Resistor tolerances: Passive Summing Box

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craigmorris74

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I am about to build a 10 channel passive summing box.  I ordered 50 10k 1% metal film resistors for the inputs.  I have a cheap meter, and I'm getting some variation in the resistor values.  Is this something I should be concerened with and use tight QC, or will the resistors I have be close enough?

Thanks,
Craig Morris
 
I would not panic about 2% or 3% match; I use a lot of 10% slop parts. A full 10% slop is audible in a well-balanced stereo signal. Mixing by ear, 10% "error" is nothing. But in the modern world where you set levels in ProTools then passive-sum, a 10% difference between channels would upset your mix if you somehow re-wired in different track/input order.

I agree that even a cheap meter, with a helthy battery, reading good 1% resistors all the same value, ought to give +/-1% value on every resistor. A -cheap- meter might say 9,800 on true 10,000 parts, but it should be consistent. I dunno if some sellers might buy 5%, or the rejects from a 1% product, and try to pass them off.
 
Thanks for the replies.  My meter is showing around 9800, but seems to drift with time, so I get some readings down to 9.6K.  I'll try a few these and run some signal through it and see what happens.  If they're that far off I'll get something else.

Craig
 
Just a few thoughts:
a) Metering - use a fresh battery, test leads with clips (not pin points), leads twisted together, meter resting on desk not in hand, not near sources of EMI/RFI like computers.
b) When measured with a precision meter, resistors will often group with almost identical values. That is you may see a groups at 100.08 and 99.94.
c) Using a budget meter, it may not be 1% accurate but it repeatable.  So you can select near identical values for important circuit locations.
 
craigmorris74 said:
Thanks for the replies.  My meter is showing around 9800, but seems to drift with time, so I get some readings down to 9.6K.  I'll try a few these and run some signal through it and see what happens.  If they're that far off I'll get something else.

Craig

The resistance should not be changing with time fast enough to see on a meter so I question the measurement. If your fingers are touching the test leads that could make a small difference. If the meter has a tired battery of questionable design, that could give unreliable measurements.  The odds are that the resistors are more reliable than your meter, but this will be a learning exercise.

JR

 
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