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Discussion Starter #1
Can't remember how this works. Would this be okay?? Not a very powerful 16 ohm amp.
 

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Not advisable, will probably work.

What is the amp?

I was reading an old Peavey manual for a 4 ohm amp, it said 2 ohms can be used with a risk of damage to the transformer. No one would write that these days.
 

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Lowering the speaker impedance stresses the output transformer, causing overheating and possible failure of the transformer. Big iron transformers, like those in old Fenders and Peaveys, can normally handle it for awhile. That doesn't mean it's a good idea.

Going the other way, 8ohm amp into 16ohm speaker, doesn't do much damage, but you lose a lot of the amp's efficiency.
 

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Lowering the speaker impedance stresses the output transformer, causing overheating and possible failure of the transformer. Big iron transformers, like those in old Fenders and Peaveys, can normally handle it for awhile. That doesn't mean it's a good idea.

Going the other way, 8ohm amp into 16ohm speaker, doesn't do much damage, but you lose a lot of the amp's efficiency.
Nope.
 

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Let's just say, you've opened a can of worms. Lol.

You'll hear experienced amp techs and professional builders argue passionately for either of the following points:
- You should never mismatch impedence
- You're safe going up or down by one level (8 into 16, 16 into 8, 8 into 4, or 4 into 8. But not 16 into 4 or 4 into 16)
- You're only safe going up one level
- You're only safe going down one level (like your example)

Best of luck sorting through it all! :confused:

I say go with the advice of the maker of the amp you own. Especially if it is under warranty.
 

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The amp is a One watt Marshal DSL tube amp. I also have a 15 watt Fender with an attentuator. I have a 1x10 cab with an 8 ohm speaker I was hoping I could just flip the chord from one amp to the other. I just play at home in an apartment. Don't want to get another cab. Stacking one head on top of the other fits nicely, especially in an apartment
 

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The amp is a One watt Marshal DSL tube amp. I also have a 15 watt Fender with an attentuator. I have a 1x10 cab with an 8 ohm speaker I was hoping I could just flip the chord from one amp to the other. I just play at home in an apartment. Don't want to get another cab. Stacking one head on top of the other fits nicely, especially in an apartment
I'm not experienced with those amps in particular, but you should have no issues. If it was an old Fender you wouldn't ever worry about it at all.

The Weber Z Matcher is also a cool piece of gear. I love mine. It lets me safely use my 8 ohm vintage Jensen in my 2 ohm Super Reverb.
 

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Discussion Starter #9
The Fender is a Tube/DSP hybrid (Super Champ X2), but I usually use an attenuator to push it into tube over drive.
 

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Marshall doesn't want you to do it.

"WARNING: Only ever connect a single 1 x 16 Ohm speaker cabinet. Any other speaker configuration may stress the power amplifier section and in extreme cases may lead to valve and/or output transformer failure."

Someone posted recently in this or another forum that solid-state amps can usually go up in ohms, but tube amps can't, because in a solid-state amp (without an output transformer?) you are lowering the power, but in a tube amp you are getting the tubes to work harder, or out of their range, or at a higher voltage or something.

I wouldn't do it.

I think the solution in the other forum was to add a series resistor or get a different speaker.

The Z matcher does like a sound good, or a 16 to 8 ohm transformer. You may be able to do that cheaply.

The Z matcher could solve lots of problems! Like, how do I use my 2 ohm Suoer Reverb with a load box. I want one!

You don't need 100W, but I can't find cheap transformers.
 

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the transformer on the amp is rated for X ohms, so when you plug your speaker in, it expects to see X ohms with the amp turned on. If it sees a different resistance number it will try to compensate. So in the scenario of 16 into 8 ohms, voltage at the speaker rises but current is only about 1/2 of what the transformer is supposed to be putting out.

8 ohms into 16 causes current to rise and voltage to drop, so the transformer is putting out too much current and not enough voltage, too much current equals too much heat in most cases.

So if you have to mismatch bigger into smaller is better for the transformer
 

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Everybody seems to have differing opinions on this, but it basically boils down to two things. The actual design of the amp, and the quality of the transformer.
I will attempt to correct some of the basic misconceptions, and hope this doesn't get too wordy.

