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Using Hartke 3500 as a power amp, ideas, help....

Discussion in 'Amps and Cabs [BG]' started by CYoung, Aug 12, 2007.


  1. CYoung

    CYoung

    Nov 30, 2000
    Gainesville, FL
    Ok, here is the situation: I have a Hartke 3500 head. It is rated at 350W into a 4 ohm load (which is how I usually run it).

    Anyway, I have a situation coming up where I would like to basically use the 3500 as a power amp, bypassing all the gain, compression, and EQ.

    My question is:

    If I patch a line-level signal (mixer, bass effects unit, etc.) into the effects return jack on my 3500 amp and set the effects balance all the way to return, will that effectively let me use the 3500 as a 350W/4ohm power amp?

    Thanks!
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Yeah, sounds about right. Some effects loops are weird, they don't all follow the same standard of input and output levels or impedance. But it is worth trying, it may well work.
     
  3. figuredbass

    figuredbass Supporting Member

    Jul 11, 2007
    NYC vicinity
    You can safely and effectively use the Hartke 3500 as a power amp by feeding the effects return with a line level signal. I still ocassionally use it as a power amp myself. The effects return point is after the preamps and compression, but before the contour tone controls and the graphic equalizer. You can completely bypass the graphic EQ from the signal path simply by leaving the EQ's switch in the "out" position (where the red LED's in the sliders go off). If you set the contour controls to their mid 12:00 position, they are also effectively out of the circuit and providing flat response. Yet you can still use them if you wish to tweak. At the effects return point there is no internal tonal voicing, and the power amp response will be flat. In fact, with the contour controls flat and the EQ disengaged, the overall 3500 response is flat except for the voicing of the tube preamp. (The solid state preamp is flat.) One word of caution: if your 3500 is the older MOSFET model, the effects return inverts the phase of your signal when you use it as a power amp input! This is because the effects send ALSO inverts the signal so when it returns it's back in absolute phase (like "two wrongs making a right.") This may not be a problem unless you are also running another power amp simultaneously with your rig, where it would then be a BIG problem. If you need to preserve absolute phase with the mosfet model, the best thing to do is to slightly attenute your source signal, plug into the "active" jack, use only the solid state preamp, turn the compressor "off," bypass the graphic EQ, and set the contour controls flat. Whew! A lot to do, but it will work!
     
  4. CYoung

    CYoung

    Nov 30, 2000
    Gainesville, FL
    I am 99% sure mine is the older MOSFET model, so I am glad you told me this! For this particular application, a phase issue could result in some horrible sound! I think I will try feeding an attenuated signal into the active in and carefully control the gain structure.

    I'll report back after I test this.
     
  5. figuredbass

    figuredbass Supporting Member

    Jul 11, 2007
    NYC vicinity
    +1 You'll find the 3500's power amp to be pretty darn good. Nick Epifani even admitted it is when we were discussing power amp stages of several amps. Looking forward to your test results...
     

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