Once upon a time on usenet 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????

https://www.aliexpress.com/item/Low-...590327578.html

I've used one of these and it seems to work fine. For $5 delivered it's hard
to not try it.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)