Ohms. Somebody help me understand.

Pix

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Hey Guys,

I haven't posted in years.
I have forgotten a lot. Can you guys explain how ohms work to me. I know, search for a thread, I wanted to ask myself.

FE; I have a HW OTT, I want to plug it up to 2 M4X12 cabs. I just want to understand.

Thx guys, I'm really rusty.
 

wildhawk1

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While we're at it I need a dummies guide to ohms, watts, amps, yada yada.

Clueless. Absolutely clueless.
 

Pix

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Yeah, proceed with your best... I was in whiskey and women for my younger years. I just picked up again. I could have googled it, however I've always enjoyed my fellow bothers candor.
 

Deftone

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You gotta match the ohms on the amp with the cabs. Check the ohms on the speakers, then you need to determine how it's wired to know what ohms the cabs are. Should be marked.

 
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Brazilnut

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Yeah, a 2-ohm load to an amp designed to run an 8 ohm load is not cool. Literally!
Cabs can have the speakers wired in series or in parallel. That will cause the cab to have a different load, depending. It's all very confusing to me, too.
 

strayedstrater

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Hey Guys,

I haven't posted in years.
I have forgotten a lot. Can you guys explain how ohms work to me. I know, search for a thread, I wanted to ask myself.

FE; I have a HW OTT, I want to plug it up to 2 M4X12 cabs. I just want to understand.

Thx guys, I'm really rusty.

Is a HW OTT an Orange Hard Wired Tiny Terror with one 16 ohm output jack and a pair of parallel 8 ohm output jacks?

M4x12 could be Marshall (usually 16 ohms) or Mesa (usually 8 ohms). Or Matamp (16 ohms, I think?). Assuming stock speakers.

If your cabs are 16 ohms, if you want to use one cab you plug it into the amp's 16 ohm jack. If you want to use both cabs you plug them into the two 8 ohm jacks. (The 8 ohm jacks are both connected to the transformer's 8 ohm tap; the jacks are in parallel and two 16 ohm loads in parallel is an 8 ohm total load.)

If the cabs are 8 ohms you can only use one with a Tiny Terror. Plug it into either 8 ohm jack. Orange labeling isn't very clear on the amp but explained in the online manual -- you CANNOT safely plug two 8 ohm cabs into the two 8 ohm output jacks (two 8 ohm cabs in parallel is a total 4 ohm load).
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If the cabs are 8 ohms and you want to use both, you can buy/build a series junction box or buy/make a custom series Y cable and connect the two 8 ohm cabs in series for a total load of 16 ohms and plug into the OTT's 16 ohm output.
------------------------
Be sure to use actual speaker cables to connect the amp and cab(s), not instrument cables.
 

sonar1

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One’s enough to kill ya!
Bought a pickup once that had 10,000!
Should have a sticker:

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Big John

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...HW OTT, I want to plug it up to 2 M4X12 cabs...
Whatever ohms one of those cabs are, divide that number in half. Go to the amp, select that number on the ohms switch. Plug in both cabs. Go.
 

cooljuk

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Speaker Ohms are like drinking straws.

It's hard to breathe through a straw. That's resistance.

It's easier to breathe through two straws parallel / next to to each other than it is just one. That's less resistance (cut the Ohms in half if you have two speakers in parallel)

It's harder to breathe through two straws connected end to end in series than it is just one. That's more resistance (double the Ohms if you have two speakers in series)
 

CB91710

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You gotta match the ohms on the amp with the cabs. Check the ohms on the speakers, then you need to determine how it's wired to know what ohms the cabs are. Should be marked.

Oh come on..... McKnight?

Electroboom has GOT to have something that covers this!
 

Deftone

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Yeah, a 2-ohm load to an amp designed to run an 8 ohm load is not cool. Literally!
Cabs can have the speakers wired in series or in parallel. That will cause the cab to have a different load, depending. It's all very confusing to me, too.
Confusing is Marshalls with their (4)16 or 8 switch...WTF?
 

efstop

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Confusing is Marshalls with their (4)16 or 8 switch...WTF?
It's only confusing if you don't know how ohms work ;)
Marshall amps have various output schemes, it's true. I had a DSL15H with one 16 ohm jack and two 8 ohm jacks. My DSL1HR is the easiest, one 16 ohm jack, nothing else can be plugged in (except a pair of 8 ohm in series. I made a series cable for that.)

Then there's the cabs with switches. Four 16 ohm speakers can be either 4 ohm or 16. Pairs in the same cab can be run in stereo, 8 ohms per side.
Simple :)
 

CB91710

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Then you have this set up. Seems to make sense to me. View attachment 624773

It's absolutely clear with its labeling.
Yep... the paired jacks are in parallel, so two 16s is correct for the 8 ohm tap, likewise, the two 8s is correct for the 4 ohm tap.

The 4x10 that I built for my Carvin (and generally use with the Blues Junior) is 8... it has four 8 ohm Carvin VL10 speakers in series/parallel.
Won't be able to use it with the new DSL1... unless I build a matching 8 ohm cabinet (maybe a 1x12) and run them in series.
 

efstop

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Yep... the paired jacks are in parallel, so two 16s is correct for the 8 ohm tap, likewise, the two 8s is correct for the 4 ohm tap.

