Anyone used 0.01uf caps in passive crossovers? - diyAudio
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Old 23rd October 2012, 07:07 AM   #1
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Default Anyone used 0.01uf caps in passive crossovers?

Hi.

Can anyone tell me if they know of using 0.01uf caps in the tweeter or mid range of their passive crossovers?

I'm currently experimenting with my custom made crossovers. They have a 6.8uf cap at the start of the tweeter section and a notch filter 3.3uf cap with a coil over the mid section.

The bypass caps are Jensen PIO Silver in oil. They are currently strapped across bypassing the 6.8uf caps to which I think I'm getting a change in sonics but it's that small I can't tell what it's actually doing.

I feel like the sound has more space/air and also quicker if that makes sense. No actual physical change in brightness or characteristics of the HF can be heard but it somehow sounds more open.

Also I feel that at higher volumes the HF seems more controlled.

The 6.8uf caps are Claritycap MR's which are very good caps indeed.

Can anyone shed any light on what I'm hearing or maybe I'm just fooling myself?.. lol

Many thanks

Last edited by ringo_the_hifi; 23rd October 2012 at 07:10 AM.
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Old 23rd October 2012, 08:02 AM   #2
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I've tried a 'Plastic Capacitor' 0.01uF F/F in glass, and a Silver-Mica from Intertechnik, and I cannot hear a difference in either across another cap, or across a series resistor to enhance 'lift' or air in the topend.

I have heard the difference in a 0.1uF cap across the resistor, and that was not subtle. I have a couple Sprague Orange-drop 0.05uF that I may be implementing shortly to try and bring some air back to some BG Neo3's. I don't know if it'll help, but i fear a 0.1uF will be too large since I already CR'd the sssibilance out to tilt it down in the first place. I'll have to see...

If you can hear it more power to you, but I think that 0.01uF is a value that is just too small in most cases.

Later,
Wolf
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Old 23rd October 2012, 09:27 AM   #3
tvrgeek is offline tvrgeek  United States
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I think you are talking about bypassing NPE's with a film cap, not using 680 of them to make one cap.

I can hear a clear improvement in using films paralleled with the NPE. I usually use closer to .1u depending on measuring the actual electro value and that a decent .1u is still pretty cheap. I found it is even better just to go to a 5 % Dayton polypro film and the cost is not that high under 10u. You also eliminate a tolerance problem and ageing problems. (Ever measured the value of those NPEs? That 20% is for one voltage, one temp, one current. In a circuit, expect more like 40%! Many are -20, +100%. Read the spec carefully. )

I have used special audio caps like Clarity, but I am not convinced the cost difference is best spent on the cap for the speakers I have built. Maybe when I step up to an air-circ tweeter. I usually use the 1% Daytons if they fit the project budget. Only above about 10u do I resort to NPE's and I measure the filter response and select bypass caps that both reduce distortion as well as adjust the filter value. Even by grab bag of NPE's I use for quick prototyping are measured and labeled with their real value.
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Old 23rd October 2012, 11:45 AM   #4
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JBL was one of the first to implement bypassing on a commercial basis. Check out the schamatic for the model 4412L,R Studio Monitor speaker. It was loaded with 0.01 uF caps. One was used on an NPE as large as 40 uF.
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Old 23rd October 2012, 03:00 PM   #5
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Cheers chaps... Well, still listening so I'll report back on the decision.

I feel it's got something to do with speed, things seem to sound that little bit clearer/quicker/airier. Does this make sense?

Easy to say (as I've done it) that there is no difference because I feel it's more apparent on certain recordings.

Last edited by ringo_the_hifi; 23rd October 2012 at 03:03 PM.
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Old 23rd October 2012, 03:59 PM   #6
system7 is offline system7  United Kingdom
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All very interesting. It's quite common at radio frequencies to bypass caps with smaller ones to get the ESR and ESL down and avoid amplifier instability.

