Chorus II crossover conundrum! leok, deang, alk, mike stehr; share your wisdom!!!!!

[leok]

Dean's description is good. I have run across this problem in several products .. mostly with tantalum caps, which is where I became aware of the issue.

With a self-healing mechanism part of the design, a cap manufacturer may push the limits of dielectric strength (esp in terms of thickness) and quality control because any defects will be "healed" when sufficient voltage is applied. However, If sufficient voltage is not applied, as is the case in a crossover, some high frequency portions in particular, the defect may remain intact causing excess conduction. The degree of conduction would appear as a statistical distribution across caps within a particular run. Some runs would be worse than others. All caps, from all runs, could be made equivalent and of nominal quality by applying sufficient voltage, in both polarities, to "heal" or "clear" the manufacturing defects.

It is the fact that the caps have it so easy in crossovers that aggrevates the issue in that environment. In a power application the cap would either clear or self-destruct at first application of power.

Leo

[Al Klappenberger]

Leo,

The explanation of microscopic holes sounds to me like a "given" for virtually any dielectric. The metalized type (Like Solen FasCaps) I wouldn't think would have that stretching problem. I guess it could still happen when they are rolled up. In any case though, a manufacturer should factor this sort of thing into the voltage rating they put on their caps. As to tantalum caps, YUCH! You don't want to use them in an audio application anyhow! Not even in active circuits.

It sound to me like the "conditioning" voltage is really just an initial quality control test. This is always a good idea. I still don't believe any real conditioning is going on. AC just erases such things very quickly. I suggest that temperature cycling is a true and effective way to break in a component. This is perticulary true with inductors. Going hot - cold - hot - cold for multiple cycles relieves mechanical stresses. The filter company I used to work for would do this to every filter they made. Some more than others, depending on the application, but every filter they shipped was heated and cooled at least once. They had a big machine with a hot and a cold champer. A shelf would alternate between chambers every hour or so for as long as you left it run.

All I do is grade them for value and pick matched sets.

Al K.

[Deang]

Well then, I guess I'm just going to have pop my networks into the oven for a few and then into the freezer. Wow, what an awesome marketing strategy. I could double the price of my networks for the High-End guys -- they love that kind of stuff. Cooked and Frozen!!

I found out that if I wrap Solens in yellow electrical tape -- they sound just like Hovlands! Man, I have no idea how to explain that one

[BEC]

Dean,

Don't just talk about it. Get the marketing moving.

Bob

[leok]

Al,

I had a response here, but decided I want to think about it some since it's mostly repeat.

Leo

[Al Klappenberger]

Bob,

That's only half the procedure! Now you need an oven!

Dean,

I'll have to try that yellow tape idea. It sounds good!

Seriously, Leo and I have started and email conversation about the "conditioning" subject. I hope to actually test this thory and see what reality actually is. I still believe it's B.S. but I am open minded enough to let him convince me! If and serious evidance shows up, I will pass it along.

Al K.

[BEC]

Al,

The double pole double throw on-on switch method I described earlier in this thread will get to the truth on the cap conditioning question within minutes.

I may have to drop the cryogenic process I showed earlier. Makes the ice in my shop fridge taste like cedar.

Bob

[krustyoldsarge]

Thanks to everyone for their input! Have been away from the forum because of a no-notice move; thus my thread "Hey dude, where's my Chorus?"

Dean,

"You say you are concerned about the new parts changing the "voicing -- yet you stated you upgraded your KG4s with good results. What's the difference?"

The voicing I'm referring to would be a change in SPL after a switch in components. I suspect the problem didn't arise in my KG4's because the circuit is much simpler, no squacker involved.

" -- you are going to have to ditch the PCBs, and rebuild the crossovers on separate boards using point-to-point wiring. "

Have come to the same conclusion. If I do upgrade the Woofer portion of the crossover, I'll give it a separate board and mount it on the floor of the box. No way to get a respectable inductor, much less 68uf worth of film cap on the PCB.

..and I'll buy lots of yellow tape so all my new caps sound like Hovlands

[Al Klappenberger]

Bob,

Your switch method to compare components sounds like a good way to do a listening test. The problem is that all it tells is which component I would happen to like best. My personal opinion does't amount to squat! I have to start with instrument measurements. I first want to see if the "conditioning" makes any measureable difference. As I always say. one desaster at a time!

Al K.

[sfogg]

Al,

"The problem is that all it tells is which component I would happen to like best."

That is why the ABX method is a better test as it will tell you straight out if the person could hear an audible difference between the two components under test without their biases, the power of suggestion or the placebo effect influencing the outcome.

If for example a person passed one of these tests for a conditioned vs. unconditioned cap (that were otherwise identical) then I wouldn't doubt they heard a difference between them.

If they can't pass the test.... well.....