The 4x10 that I built for my Carvin (and generally use with the Blues Junior) is 8... it has four 8 ohm Carvin VL10 speakers in series/parallel.
Won't be able to use it with the new DSL1... unless I build a matching 8 ohm cabinet (maybe a 1x12) and run them in series.
Tap into one pair of the Carvins. There's your 16 ohm. What's one more jack?
;)
 

Torren61

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Ohms are a speaker's impedance. Similar to resistance. If your amp requires an 8 Ohm speaker load, you can mismatch that 100% and it'll be fine. So, you can use a 4 Ohm speaker load. That's going down by 100%. You can use an 8 Ohm speaker load. That's what the amp was designed to use. Or you can use a 16 Ohm load. That's going up by 100%.

Going down by more than 100% is really bad for your output transformer. If your amp wants to see a 16 Ohm load and you use a 4 Ohm speaker load, you could smoke your transformer. If your amp wants to see a 4 Ohm load (old Fender) and you use a 16 Ohm, you probably won't smoke your transformer but you could introduce an oscillating voltage (I think) into your signal.

I like to have my cabs at 8 Ohms. That way, I can use them with any amp.

Remember, an amp is engineered to see a certain load and that's what you SHOULD use. In other words, if your amp wants an 8 Ohm load, it'll probably sound best with an 8 Ohm speaker load but you won't kill it with a 4 or 16 Ohm load. It MAY sound or feel different with a speaker load other than an 8 Ohm load.

People tend to freak out if you mismatch speaker load impedance to what the amp is designed to use but it's not something to freak over. I often mismatch impedances and have been doing so for YEARS and I don't have a pile of blown up amps.

Now, having said all that, I don't mismatch speaker impedances in the same cab or combination of cabs. I mean, I don't have a 2x12 cab with one 8 Ohm speaker and one 16 Ohm speaker. I'm not saying it can't or shouldn't be done. I'm saying I don't do that because I prefer to do things with my amps where I know it's safe.

Watts is how much power a thing uses and it's based on Ohm's law and this formula. Watts/power is voltage X current. If your voltage is 120V and the current you are using is 10 amps, the wattage/power is 1200 watts. But you want to understand guitar amplifier wattage.

5 watts is loud. 10 watts is not twice as loud as 5 watts. 15 watts is louder than 5 watts but not three times as loud. 30 watts is REALLY loud. 50 watts is louder but, again, not in the proportion you might think. 100 watts is not twice as loud as 50 watts.

And this is how I explain resistance, voltage, current and power:

Let's imagine a device. You have a balloon laying on its side and full of air. You have a straw in the end of the balloon. You have a pinwheel at the end of the balloon. Don't worry how the balloon is affixed, just go with this.

The air contained in the balloon has pressure but is not released yet. That's similar to electrical voltage. Pressure. The more "air" in the balloon, the more pressure. The larger the transformer, the more voltage is contained in the transformer.

The straw in the balloon is resistance or Ohms. If you put a larger diameter straw in the balloon, more air can escape. A smaller diameter straw lets less air escape. A larger resistor is like a smaller diameter straw. A smaller resistor is like a larger diameter straw.

The flow of air coming out of the balloon is similar to current. Current is the movement of electrons in an electrical circuit. The faster or more air coming out of the balloon, the more work it can do.

The pinwheel is watts/power. A large pinwheel requires more air to get it to spin whereas a smaller pinwheel requires less air to spin.

To put it all together, you have a very small balloon with a small diameter straw and the amount of air coming out of that balloon is not enough to spin a large pinwheel but it could easily spin a small pinwheel. You get a large balloon and fill it with air and you have a large diameter straw that lets a lot of air flow out of it and that will spin a larger pinwheel.

Okay, I'm ready for an electrical engineer to destroy my presentation. Remember, this is merely an approximation and a thought experiment but it gives you an idea of how electricity works in a most rudimentary way.
 

CB91710

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Tube vs solid state.
Solid state amps can run with a higher impedance without issue.
Amps wants a 2 ohm load and you accidentally run it without the cab plugged in?
All you get is no sounds... but no damage.
However, if a solid state amp is run at a lower impedance, it causes the output transistors to run hot and can smoke.

Tube amps are... to a point... the opposite.
Lower impedance will cause the OT to run hot, but even a dead short won't kill them for a short duration. The speaker output jacks on tube amps short to ground if no speaker is plugged in.
That said, it DOES cause the transformers to run hot due to the increased current draw, so it's not a good thing.

OTOH, an open output on a tube amp will cause the voltages in the output section to increase due to the lack of a load, and if the voltage exceeds the tube's rating, can cause internal arcing, which can smoke just about any component that is connected to the screen, grid, or cathode.


The only audible issue with running a tube amp mismatched is there will be some high frequency loss due to the impedance mismatch. Solid state amps are far more tolerant, particularly if the outputs are transformerless, as there is no coil impedance to balance the speaker voice coil... the SS amp's rated impedance is based on the current carrying capacity of the outputs.

P=I*E
E=I*R

An amp rated for 100w into 8 ohms is rated to deliver about 3.5 amps at 29 volts.
At 16 ohms, that same 100w is now only drawing 2.5 amps, but at 40 volts.
At 4 ohms, that same 100w is now sucking 5 amps, but at only 20 volts.
 

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