SDA 2B Upgrades/Amplifier Questions

[Deleted User]

Hello,
I believe there was a recent article in Audio Xpress about how to measure the characteristics of groups of parallel capacitors and judge which ones to place together. If anyone's interested I can research the article and send copies?
Let me know, Ken

F1nut

Yes please.

DAGLJAM6

Also, Yes please the info would be much appreciated.

WilliamM2

Remember, audio signals don't pass through any capacitor; they are not conductors, not even semi-conductors. That's why they don't have a current rating, only a working Voltage rating. Current never flows through them, they are storage devices.

Current never flows through them?

While capacitors are not conductors, current DOES pass through them. Capacitors store electrical energy and block the flow of direct current while passing alternating current. The audio signal is AC, and it does pass through the capacitor in the tweeter circuit.

As frequency increases, dynamic resistance of the capacitor (capacitive reactance=Xc) decreases, alowing more current to flow through the capacitor. As you know, the value of the cap determines which frequencies pass.

If you want an example, here is a simple circuit you can build to test it. If the light bulb lights, current is passing through the capacitor.

schwarcw

I think I rember reading on this forum that Bose or someone puts light bulbs in there speakers to bleed excessive wattage

WilliamM2

I read that too, but that's not a crossover, just a simple circuit to show that current (or audio signal) does pass through caps.

Stew

Ken, I would appreciate a copy of that article too.

Thanks,
Stew

schwarcw

Lots of good info and discussion. Thanks WilliamM2 and F1 for all the discussion. I was leaning towards buying the Sonicaps for my 12uF and 27 uF capacitors. I was considering getting the Dynamicap 0.47 uF, and 750 pF Wondercaps. But, as F1 and Stew pointed out mixing the cap Manufacturer could be a problem. I'm pretty convinced to go with the Sonicaps all the way around. The only question is whether to use the 0.1 uF in parallel with the 12 uF. It looks like more info is coming. This would be a more economical alternative for me. The Dynamicaps are $15.95 each (ouch) the 750 pF Wondercaps are $5.95 each. I would need 2 of the 0.47s and 6 of the 750 pFs. Using Sonicaps all around would be over $200 total for all components. But I thinks my SDAs are worth it. Love the sound!! Of course after I get this upgrade done, a pair of SRSs will come available for pickup in or around Western PA. Then, I have to do it all again!

F1nut

From a site I found some time ago and had forgotten about....

"When you purchase any kit, ask what kind of components are used. "No Compromise" crossover components can mean many things. It might mean good design. It might mean good/better/outstanding component quality. Most likely the components will be of the Bennec/Solen/Axon variety. These are fine, but there is better stuff. If you equipment is decent, and your ears are decent, you will notice an improvement directly proportional to the void in your wallet. I highly recommend the AudioCap products from Jeff Glowacki at Sonic Craft.

There are only a few people who can speak intelligibly about the guts of a capacitor and explain them. Jeff Glowacki is one of these people. I have tested Jeff's voodoo magic and found that it really does hold water. His components are very good. His site, like mine, is void of hoopla about this or that. His stuff is good, his words are true. Jeff told me that he listened/tested everything and decided on Audio Cap because it is the best in its class. I highly encourage anyone interested in getting a better capacitor to call Jeff Glowacki. He can address any form of question concerning this issue.

I recently performed an a/b comparison with an AuriCap and Sonicap behind my OW1 tweeters. I learned why the AuriCap indeed has a very solid following. It's a good capacitor. It has a nice lush midrange, but lacks some detail compared to the Sonicap. Overall, I found these two capacitors very good, and equal in quality. If they were the same price, the implementation decision would be a toss-up. However, the Sonicap is less expensive and the same quality - IMO. I'll keep using the Sonicap."

[Deleted User]

Hello,
This might help understand how capacitors work:
http://amasci.com/emotor/cap1.html
Ken

[Deleted User]

Hello,
Here's another:
http://www.allaboutcircuits.com/vol_1/chpt_13/1.html
Enjoy, Ken!

WilliamM2

Hi Ken,

You seem to be implying that I don't understand how a capacitor works, because I stated that current flows through them.

From your first link:

"Here's yet another way to visualize it. Whenever we "charge" a capacitor, the path for current is THROUGH the capacitor and back out again. The extra electrons on one plate force electrons to leave the other plate, and vice versa."

