SMT passives for audio

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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mediatechnology
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Re: SMT passives for audio

Post by mediatechnology »

I'm not sure how protective the reverse breakdown path would be.
Well it might not be. If the even-order distortion cancellation that Sam writes about works it still might be a good reason to use it. One more test for the null-tester.
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JR.
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Re: SMT passives for audio

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I wonder if we used 4 caps with two pair in series each connected opposite polarity with one pair + to +, and the other pair - to -. It seems this should both protect against DC and could cancel distortion. It seems a little Rube Goldberg, but this is fringe audio design. :D It may be interesting to see if DC charge on the caps, affects their distortion characteristic enough to degrade cancellation.

Using 4 in series parallel could slightly help matching for CM effects, but 8 caps in a simple phantom blocking circuit would surely make a bigger antenna for picking up noise.

JR
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mediatechnology
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Re: SMT passives for audio

Post by mediatechnology »

JR. wrote:I wonder if we used 4 caps with two pair in series each connected opposite polarity with one pair + to +, and the other pair - to -. It seems this should both protect against DC and could cancel distortion. It seems a little Rube Goldberg, but this is fringe audio design. :D It may be interesting to see if DC charge on the caps, affects their distortion characteristic enough to degrade cancellation.

Using 4 in series parallel could slightly help matching for CM effects, but 8 caps in a simple phantom blocking circuit would surely make a bigger antenna for picking up noise.

JR
+1 ;)
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mediatechnology
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Re: SMT passives for audio

Post by mediatechnology »

From this month's Audio.TST for what might be an interesting presentation:
By Bruce Hofer, Chairman & Co-Founder, Audio Precision

Perhaps the most important lesson I have learned since the beginning of my career in high performance analog design is that the quality of the components is paramount. The most clever circuit design cannot make up for certain component imperfections.

Consider the simple resistor. Real world resistors exhibit both thermal and voltage coefficient effects. The first is commonly known as temperature coefficient (or tempco), and usually has units of %/C or ppm/C. It causes gain and bias variations as the operating temperature is varied. Less well known is the fact that temperature coefficient can also result in distortion as the signal causes thermal modulation of the resistor value. This is typically seen at low frequencies where the resistor temperature can begin to follow the changes in instantaneous power dissipation.

Resistor voltage coefficient effects are just as real and can also cause unwanted distortion. Here the typical unit is in ppm/V. Voltage coefficient is a bit more mysterious because few vendors publish data or give a specification. DVM designers are quite sensitive to this effect because it limits accuracy with higher voltage inputs. In the world of audio, this same characteristic can result in measurable distortion at typical line levels. The move towards smaller and smaller components has been insidious because it exacerbates both thermal and voltage coefficient effects. The distortion performance in circuits built using 0402 or 0201 surface mount components will be substantially greater than using larger sizes.

The mathematics to model these effects is beyond the scope of this brief column, as are my suggestions regarding which resistor technologies to use and which to avoid. However I do point the interested reader to a seminar I will be presenting at the upcoming AES (Audio Engineering Society) convention in Rome (May 4–7). Perhaps I will see some of you there!

Bruce
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JR.
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Re: SMT passives for audio

Post by JR. »

Yup... I've known about voltage coefficient even with thru hole resistors. But tiny SMD are logically more susceptible to thermal effects.

When in doubt build it and test it. I recall JP at APB doing his own tests on SMD resistors.

Of course for the components to be important, the rest of the design needs to be very good... :lol:

JR
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