Explain a bypass cap?

[StimpyWan]

Thanks, I'll save those parts sources.
I probably don't understand the terminology correctly. What I need are two 30uf caps for the bass leg of each crossover or 4 each.

If I go with Jentzen Superior Z caps for this as I have in the mid/high legs I'd need 4ea per speaker which puts the cost at about $525 for the bass legs. I might do this just to find out what that sounds like.

I'm looking through what the Humble Home capacitor comparison has to say and found the Jentzen Crosscap is inexpensive and comes in fairly large values but is rated as "average".

What speakers are you recapping? And if you have a schematic of your speaker crossover, post it. I'd spend for good poly capacitors for the series values. Those have the greatest impact on sound quality, since they're directly in-line with the drivers. A larger 30uf cap could possibly be a cap wired in parallel. If so, they won't make as big a difference in the bass. Don't skimp, but I wouldn't think you'd need a Superior Z for that, unless it is a series cap? Which is why I'd love to see the schematic.

My Acoustic Research AR90 speakers have 8 caps each. Four series and 4 parallel. I used better Mundorf EVO Oil caps for the series values, but cheaper Axon poly's for the parallel values. That put better parts where I needed them, and good parts where quality wasn't as critical. Cheaper that way too.

 

[Salomon]

These are the Electrovoice Sentry IIIs. Here's the crossover.

 

[StimpyWan]

These are the Electrovoice Sentry IIIs. Here's the crossover.

Great. Thanks.

Let's see, it looks like 5 capacitors in the EV's. A 2uf on the tweeter, with both a 17.7uf and a 30uf on the midrange. All three are series caps. If you want to spend for upgraded caps, spend for poly's on those 3. The final 2 30uf caps are parallel caps to ground, for the woofer. You could use NPE's for those. Even new electrolytic's, for all the caps, would most likely be an improvement over stock. But they're your speakers, spend your money for what makes you happy. I did, believe me!

 

[larrybody]

Those Electro Voice Sentry III's are really good speakers. I agree with everything StimpyWan says, but if it was my choice I would go with Dayton 5% polys all the way. The 30 uf's are less than $10.00 each and the whole lot would be around $80.00 including six Dayton .01 film and foil bypass caps for the tweets and mid ranges. Add another $20.00 of stuff (get the flashlight) and Parts Express ships for free. I have no doubt that the Jantzen Silver and Mundorf Supreme caps are excellent choices,but I doubt if I could hear the difference and the Dayton's are hard to beat for quality and accuracy especially for the price.

 

[ConradH]

IMO, most of the conventional wisdom about small bypass caps across other caps, is wrong. The explanation in terms of the smaller cap providing a low impedance path as the inductance of the larger cap rises, makes perfect sense... until you start measuring things. The fallacy is that larger caps have some large inductance at high (audio) frequencies and don't pass the signal correctly. Sure, the dissipation factor rises (or ESR, if you want to work with that awkward construct), but we're still talking milliohms total impedance for larger electrolytics. Even at the self resonant frequency the impedance may not get very high. A nice polyester 0.47 uF film cap will have an impedance of 33 ohms at 10 kHz. Hard to improve something down in the milliohm or even couple ohm range by putting 33 ohms in parallel. To put it in even simpler terms, it's like trying to improve a short circuit by putting a resistor across it.

There are many places where small value bypasses are justified, but this isn't one of them. Now, paralleling similar value caps may have some advantages, but you'll have to measure to find out.

 

[Salomon]

Thanks to all who shared their knowledge and opinions. I just finished installing all the new caps and I am very impressed with the improvement. I'd have to say it's a vast improvement.

Spending for these caps was well worth the expense. Thanks again.

 

[StimpyWan]

Thanks to all who shared their knowledge and opinions. I just finished installing all the new caps and I am very impressed with the improvement. I'd have to say it's a vast improvement.

Spending for these caps was well worth the expense. Thanks again.

Great! What was the final configuration? What caps and brands went where?

 

[Salomon]

All throughput caps are Jantzen Superior Z caps. The parallel caps in the woofer legs are Jantzen "Crosscaps".

I had used an oscilloscope to verify the crossover performance before I started and while I did not do the math believe it was performing in-tolerance. (I have worked in a calibration lab most of my life and seeing specifications through instrumentation is second nature for me)

Even though it was filtering correctly, there were still some issues in at least one of the crossovers. When I removed one of the caps a lead basically fell off and I believe some of the solder joints may have been attenuating the signal.

Even if those issues had not been present these caps definitely improve the mids/highs. The bass appears to be unchanged.

Well worth the expense....