Huge impedance myth?!? Mismatching heads and cabs ok...?!?

O

onlyrockrocks

New member
Alright guys, I bet you think that this is just another impedance thread. But you might be wrong.

First of all, I'm no tech and I'm not especially good in physics as well. But I'm always trying to find some nice gear and that's how this all started... I was searching for a tool, which enables me to set up my tube amps and cabs in my studio in a comfortable way. I wanted a switcher that connects at least a few heads and cabs at once, so that I can always switch back and forth between them in various ways on the fly.
A few days ago I found out about the Ampete systems. The 444 is one model I got really interested in, but I was wondering if this thing will be auto matching impedances between heads and cabs or if I would need to make sure that the impedance of the cab isn't lower than the one of the amps output myself to avoid any damage.
I know that there are a lot of myths out there, especially regarding impedance, but I thought that at least one thing is safe: Don't run your amplifier into a cab with a lower impedance rating than your amps output impedance. This one rule you can find in a hundred threads, articles and of course even in most manufacturers manuals. Might this be a myth?

Since I wanted to know how the Ampete amp/cab switchers (the 444 in my case) handle different impedances, I got in touch with the company and got back a mail with the manual. I read it and couldn't believe it, so I mailed them a second time and was assured, that I definitely got everything right: You should never run your amp with no load, but according to Ampete a cab even with a lower (!!!) impedance rating than the tube amp will be absoultely fine and won't damage anything (read the manuals pages 16-18 here: http://ampete.com/wp-content/uploads/2015/11/Ampete-444-Manual.pdf ) [EDIT: new link to most recent version of the manual].
Their switchers protect the amps with a certain load as soon as they are connected, but when they are patched into a cab they just let the signal flow no matter if it's a 16 Ohms head into a 4 Ohms cab, a 8 Ohms head into one 8 Ohms and one 4 Ohms cab or whatever. And only because physics allow you to do so. With or without the Ampete gear - always.

I was a little shocked, because why does nobody know that? I mean, there are devices like the Fryette Power Station, that has a input and output impedance selector to be able to match amps and cabs with different impedances from 4 to 16 Ohms. In case Ampete is right - why? [EDIT: According to Ampete the Power Stations impedance selectors could be extremly useful anyway, because you can try different setups with different sounding or feeling results]
I mentioned earlier that I'm not into physics that much, so I'm just telling you what I read and what I have been told. But Ampete is a well known company. I mean, Dave Friedman does like their switchers. They also have set up their switching system in a large testing room of a well know store in Germany as well ( http://gearhead-distribution.com/images/brands/Ampete/Artists_User/MP-Showroom-01.jpg ). And I bet they have tested what they sell (and write). So...WTF?!?

At this point, this seems to be a game changer to me. And now it's your turn. Let the fighting begin... ;)
 
Here's some info about why impedance matching is important:

http://aga.rru.com/FAQs/technical.html#imp-1

(Read that point, and the one below it.)

Mismatching either way can be bad. That's not to say it will be bad every time. But mismatching either way has its risks. Consider that if you have a dirty jack or cable end (or questionable solder joint etc.), it can make the situation worse. Matching impedance is still the best way to go in general.

Mismatching either way affects the sound, too...usually in a way you probably won't quite like.
 
If you have a 16 ohm cab you can plug into 8 or 4 with no issue. Vice versa is here you will stress your OT and can easily wind up with a shorted transformer. I think that is the way it works, especially with modern transformers. Some of the old ones were so overbuilt they may have handled it.
 
glip22":3os38p45 said:
If you have a 16 ohm cab you can plug into 8 or 4 with no issue. Vice versa is here you will stress your OT and can easily wind up with a shorted transformer. I think that is the way it works, especially with modern transformers. Some of the old ones were so overbuilt they may have handled it.
Click to expand...

Read the link I posted above. And consider that if you have a dirty jack or cable end (or questionable solder joint etc.), it can make the situation worse. There's no rule-of-thumb type answer.
 
onlyrockrocks":33mlix43 said:
Alright guys, I bet you think that this is just another impedance thread. But you might be wrong.