Transformers have an impedance based on many factors - its wiring resistance, inductance, and a variety of capacitance. However the impedance are based on turns ratio and an abstract called reflected impedance. Reflected impedance (RI) is the impedance of one side when the other side is loaded based on the turns ratio. So if your tranny is supposed to be rated at 8 ohms, and has a turns ratio of 20:1 then the impedance ratio is the square of the turns ratio 400:1. So in our example the primary impedance would be 8x400 = 3200 ohms. IF the amp is designed to run the tubes at 3200 ohms all is well. If we connect a 4 ohm load to the transformer then the load on the tubes is 4x400 = 1600 ohms.
This will result in an increase in current and runs the tubes harder. If the tubes and transformer can handle the current then the result is a loss of power at the speaker due to a mismatch at the tubes (they want to see the 3200), if the mismatch is the other way 16 ohms load, then the tubes see a decrease in current, and still have a reduction in power due to a mismatch.
It is all about what the tubes want to see to make them run as the designer intended. The current in first example is usually not a problem, as the tubes will cut off sooner and still not be run as theoretically possible. In the second example they can't supply enough current.
These examples also don't take into account the bias on the tubes, and the actual plate voltage on the tubes. Both of these factors will change the impedance the tubes want to see.

Bottom line is, a mismatch either way is not necessarily going to destroy either the tubes or the transformer, it should just result in a loss of power. Unfortunately a lot of transformers are made so poorly they can't take the added current of a low mismatch and the higher mismatch results in the tubes running poorly. You have no way of knowing if any of this is going to destroy a transformer except for other peoples experience, and the manufacturer's say so. I doubt though, that under household use, you will have a problem

Right now I need to replace an output transformer in a Marshall JCM2000 DSL201 amp. It died just because it is not big enough for the task, and is quite frankly a poor transformer. I've also owned an old Traynor bass amp that had a transformer so large you couldn't hurt it no matter what you did.
 

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A speaker with a bigger number of ohms plugged into a transformer with a smaller number of ohms?
Only read the last line? If you are going to mismatch it is better for the transformer when output in ohms is larger than the speaker. If the transformer has less ohms than the speaker you take the chance of overheating the transformer.
 

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Z-Matcher-100 100w Impedance Matcher

Too bad they don't make a less expensive junior version.
They do make a 50W version and you can buy the transformer.

Peavey used to sell one that could handle 400W that was a repurposed 70/100v line transformer. There are 2W and 5W line transformers, I couldn’t find one that was really cheap from Hammond, but I’m sure there are cheap ones out there.

I was reading some information about using a line transformer for impedance matching. I went in pretty sure I understood everything and came out needing a break. I stopped part way into Turner of Australia’s explanation.
 

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Discussion Starter #17
This is getting more confusing. Experts here,... if have only two choices, which is potentially less a hazard, less stress on the transformer ,...

1) 16 Ohm amp into 8 ohm speaker,... or 2) 8 ohm amp into a 16 ohm speaker
 

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They do make a 50W version and you can buy the transformer.

Peavey used to sell one that could handle 400W that was a repurposed 70/100v line transformer. There are 2W and 5W line transformers, I couldn’t find one that was really cheap from Hammond, but I’m sure there are cheap ones out there.

I was reading some information about using a line transformer for impedance matching. I went in pretty sure I understood everything and came out needing a break. I stopped part way into Turner of Australia’s explanation.
I bought my 50w one on here for 100 used. My 45W Super doesn't seem to stress it any.
 

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Number one. That being said, a 100% mismatch up or down should be easily tolerated.
Agreed. I look at this way, NEVER run a tube amp without a load attached. They don't like high impedance loads. But, you can actually short the transformer and you will do no damage. In fact, Traynor used to use shorting jacks on their heads, so if the speaker got unplugged, there would be no damage to the output transformer.
So 16 into 8 is better.
It's no wonder Marshall doesn't want you to mismatch. I have replaced more Marshall output transformers than any other brand, including HiFi amps (not that it is that many though).
 
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