MartyStrat54

Hey Procter. I thought you got your amp fixed? Is it blown? If it is, I feel sorry for you. Hope you get it back together.

MARTY

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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.

pet0r

Connecting multiple cabinets with different impedances is easy too. Most amps with 2 speaker outputs have the outputs wired in parallel, and are switchable between 4, 8 or 16 ohm.

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!

The formula for the correct parallel impedance is: "1/ (1/cab1 impedance + 1/cab2 impedance)"

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.

For one 16 ohm and one 4 ohm cabinet, the formula is 1/ (1/16 + 1/4) = 3,2 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.

Procter2812

Cheers Marty

It is fixed kind of... its just not how it was though...

when i first bought it, the tone from the overdrive channels was so unique.. just awesome... i used it for 1 year ( 2 times a week for 3 hour practices) with the band and it helped me so much with my guitar playing and then it blew just before my first ever gig haha

Now there is a weird hum present when there is no input to the amp and the tone has been lost

Although i might sell it and buy a 1960ax and a thd hotplate for my 2203X


Alex

Hayride13

As a prior half stack owner that's been playing through a combo for the past few years, I knew I'd better double check before getting back into a JCM 900 (4100) / 1960A. I might not be the sharpest knife in the drawer but since my used gear didn't come with manuals, I went to get them before even trying to rig up.

http://www.marshallamps.com/download...4100%20Hbk.pdf

http://www.marshallamps.com/download...Cabs%20Hbk.pdf

Great thread and point well taken.

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John Long
HAYRIDE TO HELL
http://www.hayridetohell.com
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MajorNut1967

Great point Hayride,
If you don't ask or get the manuals then its your own fault. Just remember "there are no stupid question, just blown up amplifiers for not asking".

I'm an old fart so in my day there wasn't any stereo 1960 cabs, if I want to listen to the Stereo I turn the "Marantz" not the Marshall. If I want my baby to crap his diaper or my wife to leave me alone I turn on the Marshall and boy it feels GREAT!!!!!

Graunke

I've read, and all the numbers are confusing me.

I have a JCM 900 4100 head. Running into two 1960B cabinets.

I have the head set to the 16(4) setting

The cabs set to the 16 setting?

Is this correct? I haven't turned it on or anything, just want to be sure before I go live. Normally I only use 1 cab, so this is the first weekend I"ll be using two.

American Viking

The 16(4) setting on the 900 head runs 16ohms only. On the combo versions it is 4ohms only with the same print, 16(4). A little confusing.

What you need to be doing when running two cabs set to 16ohms is make sure the head is set to 8ohms.

Two 16ohm cabinets together requires a draw of 8ohms from the head. An easy way to think of it is backwards multiplication. It's a little more complex than that but that's how I first got a grip on the whole ohms thing.

Go back to the original post and check out the little ohms table I tried to assemble. With two 16ohm cabs the head needs to be set to 8ohms. With one 16ohm cab the head needs to be set to 16ohms. If you continue to run two 16ohm cabs with the head at 16 you run a severe risk of permanently damaging your amp. I hope you read this soon so you can correct the problem and preserve your Marshall.

Feel free to ask any more questions you might have on the subject. We all love Marshalls and are more than happy to give you a hand.

__________________
-I'd rather be a good liver than have one...

JCMenace

im thinking this may be what happened to my slx... not completely but possibly some of it...I run a 1960a cab i keep the head switch all the way left 4 (16) and run into the left jack on the cab...Is this correct, I just wanna know for sure so when i get her back i have no further problems because it shows 2 different sets of ohms and im no idiot but it is confusing to me...Thank you, cuzz honestly i didnt realize how crucial this is I hope i didnt permanently fry mine.

thelorddread

hey guys

man i thought i was sure of this but now im feeling weird.
i have jcm900 combo and im not sure if the 12s are 8 or 16 ohms?
for whatever reason i was under the impression that they were 16
but maybe im very wrong?