First of all, I'm no tech and I'm not especially good in physics as well. But I'm always trying to find some nice gear and that's how this all started... I was searching for a tool, which enables me to set up my tube amps and cabs in my studio in a comfortable way. I wanted a switcher that connects at least a few heads and cabs at once, so that I can always switch back and forth between them in various ways on the fly.
A few days ago I found out about the Ampete systems. The 444 is one model I got really interested in, but I was wondering if this thing will be auto matching impedances between heads and cabs or if I would need to make sure that the impedance of the cab isn't lower than the one of the amps output myself to avoid any damage.
I know that there are a lot of myths out there, especially regarding impedance, but I thought that at least one thing is safe: Don't run your amplifier into a cab with a lower impedance rating than your amps output impedance. This one rule you can find in a hundred threads, articles and of course even in most manufacturers manuals. Might this be a myth?

Since I wanted to know how the Ampete amp/cab switchers (the 444 in my case) handle different impedances, I got in touch with the company and got back a mail with the manual. I read it and couldn't believe it, so I mailed them a second time and was assured, that I definitely got everything right: You should never run your amp with no load, but according to Ampete a cab even with a lower (!!!) impedance rating than the tube amp will be absoultely fine and won't damage anything (read the manuals pages 16-18 here: http://ampete.com/wp-content/uploads/2014/03/Ampete-444-Manual-Dec14.pdf ).
Their switchers protect the amps with a certain load as soon as they are connected, but when they are patched into a cab they just let the signal flow no matter if it's a 16 Ohms head into a 4 Ohms cab, a 8 Ohms head into one 8 Ohms and one 4 Ohms cab or whatever. And only because physics allow you to do so. With or without the Ampete gear - always.

I was a little shocked, because why does nobody know that? I mean, there are devices like the Fryette Power Station, that has a input and output impedance selector to be able to match amps and cabs with different impedances from 4 to 16 Ohms. In case Ampete is right - why?
I mentioned earlier that I'm not into physics that much, so I'm just telling you what I read and what I have been told. But Ampete is a well known company. I mean, Dave Friedman does like their switchers. They also have set up their switching system in a large testing room of a well know store in Germany as well ( http://gearhead-distribution.com/images/brands/Ampete/Artists_User/MP-Showroom-01.jpg ). And I bet they have tested what they sell (and write). So...WTF?!?

At this point, this seems to be a game changer to me. And now it's your turn. Let the fighting begin... ;)
Click to expand...

who are you going to believe....an amp manufacturer with liability, or a switch manufacturer with absolutely no liability regarding your amp?
 
steve_k":1uv5arlj said:
who are you going to believe....an amp manufacturer with liability, or a switch manufacturer with absolutely no liability regarding your amp?
Click to expand...

Well, as mentioned, I'm no tech myself. And I don't say that what's written and told by Ampete is correct. But I ain't saying it's wrong either. I just can't make the judgment as I'm no expert. But I've read a bunch of controversal stuff about impedance before and it didn't clearify anything for me, because there were different opinions shared by different people who all claimed they were right and in some cases even experts. And as you can see, it does start again... ;-)

The claim by Ampete is that astonishing to me, that it excels the discusssions I read before. I can't judge it as a tech, that's just not my area of experetise, but based on a common sense, Ampete has to be be right. Because could and would they take that much of a risk if they weren't 100% sure? In case I'll buy a Ampete 444 and use it as I've been told, what would I do when my or my clients amps got damaged? Yes, I wouldn't be amused, I would never buy one of their products again and I might give them a bad rating in a forum like this. So, that's why I tend to believe them - based on common sense. And by the way, Ampete is a boutique amp builder as well. So, there is some credibility for sure.

