Is this bad or is the opposite bad?

Bael · Post by **Bael** » Wed May 10, 2006 12:40 pm

I was running my rocker 30 head at 8 ohms into my 16 ohm 2x12 orange caninet. This can't hurt anything, right? It would actually strain the amp less, if I'm ot mistaken. If it was the amp at 16 ohms going into an 8 ohm cab, that would be bad. Is that correct? Is my little baby OK?[:0]

riffmonster · Post by **riffmonster** » Wed May 10, 2006 1:23 pm

I always get a headache reading about cabs, ohms etc.

I think you're right, but it might be best to run it through the technical forum - to confirm.

Might also be worthwhile using the 'search' (top right) to see if this has come up before.

Hope that's some help!

Andy H. · Post by **Andy H.** » Wed May 10, 2006 1:24 pm

Your little baby would always prefer to be correctly impedance matched. And basically the way you did it is the more dangerous way to go for your amp. Heres what I wrote the other day on another forum.

(Edited from here:
http://vintageamps.com/plexiboard/viewtopic.php?t=48319)
<blockquote id="quote">quote:<hr height="1" noshade id="quote">If you are going to mismatch VALVE amps it is actually less bad, (for the amp), to mismatch to a lower impedance, (eg. amp OT 16 ohms into 8 ohm cab), rather then higher.

Unlike ss. amps, valve amps are basically self limiting current wise (the valves!) into a lower impedance, though the valves will take more wear. Into a too high impedance the risk is different - potential very high flyback voltages can fry the OT. But most valve amps with strong output transformers will take a 1/2 to 2x mismatch without complaining, so you should be okay Alltweed.

(Not recommended but technically you can short circuit a valve amps output (0 ohms) without frying it - it is trying to put a signal into an open circuit (virtually infinite ohms) that is a real killer. Total opposite from ss amps of course - short circuits will kill the power transistors pronto, but they'll sit happily all day with no speaker load applied...)

Be aware that you'll always get the highest power output from a valve amp when correctly impedance matched - you'll always lose some power output going high OR low.<hr height="1" noshade id="quote"></blockquote id="quote"> To be honest if it was me I'd just match impedance correctly!

Andy.

Amoun · Post by **Amoun** » Wed May 10, 2006 1:25 pm

Running from the 8 ohm output into 16 ohms will give you reduced power, but it won't sound as good, it may damage your amp too

And the other way around will damage your amp.

Amoun · Post by **Amoun** » Wed May 10, 2006 1:26 pm

haha ther were no replies when i started typing, when i posted there were 2

maybe i should type faster

riffmonster · Post by **riffmonster** » Wed May 10, 2006 1:28 pm

I presume that was a ****-up?

hopefully no damage done..

Rally Car · Post by **Rally Car** » Wed May 10, 2006 7:28 pm

As long as the impedance of the cab is higher than the impedance of the amp the amp will be fine. But you should use it at the propper ohms setting for the best result.

rrrajo · Post by **rrrajo** » Wed May 10, 2006 7:38 pm

If you match the impedance correctly, you will never have anything to remember formula-wise.

Andy H. · Post by **Andy H.** » Wed May 10, 2006 8:58 pm

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Rally Car
 As long as the impedance of the cab is higher than the impedance of the amp the amp will be fine. But you should use it at the propper ohms setting for the best result.
<hr height="1" noshade id="quote"></blockquote id="quote">Sorry, but that is WRONG! That is the rule which applies to solid state amps, but the R.30 is a valve amp...
(Second bit is right though - match correctly if at all possible!

)

Andy.

Rally Car · Post by **Rally Car** » Wed May 10, 2006 9:12 pm

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Sorry, but that is WRONG! That is the rule which applies to solid state amps, but the R.30 is a valve amp...
(Second bit is right though - match correctly if at all possible! )

<hr height="1" noshade id="quote"></blockquote id="quote">

Not true. With Valve amps as long as you have the impedance of the cab higher than the amp you will be ok. So if you run an 8 ohm amp into a 16 ohm cab there will no problems. But if you run a 16 ohm amp into a 4 ohm cab you will blow up your transformer.

