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Old 21st December 2010, 05:30 PM   #3881
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Good point Andrew. Others cannot use a name that might cause confusion either, witness McDonalds pprotecting their trademark against any and all McSomethings. Sorry about that, George I didn't mean to push your trademark towards being generic, I knew better. Zen Mod correctly avoided calling his thread Lightspeed. Poor Serbian Man Optical Volume Control

Last edited by BobEllis; 21st December 2010 at 05:33 PM.
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Old 21st December 2010, 11:27 PM   #3882
eljaro is offline eljaro  Spain
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Default Dac with LDR attenuator

Click the image to open in full size.I recently finished my DAC with Doedes DDDAC with 60x TDA1543 chips, I2S input from the Transport, separate 11V power supply, Uriahs LDR attenuator kit and a IR remote controlled poti kit for the volume. Sounds fantastic and no need for preamp, just directly into my 300B SET power-monos.
Thanks to this thread, which introduced me to the LDR's , I can now enjoy fantastic sound with the least possible components in the signal path.
This is what's all about, isn't it?
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Old 22nd December 2010, 12:20 AM   #3883
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Quote:
Originally Posted by eljaro View Post
Click the image to open in full size.I recently finished my DAC with Doedes DDDAC with 60x TDA1543 chips, I2S input from the Transport, separate 11V power supply, Uriahs LDR attenuator kit and a IR remote controlled poti kit for the volume. Sounds fantastic and no need for preamp, just directly into my 300B SET power-monos.
Thanks to this thread, which introduced me to the LDR's , I can now enjoy fantastic sound with the least possible components in the signal path.
This is what's all about, isn't it?
Another one that has seen the Light "KISS" that's what it's all about.

Cheers George
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Old 25th December 2010, 09:16 AM   #3884
markusA is offline markusA  Sweden
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If I'm to OT just say so and I'll drop the matter.
It would be interesting to talk a little about what matters and how much it matters.
Talk about balanced operation has been very dogmatic and "black and white".
Iirc balanced operation is mainly used to reduce distortion picked up in the cables. I don't have the correct words but I hope you get the idea anyhow.
This is done by cancellation and differential amplification.

What happens if the + and - is of different amplitude?
The rf interference picked up in the cables should be roughly the same.
It's possible the reduction in electric fields are not perfect since the amplitude are not equal?
Still, I wonder...
Is it even noticeable?
The L/R difference in output swing can be corrected with channel balance correction. (easily done)

I guess my question is:
Does it even matter if the balanced operation is a little off? Naturally you want the LDR to track well but it's mostly a matter of conveniance. If you don't mind correcting the channel balance you could pretty much use any un-matched LDRs?

Last edited by markusA; 25th December 2010 at 09:19 AM.
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Old 25th December 2010, 10:31 AM   #3885
AndrewT is offline AndrewT  Scotland
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Hi,
balanced connection's main advantage is interference attenuation.

It achieves this using balanced impedance connections, not balanced voltage connections.

It is the impedance matches that result in the good attenuation of interference.
If impedances are not balanced then the major reason for using balanced connections has gone.
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Old 25th December 2010, 10:43 AM   #3886
markusA is offline markusA  Sweden
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Hmm, balanced impedance connections you say?
How is the impedance supposed to be balanced? I have a couple of ideas that spring to mind...
I was thinking the cables pick up equal interference and when you run it through a differential circuit that interference cancell out?
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Old 25th December 2010, 11:44 AM   #3887
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Quote:
Originally Posted by markusA View Post

. . . I was thinking the cables pick up equal interference and when you run it through a differential circuit that interference cancel out?
You'll find many explanations of the circuit on the web but there's a typically articulate one on Rod Elliott's site:

Balanced Line Driver & Receiver

As an aside and IMHO, the clamour to over-elaborate and "improve" the Lightspeed circuit misses a key point. Better power supplies (as with e.g. The Lighter Note) definitely make for better performance and many users appreciate remote control but I know of no successful LDR-based attenuator that has improved on George's basic circuit.

Many have suggested "better" designs but none to date (and it's been years rather than months) have come to fruition.

I don't find this surprising - with a device as quirky (as non-linear) as an LDR, getting it to work surely means that simplicity is of the essence.

The fact is that this simple circuit, despite a succession of arm-chair theoreticians explaining why it shouldn't work, does work and, as we know, works well. This is not a trivial point.

Last edited by Ryelands; 25th December 2010 at 11:48 AM.
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Old 25th December 2010, 12:22 PM   #3888
AndrewT is offline AndrewT  Scotland
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It's worth reading Self, Jung, Jensen, Rane as well for an overall viewpoint and understanding.
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Old 25th December 2010, 12:29 PM   #3889
soongsc is offline soongsc  Taiwan
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I must agree that it's VERY hard to further improve on the audible performance of the Lightspeed. Even if it does emerge, the amount of improvement would be VERY small and controversal.
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Old 25th December 2010, 12:48 PM   #3890
markusA is offline markusA  Sweden
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Rod Elliott's saying pretty much exactly the same as what I'm trying to say.

"Only the out of phase signal is detected by the remote balanced receiver, and any in phase (common mode) signal is rejected. RF interference and other noise will be picked up equally by both wires in the cable and so will be in phase. It will therefore be rejected by the receiver."

This theoretical line of reasoning is just for fun. Understanding why things behave as they do increase the chance for success.
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