Ohms!

DudeWheresCorey · 08-02-2009, 05:48 PM

Hey guys, Im new to this thread as well as Marshall,

I just recently got my JCM 800 about 4 weeks ago. For my live set up for my band I would like to use my 2x12 cab with my 4x12. The 2x12 is 16 ohm's and the 4x12 is 8. Is their a way I can safely run both cabs with my head?

MartyStrat54 · 08-02-2009, 06:19 PM

Yeah, welcome to the Forum. It would be best to run your half stack only and set the impedance on the amp to 8 ohms. This will be plenty loud. Trying to run a 16 and an 8 ohm load at the same time will not fly for long and I know you don't want to damage your amp. A 16 and an 8 ohm load in parallel is 5.33 ohms (just so you know).

Here is American Vikings thread: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME!

And here is Sticky's thread (very good): SPEAKER WIRING

DudeWheresCorey · 08-02-2009, 06:22 PM

Yah I figured that was the deal. I was just wondering if their was a way, your right I def dont want to ruin my amp either! Thanks for the help!

MartyStrat54 · 08-02-2009, 06:35 PM

Great. I added a couple of the more important threads on this matter so you can take a look and use it for future reference.

gtrman · 08-02-2009, 06:57 PM

Amp problems? Ohm questions? Amp blowing up for no reason, READ ME!

According to the post above it is possible to use a 4x12 & 2x12 cab together.
I have tried this myself and it delivers the sound/volume you are after. I'm a little unsure of the damage it can do using this over time though.

"At what impedance should I set my amp if I have a 16 ohm cabinet, and want to add an extra cab with 8 or even 4 ohm impedance, running both at once?
Short answer: set your amp to 4 ohm!

For one 16 ohm and one 8 ohm cab, the formula is:
1/ (1/16 + 1/8) = 1/0,1875 = 5,3

So the combined impedance of both cabs is 5,3 ohm. The closest setting on your amp is now 4 ohm.
Again, 4 ohm on your amp is the closest setting. If you do not have a 4 ohm setting on your amp, I would not try this and stick to using just one cabinet. Or maybe two 16 ohm cabs resulting in a combined 8 ohm load."

MartyStrat54 · 08-02-2009, 09:03 PM

Quote:

Originally Posted by gtrman

Amp problems? Ohm questions? Amp blowing up for no reason, READ ME!

According to the post above it is possible to use a 4x12 & 2x12 cab together.
I have tried this myself and it delivers the sound/volume you are after. I'm a little unsure of the damage it can do using this over time though.

"At what impedance should I set my amp if I have a 16 ohm cabinet, and want to add an extra cab with 8 or even 4 ohm impedance, running both at once?
Short answer: set your amp to 4 ohm!

For one 16 ohm and one 8 ohm cab, the formula is:
1/ (1/16 + 1/8) = 1/0,1875 = 5,3

So the combined impedance of both cabs is 5,3 ohm. The closest setting on your amp is now 4 ohm.
Again, 4 ohm on your amp is the closest setting. If you do not have a 4 ohm setting on your amp, I would not try this and stick to using just one cabinet. Or maybe two 16 ohm cabs resulting in a combined 8 ohm load."

Yeah there was a long thread about this and everyone had varying opinions. It is really hard to say how the load will react with say a 5.33 on a 4 ohm setting. We all know that while playing music, the "load" changes drastically. The load at the low end is high (30-40 ohms) and also at the high end. So could you do it? Yes I guess, but I think it is best to go with one cab and one setting.

DudeWheresCorey · 08-02-2009, 10:07 PM

Yah. On my old amp (my dual rec) I had many speaker output options, I would run a 4ohm output to the 8ohm cab and 8ohm out to the 16ohm cab and according to mesa in the handbook it was considered a safe missmatch. Im not sure though I really dont want to mess something up. I will probably just stay on the safe side and just play my 8ohm cab. Its allready PLENTY loud! Thanks for the help though!

American Viking · 08-03-2009, 02:29 AM

The safest way possible for you would be to rewire the 2x12 to 8ohms and set the amp impedance to 4ohms to run both the 2x12 and 4x12. It's really easy to rewire a cab as long as you follow the diagrams.
Jumbo Sunshade - Speaker Wiring Diagrams

Ken · 08-03-2009, 09:08 AM

Quote:

Originally Posted by gtrman

add an extra cab with 8 or even 4 ohm impedance, running both at once?
Short answer: set your amp to 4 ohm!

."

I do that too. I have both an 8 ohm and 16 ohm 4x12 and when I run them both I use the 4 ohm setting. This will not damage the speakers or the amp.

Ken

mooger · 08-03-2009, 08:10 PM

Hi this is my first time on this forum, I have just bought my first Marshall Amp (S/H).

My Amp is a 50/50 Monobloc and I have two 1936 2x12 Cabinets.

The Amp has an impedance selector for each side which is either 16 or 8 ohms.