From your second link:

"To store more energy in a capacitor, the voltage across it must be increased. This means that more electrons must be added to the (-) plate and more taken away from the (+) plate, necessitating a current in that direction. Conversely, to release energy from a capacitor, the voltage across it must be decreased. This means some of the excess electrons on the (-) plate must be returned to the (+) plate, necessitating a current in the other direction."

Clearly, current does flow through a capacitor.

[Deleted User]

Hello,
No such implication was intended. My reason for bringing the subject up was to explain that the reason the subject of capacitors and what they do for audio is so important is that they are not conductors, in the "usual" sense of a conductor. Even their schematic symbol is two vertical lines separated by a gap. Unlike a piece of speaker wire, the voice coil of a tweeter or even an inductor there is not a continuous path. Think about it, you can't "block DC" and be a conductor. If you had a piece of speaker wire that "blocked DC" it wouldn't be a conductor either.
Understand, I'm not saying that capacitors don't work in audio, of course they do. I'm not saying they don't "give the same results" as if they were a conductor, (they do sort of). All I'm saying is that what they do is store a Voltage equal to the Voltage potential placed on their plates and then dissipate it. And that function is different than any other component in the audio chain.
You've heard the expression, "the best capacitor is no capacitor"? So, the goal is to think about the necessary "evils" a capacitor implies and try and make them as benign as possible. But, when I read, "electrons don't know the difference between good capacitors and bad capacitors", I beg to differ. Maybe electrons don't have a preference (they actually do, hence my offer to provide a well written article about how to measure the impedances of capacitors and how to match them) but critical listeners do. There are quite audible sonic differences in capacitors. I wish we didn't need them at all, but at today's level of audio technology we have to deal with them.
Regards, Ken

WilliamM2

But, when I read, "electrons don't know the difference between good capacitors and bad capacitors", I beg to differ.

But that's not what I said. I said "Elecrons are stupid, they don't know which cap they are supposed to pass through."

We were dicussing so called "bypass" caps, and although the bypass cap may cut off different frequencies, those frequencies will still pass through the OTHER cap, therefore nothing is bypassed.

Stew

schwarcw wrote:

Using Sonicaps all around would be over $200 total for all components. But I thinks my SDAs are worth it.

Ka-Ching, Ka-Ching ... That's the sound of me saving to buy all Sonicaps. You convinced me F1nut. It will cost about the same for my 2B's but I agree, they're worth it. Thanks to all for the good discussion and information.

F1nut

Ok guys, I just installed the .1uF Sonicaps. They only have about 3 hours on them, but right off the bat I can say that the highs are less edgy than with the silver mica's. In fact, no edge at all. Highly recommended.

Stew

Thanks F1nut. That settles it for me. It will be a while before I make the upgrades but, when I do, I'll post how my 2B's turn out.

schwarcw

Jesse,

Which capacitor did you by-pass with the 0.1 uF Sonicap?

F1nut

I had already upgraded the crossovers in my CRS+'s with Sonicaps, Mills resistors, new polyswitches and new silver mica's. I had also installed Cardas binding posts, added Dynamat Extreme to the steel baskets including the PR's, added four more screws to the PR frames as Polk only used four of the eight possible holes and replaced all the original #6 screws with #8. They already had the replacement tweeters installed when I bought them, so good to go there. I also upgraded the stands, but that's another story.

The results were 99% better than stock, the Sonicap by-pass cap got the last 1%.

DarqueKnight

Prior to doing my first speaker mod, on my SDA 1B's, the Polk engineer who advised me said that the "fair" quality 4.4 uF and 12 uF mylar capacitors in the top tweeter circuit were bypassed (paralled) with high quality silver mica capacitors in order to improve the transient characteristics of the mylars. He said that if I replaced the mylars with high quality polypropylenes (Rel-Caps), the silver micas would be rendered redundant and I could take them out of the circuit. He also advised that I could make subtle changes in the speaker's high frequency response by using different types and values of bypass capacitor.

