Other Amps

can I run an 8 ohm speaker on a 4 ohm amp?

1

I have an old 60's Danno 5w combo. It's got a little 8", 4 ohm speaker. I wanted to try it with some other speakers just to see what it's like. All my extra speakers are 10", 8 ohm. Can I hook up a larger speaker w/out cooking the little guy?

2

You'll probably be safe if you keep the volume down. Crank it up and things could get interesting . . . and by interesting I mean expensive.

3

Yes, as Mark stated, at LOW volumes only.

If you start "pushing it", the output tranny will be stressed, and possibly fail, along with a few other things.

It's really "cheaper" in the long run to get the correct speaker in there.

Edit: A larger speaker is fine. A 12" can make a 5watt amp sound HUGE, but, it has to be the correct Ohm for the amp.

4

From what I've always understood, you can safely go up in impedance when going to a speaker (4-ohm amp to 8-ohm speaker), but going down can do damage to your amp - especially a tube amp. It's possible that you might lose a little efficiency, but it's unlikely that it will be noticeable.

5

So how about an 8ohm resistor in parallel with the 8ohm speaker That produces a 4ohm load...

but I'm sure doing this brings up that altered inductance(impedance?) thing I know nothing about...

6

Dlaf is correct, however I've been told the "arcing" at the tube pins can be a possibility.

Dave, I don't know about the resistor thing, and what it "may" do to tone etc.

7

Run two 8 ohm speakers in parallel---that's a 4 ohm load. You can also get 4 ohm speakers at various places. Many automotive speakers are 4 ohm. You can use 8 ohms but it will only get half as loud as a 4 ohm.

8

I agree with cielski. "You can use 8 ohms but it will only get half as loud as a 4 ohm." I don't know if it sounds half as loud. but I do know it sounds different. As far as I know it will not harm your amp. 4Ohm in an 8Ohm OT DOES hurt your amp!

also, indeed two 8ohm speakers parallel = 4Ohm. So that would be perfect.

9

WOW! What timing I was going to start the same thread and I found this, Just pulled the trigger on a '65 vibro champ it had a jensen MOD speaker installed and the original was in the box that that the replacement came in.....well it wasn't until I got it home (of course) that I noticed that box was for an 8 ohm speaker and the amp is rated 4. Gotta say it still sounds pretty nice, breaks up earlier than I'd expect, but I attribute that to the speaker. Got the amp good and warm last night and started to notice some noises......now I'm afraid I may have done some damage.

10

WOW! What timing I was going to start the same thread and I found this, Just pulled the trigger on a '65 vibro champ it had a jensen MOD speaker installed and the original was in the box that that the replacement came in.....well it wasn't until I got it home (of course) that I noticed that box was for an 8 ohm speaker and the amp is rated 4. Gotta say it still sounds pretty nice, breaks up earlier than I'd expect, but I attribute that to the speaker. Got the amp good and warm last night and started to notice some noises......now I'm afraid I may have done some damage.

11

If you have multiple "extra speakers" just run two 8 ohm speakers in parallel, and you'll maintain a 4 ohm load, as previously suggested. Positive and Negative from the amp to Speaker #1. Positive and Negative from Speaker #1 to #2.

12

I highly doubt you've done any damage. Generally, a mismatch of no more than 100% is perfectly acceptable. (That is: Running 8 ohms on a 4 ohm output is fine... but 16 would be too much. And vice versa)

I think the worst that happens is shortened tube life.
You'd have to have a serious mismatch for an extended period under heavy use to damage the output transformer.

13

Greg, thanks for the reassurance, just got off the phone w/ Cameron at Torres Engineering and he told me the same thing, felt good enough about the news to buy the correct speaker from him, an 8", 4 ohm alnico Jensen. If it sounded good before, I wonder what it will sound like when I install this? Thanks again! Nice avatar, is that a recent photo? Brilliant disguise

14

I got this from a good guy on the Guitar ReRanch board:

Even though it's not intuitive, a 2-ohm load is a heavier load than an 8-ohm load. Think about it: 2-ohms is much closer to ground - that is, a short to ground - than 8-ohms.

P = i(squared)R

So for a 40-watt amp, the amount of current that a transformer has to pass into an 8-ohm load is...

40 = i(squared)8,

so i = ((square root) of 5) = 2.24 amps.

However, the amount of current that a transformer has to pass into an 2-ohm load is...

40 = i(squared)2,

so i = ((square root) of 20) = 4.47 amps.

15

I had a Tophat Prince Royale which is a 4 watt with a 8 inch 4 ohm speaker. Now keep in mind this amp was designed to be able to do this! I called Brian Gerhart and asked him about this same thing. His rule of thumb for his amps was if they were an amp without an impedence selector no more then double and no less then half! My Club series are fit with 2 parallel speaker jacks meaning I could run 4-8-or 16 ohm loads. The PR had only 1 jack but they were designed the same meaning it could handle a 2-4 or 8 ohm load! I would run out of a separate cab an 8 ohm Blue. I had more volume mostly because the 8 inch would fart out at 2:00. I could crank it with the 12 inch and it was sweet!

Now I wouldn't do this with my Gibson and I wouldn't do it with your Dano just because I don't know and if I don't know I won't try it until I know for sure that it can handle it safely! I do have both a Weber mini mass and Z Matcher for such ocassions. Now some techs will tell you this is ok and some will tell you it's not! I haven't had a problem at all as of yet but I won't tell you it's without risk. So here it goes! If you were to put a mass between your amp and speaker and set the mass @ 4 ohm it wouldn't matter what your speaker is because your mass is a speaker motor attenuator so it's maintaining a 4ohm load to the amp. The Z matcher works in much the same way except with that you can dial in say your 8ohm speaker to 4 ohm load on the amp! Again if your tech says this is bad then don't do it! I've been doing this for a few years but not as much lately and I'm always leary that there could be a problem with these 2 Weber pieces that I have!

16
Thanks again! Nice avatar, is that a recent photo? Brilliant disguise

haha... well done.
Actually, despite the fact that I'm a Canadian currently living in Germany, I'm still considered "The King of America"! :cool:

Nah, I just love his tunes and I love the guitar playing on his albums. Whether it's him, or his well-chosen sidemen like Marc Ribot or Bill Frisell.


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