I'm positive that is how it works. I've been told so by the guy who designed the Ultimate Attenuator www.ultimateattenuator.com and he also builds amps and he has been fixing and making tube amps for 40 years. That's how it works. I know for a fact because the ultimate attenuator has a load of 32 ohms and in order for the amp to work comftorbly you have to set it to 8 ohms.

Andy H. · Post by **Andy H.** » Wed May 10, 2006 10:13 pm

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Rally Car
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Sorry, but that is WRONG! That is the rule which applies to solid state amps, but the R.30 is a valve amp...
(Second bit is right though - match correctly if at all possible! )

<hr height="1" noshade id="quote"></blockquote id="quote">

Not true. With Valve amps as long as you have the impedance of the cab higher than the amp you will be ok. So if you run an 8 ohm amp into a 16 ohm cab there will no problems. But if you run a 16 ohm amp into a 4 ohm cab you will blow up your transformer.

I'm positive that is how it works. I've been told so by the guy who designed the Ultimate Attenuator www.ultimateattenuator.com and he also builds amps and he has been fixing and making tube amps for 40 years. That's how it works. I know for a fact because the ultimate attenuator has a load of 32 ohms and in order for the amp to work comftorbly you have to set it to 8 ohms.
<hr height="1" noshade id="quote"></blockquote id="quote">Yes I well remember you being keen on the UA Rally Car. You probably also remember some discussions about it, and about Mark Gregg of UA. For example:
http://forum.orangeamps.com/viewtopic.p ... attenuator

(Though didn't you come up with some other guy in Canada who actually came up with the design in the first place?)

Anyway, thing is that...
The 'UA' isn't just an attenuator. It is a dummy load / reamping system.
There is a solid state amp in it in fact, which is why you can use it in the manner you are suggesting.

What I am saying about valve amps is correct. I have linked to various sites and texts supporting that view many times here, and sorry but I don't intend to again tonight. It is all on the forum though and if you want then please do a search on the subject using my name. (Though unfortunately the Gear Page where some of those links are to is down meantime.) But I stand by what I am saying here 100%.

Solid State amps: Safe with rated load or with any higher impedance speaker load (up to and including an open circuit ie infinite ohms.) Develop less power as impedance increases. Do not short circuit (0 ohms) as this is sudden death for the output transistors.

Valve amps: Match impedance if possible. If mismatching it is safer for the amp to mismatch low. This will wear the valves but the amp shouldn't suffer. A short circuit (0 ohms) is normally survivable.

If mismatching high there is a risk to the OT, which increases with the severity of the mismatch, and with how hard you are pushing the valve output section. The ultimate 'high' mismatch is no speaker load ie infinite ohms. If trying to pass a signal into this then there is a severe risk to the OT from high flashback voltages which can arc through the insulation layers and burn out the tranny.

Mismatching between 1/2 and 2x the impedance the amp 'expects to see' is normally problem free for most amps with healthy OTs. It is never guaranteed safe though, and being manufacturer specific Marshalls fail much more often when doing this then Fenders do...

Andy.

Bael · Post by **Bael** » Thu May 11, 2006 12:33 am

I did a little research and you're right. As long as the cab is a higher ohm than the head it is safe; not the other way around. Thanks.<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Rally Car
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Sorry, but that is WRONG! That is the rule which applies to solid state amps, but the R.30 is a valve amp...
(Second bit is right though - match correctly if at all possible! )

<hr height="1" noshade id="quote"></blockquote id="quote">

Not true. With Valve amps as long as you have the impedance of the cab higher than the amp you will be ok. So if you run an 8 ohm amp into a 16 ohm cab there will no problems. But if you run a 16 ohm amp into a 4 ohm cab you will blow up your transformer.

