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Author Topic: Microdiodes in copper conductor  (Read 19813 times)

Quince

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Re: Microdiodes in copper conductor
« Reply #75 on: January 19, 2008, 10:18:48 PM »

A bit off-topic, yet in the same general line, what do you people think of the possibility of resistors affecting sound?  Of course, resistance is voltage and temperature dependent, but can't one assume that any modern metal film will not have either of these nonlinearities sufficiently large to cause an audible difference?  Same question for noise and parasitics. Are all modern resistors good enough for audio?
I was looking at a white paper from Vishay about their bulk metal foils and their claim of significant reduction of current bunching noise over that of metal films.  But can this even possibly be an issue within the limited dynamic range of hearing?
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Larrchild

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Re: Microdiodes in copper conductor
« Reply #76 on: January 19, 2008, 10:31:25 PM »

http://recforums.prosoundweb.com/index.php/mv/msg/20375/0/64 /9858/

The thread is 'Lytics, but it morphs to resistors down the page.
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johnR

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Re: Microdiodes in copper conductor
« Reply #77 on: January 20, 2008, 05:28:03 AM »

Quote:


A bit off-topic, yet in the same general line, what do you people think of the possibility of resistors affecting sound?

One of the main ways in which resistors can affect sound is due to their mechanical construction. Most axial film resistors have a spiral track of metal or carbon film, which means they are inductive. If good HF performance is critical, it's often better to use SMD resistors (despite what the "SMD is cheap crap" brigade would have us believe).
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bruno putzeys

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Re: Microdiodes in copper conductor
« Reply #78 on: January 20, 2008, 05:34:29 AM »

I'll use SMD whenever I can, which is almost everywhere. However, so-called "thick film" chip resistors (aka cheap SMD crap) do produce measurable amounts of distortion (up to -90dB at line level voltages) and noise (up to 10dB more than their Johnson noise) so in feedback networks, attenuators etc I'll use slightly more expensive metal film stuff like mini MELF resistors (Vishay). These do not distort measurably and neither do they produce noise (beyond Johnson) so I don't think there's anything to be gained from using some of the fancier stuff like NiCr or Bulk Metal Foil.
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johnR

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Re: Microdiodes in copper conductor
« Reply #79 on: January 20, 2008, 05:42:41 AM »

How are MELFs for inductance? Aren't they just a leadless version of a standard axial resistor?
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bruno putzeys

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Re: Microdiodes in copper conductor
« Reply #80 on: January 20, 2008, 01:06:16 PM »

johnR wrote on Sun, 20 January 2008 11:42

How are MELFs for inductance? Aren't they just a leadless version of a standard axial resistor?

Yes, they're identical in construction. At first sight one would think that any spiral cut would increase inductance, but look at it like this: the inductance only becomes significant at frequencies above R/(2*pi*L). Suppose R=10 ohms, the inductance would need to be 16nH to be significant at 100MHz. That's unlikely. At higher resistances we'd need even more inductance before it matters. So unless we're doing RF circuits with low impedances, any purported inductance is not going to show up.
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John Roberts {JR}

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Re: Microdiodes in copper conductor
« Reply #81 on: January 20, 2008, 04:04:18 PM »

Agreed, while I don't embrace the philosophy of "always using the most expensive parts you can find", I have experienced nonlinearity in (too) cheap leaded CF resistors.  Mostly when used in higher power amplifier feedback networks, where they were exposed to significant voltage swing.

Can't say that I've ever heard problems from excess noise, even when there's a DC bias, but that doesn't mean it wasn't there, hiding behind the signal.

JR
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