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Old 26th July 2006, 01:30 PM   #131
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Hi George,

Early on in this thread there was a lot of talk about LDR distortion
and how audible, if at all, it would be.

Well I was thinking deeply about LDR's today and came to the
conclusion that at exactly 6dB gain reduction, ie; same resistance
value for series and shunt LDR, the distortion of each should
cancel perfectly at the OP.

Since we can look at whatever distortion mechanism that exists
in the LDR as a variation of it's impedance WRT signal level, then
at 6dB attenuation the signal level through each is identical.

As such, any voltage induced impedance change of each should
result in the same exact 6dB attenuation, ie; near perfect
linearity.

Soooo, the big question, provided my assumption is correct, is
do these volume controls sound different from 6dB attenuation
to anywhere else in the range?

It's worth having a listen to see if you can actually pick
by ear any linearity change in its attenuation range.

Cheers

Terry

PS can you get the ones you recommend locally (austr)
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Old 26th July 2006, 02:03 PM   #132
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Vatofile,
I was able to matched up four for a stereo control and eight for a balanced control from a batch of 22 sorted. This was eaiser than it looks, used tighter matching for the series pairs, and shunt pairs so that stereo balance was achieved versus theoretical tracking.
I only matched mine at three currents, 1.5 ma, 0.5 ma, and 0.1 ma. Then plotted them out. The resulting curve is exponetial, but slow decay. The slopes and intercepts were not consistant, but this did allow better matching.
I have only used the stereo version as a clone. Measuring the impedance as the pots are rotated, the matching for series and shunt are very close side to side. The units have a very high tempco. Leaving on all the time should deal with this. Just touching them causes the impedance to change a little.
Like others have posted the results are great. I have no plans on going back to using the carbon PEC pots used before for attenuation. These are much better. And track just as good or better.
Allied Electronics here has the sorted for about 2.00 each. 10 or 12 should be enough for a control. 12 might allow enough for 2 controls.

George
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Old 26th July 2006, 09:18 PM   #133
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Quote:
Originally posted by Terry Demol
Hi George,

Soooo, the big question, provided my assumption is correct, is
do these volume controls sound different from 6dB attenuation
to anywhere else in the range?

It's worth having a listen to see if you can actually pick
by ear any linearity change in its attenuation range.

Cheers

Terry

PS can you get the ones you recommend locally (austr)
Terry if you connect your cd player or dac direct to the poweramp, and had a -6db series/shut resistor network SOLDERED at the input of that poweramp, no the sound would be identical, trouble is you have no way of varying the volume. Add a pot anywhere and the sound will be degraded.

And Allen glad your liking yours, a lot of people have expressed to me that the source and annoyance of their in your face (hard) sound was fixed by removing their preamps and using the Lightspeed, they addmited they were wrongly accusing their cd players for that sound instead of the pre's.

Cheers George
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Old 1st August 2006, 12:46 PM   #134
1543 is offline 1543  Germany
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Hi George,

A Lightspeed Attenuator would also be fine for 5.1 systems. 1 Stereo pot to control 6 channels.

In a 6 channel configuration the current on the pot is 3 times higher than in a stereo Lightspeed. Do you know the current values from your Lightspeed and is it possible to use a normal Alps Pot for such currents without shorten endurance?

Arne
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Old 1st August 2006, 02:09 PM   #135
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I can't see a problem, though how are you going to set your levels for front, center and rear, I think you would be better off just making 3 x stereo Lightspeeds so then you could adjust your 3 diffferent levels.

Cheers George
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Old 2nd August 2006, 08:32 AM   #136
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Alan,

Which components did you change on your NAP160 to raise the input impedance?

Regards,

Graeme
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Old 3rd August 2006, 08:12 AM   #137
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George,

My Naim NAP 135 clones have an input impedance of 18k according to the Naim manual, presumably from the 100k and 22k resistors in the attached schematic (100k||22k = 18k) ? What would you recommend to increase the input impedance sufficiently to use your lightspeed?

Thanks,

Graeme

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Old 3rd August 2006, 09:27 AM   #138
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Quote:
Originally posted by gfinlayson
[B]George,

My Naim NAP 135 clones have an input impedance of 18k according to the Naim manual, presumably from the 100k and 22k resistors in the attached schematic (100k||22k = 18k) ? What would you recommend to increase the input impedance sufficiently to use your lightspeed?/B]
Graeme, looking at all the circuits I have for the Naim amps they are all bipolar input, this would be hard to get up to 100k, if they were fet input then this would be a lot easier, maybe the Naim 160 is fet, I'm not sure as it is the only circuit I don't have, or maybe Allen has had his modded.
Anyhow I've revised the minimum input of a poweramp to be used with a Lightspeed, down to 60k or so, as at home I am bi-amped driving 2 x stereo poweramps at 68k each with one stereo Lightspeed, and that becomes 34K the Lightspeed is seeing, and it's doing it on it's ear, with no troubles, great tight low bass still and extened clean highs.
I think I was being TOO conservitive when i quoted 80k-100k.

Cheers George
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Old 7th August 2006, 06:09 AM   #139
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Default Lightspeed impedance

Hello George,

Interesting stuff!
Did I understand correctly, that the Lightspeed is similar to a 7kohm pot?

Any way to get the impedance up a lot?

I'm thinking perhaps 7k is the highest possible with "selected" devices, while there are higher that would require more work with matching or so?


/Ronnie
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Old 7th August 2006, 07:21 AM   #140
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That's around 7k for input and output and remains fairly constant, it's a happy medium for the source and to the poweramp.

Cheers George
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