Hey Guys,
I thought that I had an interchangeable output transformer but I don't, its only an 8 Ohm....... and I have a 16 Ohm speaker.
From my little internet research, it looks like it's not going to be a problem but I always like to hear other's opinion on this stuff in case I need to get a different output transformer or speaker.
Thoughts?:o
It depends on the quality of the design and the output transformer. If it's near the edge, you probably shouldn't do it. But most valve amps will cope with a step up or down in speaker impedance, but they won't be at their best and shouldn't be run near full output if you want the amp to last. It's the sort of thing you'd do to get you through a gig if your own speaker started playing up and borrowed someone else's cab, but it's not really something you want for a permanent solution.
If it were me, I'd get a new 8 ohm speaker for the amp and use the 16 ohm one for another project.
You'll have put a lot of time and effort into the build, so you might as well get it right from the start. Then you can relax and not have to worry about it, ever.
Simon for the win!
Good advice...
Both your safe options involve getting another speaker.
Get a 8 ohm speaker of wattage greater than your amp and run it solo in a 1 x ?? cab.... or
get a 16 ohm speaker of wattage greater than your amp and parallel it with your existing speaker in the same cab and run it as a 2 x ?? cab....
My 2 x 12 cab is two 16 ohm speakers in parallel to give me a 8 ohm load.... A V30 and a G12H Creamback... handles any amp I can hook it up to and sounds nice to boot....
Running mismatched load on a tube amp can be done for low volumes and workshop testing. Problems will arise as the listening volume attempted increases, though there are some amps that will not care. Most often the problem will be unwanted distortion or self squealing or unwanted self oscillation of some type, all being horrible loud sounds to the ear and indicating that the amp is not happy with the current setup. Bad mismatches can damage the amp and output tubes if left in place and not corrected, and the high chance of resulting in expensive repairs being required to the amp.
I think that Simon's advice of a new speaker is the best. Marcel's advice is also good, but I am pretty sure this is for your 5e3 which is a 1 speaker combo.
One more temporary, but safer, alternative to let you test with the 16 ohm speaker is to wire a 16 ohm resistor in parallel to the speaker so your output transformer sees an 8 ohm load. The downside is that half your output power is wasted on the resistor, so volume will suffer. But it will let you test more safely until you get a replacement speaker.
You should be able to use a 16 ohm speaker with output designed for 8 ohms. Everything else being equal an 8 ohm speaker will just not be quite as loud as an 8 ohm. But it will work just fine. The output rating generally shows you the lowest ohm load you can put on the amp. So this should not be a danger to the amp or the speaker.
If you own this speaker, I don't think you lose much by trying it.
If you want it to be louder you either add another 16 ohm speaker or swap for an 8 ohm with otherwise similar specs. If you amp has two speaker outputs and you hook up one to each of the amp's outputs the amp will see 8 ohms. Still fine.
What you don't want to do is go BELOW what your output was designed for.
I don't think the ohms are the issue with mismatching speakers and cabs, but Marcel is certainly right that it can produce some nasty results.
Of course this is very general... Is this for a guitar? Are you building or replacing? What lead to this predicament?
Hey guys that's brilliant advice. Now I have the tech talk to baffle the wife into another speaker purchase.
I knew you'd all come through for me
Sent from my Pixel 3 using Tapatalk
I think this is for the 5e3 that Andy is building.Quote:
Originally Posted by fender3x
Ahhh. Better speaker needed definitely ;-)
Sent from my ONEPLUS A3000 using Tapatalk
Ordered a WGS greenback. Excited
Sent from my Pixel 3 using Tapatalk
Andy, did you order it from The Speaker Factory? The 25w?
If so, Brad's good to deal with. I haven't bought speakers from him, but he re-covered an amp for me a couple years ago. He did very good work.
Yep, I got it from the Speaker Factory (support local eh), I thought about asking him for a swapsies buuuut Sonic gave me an idea for a twin cab....ha ha har....which means I can convince the wife (later on) for ANOTHER speaker purchase!
Attachment 34858
Ah yes, support local. I forgot you're in Brissy. (me too)
I've never built an amp, I stopped "tone chasing" with things like speaker and tube swaps awhile ago. (I still have a dirt pedal problem though :p)
What Amp(s) have you got?
How will you manage the impedance if using the same speaker in a single and later in a twin?Quote:
Originally Posted by Andy40
New speaker for the 5E3 now, then later another 16 ohm speaker to make an 8 ohm 2x12" cab.
I'm down to two now... a Fender Deluxe Reverb Tonemaster (released last year) and a Roland Blues Cube Artist.Quote:
What Amp(s) have you got?