The Cabs are 16 ohms stereo and 8 ohms mono.

My questions are as followings:

1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ?
2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ?
3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ?
4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ?

Many thanks

American Viking · 08-03-2009, 10:26 PM

Quote:

Originally Posted by mooger

Hi this is my first time on this forum, I have just bought my first Marshall Amp (S/H).

My Amp is a 50/50 Monobloc and I have two 1936 2x12 Cabinets.

The Amp has an impedance selector for each side which is either 16 or 8 ohms.

The Cabs are 16 ohms stereo and 8 ohms mono.

My questions are as followings:

1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ?
2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ?
3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ?
4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ?

Many thanks

1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ?

A1. Correct. 8ohms on the amp to 8ohms mono on the cab

2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ?

A2. you won't be able to use both cabs on one side unless you can drop the amp impedance to 4ohms to run both cabs in 8ohm mono.

3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ?

A3. Correct. 16ohms on both sides of the amp and 16ohms Stereo into each side of the cab.

4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ?

A4. both sides of the amp at 8ohms to both cabs at 8ohms, on this one I'm assuming each side of the amp is running it's own cabinet.

mooger · 08-04-2009, 07:41 PM

On the back of my cab it says 8 ohms mono and 16 ohms stereo, the mono socket is on the right, and when you plug into the stereo socket on the left it switches both inputs to 16 ohms stereo.

I just need to triple check this because I have been given conflicting information from my local dealer, they say:

1. One Amp to One Cab mono = Amp impedance 8 ohms, right input on cab.

2. Two Amps to One Cab stereo = Amp impedance 16 ohms, cables into left and right sockets from amps.

Many thanks for your help, I just can't get my around this one.

American Viking · 08-04-2009, 11:58 PM

you know what, sorry about that I misread your post! The 2x12 cabs and the 4x12 cabs are kind of flip flopped, i just read it and took it as it was like the 4x12.

I'm going to post it again here and I'm going to edit my original post to match.

1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ?
A1. Correct. 8ohms on the amp to 8ohms mono on the cab

2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ?
A2. you won't be able to use both cabs on one side unless you can drop the amp impedance to 4ohms to run both cabs in 8ohm mono.

3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ?
A3. Correct. 16ohms on both sides of the amp and 16ohms Stereo into each side of the cab.

4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ?
A4. both sides of the amp at 8ohms to both cabs at 8ohms, on this one I'm assuming each side of the amp is running it's own cabinet.

08-02-2009, 05:48 PM	#1 (permalink)
DudeWheresCorey Junior Member Join Date: Jul 2009 Location: North Carolina Posts: 13	Ohms! Hey guys, Im new to this thread as well as Marshall, I just recently got my JCM 800 about 4 weeks ago. For my live set up for my band I would like to use my 2x12 cab with my 4x12. The 2x12 is 16 ohm's and the 4x12 is 8. Is their a way I can safely run both cabs with my head?

08-02-2009, 06:19 PM	#2 (permalink)
MartyStrat54 Senior Member Join Date: Feb 2009 Location: Formerly Phoenix, now north of KC Posts: 2,580	Re: Ohms! Yeah, welcome to the Forum. It would be best to run your half stack only and set the impedance on the amp to 8 ohms. This will be plenty loud. Trying to run a 16 and an 8 ohm load at the same time will not fly for long and I know you don't want to damage your amp. A 16 and an 8 ohm load in parallel is 5.33 ohms (just so you know). Here is American Vikings thread: Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! And here is Sticky's thread (very good): SPEAKER WIRING __________________ MARTY 2009 Gibson Explorer-Hell Raising Machine 1989 Fender Strat Plus USA 2008 Fender Tele USA 2004 Schecter Elite w/DiMarzio's TSL100 with custom 4x12 cab. TSL122 with Man 'O War Speakers. TSL602 #1 with JBL D123 Speakers and 602 #2 with Altec 417 Speakers. "Oh so sweet my friends." DSL401 #1 with Red Fang Speaker and 401 #2 with JBL D123 Speaker. Tubes: Let's just say they are NOS that kick ass.

08-02-2009, 06:22 PM	#3 (permalink)
DudeWheresCorey Junior Member Join Date: Jul 2009 Location: North Carolina Posts: 13	Re: Ohms! Yah I figured that was the deal. I was just wondering if their was a way, your right I def dont want to ruin my amp either! Thanks for the help!

08-02-2009, 06:35 PM	#4 (permalink)
MartyStrat54 Senior Member Join Date: Feb 2009 Location: Formerly Phoenix, now north of KC Posts: 2,580	Re: Ohms! Great. I added a couple of the more important threads on this matter so you can take a look and use it for future reference. __________________ MARTY 2009 Gibson Explorer-Hell Raising Machine 1989 Fender Strat Plus USA 2008 Fender Tele USA 2004 Schecter Elite w/DiMarzio's TSL100 with custom 4x12 cab. TSL122 with Man 'O War Speakers. TSL602 #1 with JBL D123 Speakers and 602 #2 with Altec 417 Speakers. "Oh so sweet my friends." DSL401 #1 with Red Fang Speaker and 401 #2 with JBL D123 Speaker. Tubes: Let's just say they are NOS that kick ass.