I'm positive that is how it works. I've been told so by the guy who designed the Ultimate Attenuator www.ultimateattenuator.com and he also builds amps and he has been fixing and making tube amps for 40 years. That's how it works. I know for a fact because the ultimate attenuator has a load of 32 ohms and in order for the amp to work comftorbly you have to set it to 8 ohms.
<hr height="1" noshade id="quote"></blockquote id="quote">

Bael · Post by **Bael** » Thu May 11, 2006 12:36 am

No, I'm sorry but you're mistaken. I'm to lazy to link up what I found but doing some research, all info says that if the cab is higher than the amp ( 8 ohm amp into 16 ohm cab) it is safe. The link you have is just some other dude on a forum saying something is right or wrong; exactly the situation we have here. If you try to ram more juice down a cab that can't take it (16 ohm amp into 8 ohm cab) you can blow a transformer. Just to let you know. Now don't get mad or anything, I'm just trying to inform you as to what a few reputable FAQ amp sites had to say about the subject. And thanks for the advice to just try and match the amp and cab in the future.

]<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Andy H.
 Your little baby would always prefer to be correctly impedance matched. And basically the way you did it is the more dangerous way to go for your amp. Heres what I wrote the other day on another forum.

(Edited from here:
http://vintageamps.com/plexiboard/viewtopic.php?t=48319)
<blockquote id="quote">quote:<hr height="1" noshade id="quote">If you are going to mismatch VALVE amps it is actually less bad, (for the amp), to mismatch to a lower impedance, (eg. amp OT 16 ohms into 8 ohm cab), rather then higher.

Unlike ss. amps, valve amps are basically self limiting current wise (the valves!) into a lower impedance, though the valves will take more wear. Into a too high impedance the risk is different - potential very high flyback voltages can fry the OT. But most valve amps with strong output transformers will take a 1/2 to 2x mismatch without complaining, so you should be okay Alltweed.

(Not recommended but technically you can short circuit a valve amps output (0 ohms) without frying it - it is trying to put a signal into an open circuit (virtually infinite ohms) that is a real killer. Total opposite from ss amps of course - short circuits will kill the power transistors pronto, but they'll sit happily all day with no speaker load applied...)

Be aware that you'll always get the highest power output from a valve amp when correctly impedance matched - you'll always lose some power output going high OR low.<hr height="1" noshade id="quote"></blockquote id="quote"> To be honest if it was me I'd just match impedance correctly!

Andy.
<hr height="1" noshade id="quote"></blockquote id="quote">

Andy H. · Post by **Andy H.** » Thu May 11, 2006 10:40 am

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Bael
 No, I'm sorry but you're mistaken. I'm to lazy to link up what I found but doing some research, all info says that if the cab is higher than the amp ( 8 ohm amp into 16 ohm cab) it is safe. The link you have is just some other dude on a forum saying something is right or wrong; exactly the situation we have here. If you try to ram more juice down a cab that can't take it (16 ohm amp into 8 ohm cab) you can blow a transformer. Just to let you know. Now don't get mad or anything, I'm just trying to inform you as to what a few reputable FAQ amp sites had to say about the subject.* And thanks for the advice to just try and match the amp and cab in the future.

]<hr height="1" noshade id="quote"></blockquote id="quote">

Certainly not going to get mad Bael, Rally Car - no sweat there!

But this is important stuff, and the advice that it is safe to run the amp as long as it is going into any higher impedance load is plain dangerous for valve amps!!! (It is of course the correct advice for solid state amps!)

So I'm happy to go into this once again, in a bit more detail. Please at least keep an open mind meantime and really read the links I give.

*I would like you to link to what you found, because while that is correct for solid state amps, it is absolutely wrong for valve amps!!! Please bear in mind that even reputable amp companies are known to put out incorrect information BTW. Usually just making a statement without really backing it up. (Not least Orange, with many simple technical mistakes sadly still on their site, but there are plenty of others too...

)

Also just picking out snippets can have you thinking they are talking about one type of amp (eg valve), when they are perhaps referring to ss amps at that point...

At any rate I'm trying to back up what I say here with clear and detailed explainations, and not just giving my opinion, okay folks?

There is a lot of misunderstanding about impedance and mismatching issues, but I repeat that the advice I'm giving is correct for valve amps. (The exact opposite is true for solid state amps, but they work very differently, usually having no output transformers for starters!)