i also have the jcm 900 1960a cab.
which i was under the impression that those were 16ohm speakers too.
so i thought if the ohmage matched in a parallel setup, it would be the 8
ohm setting on my amp.

geeze im confused now.

thelorddread

yeah i just found the schematics for the amp and the cab and all of the
speakers are 16 ohm.

so yeah, 8 ohm is the proper setting?

right?

pinto79

For the guys with questions about the 6101 Anniversary combo, I just checked the manual, the matching 6912 1x12 extension cabinet is 8 ohms, and so is the internal speaker, so if using the two together, use the 4 Ohm selection. The Combo selection is 4 or 8 and the Head selection is 8 or 16.

I'd like to add too for us Canadians, my CSA edition JCM800 2203 has only 4 and 8 Ohm choices, so I have to run it's cab at 4 ohms.

Ironically, I have to do the same with my 1959RR as my Scholtz Power Soak only has matching 4 ohm selections, so I run it at 4 ohms too.

This is good information Viking, but not always law! Thanks for it tho!

__________________
My Marshall Gear:

1983 JCM800 2203
1986 5210 1x12 Combo loaded with a G12M-70
1992 Anniversary Series 6100
1992 6960A Cabinet loaded with G12T-75s
2008 JMP 1959RR
Old, beaten 1960A loaded with G12M-25 Greenbacks
Ed the Compressor
Regenerator

American Viking

If it's a head the 4(16) is 16ohms.
If it's a combo the 4(16) is 4ohms.

Plugging into the left input of a MONO/STEREO 1960A cab is 4ohms when the MONO/STEREO switch is also set to the left. You need to keep the switch set to MONO and plug into the right input on the cab which is 16ohms.

__________________
-I'd rather be a good liver than have one...

American Viking

The correct and safest way to use your combo with the cabinet is to disconnect the speaker within the combo and rewire the JCM900 cab to 4ohms and use the 4ohm output on the combo to run it.
The speaker in the combo is an 8ohm speaker. The switch on the back of the combos only goes from 4ohms or 8ohms, so it's always supposed to be on 8ohms when used on it's own and can only be used with an extension cabinet that is 8ohms, then you would set the head to 4ohms.

Hope this makes sense. There are a few places to view easy to read wiring diagrams. Rewiring a cab is very simple and is always best to check with a multimeter before plugging in to make sure it's right.
Jumbo Sunshade - Speaker Wiring Diagrams
Wiring a 4 X 12 Speaker cabinet

__________________
-I'd rather be a good liver than have one...

thelorddread

im sorry i forgot to mention that the cab is the 2x12 cab.
im assuming thatll make a difference.

thanks for the answer tho i appreciate it and right now im currently using
it without the extension cab on 8 ohms.

the jcm 900 combo i have is the 100 watt 2x12 combo as well...
i apologize, i really shouldve mentioned that earlier.

American Viking

Yeah I thought you mean a 4x12... that's not a problem though.
Ok, then the cab should be 8ohms. Then when you hook it up just plug the cab in and set the amp to 4ohms and everything should be alright. The two 16ohm speakers are wired to an 8ohm load so adding another 8ohm cab will yield an impedance of 4ohms.
That'll work!

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thelorddread

awesome!

thanks vike!

by the way this forum rules and im on everyday!

bullet22

Hey AV

Similar question here: Correct impedance with 1923 combo and 2x12 extn cab

I have a 2x12 combo and a 2x12 extn cab.

The combo's internal 2x12 is 16ohms, and it has 2 switchable parallel outputs (4 or 8 ohms).

The parallel 4/8 ohm jacks are disconected when the 16ohm jack is used.

So I have to use the 2 parallel jacks (one to the internal 2x12 and one to the 2x12 cab) if I want to push 4x12.

