Film Caps vs. Electrolytics...

[DrWho]

Very interesting.

[NOSValves]

and?????

[Audible Nectar]

Very interesting.

My thoughts exactly[]

[Groomlakearea51]

For us "less than cap literate", what are some of the differences in applications, say cap replacements in crossovers or amps? That would be an interesting read!!

[mike stehr]

It never hurts to be specific.......

[homemadeheresy]

Thats exactly what I was thinking[:^)]

[DrWho]

Expensive? []

Actually, we're not done testing.

[Deang]

I doubt that you guys will break any new ground.

http://www.reliablecapacitors.com/pickcap.htm

http://members.aol.com/sbench102/caps.html

http://www.williamson-labs.com/480_rlc-c.htm

[fini]

For us "less than cap literate", what are some of the differences in applications, say cap replacements in crossovers or amps? That would be an interesting read!!

Good question!

[Guest " "]

9 small paragraphs

http://www.partsexpress.com/crossover-capacitor-index.cfm?CFID=11565013&CFTOKEN=43240608

 

 

[DrWho]

I doubt that you guys will break any new ground.

Probably not, but it's been educational so far.

[Professor Thump]

Very practical question Dr Who. IMNHO passive crossovers are quite linear until driven to very high powers for long durations. When Klipsch does power tests using EIA noise source long term you can see the stress levels that are occurring from the thermal dissipation. Inductors seem to suffer more than caps. Part of this is due to the fact that copper, iron and steel are expensive. The quality of the inductor is really important for linear power capacity. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Size matters For capacitors size determines Wattage or Volt Amp ratings. So generally the larger the physical size the better. We have had issues with vendors where we get samples of capacitors and design with them but once we get to Beta or Pilot builds the part source is changed and the size of the cap is smaller. The label says that it is the same value and the capacitance reads the same but it is obvious that the heat dissipation is less. So we always try to ask for cap samples prior to PCB builds. On Reference IV we purchased $2500 dollars worth of sample cap to develop the crossovers. When we got to Beta build the parts supplier changed vendors (to save cost) even though we asked that the samples we purchased be from the source that we would use for production. We required that the quality be what we asked for originally.

Be careful with the power rating also. Volt Amp ratings are only 70% of Wattage ratings due to the way power factor is calculated. See references:

http://www.apcmedia.com/salestools/SADE-5TNQYF_R0_EN.pdf

http://www.mediarecovery.com/hot_topics/watts_volt_amps.php

Thermal increases are the biggest issue with linear performance of crossovers. If the DC resistance of an inductor triples from 1 to 3 ohms your filter cutoff frequency (f_c) and amplitude of that circuit is altered. This you can hear easily. It is bad enough that the voice coil heats up and compresses the sound

[DrWho]

Yea, inductors are a big mess too. We're designing one of them fancy

digital amps which requires a filter at the output, which I never would

have thought would be one of the limiting factors on performance. We've

been spending a lot of time making our own inductors and making sure

the ferrite gets hot enough so that it operates more efficiently (thus

reducing output impedance and distortion). For the MOSFET drivers,

we're actually taking advantage of the non-linear characteristics of

tantilum caps to address the insane current spikes - which dramatically

reduces ringing and overshoot...much more so than say an "equal" spec'd

foil cap. We're using foil in the output filter though, but

electrolytics on the power supply. Lots of different types, each with

their own advantages and disadvantages.

There was a minor amplifier change inbetween hearing my Chorus II's

with their stock filter and then with a few hundred dollars of foil

caps thrown in (we got them for free). It was hard to tell whether or

not the improvement was from the caps or the amp. We all knew better

than to change two things at once, but now I forget why we had to do

the change. Anyways, I'm going to lug my other Chorus II into the lab

so we can do side by side comparisons.

But from what I've heard so far, I don't think playing around with a

bunch of non-linear parts (even really expensive ones) is going to

offset the advantages of having each driver directly coupled to an

amplifier designed to drive it. I guess I'm becomming even more

convinced that active crossovers are the only way to go.

[michael hurd]

Go get 'em grasshopper..... hehe.... might have to get you a Behringer DCX 2496 to play with, did you know that you can do 96 db/octave slopes and level match to 0.1 db, as well as continuously alter the phase relationship between drivers? []

[DrWho]

Who needs a Behringer when you've got one of these?

http://www.analog.com/en/epHSProd/0,,21364-HARDWARE,00.html

I can do whatever DSP I want - or rather know how to do myself... []

[Professor Thump]

Yes the Dr is in

Yep you cant beat a digital crossover, although a 24 dB/Oct analog is wonderful also. Then things are much more linear with power swings. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

I was a little confused when you mentioned hot ferrite lowering resistance, because I was thinking about increased temperature, but I believe you were talking about a better ferrite core with increased flux capabilities which lowers DCR because less windings are required. Have you ever looked at German powder cores? Most impressive also.

Were you working on digital amp optimization with the nonlinear tantalums?

I would like to hear your cap test on the Chorus. Maybe we could do this at the next Pilgrimage

[DrWho]

Steve Ward is doing most of the work on the amplifier - the guy is a power circuits genious. Here's his website on tesla coils (including ones that play music):

http://www.stevehv.4hv.org/

I've been more of a support role since my main focus is the DSP.

My understanding of the idea behind heating the ferrite on the inductor is that at 50 degrees C the ferrite is operating at its peak efficiency. I think it has to do with the molecules being able to move around more easily inside the ferrite, since that's how the changing magnetic field is created. The downside is that increasing the temperature of the core also increases the temperature of the wire inside (since they're touching), which means we need to go with larger magnet wire in order to keep the wire resistance down. I think we settled on either 14 or 16 guage.

I'm pretty sure Steve put in an order for one of them fancier inductors - I'll have to bother him and see if it's not a german powder core or not (and if not, I think we'll order one just to check it out).

As far as the tantalums, my understanding is that their nonlinear behavior allows one to decrease overshoot without requiring a slower switching frequency. Ultimately a low pass slows down the rise time of a square wave (which is a great way to reduce overshoot), but the way the tantalums work, their capacitance decreases after the large voltage spike, which means it's not rounding off the top corner as much - or something to that effect. I don't quite understand it fully, but Steve seems pretty adament about their use. You could easily see the difference on the scope which was enough to sell me on the idea.