8 vs 16 ohms (Marshall content) (2024)

I feel like I should know this already but I don't.

Is there any major discernable difference between running a particular guitar amplifier at 8 ohms or 16 ohms?

Is it a larger factor when using the amp into a 4x12 cab vs a 2x12 cab? Mono vs stereo, etc.?

I have a single channel early '80s Marshall JCM 800. I've always run it at 16 ohms, sometimes into a mismatched 4x12 cab.

I've since used it via an attenuator into a 2x12 cab loaded with an older Celestion Vintage 30 and a Mesa/Boogie Black Shadow MC90. Both speakers are 8 ohms. I run it in stereo, i.e. 8 ohms per side.

I really like how it sounds, even at low volumes. It seems to have a really good edge to it, whereas before (with the mismatched cab) it was way too midrangey and less crunchy.
I think what is happening is that more power is going to the speakers, so they are getting pushed harder.

Anyway, I "discovered" that some speakers I had ripped out from another cab, are actually 8 ohms rather than 16 ohms. So my mind starts ticking into putting this pair of speakers with the pair of speakers from the 2x12, into a 4x12 cab. Then I just run the JCM 800 at 8 ohms mono.

Would it be worth it? For some reason I think it would, but I can't work out how. Hence my opening question.

You’re mostly hearing the difference between the types of speakers you used, and the difference between cabs.

But there can be a discernible difference between running different impedances. Generally 16 will be more compressed and have some top end roll off and more warmth. 8 will be brighter and a little more punchy, but a tad harsher.

I used to think "16 ohms or bust!" until someone pointed out that all of my guitar heroes who used full stacks were probably running them at 8 ohms.

Matching the head to the total load is probably more important than whether it is 8 or 16 ohms.

fiveightandten said:

But there can be a discernible difference between running different impedances. Generally 16 will be more compressed and have some top end roll off and more warmth. 8 will be brighter and a little more punchy, but a tad harsher.

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Thanks for that.

michael patrick said:

I used to think "16 ohms or bust!" until someone pointed out that all of my guitar heroes who used full stacks were probably running them at 8 ohms.

Matching the head to the total load is probably more important than whether it is 8 or 16 ohms.

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Well the whole reason for deciding between 8 or 16 ohms, is to determine how to set the speaker cab up.

At the moment the amps is (rated at) 50 watts, pumping at least 25 watts into the 60 watt V30 at 8 ohms on one side, and 25 watts into the 90 watt Black Shadow MC90 at 8 ohms on the other side.

The total load is 16 ohms (I have a THD Hotplate Attenuator in between).

I really like the sound, but am wondering about putting the speakers into a 4x12 cab with two other 65 watt 8 ohm speakers, so the total load is 8 ohms and run the amp at 8 ohms mono instead.

ChorusCrackpot said:

Thanks for that.

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It may also interest you to know that the negative feedback loop of your amplifier was run off different taps, depending on the tubes the amp was loaded with from the factory. The NFB loop is what powers the presence control, but it has an affect on the overall sound and feel of the amp as well.

UK models (and I believe Canadian as well) were loaded with EL-34's and had the NFB running off the 16 ohm tap. US models were loaded with 6550s and had the NFB running off the 8 ohm tap. This is the purple wire soldered to the impedance selector (connected to the corresponding tap).

This is an example of the designer of the amp discerning the response difference between the 2 taps, and choosing the best option to suit the tube type that the amp shipped with.

ChorusCrackpot said:

At the moment the amps is (rated at) 50 watts, pumping at least 25 watts into the 60 watt V30 at 8 ohms on one side, and 25 watts into the 90 watt Black Shadow MC90 at 8 ohms on the other side.

The total load is 16 ohms (I have a THD Hotplate Attenuator in between).

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If I'm understanding it correctly, the total load is 4 ohms, not 16. Two 8 ohm loads in parallel is 4 ohms.

According to the Hotplate product manual:

IMPORTANT: WHEN USING BOTH SPEAKER OUTPUTS FROM THE HOT PLATE, THE TWO SPEAKER CABINETS SHOULD HAVE THE SAME IMPEDANCE AS EACH OTHER, AND THAT IMPEDANCE SHOULD BE DOUBLE THE
IMPEDANCE OF THE HOT PLATE.

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fiveightandten said:

It may also interest you to know that the negative feedback loop of your amplifier was run off different taps, depending on the tubes the amp was loaded with from the factory. The NFB loop is what powers the presence control, but it has an affect on the overall sound and feel of the amp as well.

UK models (and I believe Canadian as well) were loaded with EL-34's and had the NFB running off the 16 ohm tap. US models were loaded with 6550s and had the NFB running off the 8 ohm tap. This is the purple wire soldered to the impedance selector (connected to the corresponding tap).

This is an example of the designer of the amp discerning the response difference between the 2 taps, and choosing the best option to suit the tube type that the amp shipped with.

Click to expand...

This is interesting and it does matter. the tone is different so with the DLS I use it at 16ohms into the mono cab - it sounded better than the cab in stereo mode @ 8 ohms

BADHAK said:

About a month ago I got my Ceriatone JCM 800 2203 back from the Tech who had retubed it with EL34 ll's. I plugged it into my 16 ohm 77 slant with 55hz 30 watt Blackbacks on top and V30's on bottom and was blown away with how great it sounded. At the end of the session I noticed that the Tech had put it on 8ohm and when I put it back to 16 it sounded just as good. Maybe a tad more compressed (but your ears tend to compress after a while)but really, whatever differences were pretty subtle.

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Just be careful as you know the rule of thumb of mismatched impedances...
The PT either has to push twice as hard against the resistance or the resistance is twice as low it wants more current.
IMO just better to stick with matched.

Now if were talking sound from strait 8 to 8 or 16 to 16 that is debatable.

michael patrick said:

I used to think "16 ohms or bust!" until someone pointed out that all of my guitar heroes who used full stacks were probably running them at 8 ohms.

Matching the head to the total load is probably more important than whether it is 8 or 16 ohms.

Click to expand...

I spent a good deal of time trying different loads with my first JCM 800 years ago. After really trying I had to be honest with myself and admit I don’t think it made any real significant difference.

Now with a Plexi I swear to god I hear a difference between 8 and 16. Using my Ox at home I was not “feeling it” when I ran the amp with an 8 ohm load but once I switched to 16 it sounded less “splatt-y” and fuzzy.

Sean French said:

Always. I mean ALWAYS match a Marshall to the ohms of the cab used. Period.

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Well, duh.

bdm said:

Well, duh.

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Obviously , you ,I and many others know this.
Some reading this thread may not.
They could have read that Fender amps are fine running a mismatched load.
Try that with a Marshall and the transformer won't last long.

Thanks for making my post look silly and unwarranted.

Sean French said:

Obviously , you ,I and many others know this.
Some reading this thread may not.
They could have read that Fender amps are fine running a mismatched load.
Try that with a Marshall and the transformer won't last long.

Thanks for making my post look silly and unwarranted.

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My (Mesa) Heartbreaker manual actively encourages impedance mismatching for tonal variation. I seem to remember Fender's ToneMaster having an impedance switch that didn't even have numbers on it. But the word is certainly that Marshalls are more sensitive to it... My guess - honestly - is that in the late 60s and early 70s people were running Marshalls flat out so impedance mismatching did become an issue, whereas Fenders were likely to be given an easier ride. So it's not the amps themselves so much as the conditions they were subjected to that drive these reputations...

But I would be absolutely happy to be schooled on the subject... (I mean that, btw, I'm not being passive aggressive!).