What impedance should I select? I'm tempted to say 2 x 8ohms. Only tempted though. My thoughts being the internal is 16ohms, and the external is 8ohms, which is a total impedance of 8ohms, right..? It seems I'm mixing impedance though - with the 16ohm 2x12 internal and the 8ohm 2x12 external.

Any ideas? I'm starting to think I'd need a 16ohm cab - thus using the 2 outputs set to 8ohms - which would be a downer cos the 1922 I've got access to is 8ohms mono!

Cheers

Ryan (bullet22)

American Viking

I'm looking into it, I'm just letting you know I will place my responses in your other thread.

__________________
-I'd rather be a good liver than have one...

Nightwinflyer

Hello to all, new here!

I never realized tube amp head/cab's were so confusing.
Anyway, American Viking: your chart is very helpful, but I am not sure on one point:
I have a 100w Peavey Windsor head with 4,8,16 ohm selector and the 1960av 4x12. I have the head and the cab connected with head:4 ohms, cab: 4 ohms. This should be OK, but you state:
"The mono jack on the back of a 1960 cab is 16ohms, when you switch to stereo they are at 8 ohms. When you are running one cabinet your amp needs to be set to 16ohms and you need to be plugging into the 16ohm MONO side of the cab."

This is where I am confused, as long as ohms are matched what is the difference?

Thanks for any help.

Chris

American Viking

You're fine. As long as the impedance is matched up you're all good. I only mentioned 16 for that one example since 16ohms is typically the Marshall standard. Glad you found some of this information helpful. Take care.

__________________
-I'd rather be a good liver than have one...

Nightwinflyer

Thanks again for the help!
Time to get rockin...

TubeStack

Why is this? Any sources that back this statement up?

If I remember right, I've seen the main dude from AmpWorks stating (over at TheGearPage) that as long as the ohms are matched, there should be no difference between 4-8-16, in terms of strain on the head, overall tone, or anything else.

I have to run at 4 ohms with my 1960A cab, as my Canadian 2204 doesn't have a 16 ohm tap, just 4 and 8, and the cab is only 4 or 16.

Great post by the way, thank you!

__________________
"And I'm sorry but I can't be kind about this, if you are bitching about "my Marshall is too loud" or "I need a hot plate or a PowerBake to manage the volume," then you don't need or deserve a Marshall all valve amplifier! ... You're like a guy that goes and buys 1970 Chevy SS 454 with 500 horse power and then puts his golf clubs in and drives around the golf course at 3MPH..." - MajorNut1967

American Viking

As far as resources to back that statement up there are few but also conflicting opinions on the subject. Over the last week I've seen where one school of thought is that as long as the current is regulated properly then everything is fine. Mesa/Booger says to expect a slightly shorter tube life when using lower ohm settings. My thought is that either way, there is more current travel in lower ohms than higher so the only thought I can get from the two theories is that if anything, the only added stress is on the output tubes. Shouldn't be that much though. I would like to find a solid fact to explain all this either way, would be nice!
I agree there is no tonal difference between ohm settings as long as the impedance is matched.

__________________
-I'd rather be a good liver than have one...

TubeStack

Thanks man. Hope I didn't sound rude - was just wanting to be sure.

Great thread and great info here.

__________________
"And I'm sorry but I can't be kind about this, if you are bitching about "my Marshall is too loud" or "I need a hot plate or a PowerBake to manage the volume," then you don't need or deserve a Marshall all valve amplifier! ... You're like a guy that goes and buys 1970 Chevy SS 454 with 500 horse power and then puts his golf clubs in and drives around the golf course at 3MPH..." - MajorNut1967

American Viking

Oh no, I didn't think you sounded rude at all. I know how to read most of you regulars.

__________________
-I'd rather be a good liver than have one...

Vovka

American Viking this is a great post! Thanks! There is a lot of explanation and I’m very close in understanding the impedance.

