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Attenuator solutions?

Discussion in 'Amps and Cabs [BG]' started by RobbieNuke, Dec 25, 2012.

  1. RobbieNuke


    Jan 22, 2008
    I have a tube amp with only one output jack (rated for 8 Ohms). I usually use an 8 Ohm cabinet when performing, but occasionally would like to use a second 8 Ohm cabinet or use a cabinet with a different (lower) impedance.

    Are there any devices available the can be plugged in-between the amp/cabinets to solve this problem? Maybe a power attenuator?

    I'm thinking it may be best to just replace the output transformer with one that has an 8 Ohm and 4 Ohm tap and reconfigure the line-out jack to a second cabinet jack.
  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    AFAIK Peavey used to sell a speaker level matching transformer. Alternatively, upgrading the amp would probably be the way to go.
  3. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    What amp is this?
  4. bigchiefbc

    bigchiefbc Supporting Member

    Oct 9, 2006
    Rhode Island, USA
    Yes, an attenuator can do this. I have of the old Tom Scholz Power Soaks and it can present the amp with either 4, 8 or 16 ohm loads, and has two speaker out jacks. Using either or both jacks doesn't affect the load that the amp sees.
  5. RobbieNuke


    Jan 22, 2008
    Amp I have is Fender Studio Bass (tube head, chopped from a combo; six 6L6 output tubes- 200 WRMS @ 8 Ohms). Mercury Magnetics makes one with a 4/8/16 Ohm tap.

    I would like to consider an external device, since I could use it with other amps as well... but my other tube amps have multi-tap outlets or selection switches.
  6. Jazz Ad

    Jazz Ad Mi la ré sol Supporting Member

    According to these schematics, the output transformer to your amp should be a 012413. These are supposed to be switchable. There should be several output on the transformer with different values, all your amp may be missing is a switch to go from 8 to 4.

    An attenuator is a bad solution in your case. You're simply going to lose half of your power.
  7. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
  8. RobbieNuke


    Jan 22, 2008
    The are some schematics going around, like the one you posted, that have the "180 Watt Studio Bass" imposed upon the nomenclature and the Super Twin output tranny, p/n 012413 (which is actually 4 Ohms, not 8 Ohms... it was connected to a pair of 8 Ohm speakers in parallel). The correct schematic is titled "Schematic- 200 Watt Bass amplifier" and has an output tranny, p/n 012991, which is 8 Ohms.

    As far as I know they are two very similar transformers, but neither is multi-tapped or has a selector switch (my amp does not). Of course, these are both very similar amplifiers with the Super Twin having a Distortion/Boost circuit and the Super Twin Reverb having reverb as well.

    Attached Files:

  9. get a different OT or cab
  10. RobbieNuke


    Jan 22, 2008
    No need for a different cabinet. The main cabinet I use with this amp is 8 Ohms and matches. It's mostly if I want to use multiple 8 Ohm cabinets or cabinets of a lower impedance.

    OT replacement is a good consideration... it's just that if there is an external device that would provide the same 'fix' (i.e. allow amp/load impedance mismatch w/o damage) that would be better since I could use it with my other amps as well.
  11. RoadRanger

    RoadRanger Supporting Member

    Feb 18, 2004
    NE CT
    I have a Peavey Automatch II, either that or the older non-"II" will work. They are rated at 400W. They come up on eBay for time-to-time under $100. It really needs to be built into a ventilated case of some sort if you're going to carry it to gigs.
  12. xk49w

    xk49w Supporting Member

    He needs a 200W something. This probably contains a Weber WZC-100 impedance converter transformer which is about half the price.

    I'd suggest a SS slave amp, either with a speaker DI or using the line out. The speaker DI would give the added benefit (if it is in fact one) of a speaker load on the amp output; if both cabs were the same make/model then he should get the same output from both.