Yes running 8 ohm amp --> 16 ohm cab is probably within normal safe limits (within 1/2 to 2x impedance range) for most valve amps. In fact you'll often get away with playing Russian Roulette by running a 4 ohm amp to a 16 ohm cab, but the risk to transformers is definitely greater when going into a higher then intended impedance. You really are always better to have the speaker impedance lower if mismatching! If you value your amp that is. Going lower strains the valves more then normal, but they are disposable in a way that the output transformer isn't. (Which is after all why valves are removable from their sockets...)

Since I'm no longer just heading to my bed, as I was last night, I'll happily take a little more time to link to some of the places which will confirm all of this:

Randall Aitkens general and technical sites are very good. He is one amp designer who really knows his stuff and cuts through the voodoo:

http://aga.rru.com/FAQs/general.html#imp-1
http://aga.rru.com/FAQs/general.html#imp-2

And in more detail, with some more theory and reasoning behind it:
http://aga.rru.com/FAQs/technical.html#imp-1
http://aga.rru.com/FAQs/technical.html#imp-2
(Not quoting these as they go direct to the question in hand. Please do read them through - they are fairly short.)

http://www.geofex.com/
--> Tube amp FAQ (top left of the page),
then scroll down the index bar. There are a lot of transformer topics. Click on 'Match speakers to output impedance?'.
(Which I've edited here, but please do read the whole topic - explainations and all are given! AH.)
<blockquote id="quote">quote:<hr height="1" noshade id="quote">
Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
Say for example you have two eight ohm speakers, and you want to hook them up to an amp with 4, 8, and 16 ohm taps. How do you hook them up?

For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load...

(Two 8 ohm loads in series --> 16 ohms, in parallel --> 4 ohms. AH)

...Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.

Extended A: It's almost never low impedance that kills an OT, it's too high an impedance...

(Plenty more explaination about why... AH)
<hr height="1" noshade id="quote"></blockquote id="quote">

This is a great guide to working out what is happening with those confusing amp / cab impedances, and the different rules between solid state and valve amps. Doesn't go into mismatching with valve amps, just advising not to - reasonable advice!

http://ebassist.com/vb3/showthread.php?t=11117

It is a great pity that 'The Gear Page' forum is offline right now. There is a wealth of tech discussion from some very knowlegeable bods* there. Hopefully it will be back in a few days. Here are some more links to go back to for when it is:
http://www.thegearpage.net/board/showth ... post544946
http://www.thegearpage.net/board/showth ... nce+switch
http://www.thegearpage.net/board/showth ... t=mismatch
http://www.thegearpage.net/board/showth ... p?t=123067
http://www.thegearpage.net/board/showth ... p?t=126001
*(I'll just remind that John Phillips on TGP forum used to be my own amp tech in Scotland and remains a close friend. He is a total walking encyclopedia on valve amps, and is one of the most respected tech bods on that forum. Even builders there readily admit to learning a lot of stuff from him. I know I have...!)

And just in case you thought I hadn't had this discussion before, (as if...), here is a fun thread... [:p]
http://forum.orangeamps.com/viewtopic.p ... hichpage=1
The unfortunate gaps in the thread, partially filled in by quotes, were due to one of our regulars contributors who self censored ALL of their own posts at one point. (Not just the ones on that thread!)
Ah, that takes me back...

:)[:p]

<hr noshade size="1">

Now I've presented you with a lot of stuff. But it is not just opinion, it is backed up by hard facts! If you are going to experiment with mis matching impedances then those are facts worth being aware of. If you choose not to accept them then fine, it is your gear!

But the facts with valve amps are...
(just one last time - I'm nearly done now - honest!

)

Too high impedances on the speaker outputs are much more dangerous for valve amps then too low impedances are.

You can short circuit the + and - speaker output connections by connecting them together. (This gives very low impedance, close to zero ohms.) Valve amps can survive this.

But if you don't believe me then try this: power up your own valve amp, unplug your speaker, take it off standby and crank that baby into an open circuit very high impedance load. (Fresh air)
You stand a very good chance of frying your amps OT!

This isn't just theory - it happens often!!! [:0]

HAVE A NICE DAY!

Andy.

riffmonster · Post by **riffmonster** » Thu May 11, 2006 10:57 am

blimey! now i've really got a headache...

Thanks for the info!

Is this bad or is the opposite bad?

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