Speaker Loads for a Fender Twin

Grant Johnson · Post by **Grant Johnson** » 11 Jul 2005 8:52 am

Forum Amp Gurus, I have a question or two for you...
I have found a great deal on a Silverface Twin Head CA 1975. If my memory serves me, that is a 4 ohm load correct? I have an 8 ohm Weber 15. Will a 8 Ohm speaker screw up a 4 Ohm output tranny or is that a safe mis-match?

Thanks,
Grant

Ricky Davis · Post by **Ricky Davis** » 11 Jul 2005 8:54 am

It is perfectly safe; you will only loose like 1 number in volume....>I ran a single 8 ohm speaker for years and years and it did just fine. It is the solid state amps you need to worry about ohm load.
Ricky

Stephen Gambrell · Post by **Stephen Gambrell** » 11 Jul 2005 9:16 am

Ricky's right, and he's wrong!
A Twin wants to see a 4-ohm load, but 8 won't hurt it--lower the output, but that's about it. But if you put a 4 ohm speaker in a tube amp that wants to see 8 ohms, you're asking for trouble! Solid-state amps are a LOT more forgiving as far as speaker impedance mismatch.

Grant Johnson · Post by **Grant Johnson** » 11 Jul 2005 9:35 am

Thanks Guys. I knew that Fender Tube amps could handle a mis-match, but I wasn't sure how much and in what direction....

Dave Van Allen · Post by **Dave Van Allen** » 11 Jul 2005 10:39 am

Grant- I predict that once that Weber is "broken in" you are just gonna LOVE that amp!!!

Congrats!

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David Doggett · Post by **David Doggett** » 11 Jul 2005 1:03 pm

Grant, it's kind of subjective how much volume you loose. What seems like one notch on the volume knob to some, seems like about three to me. In previous threads on this, people have gone through a calculation (which I can't remember) that supposedly shows a loss of between a quarter and a third of the potential volume. While even that much might be something you could live with, my objection is I don't want to be carrying around the weight of a 100 watt amp if I am only getting 70 or so watts. Weber makes 4 ohm speakers. I would get one and sell the 8 ohm one. Another solution is to get another 8 ohm speaker in a separate cabinet and connect both speakers in parallel. You get the extra volume of two speakers, and the amp sees 4 ohms. For quieter gigs you could leave one speaker home, but you are still carrying around extra weight.

Bill Yoder · Post by **Bill Yoder** » 12 Jul 2005 4:20 pm

Why not just put a 8 ohm resistor in parallel,bringing the lo0aad to 4 ohms?I did it my twin with an 8 ohm jbl,and i t works fine.Just a suggestion.

Bill Yoder · Post by **Bill Yoder** » 12 Jul 2005 4:25 pm

Why not put a 8ohm resistor in parallel with the speaker bringing the load to 4 ohms.i did it in my twin with a 15" 8 ohm jbl,and it works great.just a suggestion

Bill Yoder · Post by **Bill Yoder** » 12 Jul 2005 4:26 pm

sorry i posted twice,fast fingers i guess.

Ken Fox · Post by **Ken Fox** » 12 Jul 2005 4:57 pm

You could do that, but it best be a 100 watt (foot long resistor or a fire will result! I use a 200 watt resistor at 4 ohms as a test load for amp repair! It is huge.

Actually I agree, a mismatch at an 8 ohm load is fine. You will just get less power out of the Twin. You can also pull two of the power tubes and the amp would be correctly matched for an 8 ohm load. It would then basically be the same as a Super Reverb, a 40-50 watt amp. No advantage there, as you already had a Vibroverb at 40-50 watts!

Grant, if that is a 135 watt Twin then there is a way to get at the 8 ohm tap. Those amps had the UL transformer and had a 4 ohm tap for the main and an 8 ohm tap when using an extension speaker. Thru the jack switching contacts the external 4 ohm speaker would be placed in series with the internal 4 ohm load and switched to the 8 ohm tap.

Email me if needed and I can go over a way to do that with a shorting jack.

Donny Hinson · Post by **Donny Hinson** » 12 Jul 2005 5:28 pm

Why not put a 8ohm resistor in parallel with the speaker bringing the load to 4 ohms. I did it in my twin with a 15" 8 ohm jbl,and it works great.

Yeah Bill, it "works", but you're likely not gaining anything. In fact, you're probably losing more power in the resistor than you would via just the speaker impedance mismatch.

