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Old 31st August 2012, 08:31 PM   #601
AndrewT is online now AndrewT  Scotland
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Mooly,
I am glad you're awake.
the others are not.!
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Old 31st August 2012, 08:51 PM   #602
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Stupid off subject question here. I was getting updates in my email whenever a new posting was happening and now they are not showing up. I am still showing that I am subscribed to the threads but the messages have stopped. What have I done. Perhaps it is that big capacitor I put on the CAT 5 cable to block spam, just kidding. How do I fix this, I want to keep up and I have to look to see if anything new has been posted?
Steven
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Old 31st August 2012, 09:29 PM   #603
redjr is offline redjr  United States
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You have to visit the site before more updates are pushed to your email. Your email should include this statement at the bottom.

'There may also be other replies, but you will not receive any more notifications until you visit the forum again.'

Rick
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Old 31st August 2012, 09:45 PM   #604
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Rick,
Thanks but I was getting those messages every few minutes whenever someone would post something new. It would only show the first message but now I am getting no updates on any thread at all. I guess I will have to go to support and see what has changed.

Steven
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Old 31st August 2012, 09:47 PM   #605
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by AndrewT View Post
Mooly,
I am glad you're awake.
the others are not.!
Actually, and perhaps I've missed something here, but..

Relative to the wiper the 10K resistor has the thevenin equivalent resistance of a 2.5K resistor worst case whereas the 1K pot would be 250 ohms worst case. Johnson noise from thevenin equivalent source resistance at the pot wiper will be about 10dB worse for the 10K pot than for the 1K pot. Now if you wired a pair of ~560 ohm resistors across the pot from one end to wiper, and wiper to other end the situation would be different, the noise would be very close to what you would expect with a 1K pot.

Note that these comments wrt noise apply to the example mentioned in a previous post where a single 1K resistor shunts the 10K pot as well as in the case of an unshunted pot. In the case where a near ideal voltage source (any op-amp really) drives the pot and 1K resistor, the 1K resistor has NO effect on the noise seen at the wiper for the reasons stated above.

Now if one end of the resistor (edit) is connected to the wiper the situation will be different, but the taper resulting from such a connection would not be the most useful I could think of.
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Last edited by kevinkr; 24th October 2012 at 09:52 PM. Reason: meant resistor not pot
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Old 31st August 2012, 11:42 PM   #606
owdeo is offline owdeo  Australia
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Quote:
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I am not "copping out" from anything.
I did not build the pre-amp.
I did not modify the pre-amp.
You did.
Still dodging the question

You didn't build the preamp and you aren't prepared to offer any justification for your assertion that I have modified the design and therefore the sound quality - so what is your point then? Should we just take your word for it?
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Old 31st August 2012, 11:53 PM   #607
owdeo is offline owdeo  Australia
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Seems a bit strange to be talking about how to use cheap nasty carbon pots in a design aiming for the highest performance. Even if you can find one in the batch that has adequate mechanical alignment between the two wipers. You also need to check the power rating for this design (as stated in the article).

Even the Omeg pots (while conductive plastic and electrically better) are not up to scratch IMO as the "feel" is not smooth enough - they are all plastic and with all of the ones I have there is some uneven friction when you turn them. The centre detents (used on some of them) are not well defined either.

For a design you build yourself it's worth spending the money on good pots.
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Old 1st September 2012, 12:48 AM   #608
kevinkr is offline kevinkr  United States
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With regard to the 1K pot the obvious answer is to build a 1K stepped attenuator - completely circumvents the issue of availability..

I like the ladder type best personally..
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Old 1st September 2012, 12:56 AM   #609
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kevinkr,
I was thinking what you just stated but didn't want to look stupid. What steps would you use, 1db or less per step and what would the values have to be to do that? How close does the precision of the resistors have to be 1% or less?
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Old 1st September 2012, 02:06 AM   #610
redjr is offline redjr  United States
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In this application, isn't a 'continuously variable' type control better and give a higher degree of resolution/precision than a stepped attenuator? It really doesn't matter in my case since I've already purchased said 1k pots as specified by the design.
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