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Old 24th February 2008, 11:25 AM   #11
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Quote:
Originally posted by AndrewT
-80db or -infinitydb are the choices. The 8 is an attempt to write the symbol for infinity which is similar to an 8 on it's side with the right hand end open.
If Rg=0 then attenuation is theoretically infinity.
If Rg = 1r0 then attenuation is -80db.
Yes,I understand now.
Thank you all for your responses.
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Old 10th July 2008, 01:45 PM   #12
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Default Clarification

AndrewT: Could you clarify your "fake log pot"? Between what should you put the resistor? Was it just between the pot and the signal ground? Probably it's just my English, that makes me not understand this...

I'm thinking of buying a simple Remote with preinstalled 100k (probably lin - not specified) pot.

Another thing: If you do this fake log pot, will that also resolve the problem with added noise with a high value pot (I guess it will, but ask the qst anyway...)?

Thank you!
Sincerely
Andy
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Old 10th July 2008, 02:09 PM   #13
Nordic is offline Nordic  South Africa
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http://www.vt4c.com/shop/program/mai...=60&group_id=2

cheap source for the switches 2x24 step switches starting at $14 for single items, discount with larger orders...
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Old 10th July 2008, 02:23 PM   #14
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What is the shipping for the above shop (roughly)? I tried to find some info about it, but couldn't...

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Andy
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Old 10th July 2008, 02:32 PM   #15
AndrewT is offline AndrewT  Scotland
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Default Re: Clarification

Quote:
Originally posted by andySweden
[B]Could you clarify your "fake log pot"? Between what should you put the resistor? ...................
Another thing: If you do this fake log pot, will that also resolve the problem with added noise with a high value pot .....
the faking resistor goes between the wiper and the audio/input ground.
Zin of the amplifier can also provide the faking resistor value if there is no DC blocking cap between pot and Zin. But 100k varies Rs too much for many power amps.

The amp sees a worst case source resistance of [100k+Rs]/4 // 12k ~=8k1. this is still much higher than the 2k5 seen when a 10klog is used. But lower than 25k without the faking resistor.

Have you tried the search facility on the Forum, or even Google?
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Old 10th July 2008, 03:18 PM   #16
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Thank you!

That was most informative! (I believe that the English word "wiper" refers to the arrow pointing to the pot!?)

Now, the Ebay seller answered my question about the pot. It is a 100k LOG pot. Is that a problem?

I will also search the forum for more info!

Sincerely
Andy
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Old 10th July 2008, 03:57 PM   #17
Nordic is offline Nordic  South Africa
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first item on the menu.. How to buy, has shipping info...

I think to make a fake law pot, you need to start with a linear one...
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Old 10th July 2008, 04:07 PM   #18
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Thank you for helping me, Nordic!

Quote:
It is a 100k LOG pot. Is that a problem?
What I meant was: I will not be faking a log pot if I already have one... But is having a log pot with such a high value a problem when making a 3886 GC?

Sincerely
Andy
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Old 10th July 2008, 04:14 PM   #19
AndrewT is offline AndrewT  Scotland
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It depends on the topology you adopt.

Variable Rs without a DC blocking cap results in variable output offset.

The higher the range of variable Rs the worse the change in output offset becomes.

100klog > Rs=0r0 to 25k
100klin//12k > Rs=0r0 to 8k1
10klog > Rs=0r0 to 2k5
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Old 10th July 2008, 04:19 PM   #20
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I will be using a DC blocking cap...
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