Both around the 1200 dollar mark. I sold my last two tube amps last year.
Of course. I misread Andy's comment about "swapsies", thinking he made a swap rather than just considered one.Quote:
Originally Posted by Simon Barden
I still regret selling my Peavey Classic 50. But the neighbors don't, those things are far too loud for home use.Quote:
Originally Posted by McCreed
That's true for solid state amps, but my understanding (from a chap who designs amps for Mesa) is that valves can be rather more particular. If I remember what he said and understood him correctly then apparently the tubes will get hot and may even overheat.Quote:
Originally Posted by fender3x
It depends on the amp design and the standard of component. It was suggested in the manual for my old 100W Mesa Nomad, that in the 50W/half power mode, you plugged the 8ohm speaker into the 4 ohm output for the correct impedance match (with only two valves working). But it also said that it was fine to leave it in the 8 ohm jack and that it wouldn't cause any damage, you'd just get a fatter, darker sound. But note that it was an output transformer rated for at least 100W, which would be running at 55W, so the mismatch wasn't going to cause the transformer any issues. (at least at one speaker ohmage step difference).
If the question is "is it safe" to run a 16 ohm speaker out of a tube amps 8 ohm jack, I think the answer is yes. Will an "all things being equal" 16 ohm speaker sound the same as an 8 ohm speaker? No, but that is not necessarily bad, particularly if you have high enough power. There's a good article on it here.
http://blog.hughes-and-kettner.com/o...and-impedance/
What Simon describes is what I understand to be generally true. It's why a lower (16 Ohm) resistance speaker sounds quieter than a 8 Ohm.
I think what JimC is referring to is the problem of running with no load. If the amp is "on" a valve amp in particular should have a speaker connected. I don't think it makes a difference whether it's 8 or 16, but their should be some resistance. The other thing that is confusing for a dyslexic person like myself is that "lower" resistance is a higher number.
Quote:
Originally Posted by fender3x
No, no and no for valves. Solid state amps are basically voltage amplifiers, so as the speaker resistance increases, the power output of the amp decreases. Roughly a doubling in speaker impedance results in 50% drop in the output power produced. in So the same model of speaker in a 16 ohm guise will be quieter than the 8 ohm version.
But valve amps are basically current amplifiers, and they need an output transformer to match the speaker impedance to the valve power amp circuitry. Because of this, a 50W valve amp with, 4 8 and 16 ohm output taps on its transformer will put out 50W into a 4 ohm load (using the 4 ohm tap), 50W into an 8 ohm load (using the 8 ohm tap) and 50W into a 16 ohm load (using the 16 ohm tap). But it also means that if you set the tap wrong (or the amp doesn't have a suitable tap for the speaker connected), the amp will see the wrong impedance.
In the case of most valve amps, the output transformer primary also forms part of the output stage biasing circuit arrangements. The speaker impedance is reflected across the transformer and becomes part of the biasing circuit. If that impedance is wrong, the output stage is biased incorrectly and that can result in very unhappy output valves.
At best, the amp will 'sound different' at worst, it will go pop.
Modern amps will normally tolerate a small impedance mismatch e.g. 8 ohm tap into a 16 or 4 ohm speaker,as long as you don't run the amp flat out. But a 4 ohm tap into a 16 ohm speaker is normally pushing the limits. But it really isn't a great idea, especially with vintage amps or faithful copies of them, where the manufacturers normally skimped on equipment ratings to fit the cheapest components they could.
What H&K say should really only be applied to H&K's own amps, where they know the designs and equipment ratings. But don't quote H&K saying it was OK to do a 4 ohm/16 ohm mismatch if you are using a different manufacturer's valve amp and it goes up in smoke!
And never, ever, run a valve amp without a speaker connected.
Well at least I got that part right... I stand corrected! I do not want to be responsible for an amp going "pop"!Quote:
Originally Posted by Simon Barden
SNAP!Quote:
Originally Posted by McCreed
I love my Roland BC Artist! Got all the juicy Tone Capsules too.
I tried the Tonemaster at Guitar Bros but couldn't really get into it due to time and noise restrictions (of course).
Simon and I are on the same page hereQuote:
Originally Posted by Simon Barden
Quote:
Originally Posted by Simon Barden
I thought Valve amps were voltage-amplifiers and Transistor amps are current-amplifiers, there are a few reasons why Valve amps use output transformers, firstly it isolates the high anode voltages on the anodes of the power Valves from the speaker, secondly it transforms the impedance of the speaker up to an impedance that the power Valves are happy working with so they can deliver their maximum power into a speaker load, thirdly the output transformer allows push-pull operation, although some Valve amps use a single power valve.
