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Thread: Need some help choosing an amp

  1. #1
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    Need some help choosing an amp

    First post on here!!

    Currently own a set of vintage Altec speakers. 2 - 15" 515 subs, 2 808-4Z drivers attached to what I believe are 511B horns, running through N1201-8A crossovers.

    Right now I use them for outdoor parties at home and run them through my audio head unit/amplifier. However, in a couple of weeks I will be using them to provide the sound for a parade float. The head unit is old and unreliable so I'm looking into renting a more modern amp to do the job. However my knowledge in this area is limited so any suggestions/advice/recommendations would be much appreciated.

    What kind/size/wattage amp should I be looking for?

    Do I also need a preamp to go along with this?

    Thanks!!

  2. #2
    Administrator Mr. Widget's Avatar
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    Welcome to the forum!

    You probably should use an amp that is between 100 and 200 wpc. Since you are not after an "audiophile" experience, a simple solid state amp is likely all you need. What you need depends on the particular application. You certainly need a line stage if your input sources are line level as in a CD player or a computer with DAC or an iPod etc. If you are using a mic you will need an appropriate mic preamp.

    A basic power amp does not have a line stage built in and requires an external preamp. An integrated amp has a line stage incorporated into the single chassis and in the older gear it typically had a phono preamp as well. Some integrated amps have a mic input though they are not typically suitable for professional low impedance mics.

    There are tons of semi-pro audio solutions with many configurations that can also work. These may be powered mixers or various types of head amps which are use specific integrated amplifiers.


    Widget

  3. #3
    Senior Member grumpy's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    ...
    There are tons of semi-pro audio solutions with many configurations that can also work. These may be powered mixers or various types of head amps which are use specific integrated amplifiers.
    Widget
    +1 ... That's what I was thinking. Something -like- this: http://www.musiciansfriend.com/pro-a...-powered-mixer

    There are better and worse versions of this type of unit out there. Renting one shouldn't be too bad if the speaker jacks aren't worn out.
    Stable AC on the float? Something with a -good- universal power supply (switcher) might work better in a generator environment... you'd
    want to make sure the rental provider understands your use/environment.

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    thanks for the reply!!

    I will be using a Numark Mixtrack Pro running off my PC for the music...it has RCA outputs on it.

    http://www.numark.com/product/mixtrackpro

    would a line stage still be neccessary?

    What type of inputs would commonly be found on a typical amp?

  5. #5
    Senior Member grumpy's Avatar
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    You could probably get away without a line stage with that unit (which has RCA out, so stay with that for your amp).

    The numark mixer has a mic input also (probably for a dynamic, non-condensor type only... e.g. shure SM58), so you're good there
    if you need it.

    Keep the line-level lengths as short as possible (trade off for longer speaker cables if necessary). Float is going to be
    an electrically noisy environment.

  6. #6
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    Quote Originally Posted by MikeyMoNYC View Post
    thanks for the reply!!

    I will be using a Numark Mixtrack Pro running off my PC for the music...it has RCA outputs on it.

    http://www.numark.com/product/mixtrackpro

    would a line stage still be neccessary?

    What type of inputs would commonly be found on a typical amp?
    A typical pro amp uses balanced inputs with XLR or TRS connectors. If you're coming out as RCA, you'll need an adapter cable that grounds the - input of amp to the RCA ground. That's better than adapting at the amp input with an RCA-XLR adapter; if you go that route using an adapter, put the adapter at the RCA end and run XLR-XLR cable. That way you take advantage of the common mode rejection at the amp input to reject hum and noise.
    Attached Images Attached Images  
    Oppo BDP-95 DCX-2496 RMX-850 Parasound A21 First Watt J2 Dayton RSS390HF-4 MTM Quads of SEAS W18E001 511Bs TAD TD-2002

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    Senior Member ratitifb's Avatar
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    may i suggest that way to connect the ground and shield

    Name:  XLR to RCA.jpg
Views: 262
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    from http://www.rane.com/note110.html

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    Quote Originally Posted by ratitifb View Post
    may i suggest that way to connect the ground and shield

    Name:  XLR to RCA.jpg
Views: 262
Size:  70.1 KB

    from http://www.rane.com/note110.html
    Not connecting the shield at both ends has pros and cons. You avoid 60Hz currents in the shield from ground rise, but the shield is then only good for electrostatic (vs magnetic) shielding, since there is no complete circuit. I generally prefer the shield grounded at both ends because it offers better shielding of RF interference, which the input op-amp is not equipped to reject.
    Oppo BDP-95 DCX-2496 RMX-850 Parasound A21 First Watt J2 Dayton RSS390HF-4 MTM Quads of SEAS W18E001 511Bs TAD TD-2002

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    Senior Member ratitifb's Avatar
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    Quote Originally Posted by fpitas View Post
    Not connecting the shield at both ends has pros and cons. You avoid 60Hz currents in the shield from ground rise, but the shield is then only good for electrostatic (vs magnetic) shielding, since there is no complete circuit. I generally prefer the shield grounded at both ends because it offers better shielding of RF interference, which the input op-amp is not equipped to reject.
    that's true but the practical answer is probably "try both and see what that do work best".

    Depending on the chassis/ground equipment concept we generally have to deal with hum & noise at LF (ground loops) and with EMI at RF.Shield grounded only at the output end (XLR) with no low-frequency ground current and grounded through a capacitor at the input end (RCA) would be good at RF if the capacitor type and positioning are correctly designed. In addition you can deal with RF by adding a ferrite bead through the input wire (see Neutrik EMC connector series)

    But the best practice is to play with full balanced interconnection system

    Great lecture from http://www.bennettprescott.com/downl...g_tutorial.pdf

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    Quote Originally Posted by ratitifb View Post
    that's true but the practical answer is probably "try both and see what that do work best".
    Depending on the chassis/ground equipment concept we have generally to deal with hum & noise at LF (ground loops) and with EMI at RF.
    Shield grounded only at the output end (XLR) with no low-frequency ground current and grounded through a capacitor at the input end (RCA) would be good at RF if the capacitor type and positioning are correctly designed. In addition you can deal with RF by adding a ferrite bead through the input wire (see Neutrik EMC connector series)
    But the best practice is to play with full balanced interconnection system
    Yes, no argument here.
    Oppo BDP-95 DCX-2496 RMX-850 Parasound A21 First Watt J2 Dayton RSS390HF-4 MTM Quads of SEAS W18E001 511Bs TAD TD-2002

  11. #11
    Senior Member ratitifb's Avatar
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    Quote Originally Posted by fpitas View Post
    Yes, no argument here.
    ground loops

    This would not be an issue if both ends of the cable were at exactly the same potential, which is almost impossible to create... while a small capacitor at the "open" shield end will do the job against RF ...

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