Newbie question.. Preamp and Sub

I didn't see any specifications for a sub output on any of the preamps i've checked ..

how do we usually connect a powered subwoofer with a normal preamp ? ( the one i checked are bryston and classe stereo preamps.. )
i thought they would have additional RCA or balanced outputs for subwoofers..

are stereo preamps designed to be used with 2 speakers + sub?

i know i will need a subwoofer for sure as my Mirage OM-10 are really lacking in deep bass.. ( 5.5" driver )

thank you!
Jinmtvt: no problem. Connect one of the outputs of yr pre to the input of the sub -- the same way you do with the power amp. If yr pre does not have two sets of outputs, you can use Y connectors (i.e., one rca on the one side, two on the other: so you can hook up yr power amp and yr sub).

The pre provides the full range signal to the sub, the sub cuts off the mid & higher register frequencies. Indeed, most subs allow you to adjust the frequency cut-off (i.e. from which frequency --and down-- it will play).

BTW, you still need to hook your regular power amp to the pre in order to play the OM10!

A sub output is a purely Home Theater feature. It has a fixed bandwith (the LFE channel of 5.1) of app. 20-120, and has no care of integration with your speakers.

In the two channel world, however, sub integration is a HUGE part of putting together a musical system. There are two schools of thought on how this should be done.

Number one is called line level. Your sub is equipped with RCA inputs, RCA "high pass" outputs, and usually a "link" output. The link outputs are either full bandwidth or just low effects, for adding another sub. To hook up your setup line level, you run a pair of interconnects from your pre-amp outputs into the inputs of the sub. Then, you run another pair of interconnects out of the "high pass" output into your amplifer. If the sub has an adjustible crossover, you need to adjust it to where the sub takes over just as your speakers lose most bass response (most easily done with an SPL meter from RaT Shack). This is also a nice feature of line level, as the low frequency info is not sent to your amp, causing it to not have to work as hard amplifying information that can't be output by your speakers. An SPL is also very useful for setting the sub's level from the listening postion.

The other way is called speaker level. Run cables to your speakers as usual from your amps, but also run ANOTHER set of cables into the speaker inputs on the back of your sub (not all subs have this capability...but most do). This way is really only feasible if your sub has an adjustible crossover.

In my experience, line level is FAR superior to speaker level, but you'll have to make your own judgements. Cheers!
To amplify (sorry :-) what Greg said, the sub is inserted between your pre and your speakers by either using line level (RCA) inputs/outputs on the sub (inserted between pre and amplifier) or speaker level inputs/outputs (inserted between amplifier and speakers). Most subs have more flexibility in adjusting the crossover frequency (what goes to your sub versus what goes to your speakers) using the line level I/O.
All these answers are good, but to get an exact answer we need to know the exact model number of the sub. I agree line level is the best way to go but different subs do different things to the line level pass through to the main amp. Some may use a crossover set at 80, 90 or 100Hz. Some may not even have a line level pass through. For integration it is best to consider what is happening to the signal all the way through.
thank you for the inputs guys :p

i just learned that the preamp i am looking for now the most
( bryston BP-25 or BP-20) has 2 sets of RCA outputs in the back...

the sub i will get are probably gonna be matching OM Mirage BPS-150 or BPS-400 wich have a crossover adjustment on them.. my speakers the OM-10 also have crossovers but they can't be adjusted ..

so could i use one of the RCA out of the preamp to the amp and one to the sub ?
would that be also a good way to do it ?

if not, i think that i can use the way you described..the line level thing, with the BPS speakers ..

thank you :)
Buy a REL Strata III or Storm III. One of the best brands for music listening. This sub connects directly to the amp speaker terminals (does not interfere with speaker connections). It "listens" to the amp output and just fills in the bottom frequencies below where your speakers cut out (you can dial this in on the back of the sub). Buy one, others here will agree.
I'd have to second argent. I listen only to 2 channel music, from chamber classical through to AC/DC, depending on mood. I bought a Rel strata 3 and it's wonderful. No boom, just depth, and impossible to hear where it takes over from the mains. I have to admit I didn't demo any other subs ... it wasn't necessary. RELs are a bit pricey, but have great resale, so I wouldn't worry about losing money. It probably would not serve well for HT, though, as its strength is speed, rather than SPL.
I do use the Strata III for home theater, but for large rooms would recommend the Storm III. As it is I may upgrade to the Storm III, and my room is 15x20. For some real home theater punch try the REL Q201E.