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how to build a sub-out from scratch

Discussion in 'Amps and Cabs [BG]' started by God's Element, Oct 1, 2005.

  1. God's Element

    God's Element

    Sep 27, 2005
    I am looking to build a sub-out on my amp to use with my other amplifer. I like the LOWs. I need to know the best way to do this.


  2. It might help if we knew what amp(s) you have and what cab(s) you intend on using....
  3. ESP-LTD


    Sep 9, 2001
    Not trying to be snotty, but if you have to ask how to do it, you probably shouldn't be doing it.

    You might consider getting an external rackmount crossover; I hear folks suggest Rane a lot. If your amp has an effects loop you could take a signal there, run it thru the crossover, and out to another power amp.
  4. Crockettnj


    Sep 2, 2005
    North NJ
    esp- while i disagree with your post about not knowing therefore not doing, I think that is VERY good advice in terms ofth ecrossover. The xover could also be used for something else later on, and the amp will be unmodified therefore retain more resale.
  5. While I disagree with your disagreement about the post about not knowning therefore not doing, I also think it's very good advice in terms of the crossover, for the reasons you stated, i.e. resale of the preamp.

    If you don't know what you're doing with electrical stuff, you're better not messing with it. The possibility of damage, potential shock hazard, etc, just not worth it. Too many things can go wrong. Its not like a paint by numbers thing. Not just the electronics, its mounting them securely, insulating everything right, so it does not cause premature failure later.

  6. ESP-LTD


    Sep 9, 2001
    If someone wants to build a random sized box, tune it to 40hz, stuff in a used speaker they have laying around, and play bass thru it, more power to them. That's the sort of experiment that folks can learn from and have pretty good control over the cost/benefit ratio.

    However solid state electronics are not very tolerant of random experiments and tube circuits can be deadly if not treated with respect. The wrong move with a soldering iron can cost you a lot of money or body parts.

    When someone asks a question requiring a technical answer, using technical terms, I tend to think they understand the technical issues involved. When someone asks a fairly simplistic question, which requires a technical answer (no offense intended to the original poster), I think it's doing them a disservice to encourage them to take some of the risks they may not understand.

    I used to assume that folks used some common sense about such things until I read about Circuit Bending .

    Joseph, where your plan falls off the tracks is the modification of the amp part. There may be a way to get what you want without modifications which may not be cost effective. You need the ability to split your signal into high and low (a crossover does this). You probably want to do that at the 1v signal level (like an effects send/return) instead of at the amp input (instrument level- would have more noise) or at the speaker level (would be more expensive).
  7. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    +1 on not modding your amp.

    and yes, it would be very helpful if we knew what your equipment is, i.e., what your amp is, what your "other" amp is, and what sort of cabinets you have.

    there are a lot of ways to get more lows out of a multi-amp/multi cab setup. First off, often using more cabinets and/or using more amps and cabs will give you an apparent increase in the low end even if you are running them all full range.

    If that's not enough lows for you, there are a few ways to skin the cat. Running a bi-amp setup really won't give you an increase in lows, so as you seem to be suggesting, the idea is to run one amp/set of speakers full range, and then run lows to the second amp/speakers.

    One way to do this is to use two amps that both have eq sections. you can run a line from the line out or effects send of the first "full range" amp to the input of the second amp. On the second amp you can use the eq to cut highs and mids and boost lows. However, that generally doesn't sound all that good, and boosting the bass eq will limit how loud you can get that amp as bass boost tends to eat up watts and cause clipping pretty quickly. All that bass boost can be hard on whatever speakers are running off of that amp as well.

    As has already been suggested a few times, a more effective method is to use a crossover in between the line from the full range amp to the second amp you want to use for the lows. You just use the low pass output of the crossover to feed the second amp and ignore the high pass output entirely. This kind of setup is more common than you think. a lot of PA setups send a full range signal to the top cabs, and then everything from 120 or 80 Hz down is also sent to the subs. The Alembic F1X preamp also suggests a setup like this in their manual for those that want more bass response. you can use the full range output of the preamp to send to one side of a poweramp and to a full range speaker, and then use the low pass output of the preamp's crossover to the second side of the poweramp and a sub, (or a full rnage speaker with good bass response - making it a mock sub). In a setup like this it's important to use speakers that can handle the bass frequencies very well, and to have am amp/poweramp with a good amount of power as the bass frequencies eat up watts even when the eq isn't boosted.

    I've used the alembic preamp in the way describd above a few times, and it worked well, so using a crossover (or a preamp with a crossover that allows you to access full range and low pass signals at the same time) would probably be your best bet. Another Alembic item that was good for that sort of thing is the SF2. IT can be used as a stereo unit, so a few times i used the low pass filter on one side mixed with the dry signal to feed my 15" and the second channel with dry signal mixed with high pass, band pass or even a low pass set to a higher frequency to send to my 12".

    Experimenting with crossovers and other types of filters can be a lot of fun, just be careful not to overboard, (otherwise you'll sound more like a foghorn and less like music) ;)
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I agree that if he has to ask he shouldn't try. You could quite easily pull a line level out from the back side of the master volume pot if there is one, or from the back side of the gain stage volume pot if there isn't, run it though an isolating op-amp that's low-passed at 100 Hz and derive a sub out. You could tap an output at any one of a half dozen places with a tube rig. Someone with the requisite chops could do so in an hour or two, and wouldn't be asking the question to begin with. Anyone without the requisite chops better acquire them before messing with potentially lethal voltages.
  9. Asking how to hot wire a sub-out into an existing preamp an not knowing anything about electronics is like a beginning bass player asking how to play a jaco solo. If playing a jaco solo was potentially deadly if done wrong.

  10. Petebass


    Dec 22, 2002
    QLD Australia
    Keep it simple. Use the balanced line-out or effects send from amp 1 to feed the signal to amp 2. Then adjust the dials on amp 2 so that all the mids and highs are cut.

    You could even add a inductor to the sub cabinet to further block the mids and highs post amplification.
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Hardly worth the trouble, actually. The cab would have a rising impedance above the corner frequency of the inductor, but in the abscence of a lower impedance path for the high frequencies to go through, ie, a midbass cabinet, there would be minimal attenuation for the first couple of octaves at least.