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Power amp problems

Discussion in 'Amps and Cabs [BG]' started by bassotus, Mar 17, 2003.

  1. bassotus


    Nov 24, 2002
    Hi all,

    I had a weird incident at last night's practice with my power amp (Phonic MAX1500), using the EBS-1 preamp and just my 1x15" cab. Right at the start of the session when warming up I did this one long fast slide ending in some 16th notes way up on the E string, and the Phonic goes absolutely mute for approx. 5 seconds! Now I was looking straight at the clip led of the power amp at that same time and would swear that the red light didn't even get a chance to light up. I know that it has all kinds of internal protection thingys, but this is not how I'd expect them to work (like with thermal protection I'd understand a shut-off if I had been playing loud for some time..) The internal limiter was off and the gain was only about halfway up, nowhere near clipping when slapping. The amp had been on for only about two minutes before this, no playing during that time. Later on I was able to repeat this shut-off by doing the exact same thing, not everytime though. I'm not even boosting the lows, just a bit of low mids@400hz or so.

    Is there some rational explanation for this or did I just get what I paid for when going cheap and buying this Phonic? :( I'm looking at getting a QSC or similar reputable brand in hopes of getting rid of this feature (??)

    The other weird thing is that it seemed like I had to max the poweramp gain to get the volume I needed just to practice. I would have thought that 450W to a single 15" would be plenty for keeping up with our not-too-loud drummer, but noooh. My 280W Trace Elliot head simple kills with that same cab when cranked at almost 2. I know there's been many debates over volume issues with heads vs. pre/power setups, but still ... I didn't expect any noticeable volume gains but rather to get the same volume without having to clip the poweramp.

    Any advice appreciated,
  2. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You were probably putting out a lot less power than 450 watts. A lot less power than you usually put out of your Trace Elliott, too.
  3. bassotus


    Nov 24, 2002
    ... I know that the volume dial readings are definitely not comparable, but I thought that I would be utilizing most of the setup's power with these;

    - bass volume maxed
    - preamp input gain set near clipping limit
    - preamp output maxed
    - power amp gain set as high as possible so that playing hard fingerstyle barely makes the clip led flash

    I was under the impression that I would not be able to draw any more watts out of the power amp when run this way (bridging aside) ... At least I'm unaware of anything that I could still turn up :) ! I'm also using a limiter in between pre and power to tame (only) the open E slaps.

    Any comments?

    Mr. Lee, are the QSC power amps reputed to have this kind of protection behaviour like I've described? I expecting to have some humiliating situations on the first gig with this current power amp (coming sunday)..

  4. zoran


    May 10, 2002
    I also noticed similar problem when I changed Trace 220w head with preamp/poweramp configuration (400W bridged). Trace was twice louder, but.. big but... lows was much more defined with new equipment. You need more power to hear low notes .
  5. Ziggy


    May 9, 2001
    Orange County, CA

    Zoran put's on the line... having your 'bass' knob cranked wide open makes for heavy, heavy work load on the head. It takes far more to push those lows, than if you had your gain cranked up another couple of notches.

    Additionally, there shouldn't be any need to have anything turned up full blast... after 3/4 (3 o' clock) on the dial, the increase is practically insignificant. The 'real' gain is in that plus 2, to about 6 or so on the dial. The difference between that, 6 or so, is little if any at all.
    michael s.
  6. bassotus


    Nov 24, 2002
    No no no, sorry for this misunderstanding .. By 'bass volume maxed' I meant the volume knob on the instrument turned to max; active bass/treble controls totally flat, and I'm not boosting the lows on the preamp either. BTW, I can boost the lows on my Trace head and it still whips the Phonic setup. I really don't get it .. Someone please tell how to get the most out of the power amp (when not bridged), I though I got it cleared with the settings I wrote in the previous post.. already feelin' kinda dumb here :( ..