A typical Transistor amplifier doesn't really need an output transformer because the output is already at a low impedance, however, there have been Transistor amp designs in the past that do use an output transformer, most modern Mosfet amplifiers usually run off a +/- DC supply, usually something like +/- 70V or so, at a few amps, normally the output voltage at the speaker, when the amp is running idle, is usually something close to zero as ideally possible.
Interestingly enough, my Peavey Renown, which is a 100% Transistor/Solid-State 160 Watt amplifier that can handle a minimum speaker load of 4 Ohms (it uses some ICs in the pre-amp circuitry, and two of those metal TO-3 packaged power Transistors in the power amp), uses an output transformer, my guess is that Peavey did that to try and get the amp to sound more Valve-like, they were doing a lot of experimenting with Solid-State amps back in the 80's when Valves were starting to become scarce, personally, I think the Renown has kind of a hybrid Valve/Solid-State sound to it, you can get some good cleans and overdrives out of it, if you set the tone controls, etc right.
On a side-note, here's an interesting Wikipedia page on something called the Maximum Power Transfer Theorem:
https://en.wikipedia.org/wiki/Maximu...ansfer_theorem
It does have some complex maths equations on it, but there are some simple to understand diagrams and explanations on it, this is the main reason why a Valve amp needs an output transformer to match the impedance of the speaker load to the amplifier, although there are Valve amps in existence that don't use an output transformer, these are known as OTL, or Output Transformerless amplifiers, which you'll more likely see used in Audiophile HiFi applications, for example driving a pair of HiFi headphones, I find them quite fascinating, would love to build myself one.
Here's another interesting article I found, it basically shows how a speaker's impedance varies with frequency, I thought it was relevant enough to post a link to it:
http://education.lenardaudio.com/en/05_speakers_3.html
So, what that says is that the 8 or 16 Ohms impedance rating of a speaker is really just a nominal rating.
Nominal, but not that nominal. It's still an indicator of the overall impedance, so a 16 ohm speaker will have a higher overall impedance across the frequency range than an 8 ohm speaker.
Impedance matching (apart from being necessary in this instance to get a lot of power from output valves) is done to get maximum current (and therefore power) transfer from the power section to the speaker. Valve output impedance is well up in the kilo ohms, maybe 8k ohms for a push-pull pair, so you need a high ratio transformer to translate 4, 8 or 16 ohms into the kilo ohms range. So you are using the transformer to turn 4, 8 or 16 ohms into something approaching 8k ohms. So the different impedance the power valve outputs see if the wrong speaker tapping is used isn't in the 4 to 12 ohm range, but the 8k to 32k ohm range. The output transformer is used to keep the impedance the amp sees around that 8k value (or whatever the value is for that particular amp), which is why the amp's power output remains constant despite different impedance speakers being used with it, as long as the correct transformer tapping is used.
Before the advent of transistors, impedance matching used to be the way signal levels were transferred between items of equipment to maximise current transfer, but these days, low impedance signal outputs feeding high impedance inputs are the norm, where it's all about signal voltage levels, not current.
Solid state power amps have a very low output impedance, and can quite happily drive 4 ohm speakers directly, (some can do 2 ohms). But without a matching transformer, the output voltage level remains almost constant but the output current drops as the speaker impedance increases. So as the speaker impedance increases, the amp's output power decreases. Too low a speaker impedance load and a solid state amp can burn out its power transistors as it tries to provide more current than the devices are rated for. But most tranny amps will run all day into an open circuit (though some designs can become imbalanced and don't like it for too long). You can't do that at all for a valve amp.
In that instance, the valve power amp sees an infinite resistance but its still trying to drive a lot of current through the transformer. None of that power is being transferred to the speaker, and it has to go somewhere, namely into heating up the output transformer and the output valves. It's a matter of seconds at any reasonable power output before the transformer winding insulation burns off and shorts out, and/or the valves burn themselves out.
I'm learning things by the minute here:D
Quote:
Originally Posted by Andy40
I think we are all learning things here, including myself.
This is what Dr Z says.
http://www.youtube.com/watch?v=TVVRFv3A-C0
Interesting, thanks.
That's someone that definitely knows their stuff.
That pedal show also did an interesting show on speaker impedance "impy dance" this week.
Sent from my Pixel 3 using Tapatalk
Your experience with your amp build seems to match the Dr Z comments, since you describe the 16 ohm speaker as more compressed and lower volume.
That's what i thought, except because its all subjective, it made me wonder whether because I heard Dr Z say it....does that mean I am listening for it? lolQuote:
Originally Posted by jugglindan
Nah its in comparison to my other Jensen and the greenback. the G12Q is def quieter.