In the end, I don't want to convince anyone. I just found something that I feel is worth sharing. I wanted to watch the thread and see what happens. And it did start as expected. :D

AND PLEASE READ THE MANUALS PART ABOUT IMPEDANCE!!! It just does not make sense when you go: "Well, I don't have to read that as I just know better already..."

By the way, it might be important to inform everyone, that I just updated the manual link and the part regarding the Power Station in my original post.
 
glip22":1w0ggfbw said:
If you have a 16 ohm cab you can plug into 8 or 4 with no issue. Vice versa is here you will stress your OT and can easily wind up with a shorted transformer. I think that is the way it works, especially with modern transformers. Some of the old ones were so overbuilt they may have handled it.
Click to expand...
I always thought this was the case too. If you do mismatch this way though you stress your tubes harder.
 
Racerxrated":1gazcdsp said:
glip22":1gazcdsp said:
If you have a 16 ohm cab you can plug into 8 or 4 with no issue. Vice versa is here you will stress your OT and can easily wind up with a shorted transformer. I think that is the way it works, especially with modern transformers. Some of the old ones were so overbuilt they may have handled it.
Click to expand...
I always thought this was the case too. If you do mismatch this way though you stress your tubes harder.
Click to expand...
Thats what I thought but I never had an issue doing it but I usually just match my cab to my amp. It's not something I need to worry about and James would know. He's about as tech geek as they come.
 
In my avatar, there is a 1971 Ampeg V-2 cab, it is 60 watts and 8 ohms, I ran a Peavey Rockmaster preamp into a Peavey classic 120 power amp at 16 ohms and look what it did to it.. blew the grill off, ragged the speakers out, pure brutal DESTRUCTION! :LOL: :LOL: I really did run it that way from 95 to 2008, the amp is fine, the cab looks rough, but is a beast, the tubes are the super 6 6l6gc str387, made in USA, and they still test like new, I thought it would mess it up, but it had a better sound at 16 ohms than at 8 so.. I ran it that way. I'm no tech whatsoever, but that's just my experience with it.
 
HilltopExplosion":3tol6cbc said:
In my avatar, there is a 1971 Ampeg V-2 cab, it is 60 watts and 8 ohms, I ran a Peavey Rockmaster preamp into a Peavey classic 120 power amp at 16 ohms and look what it did to it.. blew the grill off, ragged the speakers out, pure brutal DESTRUCTION! :LOL: :LOL: I really did run it that way from 95 to 2008, the amp is fine, the cab looks rough, but is a beast, the tubes are the super 6 6l6gc str387, made in USA, and they still test like new, I thought it would mess it up, but it had a better sound at 16 ohms than at 8 so.. I ran it that way. I'm no tech whatsoever, but that's just my experience with it.
Click to expand...
:LOL: :LOL: :rock:
 
HilltopExplosion":40nfvm3z said:
In my avatar, there is a 1971 Ampeg V-2 cab, it is 60 watts and 8 ohms, I ran a Peavey Rockmaster preamp into a Peavey classic 120 power amp at 16 ohms and look what it did to it.. blew the grill off, ragged the speakers out, pure brutal DESTRUCTION! :LOL: :LOL: I really did run it that way from 95 to 2008, the amp is fine, the cab looks rough, but is a beast, the tubes are the super 6 6l6gc str387, made in USA, and they still test like new, I thought it would mess it up, but it had a better sound at 16 ohms than at 8 so.. I ran it that way. I'm no tech whatsoever, but that's just my experience with it.
Click to expand...

Sometimes playing is better than talking. That's rock n roll! :D
 
Plugged in plenty mismatched.. $3K to $300... fear of breaking your gear, do what they (manual) suggests ;)

Know the rules to break them.
 
Hi again and first of all thanks for taking part to everyone.

What I really would like to see as an addition, is that some more manufacturers and techs are taking part, reading what the guys from Ampete have to say and giving their view on it...

That would be cool, as I think this is a really intersting topic.

