Chinese fun and games - electronic components this time

Ran into this little gem from an electronic music website. From electro-music.com

Be very careful when ordering resistors from china!
A while back I was selecting 100k resistors for the summing stage of a VCO, the most common value in my belt was something like 100.6k

when I later wanted to select from that group the values where nowhere near what I had initially measured, even worse .. the longer I measured a resistor the lower its value got.

I first thought the multimeter was at fault, but another one gave me the same readings.

So then I suspected the resistors ( having seen fake transistors I wondered if they would mess with something as cheap as a resistor )

I took a few resistors and decided to do some temperature testing on them, I picked a "suspect" resistor, a carbon film resistor desoldered from a board from the junk box, a resistor from farnell, one from Conrad, and another one from a local shop.

I tied them to a power resistor together with a temperature probe and plotted the resistance versus the temperature.

The result is quite clear, I bought two sets of resistors from two different suppliers and both where ordinary 5% carbon film resistors marked as 1% metal film.

The fake ones are fairly easy to spot

1. Most if not all fake resistors I had had iron leads ( a magnet will help you out there )
2. The leads of these resistors are VERY flimsy
3. if you heat them ( soldering iron ) the resistance drops, in a metal film the resistance increases (slightly).

So be very careful where you buy, especially for synth applications the precision and the temperature coefficient really matter!

This is absurd. The cost difference between the 5% tolerance carbon and the 1% tolerance metal film is a few pennies at most.

The graph at the website makes it crystal clear the difference between the genuine 1% metal and the Chinese fake.

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This page contains a single entry by DaveH published on January 31, 2009 11:13 AM.

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