SWR send return problems

Discussion in 'Amps and Cabs [BG]' started by david_l_perry, Feb 11, 2004.

  1. I have also posted this thread in the effects forum

    I have never had any luck setting up my SWR SM900 or my SWR Grand Prix with my effects in the send return.

    The problem I have is that when I plug my effects unit in through the back end (currently a TC G-Major) the natural sound of the bass is changed even when the effects unit is bypassed (it sounds as though it has been EQ'd).

    When I run the effects through the front end of the amp (ie the input), any effects unit I have used has no change on the sound of the Bass this way (this is how I have been running my effects for several years now).

    I tried experimenting last night again with the send/return. If I place a patch lead between the send/return the sound is completely unaffected (as I would have expected)
    When the effects unit is put in the send & return (with a clean bypassed signal) the nasty EQ'd sound returns.

    When effects units is bypassed surely it should be the same as the patch lead?

    Can anybody shine any light on this

    Cheers, Dave
  2. your pedal isnt true bypass therefore your signal is still going through its circuits and getting messed up.
  3. But...when I run the effects in line with my bass the effects unit (when off) has no change in the tone at all...Its only when I use the send return...
  4. kmacleish


    Nov 19, 2003
    Atlanta, GA
    Possible explanation: Your SWR has a parallel, as opposed to serial, effects loop. If the amp has a "Blend" or "Mix" control for the effects, then this is almost certainly the case.

    If so, what is happening is that the bypass signal from the TC is not a real, hard-wire bypass, but has some propagation delay from the TC's circuitry. Then, when it is recombined with the straight signal, there is a noticeable amount of phase cancellation happening, which usually results in a kind of tinny, nasty sound.
  5. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    If you have the blend control set anywhere except all the way on, your effect unit is probably inverting the phase of the input signal.

    If the problem goes away by turning blend either all the way off or all the way on, that clinches it.
  6. kmacleish


    Nov 19, 2003
    Atlanta, GA
    Yup, SWR's Web site says that the SM-900 has a Blend control (my curiousity got the best of me), so the parallel loop is definitely the problem.

    My guitarist went through a painful and expensive learning experience on this precise issue, and ended up switching from a Mesa Dual Rectifier to a VHT Pittbull because of it. It is faintly possible that your amp could be modified to correct the problem, but that should be done carefully if at all, and only by someone who really knows what he/she is doing.

    Good luck.
  7. 'Which usually results in a kind of tinny, nasty sound'

    It is no problem if the effects blend is all the way wet, but then if you can't use the blend whats the point in having it ?

    Cheers guys.

    The thing is that the people at SWR could not answer this when I asked them..(Prior to fender taking over before anybody asks..!!)

    Funny you should mention the Dual Rectifier ....My guitairist has the same problem when he goes in to the send & returns, but the other guitarist with his Mesa Boogie MK3 has no such problems..All makes sense.

    Thanks again chaps...

    PS Headless Basses Rule the World..!!!!
  8. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    The point is that some effects units (like yours obviously) invert the signal phase. So it's not SWR's fault, it's TC's fault!!! I've used the effects blend successfully with my SWR amps.

    It would also be an issue if you used this box with a PA board where FX are blendable. I would contact TC and see if they can suggest anything.