Quote:
Equivalent series resistance (ESR)

Equivalent series resistance is an effective resistance that is used to describe the resistive parts of the impedance of certain electronic components. The theoretical treatment of devices such as capacitors and inductors tends to assume they are ideal or "perfect" devices, contributing only capacitance or inductance to the circuit. However, all (non-superconducting) physical devices are constructed of materials with nonzero electrical resistance, which means that all real-world components contain some resistance in addition to their other properties. A low ESR capacitor typically has an ESR of 0.01 Ω. Low values are preferred for high-current, pulse applications. Low ESR capacitors have the capability to deliver huge currents into short circuits, which can be dangerous.

For capacitors, ESR takes into account the internal lead and plate resistances and other factors. An easy way to deal with these inherent resistances in circuit analysis is to express each real capacitor as a combination of an ideal component and a small resistor in series, the resistor having a value equal to the resistance of the physical device.

Electrolytic capacitors tend to have much larger ESR than other types; ESR can increase with time and temperature, commonly enough to cause circuit malfunction and component damage.


Equivalent series inductance (ESL)

ESL in signal capacitors is mainly caused by the leads used to connect the plates to the outside world and the series interconnects used to join sets of plates together internally. For any real-world capacitor, there is a frequency above DC at which it ceases to behave as a pure capacitance. This is called the (first) resonant frequency. This is critically important with decoupling high-speed logic circuits from the power supply. The decoupling capacitor supplies transient current to the chip. Without decouplers, the IC demands current faster than the connection to the power supply can supply it, as parts of the circuit rapidly switch on and off. Large capacitors tend to have much higher ESL than small ones. To counter this potential problem, circuits frequently use multiple bypass capacitors—a small (100 nF or less) capacitor rated for high frequencies and a large electrolytic rated for lower frequencies and, occasionally, an intermediate value capacitor.
Types of capacitor - Wikipedia, the free encyclopedia

Tweeter Zobels of say 8 ohm and 1uF in series seem to punch beyond their weight in tidying up the sound. I have also seen commercial speakers with metal tweeters where a 50 ohm 1 watt metal film is shunted across the tweeter. This realy ought to do nothing, but it will stop the speaker impedance going very high at ultrasonic frequency, so might help amp stability. You can also fit these components across the speaker terminals and hear noticeable effects with transistor amps. All very odd really, but it's gotta be an amplifier effect really.

Troels Gravesen has a new article on "Super" capacitors. Always interesting.
super-caps
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Old 23rd October 2012, 04:27 PM   #7
Pano is offline Pano  United States
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What can a bypass that small do? Could it reduce distortion of the bigger cap? I don't see how. Offer a lower impedance at higher frequencies? Would that even be a good thing?

I've been curious about this for awhile, but can't figure out the advantage in a crossover.
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Old 23rd October 2012, 05:39 PM   #8
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I've run some very controlled tests with bypass caps on a film cap using WT2 tester that is calibrated. The basic cap was an Erse 8.2 uF PulseX MPX 250V type. Bypass caps used were 0.1 uF AudioCap Theta PP film and an orange drop type 0.1 uF PET film cap.

There is little or no change in ESR with or w/o either BP cap. uF value rose the 0.1 uF with the BP's in use. Capacitive reactance was also essentially unchange as well. Elect. phase remained the same as well.

OTOH, with testing a 4.7 uF 100V non-polar electrolytic, ESR rose a paltry 20 mohms with the Theta bypass cap and capacative reactance changed about a 1/2 ohm lower at 1124 hz. and about 5 ohms at 106 hz.

These tests indicate the electrical effects are somewhat more differentiated when bypassing NPE's than when bypassing MPP film caps vs no bypassing.
PM me if you would like to examine the tests in detail. I will scan them in and email directly to you as a jpeg file.
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Old 23rd October 2012, 07:18 PM   #9
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Pano View Post
What can a bypass that small do?
to my ears it always cause some kind of weird phase issues when using paralel 'bypass' caps that way
some kind of high frequency weirdness

but if you have not so well balanced speaker with maybe a bit closed and muffled reproduction, I can imagine it could sound like it helps on that
but that would be more like putting plaster on a leaking plumming tube

if paralel caps cant be avoided because of missing value, to my ears it always sounds best when paralelling caps of equal size
but I try to avoid it
same goes for resistors
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Old 23rd October 2012, 09:35 PM   #10
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lol.. maybe I am hearing things then... Thanks
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