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Old 28th November 2012, 12:28 PM   #8661
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Also: Capacitor Characteristics and Specifications

Temperature Coefficient, (TC)

The Temperature Coefficient of a capacitor is the maximum change in its capacitance over a specified temperature range. The temperature coefficient of a capacitor is generally expressed linearly as parts per million per degree centigrade (PPM/C), or as a percent change over a particular range of temperatures. Some capacitors are non linear (Class 2 capacitors) and increase their value as the temperature rises giving them a temperature coefficient that is expressed as a positive "P".

Some capacitors decrease their value as the temperature rises giving them a temperature coefficient that is expressed as a negative "N". For example "P100" is +100 ppm/C or "N200", which is -200 ppm/C etc. However, some capacitors do not change their value and remain constant over a certain temperature range, such capacitors have a zero temperature coefficient or "NPO". These types of capacitors such as Mica or Polyester are generally referred to as Class 1 capacitors.

Most capacitors, especially electrolytic's lose their capacitance when they get hot but temperature compensating capacitors are available in the range of at least P1000 through to N5000 (+1000 ppm/C through to -5000 ppm/C). It is also possible to connect a capacitor with a positive temperature coefficient in series or parallel with a capacitor having a negative temperature coefficient the net result being that the two opposite effects will cancel each other out over a certain range of temperatures. Another useful application of temperature coefficient capacitors is to use them to cancel out the effect of temperature on other components within a circuit, such as inductors or resistors etc.
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Old 28th November 2012, 12:37 PM   #8662
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What does Percy charged for matching? I am doing the folded cascade version
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Old 28th November 2012, 02:09 PM   #8663
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How do you match capacitors? If do you buy matched, do you know how are matched & the real value?
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Old 28th November 2012, 03:36 PM   #8664
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Quote:
Originally Posted by buzzforb View Post
What does Percy charged for matching? I am doing the folded cascade version
Please wait for Salas review.... My build is quite different from Salas initial schematics.

You must speak with Michael... it depends.
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Old 28th November 2012, 03:40 PM   #8665
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Quote:
Originally Posted by merlin el mago View Post
@Rcruz
How do you match capacitors? If do you buy matched, do you know how are matched & the real value?
I always ask for matched capacitors because otherwise there will be great differences between them... but even if they are matched, there are always small differences... so If I need two caps, I always buy 6 or more... Then I do matching myself... I have a calibrated LCR.

Anyway there are only three critical caps per channel in a simplistic so it is not a big deal.

I also match all transistors and resistors.
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Last edited by RCruz; 28th November 2012 at 03:44 PM.
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Old 28th November 2012, 03:44 PM   #8666
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With 4 cables Kelvin wiring connection? post a pic, thanks.
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Old 28th November 2012, 03:58 PM   #8667
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IMO, if you use polystyrene or teflon you will not need to worry about cap value drifting because these are the most stable.

For instance, when I am short of T$me, I use regular 2% small polystyrenes to top up the main 47n and 15n caps.

It is quite normal to get a wide variation in a batch of caps... for example, I just bought 20 150p 2% styrenes from reichelt and was able to get some matching pairs 149p // 149p, 151p // 151p, 147p // 147p, so I choose the pairs and use them.

If I use those two 151p I am convinced they are exactly the same and will not drift differently with temp.

Off course, if you do not match them for yourself, you must buy 1% or less.... some russian micas have 0.3% spec !!!
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Old 28th November 2012, 04:01 PM   #8668
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Post #8608
Simplistic NJFET RIAA
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Old 28th November 2012, 04:04 PM   #8669
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Ricardo I don't see the calibrated LCR.
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Old 28th November 2012, 04:06 PM   #8670
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Sorry, I did not realize you wanted a pic of the LCR

You can search for this: TENMA 72-8150

I used a bunch of 0.5% caps to calibrate it myself.

Inexpensive but effective... no kelvin thou
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