Amps

[44caliberKid]

Just nailed a pretty solid deal on a Mesa nomad 55 1x12 combo. I already have a nice worn in vintage 30 rated at 16 ohms 60 watts I'd like to put in this amp. The Mesa has one 8 ohm out and 2x 4 ohms outs. I can run my speaker from the 8 ohm out right? I know this isn't really a prob with solid state amps but is it the same for tube amps? Will I lose any power if I do? I Think it might be ok but I just wanna make sure.

[JetCityMatt]

Sounds like a bad idea.
You don't ever want to run into a load that is higher impedance (more resistance/load) than the amp is designed for because you might kill the tranny.

Several years ago I asked Mike Soldano if there is a correct way to mismatch impedance and, if so, why it won't hurt the amp.
He said that running a higher load than the amp is designed for is really bad, but that a lower load is okay, but you wouldn't want to mismatch by more than one "notch". Running an 8 ohm amp into a 4 ohm load is fine, but mismatching any further would not be a good idea. You can run an 8 ohm head into a 4 ohm load, your tubes will just wear out a little faster. You cannot run an 8 ohm head into a higher resistance without

possible damage.

You do not want to run into a higher resistance than your amp is designed for because the power created in the power transformer cannot get out of the

transformer as quickly or completely as it was designed to, so there is power left in it that should not be there. 

If 100% of the power created by the primary winding of the transformer cannot escape from the secondary winding by going out to an equal (or lesser)

resistance than designed for, that power which is trapped in the secondary winding will continue to stack/increase as the primary winding continues to

refill this secondary winding at the normal rate of 100% of the power it was designed for.  This excess power must go somewhere... the insulation melts and

you get a blown tranny and possibly a fried tube and socket.

Soldano's standard 50+ watt amps have a a load selector switch to select which ohm setting you want, but the 20 watt Astroverb does not have this switch so

he designed the Astroverb to run into a 16 ohm load so that no matter what you plug into (4 ohm cab, 8 ohm cab, 16 ohm cab) you never plug into a higher

load than the amp wants. Mike said that running the 16 ohm Astroverb into 8 ohms simply makes the tubes run a little hotter so they wear slightly faster.

[HKSblade2]

Not usually a good idea. Read up on OT flyback voltage. IIRC Weber had a great article about high impedance loads on low impedance outputs.

I know a ton of people who ran 16 ohm cabs on 8 ohm out loads and were fine. Doesn't mean it's ever the right thing to do. Would I recommend it? Not really. See if you can find a used 8 ohm speaker for $50-75.

Contact Mesa support and see what advice they have if you are concerned about any amp damage.

[MrKnobs]

It's probably ok, but in the past the problem was that if you don't load down the transformer output enough the voltage would get too high and eventually short out windings in the transformer.  I think transformers are made better than that now.  I know that the Bad Cat people say it's no big deal as does Zinky.]

Terry D.

[*BLEEP*]

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MrKnobs wrote:

...if you don't load down the transformer output enough the voltage would get too high...

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Actually, the *current* (amps, i.e. -- electrons) flow would be too high at a given voltage (volume).  

[JetCityMatt]

Also, the Warehouse Guitar Speakers Retro 30 kicks the Vintage 30's ass so severely that you might as well pick one up new from their site for $79.  www.wgs.com 

Unless you enjoy the hearing damage from the vintage 30's harsh upper mid spike.

Also, unlike the vintage 30, the Retro 30 also does not lack the highest upper treble/presence frequencies.
The Retro 30 just kicks ass. 

[Pine Apple Slim]

I asked the same Q not long ago about running a 4 ohm Bassman head into an 8 ohm cab.
Answer:
If it was a solid state amp it would be ok. Tubes, its risky, could ruin your transformer. I wouldn't do it.

[44caliberKid]

As always fellas I really appreciate the help. Say what you will about the v30, it's a great speaker and is the only thing that made my valve king bearable. I'm pretty excited about my Mesa, as it's definitely the nicest amp I've ever owned, can't wait to get it. I hate to see my v30 go but I was already looking into a scumback just in case the impedence was gonna be an issue. Though maybe I'll take a look at those warehouse guitar speakers or whatever theyre called. I have heard good things about them. Soooo anyone interested in a peavey valveking 1x12 with a Celestion v30??!! Heh heh.

[WittyMonikerHe…]

Hold on, I have a related question: I currently have a 2x12 8 ohm mono cab that has two 16 ohm Eminence Wizards wired in paralell. I wanted to swap out the speakers and retain the 8 ohm output to maximize compatability, so I was told getting two V30s @ 16 ohms would do the trick. This info accurate?

Thanks!

[JetCityMatt]

Here's a post someone made on this forum years ago:

"

1. Impedances in series: total impedance is the

sum of the impedances.

2. 2 impedances in parallel: total impedance is

the product (x) of the impedances divided by the sum

of the impedances.

So if you put an 8 ohm speaker in parallel with a 4 ohm

speaker, the impedance is 8 x 4 divided by 8 + 4,

or 32 divided by 12, which is 2.67 ohms.

3. Multiple impedances in parallel:

Total Impedance = 1/(1/R1)+(1/R2)+(1/R3) etc...

(I know, the correct abbreviation for impedance is Z, but I

though this might be easier to follow)

So as an example,  for 4 speakers in parallel, a 4 ohm, an 8

ohm, and 2 16 ohms,  the calculation is

1/(1/4)+(1/8)+(1/16)+(1/16), or with a common denominator-

1/(4/16)+)+(2/16)+(1/16)+(1/16), which is 1/(8/16).

1/(8/16) is the same as 1/(1/2), which is 2. So the four speakers

in parallel give a 2 ohm impedance.