EDIT: I just invited some guys from the manufaturer forums. I guess I started with only five for the beginning, so that everything can stay clear and it doesn't become a mess. Hope to get some nice input... :rock:
 
Interesting stuff for sure, but I would follow the manual of the manufacturer. They grant the warranty on your amp, not the amp switcher company. I'm no tech at all and very carefull, so this is the common sense that I use. Having said that, Mesa Boogie give a few examples of safe mismatches. They know what the OT can handle. Check out the manuals of the Mark or recto series on their website. Here is a part from it:

Wiring up speakers to provide the most effective load and making sure that all of them are in phase will help in creating the best sound possible. This is not too difficult, as long as you understand a few things about loading and how to connect your speakers to provide an optimal resistive load.
MESA/Boogie amplifiers can handle 4 and 8 ohms effectively. Never run below 4 ohms in a tube amplifier unless you are absolutely certain that the system can handle it properly; this can cause damage to the Output transformer. A few amplifiers can handle 2 ohms effectively without damaging them ( for example the MESA’S Bass 400+ ). You can always have a higher resistance ( 16 ohms, for example ) without damaging results, but too low of a resistance will likely cause problems.

MIS-MATCHING: When running a higher resistance ( for example: 8 ohm output into 16 ohm cabinet ), a slightly different feel and response will be eminent. A slight mismatch can provide a darker smoother tone with a little less output and attack. This response is a result of the amplifier running a bit cooler. Sometimes when using more than one cabinet a mismatch will be the only option.
 
Laurens":1m3v99ub said:
Interesting stuff for sure, but I would follow the manual of the manufacturer. They grant the warranty on your amp, not the amp switcher company. I'm no tech at all and very carefull, so this is the common sense that I use.
Click to expand...

Well, then I guess we are much alike here. I tend to be super carefull as well. But the Ampete company isn't just anybody. They do R&D for some renown companies and warranty repairs for brands like 65 Amps, Bad Cat Amplifiers, Hughes & Kettner, Friedman, Custom Audio Amplifiers and Suhr. That's why I was surprised and got seriously interested in their point of view. And of course they assured, that they have done some serious testing regarding this topic.
 
There is no rule of thumb other than "be careful" and to follow the instructions of the manufacturer of your specific product. By default, always match impedance since it's the safest way to go. That information I linked to is the reason.

The idea that "modern transformers can handle big mismatches" doesn't speak for all situations. What if your newer amp's transformer is somewhat more prone to failure from a mismatch in impedance since it's a "clone" of an older transformer or just designed to be like one (including using material types more common for the time). There's a revival of "new old-school designs" where the idea is to be "as close to the original old design as possible", and all shades between that and "more modern designs" these days.

And what about those flyback spikes. So what if the output transformer can take it--what about your tubes and other components in the power supply (including the sockets themselves). Ever see a socket that's been ruined from an arc? It can have conductive material left behind after an arc, from pin to pin, that you can't just scrape off since it actually penetrates the material of the socket. In that case, the socket needs to be replaced, and that's no fun. Best-case scenario, you blow a tube; great, now effectively there goes a set of tubes!

Sorry if I come off like a jerk over this. I just don't see what the big deal is about matching impedances, like it's some awesome idea that you don't have to match them. :) I'm not going to read specifics from any one manufacturer on their take on this since it's not necessary in general. If I'd have saved all the parts that have fried from amps I've repaired from mismatching impedance (and cranking the amps--the two together are what really make it a problem), I could dump a bucket of gross burnt garbage at your feet as evidence. :) Included in that garbage would be some flyback protection diodes...yes, sometimes they fail too.
 
Regardless of what Ampete says... why change the rules now? I worked at WGS guitar speakers & Acoustic Design Inc. years back and they have over 60 years experience in all aspects of physics and how magnetic fields respond to iron with different impedances and conditions. Basically to make this short, I don't have a physics degree, but if the CEO and all the Physicists of Acoustic Design & WGS Speakers (who makes speakers for countless boutique guitar and high-end audio amplifier company's) say that you should never have a lower rated impedance speaker to a higher impedance transformer... then I'd abide by that rule. Higher impedance speakers into a lower impedance amp is totally fine, but tones do change with mismatches for better or worse.

