Ohms. Somebody help me understand.

Pop1655

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On the bright side, if you understand all this you are well on your way to being able to pass the license exam to be a ham radio operator.
 

Torren61

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I think the confusion starts with these:

iu

A lot of people replace them with a single input.
Easy. In "mono", choose either 4 Ohm or 16 Ohm. In stereo, you'll have two speakers on one side with 8 Ohms and two speakers on the other side at 8 Ohms. So you'll need two heads wanting 8 Ohms and using two speakers each or one head using only two speakers of the four in the cab.
 

Deftone

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Easy. In "mono", choose either 4 Ohm or 16 Ohm. In stereo, you'll have two speakers on one side with 8 Ohms and two speakers on the other side at 8 Ohms. So you'll need two heads wanting 8 Ohms and using two speakers each or one head using only two speakers of the four in the cab.
Yea, makes sense to me. But some of the Marshall heads (JCM900's) have a two way switch that read: "(4)16 8"

3853408683_c0ca7a049b_b.jpg


I think that gets confusing. I assume "(4)16" means 16ohm out of one tap or 4 ohm out of two, correct?

I think the confusion starts when cabs or heads are not marked or marked in different or confusing manner....then when someone tries to use two cabs...?

Not sure how the HiWatt is set up for speaker out.

While we are here, my Phaez amps all have three speaker outs: 4, 8 & 16. How would I hook two cabs up to that?
 
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strayedstrater

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Yea, makes sense to me. But some of the Marshall heads (JCM900's) have a two way switch that read: "(4)16 8"

3853408683_c0ca7a049b_b.jpg


I think that gets confusing. I assume "(4)16" means 16ohm out of one tap or 4 ohm out of two, correct?

I think the confusion starts when cabs or heads are not marked or marked in different or confusing manner....then when someone tries to use two cabs...?

Not sure how the HiWatt is set up for speaker out.

While we are here, my Phaez amps all have three speaker outs: 4, 8 & 16. How would I hook two cabs up to that?
Edit: TL;DR

Heads were 8 or 16 ohms, combos were 8 or 4 ohms

(Confusing label on the amps but explained in the manuals.)
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Original long post:

(4)16 is explained in the manual but not explained on the rear panel. The heads and combos had the same 4/8/16 transformers but for some inexplicable reason they decided not to give all 3 options on the amps. Heads and combos both had 8 ohm settings, with the switch changing it to 4 ohms on the combos but 16 ohms on the heads.

That's because the combos had 8 ohm internal speakers (either one 8 ohm speaker or two 16 ohm speakers in parallel). So if you added an 8 ohm extension along with the internal speakers you needed the 4 ohm tap on the transformers.

Heads are often used with 16 ohm cabs so they connected the 16 ohm tap instead of the 4 ohm tap.

The transformers have all three outputs so you can rewire a combo to give the choice between 8 or 16, or rewire a head to give 8 or 4.

Again, no one really knows why they didn't put all 3 options on both heads and cabs, or why they didn't put an explanation on the rear panel (or print different rear panels for the heads and combos).
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On amps that have single output jacks for each available impedance, to connect multiple cabs you either need a cab that has in/out parallel jacks, or a splitter box or Y cable.
 
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Deftone

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Edit: TL;DR

Heads were 8 or 16 ohms, combos were 8 or 4 ohms

(Confusing label on the amps but explained in the manuals.)
------------------------
Original long post:

(4)16 is explained in the manual but not explained on the rear panel. The heads and combos had the same 4/8/16 transformers but for some inexplicable reason they decided not to give all 3 options on the amps. Heads and combos both had 8 ohm settings, with the switch changing it to 4 ohms on the combos but 16 ohms on the heads.

That's because the combos had 8 ohm internal speakers (either one 8 ohm speaker or two 16 ohm speakers in parallel). So if you added an 8 ohm extension along with the internal speakers you needed the 4 ohm tap on the transformers.

Heads are often used with 16 ohm cabs so they connected the 16 ohm tap instead of the 4 ohm tap.

The transformers have all three outputs so you can rewire a combo to give the choice between 8 or 16, or rewire a head to give 8 or 4.

Again, no one really knows why they didn't put all 3 options on both heads and cabs, or why they didn't put an explanation on the rear panel (or print different rear panels for the heads and combos).
--------------------
On amps that have single output jacks for each available impedance, to connect multiple cabs you either need a cab that has in/out parallel jacks, or a splitter box or Y cable.
I vaguely remember reading that. Pretty dirty trick though, if you ask me. How hard is it just to slap a sticker on that says "4ohms" or "16ohms"

Well my JMP and my JCM800's have the option of 4, 8 or 16 Ohms. But apparently my JCM900's only have the option of 16 or 8 ohms.....

And my two 1960 Vintage cabs only have the 4 or 16ohms...so in order to stay consistent I'll go with 16ohms on everything.

I probably got that all confused, and I'm sure I'll forget all this again. LOL...
 

strayedstrater

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And my two 1960 Vintage cabs only have the 4 or 16ohms...so in order to stay consistent I'll go with 16ohms on everything.
One 16 ohm cab set the JCM900 head to 16 ohms, use either amp jack.

Two 16 ohm cabs set the JCM900 to 8 ohms, use both amp jacks.
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With Marshall tube amps, the 4 ohm input on 1960's is basically useless. (When you're only using one cab with the Marshall tube amps that have a 4 ohm setting, you could use the 4 ohm cab input but there'd be no benefit in doing so.)

Most Marshall solid state amps only put out their maximum wattage into 4 ohms (many other solid state amps also) And Fender Bassman and Dual Showman tube heads only have 4 ohm outputs. So the 4 ohm input isn't totally useless, just no reason to use it with a Marshall tube amp.
 
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