After replacing the mylar capacitors with the Rel-Caps, I noticed no difference in the sound with the 750 pF silver micas in or out of the circuit. The vendor for the Rel-Caps, Precision Audio Supply of Downey, California, suggested I try some polystyrene capacitors. Their suggestion was that, since the polystyrene was a much faster dielectric than either polypropylene or silver mica, I would need to use a much higher value polystyrene capacitor. They suggested 0.015 uF polystyrene film capacitors to replace the 750 pF silver micas. The polystyrenes were 20 times the capacitance value of the silver micas.

The effect of the polystyrenes was a smoothing out of the upper treble similar to the change between the SL2000 tweeter and its silk dome replacement, the RD0194.

I left the silver micas in place in my SDA CRS+'s, SDA SRS's and SDA SRS 1.2TL's.

I did replace the 750 pF silver mica capacitors in my SDA 1C's with 1000 pF MultiCap brand PPMFX series metalized polypropylene capacitors. The effect was similar to that achieved when the silver micas were replaced in the SDA 1B's.

Stew

I was trying to understand why I'm going to spend over $200 on capacitors and Jeff at Sonic Craft was kind enough to answer my questions. Specifically, I was trying to understand why high quality capacitors are necessary in the low pass section. Thought some of you might enjoy reading this:

> If I understand how the LP works, the series inductor blocks some of the higher frequencies from the mid-woofer and the shunt capacitor passes some of the higher frequencies away from the mid-woofer to achieve a faster roll off.

That is correct. But, where are these high freqs diverted to? If you guessed that some portion of the signal feed to the tweeter comes by way of the LP shunt cap, you are correct.

> Therefore, the signal going to the mid-woofer doesn't pass through the shunt capacitor.

In order for the capacitor to serve its purpose, it must go in and out of reactance (freq dependent resistor). In order to do this, it must charge and discharge while parallel to the midbass. If this cap has errors/parasitics, it will pass signal it should not while charging (audible high freq errors). While discharging, it will create low freq errors. Not to mention phase issues. Music playback does not resemble any waveform nor is it steady state. As a matter of fact, it looks like random noise (hash). Very complex and very dynamic. Caps are in error to some degree all the time in an audio circuit. These errors will effect your midbass to some degree. If they did not, you could remove the shunt cap with no audible effect as if it were never in the circuit.

> What differences should I expect to hear between a Sonicap and a Solen for the shunt?

It is hard to be specific while never hearing your system, but it is safe to say the midrange should simply sound more "realistic".

F1nut

Geez Stew, just buy the damn things.

schwarcw

Good writeup. I'm with Jesse, just buy the Sonicaps! But don't let me stop you from doing more research. Have fun with the learning process. Jeff at SonicCraft is a good guy to talk to.

Stew

Schwarcw – The learning process has been fun; Now it’s time to make a decision. In my first job out of school (mechanical engineering), one of the production shops had an edited cartoon that said, “In every job there comes a time when one must shoot the engineer and begin work.” Now is that time. Good luck with your upgrade!

F1nut – I’d love to “just buy the damn things.” Unfortunately, it will be a while as I have several other priorities I need to take care of first.

As for making a decision, I’m going to use Sonicaps (12 uF and 0.1 uF) in the high pass and Solens (20 uF and 40 uF) for the low pass. There seems to be an ongoing debate on whether high end capacitors are necessary in the the low pass. North Creek Music Systems, for instance, states that “For many applications, such as woofer low pass shunt circuits …, one need not spend a fortune on capacitors.” As for the earlier discussion on mixing caps, I’m pretty sure that is only an issue when mixing caps in the same filter. The 50/50 mix referred to in the Tony Gee article seems to refer to using two equal value caps of different type in an attempt to get the sonic benefits of the better cap at a lower price. I found several discussions elsewhere on the subject. Bottom line: I’m not convinced I’ll be able to hear any difference between the Solens and the Sonicaps in the Low Pass. Maybe some of you will convince me otherwise and I’ll exchange them down the road. For now, I think I’ll be happy with the Sonicaps/Solens and the RD 0194-1 tweeters.

schwarcw

Sounds like a solid plan Stew. You did your research and probably have good, solid advice. I'm sure you'll be satisfied with your upgrade. Good research for a mechanical engineer! I'm a chemical engineer and lost in all these elctrons. I think in molecules!

My Sonicaps have arrived, but I'm waiting for the binding posts.