiantly better not to have one, what is your output impedance of your cdp/dac and what is the input impedance of your amps?

Cheers George
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Old 24th April 2012, 10:34 AM   #4536
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"Change of frequency response" compared to what? Your previous preamp?

I dont think a simple "frequency response change" on its own is a reason for a buffer.
How big are your interconnect cables? And what is your amp's input and you source's output impedance?
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Old 24th April 2012, 11:35 AM   #4537
atupi is offline atupi  Romania
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My amplifier has an input impedance of about 100k and my sources wich dont know the output impedances are a Salas Simplistic RIAA preamp and a DAC wich is having on the analog following stage something like this Click the image to open in full size.
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Old 24th April 2012, 01:04 PM   #4538
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I have an Audio Precision and it measures frequency response amoung other things. The Lightspeed is near flat frequency response (the only place it changes is at less than 100Hz where it drops off a few dB but not even 3, zero phase shift and near zero cross talk. Crosstalk is down nearly 100dB. The frequency response being different probably actually means 'more accurate' than the other pre.
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Old 24th April 2012, 01:05 PM   #4539
udailey is offline udailey  United States
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Atupi with that output stage on your DAC and that input on your amp you do not have an issue with using a Lightspeed.
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Old 24th April 2012, 02:17 PM   #4540
BFNY is offline BFNY  United States
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Quote:
Originally Posted by udailey View Post
I have an Audio Precision and it measures frequency response amoung other things. The Lightspeed is near flat frequency response (the only place it changes is at less than 100Hz where it drops off a few dB but not even 3, zero phase shift and near zero cross talk. Crosstalk is down nearly 100dB. The frequency response being different probably actually means 'more accurate' than the other pre.
Unless you put in series coupling caps, the response on the low end should be flat to DC - it's simply a series and shunt resistor between the AP source and AP input. Or you are measuring the response of the AC coupling on the AP input.

This AP measurement will not correspond to anyone else's "real world" experience unless you have the same CD/DAC/Tuner/Phono preamp source output impedance, output coupling cap, cables, and input impedance and coupling cap on the next stage (usually an amplifier). Right?

And something also needs to be said about the Lightspeed's load presented to the source driving it. This will be dependent on the Lightspeed's volume control position.
As many of us have already observed, this load on the source from the Lightspeed can be relatively *LOW* compared to many other typical volume controlling devices - in the 500 to 1000 ohm range, or lower. In many cases this will be lower than the source output impedance, not the "times 10" number often recommended.
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