wrote:
On Fri, 8 Dec 2017 07:52:47 -0000 (UTC), gregz
wrote:

wrote:
I want to rig up a subwoofer, but I know that crossovers are expensive,
and since I am running high powered commercial amps, I'd need a hefty
setup. Then comes the need to combine the left and right channels
without loosing stereo separation.

I decided to go another route, My power amp was 600W (RMS). stereo. I
got a good deal on another amp that is also a stereo commercial amp,
rated at 500W RMS. Both amps are bridgable. The plan is to run the
outputs from my preamp into Y adaptors and feed the left and right
channels to BOTH amps. One of these amps I'll bridge and use that to
power a single subwoofer speaker.

However, I need a means to send only the bass to the amp that powers the
Subwoofer. Is there any sort of crossover made that goes in the input of
the power amps, after the preamp?

I have also thought about just putting an equalizer into the input of
the amp that feeds the subwoofer and raise the low end of the frequency
and cut the highs. I'm not sure if that will adaquately work or not.
I'll probably try it, but I have not yet built my subwoofer cabinet.

Either way, I know that 1100 watts rms is more than enough for a home
stereo...

There no need to sum bass in stereo, just use one channel. That can cause
that channel to be different with loading. You make easy line level
passive, but what order, and how is that going to mix with upper, phase and
frequency. Seems like a full active crossover of all three speakers will
work best, but you still have to determine order of filter and frequency
for combining.

Greg

When I built my tube stereo around 1968 to 71, I had an idea that was
ahead of it's time, and that was to create a 3 channel system. I had 3
mono power amps so why not.... Back then, Quad sound did not exist yet,
at least not in consumer electronics. But my idea was to create a system
that not only had 3 channels, but the rear channel was to have a delay,
so it sounded like a huge auditorium. I got my hands on both a tape loop
delay unit, which was quite a neat sounding device, but needed constant
attention because I had to make my own tape loops using some
reel-to-reel tape and splicing it to form a loop. Eventually I got tired
of the constant hassle of making and replacing the tape (which did not
last long), and switched over to a spring reverb tank device, modified
from a guitar amp circuit.

Anyhow, to get that 3rd channel, I simply added a 3rd RCA jack to the
preamp, and put an equal value resistor from the Left and from the Right
channel to that 3rd jack. That worked, but I lost some stereo
separation. That lead to adding a switch for those resistors, so I could
switch off the 3rd channel but regain the true stereo sound. A year or
two later I found a better solution. I used a second stereo preamp with
the resistors in place but had all the inputs with Y adaptors feeding
each preamp. Eventually that too was replaced by an equalizer, which had
it's own preamp circuits and that became the final solution to achieve
the 3rd channel.

Back then, there was no such thing as a sub woofer, at least not for
home electronics. However I believe they had subs in use for theaters
and such.

But the Subs bring back the 3rd channel requirement (combined L + R).
So, I learned by my past trial and error that achieving a 3rd channel is
not all that difficult, as long as there is some sort of preamp circuit
in place, rather than just using resistors.

Since posting this message, I have looked at some schematics for these
low pass filters, as well as reading articles about them. They are
basically a preamp circuit combined with the filters to separate the
frequencies. Now that I have looked at these devices and understand how
they work, it's not all that difficult to achieve what I want. The only
drawback now, is the price of these filtering units. ($600 and Up).
Of course I'll have to see what I can find in the USED market, and I am
also wondering if they sell just the pre-assembled circuit boards on
ebay or other places. From what I'm seeing, these are just small circuit
boards, with a few Op-Amps and the passive components to achieve the
filtering. One board for each channel, a power supply, and a few
potentiometers to "tune" them....

These pre-assembled circuit boards seem to be the "kits" in this day and
age. You buy the boards, mount them in a box, add a power supply and
some pots, switches, jacks and you have a complete device. They are made
for amps, pre-amps, test equipment and lots of other stuff. So I wonder
if they are made for pass filters????

I've built boards to high/low pass, etc. Not much to it. Look around, I
think Marchand was mentioned.

Greg