I notice that Susumu make really cheap metal film resistors - maybe 5 cents in one-off quantities. Do these have inferior noise performance compared to expensive metal film ones from manufacturers like Tyco? I realise they may have a worse tempco.
Thank you,
-- Nemo
We use the Susumu 0.05% thinfilms that are specified for tempcos of 10 PPM. We pay about 20 cents each. Their tempcos are typically around 5 PPM.
There's no reason why any thinfilm (or even thickfilm) resistor should be noisier than any other resistor. Johnson noise only depends on the resistance, and shot noise is not an issue in most cases.
I wouldn't assume that the Tyco parts are better just because they're more expensive.
John
Isn't metal film supposed to be quieter?
Johnson noise is Johnson noise. It only depends on the resistance and the temperature. Without voltage across a resistor, all you can have is Johnson noise.
With current flowing through them, metal films definitely have well below shot noise. As far as I can tell, common thickfilm resistors don't have significant shot noise. Old carbon comps were said to have "excess noise" when they had a lot of voltage across them. I have seen datasheets that claimed that large value thickfilms, like Gohm and such, do have shot noise.
I tried measuring shot+excess noise on thinfilms, thickfilms, and carbon films but couldn't resolve any. My setup should have easily resolved shot noise.
John
Knock it off, Thompson.
I've been using the 0.1% Susumo resistors. They seem fine. Phil H. posted a pdf from the Ligo group about the Susumo resistors some time in the past... and if they are good enough for Ligo they are good enough for me!
George H.
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