Perfect matches give you maximum power. But if you're not using maximum power, who cares? Fenders are pretty forgiving of a mismatch. As long as you still have enough headroom (not pushing the amp into clipping), ignore the losses a few ohms mismatch might cause.

Grant Johnson · Post by **Grant Johnson** » 13 Jul 2005 10:34 am

Thanks Guys...
I am going to make it easy on myself as the only electronics work that I am comfortable with is soldering pick-up leads and speaker wires!
I am going to try the eight ohm mismatch and If I do not have the needed head-room, I will sell the speaker and buy a four-ohm.

Ken- BTW I still have the Vibroverb, I can't bring myself to sell it for all the obvious reasons!

[This message was edited by Grant Johnson on 13 July 2005 at 02:01 PM.]

Jack Francis · Post by **Jack Francis** » 13 Jul 2005 11:14 am

I have an old black face Fender Super Reverb amp that someone cut down to a head.

I am currently running it through a Celestion 15" speaker and it sounds pretty good.

I realize that it wants to see 2 ohms so I bought a transformer from Weber Speaker guys that will allow it to use 2-4-8 or 16 ohm speakers but don't know if it will change the sound...any thoughts?

It is a big jump from 2ohms to 8ohms..am I hurting the Super with what I'm doing now??

Jon Light (deceased) · Post by **Jon Light (deceased)** » 13 Jul 2005 11:19 am

If you mean that you are currently running it without the Weber Z-matcher then yes, that is more of a mismatch than the rule of thumb allows (100%=ok so 4 ohm would be the acceptable mismatch). I think you are taking a chance if you running higher than practice room levels.
I asked on the Weber board about whether the Z-matcher would affect tone and the answer was a little vague--like maybe sort of a tiny bit but not a big deal. I'd be interested in reading your report when you try it.

Jack Francis · Post by **Jack Francis** » 14 Jul 2005 1:24 pm

I am only using it in my music room....next month I will be taking the Super in for the new transformer and let you know about the sound changes, if it changes.

Jim Sliff · Post by **Jim Sliff** » 14 Jul 2005 3:10 pm

Grant - You're safe with the 8 ohm speaker to a point, but higher impedance mismatches are actually harder on Fender tube amps than lower-impdance mismatches due to a reaction called "flyback". It will shorten tube life and it does put some strain on the output transformer. You won't even notice volume loss, though, with that speaker.

If it was me, though, I'd buy the correct 4-ohm one and sell the 8.

Jon Light (deceased) · Post by **Jon Light (deceased)** » 14 Jul 2005 3:44 pm

Jack--I misread your post. Weber has an outboard unit called the Z-Matcher that takes any amp output impedance and matches it to any speaker load. That's what I somehow thought you were getting from them even though you were perfectly clear that you were getting a transformer.

Jack Francis · Post by **Jack Francis** » 14 Jul 2005 5:47 pm

Jon
You are correct it is an new transformer that they sent me to replace the original...I'm am going to have the new one put in and hope that it doesn't change the tone.
If it does I will put the old one back in.

Ken Fox · Post by **Ken Fox** » 14 Jul 2005 7:13 pm

Grant, a 1501-4SB Peavey Black Widow speaker would be perfect for the amp! I have tried one on a Twin several times and prefer it over any 2-12 arrangement. I even tested it again 2-12" JBL speakers, I liked it much better. That will give you the 4 ohm load you need and a great tone to boot.

Andy Zynda · Post by **Andy Zynda** » 15 Jul 2005 6:21 am

100% Mismatch is fine. 3db of power lost (generally)
By the way, I've been using the Weber Z-Matcher for over a month, and I tried it in all kinds of configurations.
It is the swiss-army knife of amp/speaker tools. I heard NO sound difference at all, except that I get proper volume and headroom levels when I had the amp-zMatcher-speaker set for proper impedance matching.
Great idea Ted!!!!!
-andy-

Earnest Bovine · Post by **Earnest Bovine** » 15 Jul 2005 7:51 am

I don't see here what is in the Weber Z-Matcher but I see 2 models: 50 watt, and 100 watt. So maybe you would fry it with a high powerwed steel guitar amp.

Andy Zynda · Post by **Andy Zynda** » 15 Jul 2005 10:57 am

The Z-matcher is a Transformer. Just like an output transfomer, with multiple taps. I have the 50 watt, and tried it in a Vibrolux, a Super, a Deluxe, a Twin and a MusicMan Hd130. I didn't push the Twin and MM very hard. Stayed stone cold.
-andy-