Believe it or not, that's a simplified explanation, but here's one

last rule of thumb to keep you out of trouble:

THE TOTAL IMPEDANCE (RESISTANCE) IN A PARALLEL

CIRCUIT IS ALWAYS LESS THAN THE VALUE OF THE

SMALLEST RESISTANCE IN THE CIRCUIT.

This means when you add a speaker in parallel you ALWAYS lower

the impedance (load on the amp). When you add a speaker in

series you ALWAYS raise the impedance (load)."

[JetCityMatt]

Have you used Vintage 30s before and do you like the high mid spike and the lack of upper treble?
If you'd like to ditch those shortcomings consider the Warehouse Guitar Speakers Retro 30. I love it.

[WittyMonikerHe…]

I actually do like the Vintage 30. For years, my Wizard has been great, but I've been cranking the presence and mids just to get it to open up. I rarely have to do this with the V30s. I know a lot of people hate them, but to me, thats where your guitar tone really lives in a mix — with strong mids, and tapered of treble. 

I've listened to a lot of online clips, however, and the *only* one where the V30 was beat, was when compared to a WGS Vet30. But that was for metal, and not in a live situation. Still, I have to admit, it sounded pretty great. 

2nd, I'll be getting Hellatones (which are broken in Vintage 30s), so it will have some of that treble that you say it lacks. 

[gardo]

You can get away with higher impedence in the speakers more than lower.

Lower allows too much signal to pass and will overheat the amp.

[Cirrus]

---

JetCityMatt wrote:

Have you used Vintage 30s before and do you like the high mid spike and the lack of upper treble?
If you'd like to ditch those shortcomings consider the Warehouse Guitar Speakers Retro 30. I love it.

---

Someone's already said it but I've got to reiterate. In a mix, High mid spike = clarity and lack of upper treble = not harsh at high volume, not fighting cymbals and top end of vocals. Judging speakers in isolation will quite often be a waste of time. When you're judging/ tweaking the guitar tone within a mix it's amazing how thin and upper middy it can be when you isolate it.

[Wyatt]

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gardo wrote:

You can get away with higher impedence in the speakers more than lower.

Lower allows too much signal to pass and will overheat the amp.

---

This is a commonly repeated myth. It is actually the other way around.

The amp will compenstae for a lower speaker load by running less efficiently (just don't go too low). But if you use a higher speaker loud, then then amp will deal with flyback voltage which can cause real damage.

So, for the OP, as already noted...NO, it is NOT ok to run a 16-ohm speaker load on a 8-ohm output trasnformer tap.

[gardo]

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Wyatt wrote:

---

gardo wrote:

You can get away with higher impedence in the speakers more than lower.

Lower allows too much signal to pass and will overheat the amp.

---

This is a commonly repeated myth. It is actually the other way around.

The amp will compenstae for a lower speaker load by running less efficiently (just don't go too low). But if you use a higher speaker loud, then then amp will deal with flyback voltage which can cause real damage.

So, for the OP, as already noted...NO, it is NOT ok to run a 16-ohm speaker load on a 8-ohm output trasnformer tap.

---

What happens if there is a mismatch?
If the speaker cabinet impedance load is higher than the amplifier rating, e.g., an eight ohm cabinet plugged into an amplifier with a minimum impedance load of four ohms, you're cool. You're not getting the amp's maximum output, but don't panic over it. (Again, this applies only to solid-state amps - if you have a tube power amp, the impedance needs to match!)

If the speaker cabinet impedance load is lower than the amplifier it is now time to panic! Don't try it!
Amplifiers can react in different ways, most contemporary good quality amps have circuitry that detects the current flow, and if it is higher than specified (the result of a speaker load below specifications) the amp will temporarily shut itself down. However, not all amps have this protection circuitry, so you may be playing with fire... literally!! Another distinct possibility is that you'll see curls of smoke escaping from the amp as you fry the output devices. 

[JetCityMatt]

Previous post's quote says
"(Again, this applies only to solid-state amps - if you have a tube power amp, the impedance needs to match!)"



Some website does not have more accurate information that what Mike Soldano told me on this issue when asked about it.

[Viesczy]

Check out page 36 for the 16 ohm in to 8 ohm jack mismatch.

http://www.mesaboogie.com/manuals/RoadKing2_v2.pdf

Derek

[Mogwix]

Tube amps use an output transformer to filter DC voltage (from the tube's bias circuit) from the AC waveform (the amplified audio signal), and to match the output impedance to the load impedance.

The output transformer has taps at different locations on the output coil to match the output impedance to different load impedances, depending on which tap you use. When the impdances are matched, most of the amplifier's power is being transferred to the speakers and there's very little (negligible) energy being dissipated by the transformer. When the output impedances do not match, the transformer isn't transferring all of the energy to the speakers and must dissipate the energy somehow... usually as HEAT.

If the load impedance is too low, there is much more current flowing on the output side of the transformer, this can damage the transformer and/or the speakers. If the load impedance is too high, there is much more current flowing on the amplifier side of the transformer, which can damage the transformer or the amplifier itself.

Keep in mind that the difference between 4 ohms and 8 ohms is a factor of 2. The difference between 4 ohms and 16 ohms is a factor of 4. If you have a 4 ohm load connected to the 8 ohm tap, there's twice the current flowing on the output side. If you have a 4 ohm load connected to the 16 ohm tap, there's four times the current flowing. That extra current isn't flowing to the speakers either, it's building up in the transformer and turning into heat... which will eventually damage it.

[44caliberKid]

Yes I completely agree. I have found that the much Bally- hooed " upper mid range spike" is very helpful in a live situation and really helps to cut thru the mix. I'm not big on treble either. I really like to crank my mids and get that growl. In any case Im waiting on my scumback m75, decided to try something new.