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Old 28th January 2010, 03:38 AM   #21
tinitus is offline tinitus  Europe
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Sounds like you are not really interested in the subject at all
This thread wont be any good if it turns into a LDR hate thread
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Old 28th January 2010, 09:27 AM   #22
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by hornperfect View Post
.......it needs quite lots of confidence to claim 28k of any pot out there (7k output imp of the Lightspeed impedance times four). i don't think this is true.
do the sums.
100k pot and 100r source resistance gives output impedance of [100,000+100]/4=25k025
The Lightspeed if ~7K is roughly a quarter of that.

If you can't do that bit of mental arithmetic, then get your calculator out and learn to use it.
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Old 28th January 2010, 02:11 PM   #23
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sure but what finished preamps/attenuators with pot you know with 28k output impedance? i've never heard of such....

btw are you sure that lightspeed (or any other ldr based non-bufferred device) has a fixed output impedancewhich is irrelevant of source/attenuation level? i don't think so.
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Old 28th January 2010, 02:19 PM   #24
SY is offline SY  United States
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Every 100k pot. Sorry, it's Ohm's. It's the Law.
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Old 28th January 2010, 02:29 PM   #25
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yes but why talking about parts characteristics in a thread initiated to talk about whole products as such.

and what would be a reason to use a 100k pot as a stand alone attenuator between a source and a power amp?
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Old 28th January 2010, 02:33 PM   #26
SY is offline SY  United States
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Forgot what you wrote?

Quote:
well i'm not going to argue with writing of any manufacturer but it needs quite lots of confidence to claim 28k of any pot out there (7k output imp of the Lightspeed impedance times four). i don't think this is true.
(underline mine)

There are lots of passive preamps out there consisting of a naked potentiometer. Personally, I wouldn't use one, but lots of people do.
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Old 28th January 2010, 02:48 PM   #27
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very seldomly with >10k pot.
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Old 28th January 2010, 03:02 PM   #28
SY is offline SY  United States
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Quote:
Originally Posted by hornperfect View Post
very seldomly with >10k pot.
The Pressive - A DIY passive preamplifier [English]
GOLDPOINT SA1 STEREO PASSIVE PREAMPLIFIER - eBay (item 150356937522 end time Jan-30-10 23:13:27 PST)
Glasshouse Passive Pre-amplifier No.1 parts list
Passive preamplifier - Canuck Audio Mart

And so on and so on.
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Old 29th January 2010, 02:25 PM   #29
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just read on another forum that EVA & EVA 2 has a maximum impedance of 50k. interesting.
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Old 29th January 2010, 03:16 PM   #30
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The output Z of a resistive attenuator changes with attenuation setting. Attached are the plots of a 10K and 100K pot driven from a 200R source.

dave

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