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SWR IOD speaker out into poweramp?

Discussion in 'Amps and Cabs [BG]' started by jock, Oct 8, 2004.


  1. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Can this be done? The speaker out from this preamp wants an 8 ohm load so how can I get the pure sound from this output into my poweramp? It sounds so much better than the ordinary line outs. Do I need a Marshall Powerbrake or some other load device? This preamp sounds so much better through the speaker output.
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I haven't read the manual, but IIRC the IOD has at least one EL84 power tubes and an output transformer. When used conventionally, I believe that there is an internal dummy load for the output transformer before the rest of the line level preamp.

    As will all tube amps, I would think that you'd need a dummy load of proper impedance.

    I was going to suggest that you contact SWR technical folks but then I remembered...

    I'll summon Nightbass, technically astute IOD owner for his opinion on this...
     
  3. i posted a link to the schematic for the SWR IOD in this thread. you can also view the schematic here. there is an 8 Ohm resistor load that automatically disconnects when a cable is plugged into the speaker out jack.

    what this means is that the speaker output is not designed to drive the inputs of a power amp. it also means that the sound it makes with a speaker has to do with the speaker you're using, as there is always an 8 Ohm load connected to the speaker output when you use the regular preamp and DI outputs.

    according to the user's manual your options are the following:

    experiment and see which sounds best.

    robb.
     
  4. Nightbass

    Nightbass

    May 1, 2001
    Seattle, WA
    The user's manual below has the answer I think you're looking for. I always plugged an Eden D-115 into my IOD, even when it was feeding my power amp and some other cabs. When you turn the Direct knob to give you more and more of the internal power amp's signal, what you have connected to the internal power amp makes all the difference in the world.

    You could even use something like a 1x10 for the dummy load, since an extra cab for a dummy load is a bit of a burden.

    Power brakes and hot plates might work well too, since I believe they mimic inductive loads.
     
  5. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Thanks. One more Q. When I read about these Power brakes and hot plates I see nothing about using the intended amp without a cab. Can this be done?
     
  6. tube amps (which is what the powerbrake and hot plate were designed to be used with) should not be used without a load, and the load should not exceed the transformer tap.

    solid state amps, on the other hand, should never have a smaller load than specified, and they can be used without a load.

    robb.
     
  7. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    Yes, I know. But the IOD when used with the speaker output works as an all tube head giving 5W from two EL84 powertubes so I guess a load must be present. So would a powerbreak be a good idea?
     
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I just got back from www.marshallamps.com :D

    If you look at the handbook (the links are along the top) and click on the one for the PowerBrake, you'll find that they state (somewhere in the lower middle of the page) that you can run the PowerBrake on the no sound setting with no loudspeaker attached. This allows the user to record without making a sound (but I'd bet you could hear the EL34s singing away in the back of the amp).

    Anyway, it looks like doing this is possible. However, Marshall PowerBrakes are quite expensive...even here in the land of relatively cheap gear...

    I do recall seeing the schematic for a powerbrake on-line somewhere. Seems as though one could build their own, the tapped inductive resistor (or is that resistive inductor) would be a trick...but you wouldn't need the same power handling capabilities (or the cute little fan driver circuit) if you're only trying to sink 5 watts...

    Nightbass' solution would be more cost effective (unless you had a PowerBrake or similar lying around).

    Good luck!
     
  9. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago