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Old 12-06-2012, 04:50 PM   #1
anderson80
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ohms query

i have a jcm 900 combo which runs at 8ohms. i recently got a 1960a cab and played my combo through it with the combo set at 4(16)ohms and the cab at 4ohms then the cab at 16ohms. i found the 4ohm setting to be slightly louder and definitely livelier which surprised me cos people i spoke to told me 16ohms would be better.

however, looking on forums i realise that on the combo version the ohms setting is 4(16) and the head version is (4)16 so when using the cab to play the combo through the cab should be at 4ohms and when using the head the cab should be at 16ohms. is this correct? if so this would explain why the 4ohm cab setting was best with my combo.

i realise if this is true i was missmatching impedances but it was only for a few hours!
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Old 12-06-2012, 04:58 PM   #2
Roc8995
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I'm having a hard time understanding what exactly the situation is. 4(16) doesn't make sense to me as a setting - it's either set at 4, or 16.

Can you clarify which settings you were using and what exactly was plugged into where?

If my interpretation is correct you plugged a 4 ohm combo into the cab, so naturally the 4 ohm cab setting would sound louder. What you read is that if you have the option of using the 16 ohm, you should, but you have to match the ohms first. Matching ohms is the primary goal, using the highest matchable ohm setting is just a preference thing once you've done that.
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Old 12-06-2012, 05:15 PM   #3
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Quote:
Originally Posted by Roc8995
I'm having a hard time understanding what exactly the situation is. 4(16) doesn't make sense to me as a setting - it's either set at 4, or 16.

Can you clarify which settings you were using and what exactly was plugged into where?

If my interpretation is correct you plugged a 4 ohm combo into the cab, so naturally the 4 ohm cab setting would sound louder. What you read is that if you have the option of using the 16 ohm, you should, but you have to match the ohms first. Matching ohms is the primary goal, using the highest matchable ohm setting is just a preference thing once you've done that.

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Old 12-06-2012, 05:18 PM   #4
anderson80
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i meant that the options on my combo are either 8ohms or 4(16)ohms. i cant choose 4 or 16. i can however choose 4 or 16 with the cab.

with the head its the other way round i think. 8ohms or (4)16ohms. again only 2 options. so when the combo is played through the cab the combo is set to 4(16) and the cab to 4 and when the head is played through the cab the head is set to (4)16 and the cab to 16. seems like you choose the ohmage for the cab that is not in the brackets.

following what i mean? im confusing myself
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Old 12-06-2012, 05:25 PM   #5
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I am still confused is it 4 seprate 16 ohm outs or a 4 or 16ohm output?


what amp and cab?
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Old 12-06-2012, 05:28 PM   #6
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Quote:
Originally Posted by anderson80
i meant that the options on my combo are either 8ohms or 4(16)ohms. i cant choose 4 or 16. i can however choose 4 or 16 with the cab.

with the head its the other way round i think. 8ohms or (4)16ohms. again only 2 options. so when the combo is played through the cab the combo is set to 4(16) and the cab to 4 and when the head is played through the cab the head is set to (4)16 and the cab to 16. seems like you choose the ohmage for the cab that is not in the brackets.

following what i mean? im confusing myself


the cabinet can only provide one impedance at a time. it is impossible for a speaker cab to provide 16 and 4 ohms at the same time, it doesn't really have a meaning to provide two impedances at once (kinda like dividing by zero).

i did look up your cab, looks like you have a stereo/mono option and you have two jacks. when you are on the stereo mode each jack is wired to two speakers and provides 8 ohms. when you are in mono mode one jack is wired to all four speakers in series/parallel (16 ohms setting) and the other jack is wired in parallel (4 ohms setting).

so depending on what jack you're plugged into the cabinet will either provied 4 ohms or 16 ohms. so what jack were you plugged into?
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Old 12-06-2012, 05:29 PM   #7
anderson80
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its a jcm 900 4102 100w combo. there is an 8ohm out and a 4(16)ohm out

8ohm out used when im using the combos speakers

4(16)ohm out when im connecting to my marshall 1960a cab which has 4 and 16ohm ins.
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Old 12-06-2012, 05:41 PM   #8
Arby911
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It's amazing what one can learn from RTFM!

Impedance Selector Switch
Two-way switch for matching the amplifier to
speaker impedance. Amp heads feature 8 or 16
Ohm operation. Combo versions feature 4 or 8
Ohm options.
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Old 12-06-2012, 05:46 PM   #9
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So it's just a 4 ohm out that they labeled poorly because they didn't want to make a different faceplate for the head. Mystery solved. I was trying to figure out how that 4/16 jack would make any sense electrically or practically
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Old 12-06-2012, 06:06 PM   #10
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Quote:
Originally Posted by Arby911
It's amazing what one can learn from RTFM!

Impedance Selector Switch
Two-way switch for matching the amplifier to
speaker impedance. Amp heads feature 8 or 16
Ohm operation. Combo versions feature 4 or 8
Ohm options.


Someone get this man his preference of a beer, shot, AND/OR joint.

I was so damn confused up until now about what in the hell a 4(16) ohm jack was

TS, That means that you don't have the option for 16 ohms, only the option for 8 or 4 ohms. That means to use your 4(16)ohm jack plugged into the 4 ohm jack on the back of your cab. (in case that wasn't clear yet)
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