08-02-2009, 06:57 PM	#5 (permalink)
gtrman Senior Member Join Date: Apr 2008 Location: Norway Posts: 219	Re: Ohms! Amp problems? Ohm questions? Amp blowing up for no reason, READ ME! According to the post above it is possible to use a 4x12 & 2x12 cab together. I have tried this myself and it delivers the sound/volume you are after. I'm a little unsure of the damage it can do using this over time though. "At what impedance should I set my amp if I have a 16 ohm cabinet, and want to add an extra cab with 8 or even 4 ohm impedance, running both at once? Short answer: set your amp to 4 ohm! For one 16 ohm and one 8 ohm cab, the formula is: 1/ (1/16 + 1/8) = 1/0,1875 = 5,3 So the combined impedance of both cabs is 5,3 ohm. The closest setting on your amp is now 4 ohm. Again, 4 ohm on your amp is the closest setting. If you do not have a 4 ohm setting on your amp, I would not try this and stick to using just one cabinet. Or maybe two 16 ohm cabs resulting in a combined 8 ohm load." __________________ JCM800 2203X - 1923 85th Anniversary - JCM900 SL-X - VM 2266 - 425A - 6100LM - 6101LM - Silver Jubilee 2553 - Silver Jubilee 2554 - 1960A - 1960B - 1960Slash - 1922 - 1936V

08-02-2009, 10:07 PM	#7 (permalink)
DudeWheresCorey Junior Member Join Date: Jul 2009 Location: North Carolina Posts: 13	Re: Ohms! Yah. On my old amp (my dual rec) I had many speaker output options, I would run a 4ohm output to the 8ohm cab and 8ohm out to the 16ohm cab and according to mesa in the handbook it was considered a safe missmatch. Im not sure though I really dont want to mess something up. I will probably just stay on the safe side and just play my 8ohm cab. Its allready PLENTY loud! Thanks for the help though!

08-03-2009, 02:29 AM	#8 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Ohms! The safest way possible for you would be to rewire the 2x12 to 8ohms and set the amp impedance to 4ohms to run both the 2x12 and 4x12. It's really easy to rewire a cab as long as you follow the diagrams. Jumbo Sunshade - Speaker Wiring Diagrams __________________ -I'd rather be a good liver than have one...

08-03-2009, 08:10 PM	#10 (permalink)
mooger Junior Member Join Date: Aug 2009 Posts: 6	Re: Ohms! Hi this is my first time on this forum, I have just bought my first Marshall Amp (S/H). My Amp is a 50/50 Monobloc and I have two 1936 2x12 Cabinets. The Amp has an impedance selector for each side which is either 16 or 8 ohms. The Cabs are 16 ohms stereo and 8 ohms mono. My questions are as followings: 1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ? 2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ? 3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ? 4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ? Many thanks

08-04-2009, 07:41 PM	#12 (permalink)
mooger Junior Member Join Date: Aug 2009 Posts: 6	Re: Ohms! On the back of my cab it says 8 ohms mono and 16 ohms stereo, the mono socket is on the right, and when you plug into the stereo socket on the left it switches both inputs to 16 ohms stereo. I just need to triple check this because I have been given conflicting information from my local dealer, they say: 1. One Amp to One Cab mono = Amp impedance 8 ohms, right input on cab. 2. Two Amps to One Cab stereo = Amp impedance 16 ohms, cables into left and right sockets from amps. Many thanks for your help, I just can't get my around this one.

08-04-2009, 11:58 PM	#13 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 1,510	Re: Ohms! you know what, sorry about that I misread your post! The 2x12 cabs and the 4x12 cabs are kind of flip flopped, i just read it and took it as it was like the 4x12. I'm going to post it again here and I'm going to edit my original post to match. 1. If I am only use one cab, with one side of the head in mono do I set the Amp to 8 ohms ? A1. Correct. 8ohms on the amp to 8ohms mono on the cab 2. If I am using two cabs with one side of the head in mono do I set the Amp to 8 ohms ? A2. you won't be able to use both cabs on one side unless you can drop the amp impedance to 4ohms to run both cabs in 8ohm mono. 3. If I am using one cab and both sides of the head in stereo do I set both Amp's to 16 ohms ? A3. Correct. 16ohms on both sides of the amp and 16ohms Stereo into each side of the cab. 4. If I am using two cabs and both sides of the head in stereo do I set both Amps to 8 ohms ? A4. both sides of the amp at 8ohms to both cabs at 8ohms, on this one I'm assuming each side of the amp is running it's own cabinet. __________________ -I'd rather be a good liver than have one...

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