Shawn

[BEC]

Al,

I think what will surprise you most is that often you will not get past step one of my test. That is the part where you have to determine that there is a difference between two caps, or inductors by telling the guy operating the switch that he has operated it. This is before you ever get to the point of trying to determine what sounds better. If you fail step one, you have to agree that, to you, there is no audible difference. If you pass step one and can tell there is a difference, then you are into the subjective part of what sounds better to you.

Bob

[Al Klappenberger]

One other point on this test method. It's important what material is being used for the test. Music won't do it becasue it is random, UNLESS you set up a short segment on a CD to repeat and flip the switch at each restart. The other choice would be a complex continuous waveform like a square wave. I often use pink or white noise for that sort of thing. Like I say though, one desaster at a time. I want to look for a measurable difference first.

AL K.

[sfogg]

Al,

"UNLESS you set up a short segment on a CD to repeat and flip the switch at each restart."

That is exactly what I do. The ABX box is remote controllable so the listener can switch between A and B (whoes identities are known) and X as often as they want to determine if X is A or B. Once they have decided they enter their answer and start a new trial with X again being randomly assigned to A or B.

As far as looking for a measurable difference why bother looking if you don't know for sure there is an audible difference yet? Burden of proof is on the person making the claim, not the skeptics.

Shawn

[BEC]

Al,

I thought it must be easy to tell with music. Almost the typical post on this forum concerning upgrades goes something like this. "I changed out my old ________(insert caps, inductors, interconnects, speaker wires, AC power, or whatever), put on some music and it was immediately apparent that the music was more succulent and sounded like a curtain had lifted." I am still waiting for the test to show me one of two apparently equal (by accepted electronic test methods) components that, at the flip of a switch, change my music from non-succulent to succulent. If I could locate those two components, perhaps I could isolate by further testing that elusive quality of components that they failed to teach me in all my electronics classes (if it exists).

Bob Crites

[Al Klappenberger]

Bob,

Actually, the fact is that I don't expect to get by the first part of the test. Like I said, I think the conditioning thing is 100% B.S.! I plan to let my wife listen as I flip the switch. She has no bias about it simply becasue she has no idea what I will be doing!

This is going to take a while though. I have a major and totaly unrelated job to do this week end, so I will not be able to get around to it real soon. Leo is still thinking about what test procedure he wants to recommend and I want to see what he comes up with before I do anyhting.

Al K.

[Al Klappenberger]

Guys,

Here's the results of my first experiment. Leo and I are still working to set

up a good test for "conditioning". This test was my idea to investigate

claims that polypropylene caps have a nonlinear region at the zero voltage

crossing. It's assumed that this would cause distortion at very low signal

levels. The plot shows the spectrum of a 1 KHz sine wave up to 10 Khz. The

top trace is what goes into the cap (a "virgin" 2.2 uF Hoveland Musicap) and

the bottom trace is what comes out. The voltage across the cap was measure to

me on 7 mV (7 MilliVolts). This is far lower than it will see in operation in

a crossover network. Unless this test is invalid for some reason, I see no

added harmonic distortion at all!

Al K.

[Al Klappenberger]

Guys,

The attached picture proves that "conditioning" is pure Bull S___!

The setup is shown in the top drawing. A 50 Hz square is fed through a

matched set of 1000 Ohm resistors into a matched set of 2.2 uF Hovland

musicaps (One measures 2.242 uFd, the other 2.235 uFd). The 1K resistors

both measured 1003 Ohms on my GR bridge. The two Hovlands were a matched set

of virgin caps to start with. I "conditioned" one by connecting my fluke

meter to my GR bridge set to measure DC resitance. I adjusted the voltage to

83VDC. I applied this to one cap for 30 seconds. I let it discharge through

the Fluke meter for 30 seconds then reversed polarity for 30 more seconds. I

did this twice.

The two channels of the scope were set to "chop" and trigered off channel

"A". One picture clearly shows the two traces of the two caps. I then moved

the position to set one over the other. They are identical. No difference at

all.

Al K.

[Deang]

Well, thank God. I can now put all of the batteries back in the smoke detectors.

I thought the first test was more definitive.

Why 50Hz on the second test? I always figured if running in the caps did anything at all, it would only be audible in the high frequencies.

I like these tests, they're interesting. Maybe doing some of these on a metallized cap would be interesting as well.

[Al Klappenberger]

Dean,

The 50 Hz test frequency was Leo's idea. I don't believe it makes any difference. The "conditioning" DC is gone in an instant and it leaves noting behind. At this frequency you can see the time constant, that is, the charge and decay of the voltage across the caps. That's why he picked it.

I'm quite sure a metalized cap will be the same.

Al K.

[Deang]

Perception is everything. It's like, if we think we will hear a difference -- we do. If we think we won't -- we don't. Seeing is believing, but whatever you do, don't trust your hearing!! This is one crazy hobby.