I just have one question. I bought an used Marshall JCM2000 with the 1960a cab and noticed that the previous owner was using the cabinet (only one cab) in stereo mode plugged in the left jack (which in stereo it supposed to be 8 ohm and in mono 4 ohm). The amp was set to 8 ohm. He was playing this way for the last 2 years (I asked, he though it sounded better). How bad this could be to the amp. Does this mean that he matched the impedance 8ohm amp to 8 ohm cab or this looks more like mismatch of 8 ohm amp to 4 cab? (I’m actually not sure if he used the left or right jack, there is a chance he used 16 ohm jack in the cab to 8 ohm amp). I hope that the stereo mode really cuts the impedance in half and that the amp was not abused. Thanks.

Noone

Questions:
I have a JCM 2000 with one 16 ohm out and two switchable 8 and 4 ohm outs. I'm using an 8 ohm cab and a 4 or 16 ohm cab. Would it better to plug into the 4 ohm jack rather than the 16? It's either a combined cab ohmage of 5.3(using the 16 ohm jack) or 2.666(using the 4 ohm jack.) It's better to have the higher ohm rating coming out of the head right? Does it even make much of a difference? Also, this is a no-brainer but just to make sure-if I'm running just the 8 ohm cab out of that same head, it's ok to use just one of the 8 or 4 ohm parallel jacks and set the head to 8 ohms? Any answers are greatly appreciated--I love my Marshall and don't really want to blow it up quite yet.

American Viking

Well, the 8ohm and 4/16ohm cabinet are not compatible. I can't in good conscience recommend any mismatch no matter how close. Although a higher number on the head and lower on the cabinet is less damaging than the other way around. *edit below

To your second question, yes, you only need to use one jack when using one cabinet.

* correction
Although a lower number on the head and higher on the cabinet is less damaging than the other way around

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Noone

Thank you for your reply! I should probably use just the 4/16ohm cab alone running both the head and the cab at 16ohms. This thread is very helpful.

Wilder Amplification

This is backwards. Too low of a load will cause the load to pull too much current from the OT.

Too high of a load mismatch increases flyback voltage on the OT beyond its limits. This is why open loads will fry an OT.

Bottom line...always run a matched impedance. The impedance matching is not a "tone" thing...it is an electrical thing and will come back to bite you in the ass along with your wallet should you decide to do it.

Another thing I'd like to add...DON'T MICKEY MOUSE SHIT TO TRY AND MAKE THE AMP WORK UNTIL YOU CAN AFFORD TO FIX IT PROPERLY!!! You read about these guys who come on like "Well...can I just replace the one bad valve until I can afford a new set?" NO! For two reasons - one, if one failed the others aren't far behind it and two, if one blew it may have taken out a screen resistor with it (all too common) and possibly other things, and for this reason alone you need to have a reputable tech give the amp a once over and verify that nothing else got hurt when the one valve failed. "Can I just use a bigger fuse or wrap tin foil around the blown one until I can afford to fix it?" How many times have we seen someone pull this one and the aftermath it causes?

Bottom line - you think your repair bill is bad now? Wait 'till your "mickey mouse" fix works its magic over on your amp and you're asking for a whole world of financial hurt.

I can't agree with Marty more when he states that "valve amps are not toys and they're not for beginners". You definitely play by the amp's rules and not yours when it comes to valve amps. And no there's no way to "idiot proof" them. You'll probably see some 'yay-hoos' who like to push their amp out of its design limits by underbiasing and mismatching load impedance, running them on variacs, etc etc...because they think that everything is all about tone. Well, news flash - NO IT ISN'T! There is an electrical side to these things that if ignored and disrespected it will come back to fuck you in the ass everytime. And like was mentioned earlier, when you do this shit you're "putting cookies in the oven" so to speak, and they may be done in an hour, a day, a week, a month, who knows...but when they're done they will have a very bitter taste. Eventually those who choose to ignore and disrespect the electrical side of their valve amps will get their dose of the financial hurt that's coming to them when they blow their shizz and they're having to pay a nice $400+ repair bill.

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Wilder Amplification

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