A quick note on how to calculate crossover component values for 6 dB/octave filters.
C=1/6.3 x frequency x input impedance of amplifier (or thing following the filter). It's simple.
A customer requested a 600 Hz crossover at the input of an EM7 amp. Standard EM7 amps have 150K input impedance so the value would be 1.76 nanofarad (1760 pf). The closest standard value is .0018 uF. Anything from .0015 to .0022 would be fine. For gradual crossovers the value is not critical. The only place accurate (1%) capacitors are needed is in a RIAA network or an active filter. I find it amusing when neuoritoc audiophiles want to use a 1% capacitor where the value is approximate anyway. That's just plain silly.
(more on this if you want)
He also asked about the RM-10 which has 100K input impedance. Most power amps are in the range from 15K to 150K ohms and you can usually check this by simply plugging an ohm meter into the input jack of the amplifier in question. If you get on OL on the meter or several meg ohms there is probably a capacitor in the input already and you have to get to the other side of that cap, measure the resistance and change that cap to the new value. That's all there is to it.
Any capacitor of any voltage will work fine. I would use a polypropylene or Mylar.
Currently we are making EM7 amps with a 500K input impedance as that will benefit all users. This value can easily be changed to any value by anyone who can solder. There are many reasons for this change, here are 3:
1. For passive line level crossovers of 12 dB/octave or more the higher impedance allows for better slopes and less loading on the preamp.
2. Via a second jack, Y connector, resistor switch box etc, one can simply parallel a resistance to get lower values. Making the existing resistor large gives more flexability.
3. It becomes very simple to make a switch selectable "universal" passive crossover that can be used with a variety of amps of different input impedance.
I am very interested in helping experimenters into multi-amplification. There is no doubt in my mind of it's advantages. Everyone who has followed my suggestions has been pleased with the control it gives them in the tonal balance of their system. If highs are excessive on one recording you can easily turn them down with the "tweeter volume control" on the crossover. You can also turn them up if you like more highs. The same goes for the bass and I find myself using that control often.
I find the improvement an order of magnitude greater than swapping cables or power cords. When people tell me they are changing the sound of their system with cables I wish them luck and invite them to call me back when they are ready to get their hands on the stuff that makes changes that will astound them. I liken cable changes to adding expensive bottled water to swimming pool.
The cable makers have done a good job at hawking their wares. They would have you believe that a cable is more important than an amplifier. Given the price of our amplifiers and the price of some cables you can come out ahead on the cost and the sonic improvement. Make no mistake about this, giving each driver it's own amplifier will increase detail, reduce distortion at high levels (especially intermodulation distortion), improve driver control and allow much higher dynamics and playing level than any cable possibly can. We are making these low cost small amplifiers for this very reason.
We can custom make you a 2 or 3 way amplifier, mono or stereo on one chassis with all the crossover components in place. We can also make each crossover point switchable and level controllable from the front or back panel. If desired, we can give each crossover frequency selector a "flat" position so you can use this amplifier for a multi channel Home Theater system.
You can get an approximate price by multiplying the number of channels you need by $400 per 2.5 watt channel and $500 per 5 watt channel. 2.5 and 5 watt channels can be mixed in the same amplifier. We can put as many channels in one box as you like. Depending on your needs there may be discounts for more efficient configurations.
If you have a 2 or 3 way speaker you might want 5 watts for the woofer and 2.5 watts for the other drivers. In an 3 way design you could keep the speaker crossover between the two upper drivers and use a single channel for those drivers. The greatest benefit is separating the woofer from the rest of they system and filtering the low frequencies from the input of the upper amplifier. This decreases Intermodulation Distortion thus increasing detail, dynamics and undistorted maximum volume.
For reasons I cannot fathom, Intermodulation Distortion is rarely mentioned though it is much more important than Harmonic Distortion. BTW there is nothing benign about second harmonic distortion and I welcome anyone who would like to start the pros and cons of that discussion in a new thread.
