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Kai Klaas
11/23/13 06:10
Read: 904 times
Germany


 
#190155 - No big difference, if it all
Responding to: Jan Waclawek's previous message
Jan said:
That may be the explanation - the common, cheap carbon-element potetiometer such as TP160 I mentioned above might quite well have a very different wiper current rating.

Hi Jan,

the maximum wiper current ratings of carbon trimmers and cermet trimmers should not be all too different. And I have some datasheets even telling that the maximum current rating is idential. Look here, for instance:

http://www.farnell.com/datasheets/28719.pdf

On the other hand, the minimum wiper current demands of a carbon trimmer is probably higher because of the worse contact situation on a carbon film.

In the past I often had wiper contact problems in audio applications when the audio signal wiper current was too little. In those cases carbon potentiometers were used because of cost reasons. Consequently decreasing the load impedance at the wiper and by this increasing the wiper signal current solved these problems. On the other hand, exceeding the maximum wiper current rating in an OPamp driven circuit is hardly possibly, provided a proper circuit is used.

Another important fact in audio applications is, that no DC current must flow across the wiper, because this would tremendously increase the noise and would render wiper setting changes audible. Even the input bias current of a bipolar OPamp could be too high. So, the consequent use of DC blocking caps arround a pot or trimmer is necessary.

Kai Klaas

List of 15 messages in thread
TopicAuthorDate
Power rating of potentiometers      Raghunathan      11/14/13 21:24      
   Not the point      Andy Neil      11/15/13 11:47      
      show me such        Jan Waclawek      11/16/13 13:48      
         (was) incorrect      Erik Malund      11/16/13 18:02      
            not your average "pot"      Andy Neil      11/17/13 07:40      
         Specs that are not normally told..      Raghunathan      11/17/13 03:37      
            power      Joseph Hebert      11/17/13 04:10      
            test bench vs field design       Jim Granville      11/17/13 12:13      
         That was kind of my point      Andy Neil      11/17/13 07:50      
   pot limits      Joseph Hebert      11/17/13 04:00      
      While I don't disagree ... there are different failure modes        Richard Erlacher      11/17/13 14:50      
   Bourns says: "yes."        Kai Klaas      11/18/13 16:08      
      Tesla says: no      Jan Waclawek      11/19/13 14:11      
      cermet or wirewound      Jan Waclawek      11/20/13 01:02      
         No big difference, if it all      Kai Klaas      11/23/13 06:10      

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