JCM 900 effects loop ?

MickG

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Why didn't they just have a three way switch 4/8/16 ?

Could you make a mod for that ?
 

BowerR64

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I chose not to mod my amp because i have a 2466 also and it cant do 4 ohms. I can run both amps off the same speaker setup modding the speakers instead.

Thanks for the diagram now i understand why my amp says (4)16-8 on the 2 way switch.

IMO its sort of missleading why its marked like that i actually ran it a few times with both cabs hooked up totaling 4 ohms in the (4)16 mode thinking it was ok. Didnt run it hard though
 

Eddiemc05

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Bummer!!! And i know the feeling, however blowing my power tranny was the best thing i ever did cuz now theres a brand new one in lol
 

BowerR64

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You didnt opt for mercury one or anything just put the same one back in it?

Im glad you blew yours too, cuz now i know that mine isnt actually a (4) ohm output. mine is a 2500 whats yours again?
 

MickG

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You wouldn't believe it, my brother dropped off a quadbox and a 1936. Two days after I mod'd my head.

Can I use either of these cabs with my new set-up ?
The 1960B has a 4 ohm and an 8 ohm input and the 1936 has an 8 ohm.
Is 8 ohm any different from 4 ohm in regards to volume or tone ? What is the difference ?
 

MickG

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The quadbox is definitely more ballsier than the 1936 or the 2x1922s :jam:
 

MickG

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If I set the ohms to 16 on the jcm900 and plugged in two speaker leads it would want to see 8 ohm, right ?
Then I can plug into the 1922s at the 8 ohms input, correct ?

This is doing my head in, if the head is mod'd to 4ohms and I plug in two speaker leads wouldn't that make it want to see 2 ohms ?????
 

twothemax

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amp set at 4 and connect to 2 8ohm cabs. is rite.

less resistance will be a bit louder.
4 ohms louder than 8 ohms. lower the number the less resistance so louder.
 

BowerR64

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amp set at 4 and connect to 2 8ohm cabs. is rite.

less resistance will be a bit louder.
4 ohms louder than 8 ohms. lower the number the less resistance so louder.

I asked that a while back and was told that only works with SS amps.

I think the OP needs to get an ohm meter so he can check stuff.

My 900 cost me to darn much to just start plugging in speakers without knowing the cabs actual impedance and just praying its ok.
 

ampmadscientist

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Or run it on 16 ohms ?
I have been told to run on 8 ohms by the repairer dude.
My pic may confuse some, that amp unfortunately got stolen way back and the Les Paul.

When a tech repairs an amp, they should check the cables and speakers with the amp.
There should be absolutely no question that the entire rig is correct.

Unfortunately many techs do not test the speakers / cables and this creates many problems.

Far as I'm concerned:
Until the entire thing is tested with the speakers and cables, the job is only half done.
I won't let the amp out of the shop until the speakers are proven correct.

I will tear the cabinet down, and check every speaker...every jack...every cable. Without fail.

Impedance is the major cause of amp failure, and it should never be assumed under any circumstances.
 


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