Dismiss Notice

Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

converting ohms

Discussion in 'Amps and Cabs [BG]' started by superbassman2000, Dec 12, 2004.


  1. hello,
    so i wondering...is there something that can convert ohms? for example...i have an 8-ohm head and i am looking at a 4 ohm cab. the head doesn't say anything about being 4 ohms, and suggest that you only use 8 ohms. is there something that i can put in between to convert one to the other? or would it be safe to go ahead and use that setup?

    any advice is welcome!

    Charlie
     
  2. NJL

    NJL

    Apr 12, 2002
    San Antonio
    what amp do you have? :)
     
  3. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    It is theoretically possible to use a transformer to match the amp to the cab, but even if there is a commercially available transformer to do this job, I wouldn't recommend it. I would either replace your cab or your amp.
     
  4. Let us know what kind of amp you have. It could help us determine if it would be safe.
     
  5. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I'd say it's not worth the trouble. There are a lot of decent 8 ohm cabs out there, so it would IMO make more sense to look at one of those. Or esle consider a different amp, depending of course on budget, availability, and what works for you.
     
  6. well, its a Gallien-Krueger 250BL, i had plans to use it with my 8 ohm ashdown mini10T, but then i had the idea to use it with my 1810, which is 4 ohms. i know many amps can do either 4 or 8 ohms, but GK is one company that i notice always say that 8 ohm is the only way to go, and say nothing about being capable to run at 4 ohms...


    Charlie
     
  7. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    that's very odd. i would contact gk and ask them if the amp can do 4 ohms. Most heads can do 4 ohms, i can't even think of any that i know of that are only safe down to 8 ohms. The only amps i can think of that can only do 8 ohms would be some small combos that have an 8 ohm speaker and no extension speaker jacks.
     
  8. now thats what i was thinking...but if you read the manual, it tells you to match it with an 8 ohm cab...anywhere else you look on the net or wherever, you'll only get info on 8 ohms...bizzarre...maybe i will contact them....
     
  9. I don't know anything about that particular amp, but if it's an older / vintage model there's a chance it could only handle 8 ohms.
     
  10. the 250BL is a newer GK amp
    click here for info on musiciansfriend

    Charlie
     
  11. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I believe the BackLine series only goes down to 8 ohms.

    If your Peavey 1810 cabinet has a Black Widow 18, you could always buy an 8 ohm replacement basket on eBay for pretty low bux. It's just a matter of a few screws to move the magnet from one to the other.

    An example of a closed eBay auction

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=47094&item=3764863170&rd=1&ssPageName=WDVW

    I'm not sure how the 10s play into that...I know that they're crossed over, but don't know whether the 2x10 section is 4 ohms or 8 ohms. If they're combined impedance is 4 ohms, I doubt that it would have the same negative effect on the amp as a 4 ohm woofer would (since the power burden on an amp is less at higher frequencies).

    Besides, the 4 ohm rating would be the nominal impedance which usually occurs at a lower frequency anyway and they may very well present an 8 ohm impedance (or higher) above the internal crossover point.
     
  12. 7flat5

    7flat5

    Nov 28, 2003
    Upstate NY
    The .pdf manual is available right there on Musicians Fiend and it is pretty clear:

    "Be sure not to exceed the recommended
    speaker load listed below.
    Maximum Recommended Speaker Load:
    One 8 Ohm cabinet."

    "2- Speaker Out:
    115/250BL: 125W power amp output. It delivers 125
    watts into 8 Ohms.
    Lower impedances should not be used. Higher impedances
    such as 16 Ohms or No Load are acceptable. No
    damage will result from operating the amplifier with
    the speakers disconnected."

    They go on about 50 amp current capability, and also state the output section has no current limiting/safety cutoff. It sounds like they are offering an amp with limited continuous rms power capacity but loads of transient headroom. So, with no limiting circuitry, running it into low impedences would risk blowing the output up. I would maybe be running it into 2 nominal 4-ohm cabs in series, or any 4-speaker 8 ohm cab.
     
  13. well, i emailed them just in case, and here's what i got back...

    Sorry Charlie,
    The BL250 is about the only GK bass amp that will not handle 4 ohms. Only 8
    ohms.
    Best regards,

    Gene Lopes

    d'oh!
     
  14. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago