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Changing Ohms

Discussion in 'Amp Central Station' started by tomtheguitarguy, Apr 20, 2004.

  1. tomtheguitarguy

    tomtheguitarguy Tele-Meister

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    Hopefully somewhat who is tech-saavy can help with this project.

    Is there a way to change the ohms on a speaker out of an amplifier? One of my amps has a 16ohm ext speaker jack and I would like to change it to an 8 ohm output, so I can use it with my other cabs (which are 8 ohm only).

    Thanks a bunch for your help.

    tom
     
  2. Big Cookie

    Big Cookie RIP

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    The only way to do it is..................

    Change the output transformer.
     
  3. tomtheguitarguy

    tomtheguitarguy Tele-Meister

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    Changing Output Transformer

    Big Cookie:

    Thanks for the reply - as you are tech and amp saavy, can you tell me if this is a difficult thing to do? Is it just a matter of unsoldering the old one and soldering in a new one? For clarity's sake, we're talking about a Gibson Goldtone GA-15RV.

    Thanks a bunch.

    tomtheguitarguy
     
  4. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Tom, Cookie is right...but a more practical, simpler (and maybe cheaper) solution would be to change the speaker(s) in your cabs to the correct impedance for the amp.
     
  5. tomtheguitarguy

    tomtheguitarguy Tele-Meister

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    Silverface:

    Thanks for the recommendation, however my other amps (Dr. Zs) are all 8 ohm output, hence the desire to change the ohm output on the one amp.

    Thanks again for the help, though.

    tomtheguitarguy
     
  6. Ben Harmless

    Ben Harmless Friend of Leo's

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    If the amp has a 16ohm extension jack, it's likely that the internal speaker has an impedance of 16ohms as well. That, plus an external cab would equal 8ohms, meaning the amp was designed to handle an 8phm load.

    If the jack is merely for an external speaker, and the internal one is disconnected when the jack is in use, then the amp is designed for a 16ohm load only.

    My suggestion would be to find a 16 ohm speaker, and plug it in to test this out. If both the internal and external speakers are working, then you're running an 8ohm load, and you can run your cabinet with the amp by disconnecting the internal speaker.

    I would find schematics though, and someone who can read them to tell you whether the internal speaker (presumably 16ohms) and the external jack (16ohms) are connected to the transformer in parallel (8ohms). That's the best possible way of knowing what the amp was designed to handle.

    Schematics for many, many amps can be found floating around the internet.
     
  7. Ben Harmless

    Ben Harmless Friend of Leo's

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    Oooh! I got curious.

    This, which is a schematic for the head version of the Gibson GA-15 "Maestro," without reverb, claims a desired output impedance of 8ohms. That would be akin to running your combo without the internal speaker connected.

    I'm assuming that this is for an older Gibson version. If your amp is a newer Gibson Goldtone, it could be different - but then Gibson should be able to tell you what you need to know.
     
  8. Mik

    Mik Tele-Afflicted

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    That is the set-up of my Brit-made Gibson Goldtone GA15RV. The Gibson Goldtone owners manual says that the internal speaker is disconnected when the ext sp jack is in use, 16 ohm load. That manual is downloadable as a pdf at gibson.com.

    I wouldn't mess with mine because 1. I love the amp's stock performance and tone and 2. changing out the transformer (again, for me) is a major mod for which I would trust only a expert (with knowledge and experience, who's been modding GA15RV's???) to do the job, certainly not me-hell if I know what ripples a different ohm transformer might throw back through the amp's stock circuitry, the GA15RV is a hot cathode bias "class A" amp (I know I know hence the quotes), its Trace Elliot precursor was notorious for blowing out trannies catching fire etc etc etc...

    Mik [​IMG]
     
  9. Ben Harmless

    Ben Harmless Friend of Leo's

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    Well then, the only other option is if there are 2 8ohm cabs, run 'em in series to get 16ohms. More cabs=more fun!
     
  10. tomtheguitarguy

    tomtheguitarguy Tele-Meister

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    Running two 8-ohm cabs

    Will running two 8-ohm cabs through a Y-cable off of the amps 16-ohm ext jack work? or is there something else i would have to do?

    Thanks again for the help.

    tomtheguitarguy
     
  11. Big Cookie

    Big Cookie RIP

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    Would it be that life could be that easy?

    NAH, ain't gonna happen.

    The two 8 ohm speakers need to be connected in series (+ - + -) to yield a 16 ohm load. If they are connected in parallel (++ --) they will constitute a 4 ohm load and likely cook the output transformer.
     
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