Like I said, why change the rules now? I know for a fact that amps work way harder with this mismatch. You can try your luck but I'll stick with the rules that were made decades ago.
 
Adambomb":1vbudt8b said:
Regardless of what Ampete says... why change the rules now?
Click to expand...

I do completely understand where you are comming from. And we are not too far away from another. I don't want to convince anybody, I want to animate you all to think things over any MAYBE (!!!) come to another, new conclusion. What I am wondering is: What if Ampete is right? I mean, it could be.
According to them, some manufacturers put a 'protection system' in their amps cabinet outputs, which is activated as soon as there's no cable plugged into the amp. The cabinet output gets short-circuited, which - according to Ampete - leads to a impedance of 0 Ohms.
In case that's right, either the rules you spoke of (and I learned and believed as well) or those kind protection circuits are absurd.

But again, I'm no expert, I'm just doing some research, passing on stuff I read and asking stupid questions... ;)


EDIT:

JamesPeters":1vbudt8b said:
Here's some info about why impedance matching is important:

http://aga.rru.com/FAQs/technical.html#imp-1
Click to expand...

I just had a little discussion about physics, checked the simple formulas and then read through your link: Very interesting! Most of all because 1. the article says that mismatching one tap (4 into 8, 8 into 4, 8 into 16, 16 into 8) should never damage anything as long as you have a well done amp and 2. plugging (especially) a (pentode) amp into a lower impedance cab should be the safer way than going into a higher impedance cab and only could stress the tubes more. Correct? Because I believe that most people out there would rather go into a higher impedance cab, thinking this is safer. In case I understand the V (or U) = R x I formula right, the voltage will rise the more the impedance rises. Which does make sense to me, because plugging no cab into your amp would lead to a infinite impedance, which would cause a infite voltage and a major damage, right?

PS: No, you didn't come off like a jerk over this. It's all good... ;) Thanks for your input! :thumbsup:
 
Hey man, I wasn't lyin', I ran a 120 watt amp at 16 ohms into a 60 watt 8 ohm Ampeg V-2 cab for at least 10 years, and still fire it up every now and then. Everything still works fine. Looks like hell, but thumps like nothing Ive ever heard. These are not at bedroom levels, I'm talk'n OH MY GOD MY EARS ARE BLEEDING! levels. Did I get lucky? Maybe.. but there has to be something to what you are finding out. I just learned 16 into 8 should never damage anything... My amp and cab are built like tanks (apparently). Thanks!
 
I have an electrical engineering degree. I can still remember one day in class where the prof derived what can happen to a certain amp topology when it is unloaded in terms of the EMF at the output. It was pretty amazing. At that point I had not realized anything other than a short on an output could blow up an amp.

The manufacturers' recommendation are surely padded to protect their a** but the truth is :
1. the importance of impedance/load is dependent on the amp design (some designs handle mismatches better, some cannot handle an open, other cannot handle a short), but very real.
2. Impedance is more complex than a single ohm resistance rating on a speaker; it is a dynamic quantity. A speaker is a magnet and coiled wire system that has more than going on than the simple resistance numbers and the measured impedance varies as the speaker is driven. As such the manufacturer is going to have to guess somewhat when recommending a load rating and guess which direction they're going to go with that?
3. You will hear a lot of stupid sh*t on the 'net from people who have no underlying knowledge of what they are talking about other than some handful of specific cases (NOT talking about dudes like James who is a real authority and builds kick ass amps). Some of the anecdotes may apply to you, some may be made up, some may have no bearing but sound relevant. They are probably trying to help. They are probably sincere. But so are people who claim to have been abducted by UFOs.

Bottom Line: You have not discovered some grand conspiracy and it is probably worth following manufacturers recs when loading amps even if they may be a little conservative...
 
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