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Attenuator solutions?

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

  1. RobbieNuke

    RobbieNuke

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    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

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    AFAIK Peavey used to sell a speaker level matching transformer. Alternatively, upgrading the amp would probably be the way to go.
  3. JimmyM

    JimmyM Supporting Member

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    What amp is this?
  4. bigchiefbc

    bigchiefbc Supporting Member

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    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

    RobbieNuke

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    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 Gold Supporting Member

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    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.
    [​IMG]

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

    fdeck Supporting Member

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  8. RobbieNuke

    RobbieNuke

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    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. MAMMOTHvolume

    MAMMOTHvolume

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    get a different OT or cab
  10. RobbieNuke

    RobbieNuke

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    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. Roadkill

    Roadkill Short Scale Addict Supporting Member

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    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.
    http://www.peavey.com/products/index.cfm/item/0/9556/Automatch™IITransformer
    http://assets.peavey.com/literature/manuals/00720310_3.pdf
    http://www.peavey.com/assets/literature/manuals/80370223.pdf
  12. JHAz

    JHAz

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  13. Codger

    Codger Bradley Baker Supporting Member

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    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.

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