Good Amp?

Discussion in 'Location Recording' started by Mortifix, Aug 23, 2009.

  1. Mortifix

    Mortifix Guest

    I am looking to get an rack mountable amp for my 2 Yamaha passive speakers. I am looking at this one right now:

    I am familier with amps for car audio, but I was just making sure that the same rules apply. So on that note I had a few questions about it.

    1.) Is it recommended that I get a dual channel amp or is single channel normally used?

    2.) Do you normally try to match watts with the amps and speakers? I say this because I don't know how much longer I am going to have these speakers for?

    3.) How many speakers can you / is recommended for running to one amp?

    4.) Is it better to have active or passive monitors. I was thinking passive, because if the internal amp goes out then you have to chunk the speaker right?

  2. Codemonkey

    Codemonkey Well-Known Member

    1) Well... how many speakers have you got? 2: so get a dual amp.
    Then you have the flexibility to take it to stereo later. But for now you can just set it to "Parallel" mode and only use 1 input.

    2) Match the RMS values as close as possible, to hell with the peaks. If possible have the amp be a little more powerful than the speakers. Run it lower and it'll lower your risk of distorting the speakers and ruining them. The amp will run cooler, and hopefully carry over to your next set too.

    3) 1. Also - never load an amp at 2 ohms. (ohms = per-speaker ohmage over the number of speakers connected in parallel). Never mix speaker ohmages (4 with 8 etc) and also try avoid parallel if possible. It's not necessary but generally better.

    4) Passive - yes. But active means less setup time if you want ultra-portable.
  3. Mortifix

    Mortifix Guest

    I do have 3 speakers, 2 stand ups and 1 floor monitor. I am planning on adding another floor monitor soon.

    What are the advantages of stereo? I am trying to find a cheaper 2 channel amp that has decent wattage, but I am not seeing to many.

    Would it be that big of a deal to use a mono?
  4. Codemonkey

    Codemonkey Well-Known Member

    OK, I'm unclear on what we're connecting and to where.

    In an ideal world you have 2 dual channel amps (most of these can be made to work in stereo (2 discrete signals) or mono (where the same signal is output through both channels). This gives you one amp channel per speaker (once you get your 2nd monitor).

    BUT obviously this world isn't ideal (ignore the fact that the gravity, air pressure/temperature etc. are almost all perfectly suited to humanity) and thus you may have to compromise.

    Rule: do not load an amp at 2 ohms (This means no paralleling of 4 ohm speakers). I don't know why in an electrical sense but experienced minds tell me that 2 ohms is bad.

    What we need now is the ohm rating of your speakers. If they're (the mains) both 8, you can safely load those onto a single amp channel but you have to remember that the wattage changes.
    Also I can't remember the rules for loading a different wattage onto a 2nd channel. I think it's OK though.
  5. Mortifix

    Mortifix Guest

    Well that amp that I posted doesn't say whether it has multile channels or not, but it says this in the description.

    300 watts per channel @ 4 ohms (stereo)

    Yamaha S12E x 2 are the main speakers.

    The Servo 600 is ideal for larger applications where added power is needed to drive multiple speaker chains, or larger format speakers.

    That was in the description from the website.

    2 ohms are generally used for subwoofers. I don't think there are any highs that are rated for anything below 4 ohms. This is probably true with monitors as well.

    These Yamaha's do appear to have a built-in 12" subwoofer so I could probably get a 2 channel and a monoblock.
  6. TheJackAttack

    TheJackAttack Distinguished Member

    2 Ohms is generally not used by professional audio guys at all.
  7. Codemonkey

    Codemonkey Well-Known Member

    That's a woofer. The thinner part on top is a tweeter, for high frequencies. Subwoofers are generally big heavy boxes which sit on the floor rather than have a pole mount.

    S12E according to Yamaha:
    250W/500W power/peak handling, it says, for those. The site doesn't tell me the ohm rating... hmm.

    Servo 600 according to Sweetwater:
    300 watts per channel @ 4 ohms (stereo)
    600 watts into 8 ohms (bridged mono)

    Unfortunately I have to shoot off shortly, but my gut instinct is that this is too low.
    You'd be OK if you don't push the amp too hard. But if the amp peaks and distorts very much, oh dear.
  8. stealthy

    stealthy Guest

    Get a Crown XLS 802. Good quality amp, I have two. Run your mains parallel on one channel, run your monitors parallel on the other. Now you have have all 4 speakers powered properly and only one amp.
  9. stealthy

    stealthy Guest

    Nor is stereo (in live sound)

    (in response to an earlier post)
  10. TheJackAttack

    TheJackAttack Distinguished Member

    True. Though if the venue is large enough I have often used 2 channel mono and done moderate panning of individual instruments.
  11. djmukilteo

    djmukilteo Well-Known Member

    The spec on that Servo600 states 4 ohm load each channel 300W each
    So the question is what's the impedance (4, 8 or 16 ohms) of your Yamaha's and how many watts can they take before you melt the voice coils?.....what model are they?
    If they are standard 8 ohm speakers then you could drive 2 of those speakers in parallel off one channel up to 300W and 2 more in parallel on the other channel up to 300W.
  12. Codemonkey

    Codemonkey Well-Known Member

    djmukilteo see my post, up a little.

  13. djmukilteo

    djmukilteo Well-Known Member

    Sorry....didn't see you're posting there Codemonkey
    my bad

    Looks like your basic 8 ohm speaker to me:
    no problemo with power handling

    What was the question again?

    S12E 2 Way Speaker Cabinet Specifications
    • Woofer: 12 in. steel basket
    • Tweeter: 1 in. phenolic
    • Frequency Response (-10dB): 65Hz-14kHz
    • Power Rating program/peak: 250/500
    • Imp ( ): 8
    • SPL (1W, 1m): 97dB
    • Dimensions W x H x D (approx): 16 in. x 22 in. x 13 in.
    • Weight (lbs.): 32
  14. sheet

    sheet Well-Known Member

    Forget stereo and live sound. There is no stereo imaging in live sound. There is only left and right, or dual mono.

    The OP asks about the amp. Samson is a budget/entry level brand. I would look for a good used Crown MA or some other beefy amp. Why? All of these cheap new amps lie about their power output for one. Two, they use high speed switching topologies and do not sound as good, especially compared to a good Class A/B. They are even more picky about their AC power quality. They will crap out, lose power and distort much faster than a Class A/B non-switching amp.

    You will find lots of sound companies and bands with great gear falling on hard times at the moment. It is a buyers' market. But a REAL pro amp used.

    Now, here is something else. Most of these cheap amps do not like to be run in dual mono, with the mono mains (2 yamahas) on one channel and mono wedges (2 yamahas) on the other. They share ONE power supply, when they should have two, one for each channel. Again, but a REAL amp and you will get what you need. OR you will buy one big enough to share.

    Why is this a big deal? Well, the side that demands the most will get the most. So in this case, the monitor mix will get less power almost all of the time.

    If you are really in a spot, at least buy two smaller amps, and give them their own 15A circuit so they have a chance at providing their rated current vs. sharing the same available wattage from the wall with the mains and the monitors.

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