Using Batteries to Bias crossovers into Class A, how does it work? - Page 2 - diyAudio
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Old 8th July 2008, 01:24 AM   #11
Salas is offline Salas  Greece
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Don't you see a counter benefit in using higher capacitance in series so to implement the bias? The extra parasitics of double the caps of double value isn't that attractive. Besides the costs.
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Old 8th July 2008, 01:34 AM   #12
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Honestly I never thought that the parasitics from an additional capacitor would be significant enough to be audible. This is one of those easy to try out for a DIY guy type changes. You take a simple 2 way speaker with a simple crossover and try it out. If you don't like it your done.

Rob
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Old 8th July 2008, 01:36 AM   #13
Salas is offline Salas  Greece
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I liked it when big bipolars or MKTs had to be used. On expensive smaller polys it did not add. I don't know if it is exactly the parasitics, but double the caps in series is more stuff to pass the signal through isn't it?
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Old 8th July 2008, 01:42 AM   #14
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'but double the caps in series is more stuff to pass the signal through isn't it?"

Yes it is. I guess it's just another trade off you have to decide if you want or not. More complexity and biased vs no bias less parts. It never ends

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Old 8th July 2008, 01:47 AM   #15
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Well since they are double the value the resistance will be lower, so wouldn't the parasitic series resistance be about the same? Also extremely low by any definition, most good polys are in the .0005 ohm range, not .1 ohm like some electrolytics.

I finally realized what all those darn wires were for, and what everything was going to. They designed the crossover so that if you biamp the speakers it bypasses the woofers highpass and tweeters lowpass crossover.

Well I think I understood this concept better than I realized, as that is what I thought they were doing. Sounds like the impact is debatable, and that a member attempted to measure the effect, but could not. Salas, I see you mention that he measured electrolytics. Now they biased poly caps in the Everest, any chance there would be some difference in the effect. I mean, I would think that if anything, distortion would be lower in a poly over an electrolytic, but I don't know, might account for Harmens results as compared with SY's. Also, not to doubt SY's ability, but did he have the appropriate equipment to measure low distortion? I mean, with some of this stuff, the distortion is on the magnitute of 100ths and 1000th's of a percent, which most readily available distortion measuring systems can not measure. When I contacted a company about measuring distortion with their software, they told me that computer based systems are limited by the quality of the ADC plus additional computer noise, and that they have never done better than .1% at their lab. When I talked with an Agilent engineer about the 8903A I have, he told me that it would measure much lower distortion than any computer based system not using an external filter, amplifier, etc. Again, he told me there just aren't good enough ADC's out there, and that its been a problem for them in designing better new measurement equipment.
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Old 8th July 2008, 02:02 AM   #16
Salas is offline Salas  Greece
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SY is ace in measuring. If he sees the thread he will inform you the set up and the method I guess.

I doubt the crossover distortion theory. Must be piezoelectric stability and dielectric memory effect getting better with the battery. That is why it subjectively helps plastic caps too. I have enhanced big MKTs that way.
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Old 8th July 2008, 02:45 AM   #17
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Default DC Bias

This sounds suspect. Often times it seems argumentively convenient to confuse the MACRO-world with the MICRO-world.

If one studies materials science applied to electronic theory, one learns that the dielectric effects occur within the space-charge region around the dipole molecular structure. This region is measured in the MICRO world. I doubt that a 9 Volt MACRO bias has much of any effect on the MICRO dipole kinetics.

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Old 8th July 2008, 03:01 AM   #18
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This post and the few that follow will show what I found (or didn't find!):

http://www.diyaudio.com/forums/showt...05#post1543205
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Old 8th July 2008, 03:58 AM   #19
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Interesting reading in the link and testing as well. Why 25hz for the test frequency?? If you look at the systems that JBL uses this technology in it is in the upper frequency ranges. In many cases the woofers shunting capacitors are not charge coupled and the series midrange capacitors in the bandpass and up is where it gets used. I think you may have been looking to low to see the effect. If you think about it any small shift may not be significant at a lower frequency but can become significant as the frequency rises. Think of it as time/phase shift

In the Everest they use Non Polar Electrolytics in paralel with polypropylene in the bass crossovers and part of the horn bandpass. They change over to all poly above that range.

Rob
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Old 8th July 2008, 04:22 AM   #20
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I was following Geddes's suggestion in order to look for a particular mechanism that he had hypothesized. If I wanted to look at that crossover scheme, I'd set the test up differently.
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