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In Reply to: RE: Syllogism posted by beautox on September 12, 2014 at 17:11:48
I wasn't really suggesting that blindly replacing all resistors in any circuit with only Z-foil was the path to nirvana, but it could be a path to the poorhouse. I use about six different types in my little chip amps, and I've tried many more. I can't pretend that what I have is the optimum configuration, as there are simply too many possible combinations. But what I use now was determined to be the "best" after MUCH experimentation.That was my initial suggestion: buy a few types and experiment. The OP determined by accident that resistors sound different. I agreed, and suggested he try others.
I think you meant carbon comp, not carbon film for low inductance. Even then, there are probably better choices.
Peace,
Tom E
Edits: 09/12/14Follow Ups:
Long ago I designed an amplifier (non-audio) that ran quite high voltages. It had linearity issues that I eventually traced to some MOX resistors. I'm not sure if it was tempco or voltage coefficient, but I've been wary of them every since, though they're probably fine in supply, loading or non-signal related locations.
In a different application some thin film SMT resistors were replaced with cheaper thick film. The noise increase made the circuits useless. You guessed it, I've been wary of them ever since. Again, they're appropriate in many spots, but not in my audio circuits.
Having replaced bunches of carbon comps that drifted high in value or became crazy noisy over the years, I can't see using them except as a special effect. Once they drift, I haven't seen baking bring them back. IMO, desiccant storage is probably a very good idea.
Those are all real measurable effects. What I haven't seen is any artifact resulting from the use of decent metal films (or foils) that would lead me to believe an improvement could be had. I could fault (or praise) them in a DC metrology application for ppm level drifts or changes in value from soldering or the generation of thermocouple voltages, but those things just don't show up in (my) audio applications.
In a solid state amp the two most important resistors are probably the feedback resistors, as any imperfection there becomes a fundamental part of the amp performance. Those, and the input stage, are where the right parts probably make the most difference. Carbon comps aren't suitable, wire wounds aren't suitable, thick film isn't suitable, MOX isn't suitable, so what does that leave us? Metal film and foil. Then it's just a question of what brand and specifications.
why aren't wire wounds suitable?
Wire wounds are extremely quiet stable resistors, but being wound they do have some inductance. Even "non-inductive" winding patterns can't cancel it completely. Now, at audio frequencies this inductance is rarely an issue. The problem is that our circuits and devices often have far greater bandwidth than audio. As an example, the best audio opamps often have gain bandwidth products of tens of megahertz. Power amps may have response at hundreds of kilohertz. Keeping those circuits stable and well behaved requires thinking about component characteristics far outside the usual audio bandwidth. I spite of that, wire wounds can be used to good advantage in many locations, just not where a bit of inductance could cause instability.
I've read that it can act like a coil and cause high frequency problems?????? At least thats the poop in the speaker world.
charles
Well yeah a wire wound on a coil forms an inductor. That being said, metal and carbon film resistors have their conductive element flashed on a ceramic core and the element is laser etched in the form of coil too. The construction is similar in that wayOf course there are non inductive wirewounds and non inductive film types also.
Edits: 09/13/14
Especially as Emitter followers.
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