#1
As in topic - can it kill me or something ?
I want to plug Celestion 75w 8ohm speaker to Mesa 50w (or reduced to 20w) 4ohm power amp input - can something bad happen to amp or speaker, or i should not to worry ?

I heard that 4ohm speaker to 8ohm amp is killing, but other way ?
#2
Ok, I'm going to assume your power amp is tube.

The short answer is no, either way round has the potential to kill the amp.

Long answer is that tube amps can normally survive a mismatch between 2:1 and 1:2 (that's 4-16ohms on an 8ohm input) but that requires the output transformer designed to be dead centre in the first place. Many amps have an intentionally high or low impedance on a design level which affects the overall sound which means using mismatched speaker impedance moves outside of the 1:2/2:1 boundaries
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Last edited by GABarrie at Jul 3, 2013,
#3
Hell ehh too bad, thank You.
Is there any not expensive method to plug safe mismatched ohm speaker-amp ?
I don't know like "ohm trafo", or maybe it's not hard to mod amp from 4 to 8 ohm input ?

Here's exactly deal i have 1x8ohm input and 2x4ohm input in my PA, and I have 2x8ohm speakers which I usually use separate, but sometimes I want use them together - that's why I don't want to make one 2x12 cab.
Would it be ok if I'll get splitter : jack - 2xjack and just plug two cabs 1x12 through that splitter to one 8ohm input ? For simple mans logic it sounds okay, but in technic way too ?
Last edited by stratomaster90 at Jul 3, 2013,
#4
Exactly what amp/power-amp are you trying to plug into speakers? If it can only pump one resistance rating then you need to be using that rating for whatever speaker combination you use.
"Air created the greenness. And once you've got something, that leads to otherness." - Karl Pilkington.
#5
It's old Mesa Boogie 50/50 (the one with reduction to 20/20) power amp, it has 3 speaker inputs - 8;4;4 ohm
The speakers are Celestions 65w and 75w, 8 ohm each, which I want to plug separate inputs - so i miss one 8 ohm input.


Is there an possibilty to pass that problem without connecting them into 2x12 8ohm cab ? Would that jack-2xjack splitter work (without missing signal/sound quality or whatever) ?
#6
First of all, they're outputs, not inputs. The power-amps input is where your pre-amp's output is going. The only thing you can do here is either only use one speaker from the 8ohm output. Or use one 4ohm output to plug into both speakers in parallel.

Looking at the manual, I understand that both channels on the power amp have 3 outputs each. So you actually have two 8ohm outputs and four 4ohm outputs. If you're running the power-amp in stereo, as in both channels, then you can use both 8ohm outputs either side, one for each speaker.
"Air created the greenness. And once you've got something, that leads to otherness." - Karl Pilkington.
#7
Quote by Lavatain
First of all, they're outputs, not inputs. The power-amps input is where your pre-amp's output is going. The only thing you can do here is either only use one speaker from the 8ohm output. Or use one 4ohm output to plug into both speakers in parallel.

Looking at the manual, I understand that both channels on the power amp have 3 outputs each. So you actually have two 8ohm outputs and four 4ohm outputs. If you're running the power-amp in stereo, as in both channels, then you can use both 8ohm outputs either side, one for each speaker.


since resistance adds in series wouldn't it be series, not parallel.
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#8
Okay, I reed the manual - now I have no idea how to even use this amp ... Jeez I'll better go to some electrician to learn me how to use tube stuff ... ; )
#9
Quote by KerNeL_KLuTcH
since resistance adds in series wouldn't it be series, not parallel.

Y'know, I wrote that originally, but I've honestly for the life of me forgotten. I think you're right. Yes you are, haha.
"Air created the greenness. And once you've got something, that leads to otherness." - Karl Pilkington.
#10
The speaker jacks are wired in Parallel. If you have 2 8ohm cabinets - either run 1 8ohm cab from the 8ohm jack on EACH channel. OR, run 2 8ohm cabs on one channel using the 2 4ohm jacks. The speaker outputs on MESA amps are labled for the total impedance the amp wants to see.

http://mesaboogie.com/news/2013/06/mesaboogie-speaker-impedance-matching-and-hook-up-part-1/#more-4558