air-cored vs ferite, electrolytic vs polymer. - diyAudio
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Old 17th July 2013, 10:51 AM   #1
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Default air-cored vs ferite, electrolytic vs polymer.

Finaly finished my crossover and am very happy with the sound but looking to squeeze out the last drops of performance if they're available.

If anybody with experience of the following can share their findings/recommendations that would be great!

- Thinking of upgrading from the Solen cap to an M-Cap EVO on the tweeter, I'ver heard some very mixed reviews on SOLENs but have been happy with the performance myself. That said, I've not tried anything else!

- I presume it's a no-brainer to upgrade the inductor on the mid woofer to air core? there's already resistance in there so the change in DCR is easy to accomodate

- Is it worth the cost of upgrading the mid CAP form electrolytic to solen? will I hear any difference? it's a big beast so will cost a bit.

- The bass woofer has two 7.12mH ferrite cores in parrallel for 3.56mH inductance, is this bad practice or should I order 3.56mH inductors? Would still be ferrite as DCR to woofer needs to be as low as possible

- finally, I've been using standard ceramic wire wound resistors, are these fine, and do resistors have any real effect on overall audio quality? if so any recommendations?

Thanks all for the help!
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Old 17th July 2013, 02:03 PM   #2
4Torr is offline 4Torr  United States
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Good Advice:

Don't spend money on expensive capacitors except to upgrade from electrolytic. High priced plastic caps do the same thing as low priced plastic caps. They add capacitive reactance to the circuit. You will hear a difference only if you WANT to hear a difference.

Air core coils tend to distort the audio signal less than ferrite core because they have less magnetization hysteresis.

Audio grade wire-wound resistors have extremely low inductance in the audio range and will not affect the crossover design.

When you listen to music, try not to think of the non-flat microphones, less than perfect microphone placement, electrolytic capacitors and noisy slide pots in the mixdown board, hundreds of feet of wire, not-so-great monitor speakers and arbitrary eq-ing and audio compression in the recording chain before it gets to your music system.
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Old 17th July 2013, 04:48 PM   #3
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Since I latched on to some 600uF metallized polypropylene capacitors for cheap, I'm pretty much all set with not having to worry about using electrolytics. I generally don't spend extra for caps besides going non-electrolytic as the previous poster notes, except possibly for tweeter xover use where the cost hit wouldn't be as great due to the smaller values needed. Ferrite is not even the best non-air core coil to use. Stacked core or permite would be better, although not as good as air core. Actually air core inductors pretty much are immune to hysteresis compared to solid core inductors. There's no serious problem I know of with paralleling two inductors per se. I wouldn't have thought resistors could make that much of a difference, but I was surprised when I replaced some standard sand cast types with low inductance Mills types.

Last edited by thoriated; 17th July 2013 at 04:53 PM.
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Old 17th July 2013, 05:03 PM   #4
mortron is offline mortron  Canada
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Can only speak of REBUILDS.

I have only ever rebuilt one crossover and am yet to test it... But I was instructed that keeping the stock inductors was key to maintaining the sound, so only replaced the resistors that burned out wish VishayDales and the caps I replaced with equivalent Nichicon Muse ES caps and another Nichicon NP series all of the same value and bypassed them with small cheap VishayMKP caps.

I'm yet to know if it works, but that was what I did based on my research.
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Old 17th July 2013, 09:43 PM   #5
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Air core inductors work best, but they also may have a DCR that may be too high for the use. In this case it would be fine to use laminated iron core, rate them a bit higher than the power to be applied.

Resistors, well I use Dale's too (I have a stock of them, before Vishay bought Dale). Nice gold color anodized heat sink and 1% precision.

Caps are a sorted thing. If large values are required Lytics are called for, unless you care to spend insane prices. Otherwise I'd suggest a good quality metal film polypropylene. Even "oil can" motor starter caps work very well. Metal film poly bypass caps wired parallel to electrolytics help transients.
Also biasing lytics help considerably. Easy with a couple of 9v batteries, which will last for years.
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Old 17th July 2013, 10:17 PM   #6
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Originally Posted by Greebster View Post
Also biasing lytics help considerably. Easy with a couple of 9v batteries, which will last for years.
Thanks for the advice, you just saved me a lot of cash, as I have a pair of 5.6uF poly caps that i can wire in parallel with the electrolyticsa anyway - i needed to increase the capacitance as well, so two birds with one stone and a financial saving to boot.

Can you tell me more about what you mean by biasing the caps - how you would do it and why? it's not something I've seen discussed before.

thanks
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Old 18th July 2013, 04:06 AM   #7
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This is an old thing, JBL called it Charge Coupled Crossover (or something like that) Google it, you'll find more than you ever cared to find

An old (1980) Audio mag article written by John Curl (a DIY member here) and Walter Jung on the subject of caps...

http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
http://waltjung.org/PDFs/Picking_Capacitors_2.pdf

and more...

Pre-bias capacitors in crossover

Using Batteries to Bias crossovers into Class A, how does it work?
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Old 18th July 2013, 07:15 AM   #8
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Quote:
Originally Posted by 4Torr View Post
Air core coils tend to distort the audio signal less than ferrite core because they have less magnetization hysteresis.
Air cores don't suffer from hysteresis at all. Their downsides are size, cost resistance and high stray field (so you have to place them carefully)
Ferrites don't have much hysteresis either, but saturate easily (an audible "crack" sound sometimes) if undersized and MAY suffer from hysteresis noise
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Old 18th July 2013, 12:32 PM   #9
4Torr is offline 4Torr  United States
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I meant to say air cores have no hysteresis.

Ferrites do suffer hysteresis, generate harmonic distortion and saturate at high power levels. They really do not belong in a crossover where you have spent good money to replace the electrolytic caps.

Inductor Type

http://www.physics.ohio-state.edu/~d...lInductors.doc
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Old 18th July 2013, 02:49 PM   #10
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Quote:
- Thinking of upgrading from the Solen cap to an M-Cap EVO on the tweeter.
Take the M-cap Evo oil for a little more money, supposed to be better.

Quote:
- I presume it's a no-brainer to upgrade the inductor on the mid woofer to air core?
Definitely air-cores for the mid and the tweeter, just keep the resistance the same.

Quote:
- Is it worth the cost of upgrading the mid CAP form electrolytic to solen?
Yes, use motorrun MKPs instead of Solen, Icar MKP motorruns are better and cheaper.

Quote:
- The bass woofer has two 7.12mH ferrite cores in parrallel for 3.56mH inductance, is this bad practice or should I order 3.56mH inductors?
This is done to have the DCR as low as possible and a higher power rating, I used Monacor transformer inductors in parallel to have a DCR of 0.075ohm, the lower the better for bass

Quote:
- finally, I've been using standard ceramic wire wound resistors, are these fine, and do resistors have any real effect on overall audio quality?
Yes, better off with Mundorf M-Resist, Mills MRA or Duelund

Regards,
Danny
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Last edited by danny_66; 18th July 2013 at 03:14 PM.
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