LSI-9 crossover upgrade - parts list?

Not sure what your price range is, but Sonicaps will do nicely. Sonicraft also carries the 12 watt Mills Resistors in every value you'll need. The 260uf cap is a shunt, and doesn't require a bypass cap. I used NP Electrolytics to replace the 260uf caps in my SDA 2As, until I could afford Metalized Polypropylenes.

ambiophonics wrote: »

Good info to know about the 260uf cap, I thought some people used an extra cap in that section for some reason.

The only time you would use a bypass cap with an NP Electrolytic in a crossover, is when it's in series with the driver.

Face wrote: »

This is incorrect. Since amplifiers output AC voltage, everything matters.

So then what purpose does a bypass cap of higher quality serve on an NP Electrolytic shunt capacitor?

This description below makes a lot of sense to me. My personal experience has been that a bypass cap does change sound quality. However, it can be either positive or negative.

http://www.diystompboxes.com/smfforum/index.php?topic=77762.0

All real parts have non-perfect natures that prevent them acting like a textbook part. For instance, straight wires have inductance as well as resistance. As frequency rises, the resistance starts at the DC value, then starts rising as the skin effect forces charge carriers to the outside of the wire. Quite apart from the skin effect, the raw inductance starts to predominate at some high frequency and the impedance becomes the rising resistance caused by skin effect and the rising inductance of the wire.

With that as a background, you can well imagine that something as complicated as an electro cap has even more imperfections in the real world. Electrolytic caps have Equivalent Series Resistance (ESR), which is the resistance of the parts getting charge into and out of the cap. Since they are made from thin (and resistive!) foils of aluminum wound up in a roll, there is a lot of thin metal to get through to get charge evenly distributed. They also leak a little, varying from one to the next. This is the Equivalent Parallel Resistance (EPR) and it becomes a problem with power supply caps as they get old. The winding of those foils in a bundle also adds inductance, the ESL. The bigger the capacitor, the bigger the ESL, in general.

The capacitance causes a declining impedance of 1/(2*pi*F*C) until the size of the capacitive impedance equals the ESR. At thiat point, the impedance CAN'T get any lower, and the capacitor now looks to the outside world like a small resistance. Also, the impedance of the ESL is rising. At some frequency, it becomes bigger than the ESR. From that frequency on out to infinity, you now have an inductor, not a capacitor. The curve of impedance magnitude versus frequency is a V or a bathtub, depending on construction. Any one capacitor can only get so low in impedance.

So how do you get low impedances at high frequencies? By using smaller capacitors in parallel. A smaller capacitor won't be as good as a bigger capacitance at low frequencies, but at some point, the smaller cap's lower ESL will let it go lower in impedance for higher frequencies than the bigger, but slower caps.

Electro caps store a lot of charge down around DC, but they are getting inductive somewhere around the top of the audio range. If you either know what you're doing and know you need them, or have just read the buzz words from the cork sniffing elite, you will use a paralleled low ESR cap to help the poor fat electros out at high frequencies.

There is one other instance where paralleled caps is slick and fairly elegant design work. Many active filters need frequency setting caps in the ratio of 1:2. It happens that the EIA standard set of capacitor values does not have many 2:1 ratio values. It is simpler and usually cheaper where you need two of one value and one of twice that value, to buy four caps of the same value, and parallel two of them for the twice-as-big cap.