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  • Help with rehearsal gear setup; passive system

    SM 58 > Alesis Studio 12R > Peavey Mark III Bass XP Series > Kustom 4 ohm 12" mains

    Our band was gifted this gear for our rehearsal space. I'm trying to figure out how to set the whole thing up properly from reading the manuals I found online.

    Each input on the Alesis has a trim knob, and a fader. We're using one channel for vocals only. Then there's a master slider.

    The Peavey has pre and post knobs for gain.

    We have no effects for the vocals.

    If there's a concise video out there, that would be a good thing to watch. Or maybe the steps are easy enough to be listed here. I'm most confused by the pre and post gain knobs on the Peavey.


  • #2

    First off, if your mains are really 4 ohms then you can only use one. This is a mono amp so, even though there are 2 output jacks there's really only one output. Plugging in 2 speakers puts them in "parrallel" which would be like like daisy chaining them together. Every speaker you add reduces the impedance (the ohms the amp sees). If you use both you take the amp to 2 ohms and it's not rated for that.

    Now that I've said all that, if the speakers have 1 woofer and 1 horn, then there's a pretty good chance your mains are 8 ohms and not 4 ohms. Does it actually say on the box "4 ohms"? If they are 8 ohms then plugging both in will result in the amp seeing 4 ohms, which is fine as that's the minimum that amp is rated for.

    The other thing with the amp is that it's not a PA amp, but you've probably figured that out. Since it's really for guitar/bass, it's common for those types of amps to have 2 inputs. The "pre" is used to color the sound of the input by adding some distortion or overdrive to it. The post is for the overall volumes. So if you're going to use it for a PA amp you want the pre down as low as you can get it. If you're at the point where the post is all the way up and you're getting very little sound then you'll have no choice but to move the pre up to acheive the volume you're after.

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    • abzurd
      abzurd commented
      Editing a comment

      1 - SM58 microphone plugged into any channel (1-8) via an XLR cable (a cable having an XLR male and XLR female end). Avoid the cables with XLR going to the microphone and 1/4" plug on the other end.

      2 - Sing into the microphone...heck, yell into it. Basically give that thing the highest input it will see and not a speaking volume "test, 1-2-3". As you're doing this turn the trim knob until the red LED lights up as your singing into the mic. At that point back off the trim a little. If during your practice you notice the light flickering, just back off the trim a bit more

      3 - You'll likely want to bring the Lo EQ down a touch and the HI EQ up a bit. This will brighten your vocal so it's heard better and take some mud out. It may sound a bit thin when it's just you, but when everything is playing it will be fine. It will also keep some lows out of the microphone which helps the amp as that amp is not very powerful sending only 75 watts each to your speakers. Lower notes are harder on the amp and will cause it to clip sooner so avoid boosting the LO EQ on the mixer or the amp.

      4 - Run a 1/4" cable from one of the outputs of the mixer to the input of the amp. Make sure you check the "pan" controls on your mixer. They should be either centered or turned toward the side you're sending the signal through. For instance, if you are using the left output of the mixer, you don't want the pan control for your mic channel all the way to the right.... you'll have no sound. Also do not use a speaker cable for this connection, Use an instrument or audio cable designed for this type of connection.

      5 - As mentioned in my last post, keep the pre gain of the amp off and try just using the post. I'd probably start with the post up all the way and then slowly raise the master output slider of the mixer. If you're hitting the red lights on the mixer output LED's back off a bit. If by now you've turned the post all the way and it's not very loud then add the pre gain.

      6 - If you get feedback you can try using the EQ on the amp to get rid of it. If it's a high squeal you can take the HI EQ you boosted a bit on the mixer and turn it back. If it's a bit lower then try the 1.3K, 2.6K or 5K sliders on the amp as it's likely one of those that will help. With only a few EQ bands to choose from you're not going to be all that surgical about it, but you could get a few more dB's out of the system when it starts to squeal.

      7 - Do not expect miracles. The amp isn't very powerful and Kustom is a pretty low end speaker so it's likely not very efficient. Low power + low efficiency = not very loud. For success here you need other players that aren't just there to hear themselves wail on the guitar and beat the snot out of their drums. If you're truly wanting to practice and get better and tighter as a group then this gifted PA will likely work fine, but it will lose if forced into a volume war.