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How are y'all Connecting your Preamp to your Power Amp???

Discussion in 'Amps and Cabs [BG]' started by jokerjkny, Jun 7, 2002.


  1. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    hey all,

    just outta curiousity. i've been running from my Demeter VTBP the unbalanced out into the XLR (neutrik?) of my Stewart 1.2 using a "1/4" to Neutrik (XLR?)" monster cable.

    how are you guys doing it? is this the best way for the best signal? or does it really matter and am i being mental? :D
     
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Unbalanced line out.

    Balanced is not really necessary, since the patch cords are only one foot long.
     
  3. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    A cheap mono 1/4" patch cable. The signal only has to travel a foot, and the preamp and power amp share a common AC ground through the power conditioner.
     
  4. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    k, thx guys, i guess i am just being mental... ;)
     
  5. XLR balanced all the way. Preamp, EQ, crossover, power amp.
     
  6. bben

    bben

    Feb 28, 2002
    Santa Fe, NM
    XLR balanced out from Avalon U5 to Stewart 1.2 balanced in. joker you might just as well use a 1/4" to 1/4" patch cord - the Stewart will see the unbalanced input through the XLR the same way it sees an unbalanced 1/4" input.
     
  7. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    bben, or anyone else using Stewart...

    In bridged mode, i've been using a 1/4" to Speakon for my power amp to cab connector. but just recently, i finally got around to perusing the manual and read that in bridged power, i'm supposed to use the banana adapters!!!!!!!!!!!!!!

    :eek::eek:

    did i totally damage my power amp?? it sounds ok running in that mode and actually did a few gigs at 1/3 of the power doing so. should i have it serviced just in case?

    ok, now i'm going mental!
     
  8. bben

    bben

    Feb 28, 2002
    Santa Fe, NM
    If it still works in bridged mode, you probably didn't hurt anything. I think you weren't getting bridged output the way you had it hooked up, just one side.

    BTW, I just got my Stewart 1.2 last week, and put it in my rack bag in place of a QSC PLX 1602. It's a nice amp, sounds a touch less "clinical" than the QSC, but more important for me, no fan whine.

    Mine gets hot on the underside in the middle, so I took the cover off and looked inside. That's where the power supply is - the amp channels are on each side. As a long-time electronics hobbyist, I do tend to look inside my gear. The Stewart is well laid out and well built inside, with quality components. I find this reassuring.

    The loudest I have played it is to light up the minus 20dB lights and keep them on; pretty steadily, and the heat sinks barely get warm at that level. For most of my uses, the minus 20dB lights just flicker. For me, the whole point of bothering with a kilowatt-plus amp is to get the headroom that gives you that certain punch on the attack transient when you pluck a string.

    My Pro-Tec rack bag is three slots, and I put the Stewart on the bottom, using the rubber press-on feet underneath to be sure there was air space there. I used 1" nylon spacers between the rack ears and the rack, to move it forward for a best-fit, since it's really a little bit deeper than the bag was designed for. I left the spaces on either side of the Avalon open, so the heat sinks get plenty of air.

    This is the best I have done in my search for the quiet high-power amp. I have a very low-level hum that I can't get rid of, something to do with the way the power supply magnetic fields are interacting, I think. But there is almost no hiss (hooray!), which is a particular obsession of mine.

    :)
     
  9. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Don't you actually raise the noise floor about 6 dB when you run an unbalanced line out into a balanced power amp in?
     
  10. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    bben,

    for your hum, did you try flickin' the ground/lift switch on your preamp? are you using a nice power strip?? small, but easily overlooked things... ;)
     
  11. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Never heard of that - or experienced it for that matter.
    Do you have a link or something?
     
  12. bben

    bben

    Feb 28, 2002
    Santa Fe, NM
    joker, I took the U5 out of the bag last night, it still hums, nothing to do with location near the Stewart. The ground lift switch makes no difference. The power strip I am using is a fairly good one, but not a rack-style. Hmm, have to try a different power strip.

    What mystifies me is that I had no hum with the QSC and the U5, as in zip, zero. Were not talking a lot of hum here, but still...I can hear it from a few feet away when all else is quiet.

    Phat, I have heard what you are talking about said the other way around, that you gain 3dB of noise floor using balanced vs. unbalanced amplification. (The improvement comes from how the electronics work, not from anything in the connections.)

    Nelson Pass, for example, notes this in his description of his "balanced zen line stage". He also notes how the better common mode rejection ratio of balanced line stages results in about 1/10 the background noise and hum.

    Pass is a well known for-real amplifier design guru, if you are interested check out www.passdiy.com
     
  13. VicDamone

    VicDamone

    Jun 25, 2000
    bben

    Have you tried another VAC source, I don't mean a different power strip but another outlet-maybe even in another building. Some older buildings still contain two conductor or stand off type wireing and it's simply not good enough for many audio applications.

    Try powering your amplifier directly from an outlet, dedicated if possible, and not the power strip. On the road I carry one of those little yellow outlet testers. There have been many fairly modern venues that have had miss wired outlets and/or lack of ground.

    At home I've rewired all audio/video outlets with dedicated circuts and those orange isolated ground recepticals and used an 10 guage multi strand to ground. Buy far and away this is the best bang for the buck Hi-Fi tweek going.