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Topic: Twin - ohms- ? |
John Walden
From:
Simi Valley, California, USA
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Posted 12 Nov 2013 9:40 am |
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I have an old Twin with JBLs. The speakers say 8 ohms. Tied together, will they show the amp 4 ohms ? What happens if one, 8 ohm 15" JBL is recognized ?
Thanks, J. W.
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Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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Dave Grafe
From:
Hudson River Valley NY
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Posted 12 Nov 2013 10:58 am
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Yes, your Twin's output transformer is designed to see a 4-ohm load, which the two 8-ohm speakers wired in parallel are currently presenting. And they look really nice in there, too, just saying. I don't think I'd be tampering with a sweet rig like that myself, but since you are inquiring...
Generally tube amps prefer lower over higher impedance loads, just the opposite of solid state. Supposedly Fender amps can tolerate up to 100% mis-match, which is what you are contemplating, but you will lose some power and if you are already running hot and have to push it harder to compensate, then, well, things can happen...so it really depends on which amp build you have I would say, but I'm a relative dummy in these matters.
My understanding is that you can ADD another 4 ohm load at the extension speaker jack, whether that helps in your situation I will not venture. A quick search suggests some other forum threads from wiser folk than I that may be of further assistance...
http://bb.steelguitarforum.com/viewtopic.php?t=240735&highlight=twin+impedance
http://bb.steelguitarforum.com/viewtopic.php?t=228139&highlight=twin+impedance |
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John Walden
From:
Simi Valley, California, USA
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Posted 12 Nov 2013 11:24 am Twin
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Thanks Dave. I read the threads and what I am getting is A, I'm not the only guy who doesn't understand the electronics as well as I would like, and B, I might be wise to disconnect one of the 12"s, and use an 8ohm 15" along with the 12, thus showing a 4 ohm load to the amp. Short wires are best. Do I have this correct ? Now I have to understand " in series ", vs "parallel", and see how the external speaker jack is wired. ( sure isn't going to make the Twin any lighter ).
Thanks, J. W.
_________________
http://www.myspace.com/johnmwalden
Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 12 Nov 2013 6:22 pm
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I'd say just plug the 15" into the Ext Spkr jack... your load won't be much below 4, about 2.66ohms... it'll run that fine. Check the phase with a 9v battery to make sure they're both pushing with + to tip (or pulling, whatever... as long as they're the same).
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New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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Cartwright Thompson
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Posted 13 Nov 2013 4:03 am
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From my experience, running a twin at 8ohms will not hurt it.
What you can also try is to remove two power tubes( either the inside two, 2+3, or the outside pair1+4), to double the load that the output transformr wants to see.
Unless you play really loud, you won't hear much if any of a difference. |
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Jerry Kippola
From:
UP Michigan, USA
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Posted 13 Nov 2013 8:11 am
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| U may lose a few watts of avail power, but it really won't make a diff-- |
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Mike Bowles
From:
Princeton, West Virginia, USA
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Posted 13 Nov 2013 4:56 pm twin ohms
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john are these fender speakers they look like the speakers in a twin i just got except the frames on mine are orange.
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Mike Bowles |
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John Walden
From:
Simi Valley, California, USA
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Posted 13 Nov 2013 5:46 pm Jbl D140 F ?
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Hey Mike, For the life of me I can't remember when / where I got the Twin, or what ever happened to my Ricky solid body guitar. I was in the Army from '71 to '74. What I do know is that I must have bought it new in the early 70's. It has the original JBL's in it.
Question ? What is the difference in a JBL D 140 F 15", and a D-130 F 15" ?
Question ? What OHM speaker does the Twin want to see at the extention speaker Jack, and is that to be used with the 2 12s or not.? Some have said it won't hurt anything to just add the 8 OHM 15". I would just like to do it right. Perhaps I should just trade it in on a Marshall stack ! 
Thanks, J. W.
_________________
http://www.myspace.com/johnmwalden
Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 13 Nov 2013 8:57 pm Re: Jbl D140 F ?
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| John Walden wrote: |
Question ? What OHM speaker does the Twin want to see at the extention speaker Jack, and is that to be used with the 2 12s or not.? |
Standard Fender lore states that a Fender amp is OK with a x2 or /2 match... so you could run your Twin at either 2 or 8ohms and not be too far out.
This does not hold if you're going to play at max volume for extended periods of time, 100% duty-cycle... you want to keep the amp close to factory spec if you're going to heat it up like that.
Here's the deal with impedance and tube amps... going lower heats up the amp, and going higher causes the voltage to climb. Most techs consider that going lower is best, since letting the voltage climb can result in arcing... and once it arcs, you have a carbon trail to help start more arcing.
So generally, keeping your Twin close to 4ohms is going to give longer service life for tubes etc. If you run the normal internal speakers and plug something into Ext Spkr, then you're modifying the original 4ohms, not replacing it... 8 || 4 is 2.66ohms... if you used 4ohms into Ext Spkr, you'd be running a 2ohm load, which is about as low as you'd want to try. If you connected 16ohms to Ext Spkr, you'd be running 3.2ohms, so close to 4 that the difference would probably not be detectable.
Here's a big clue... *never* disconnect Spkr and use Ext Spkr! Leo made Spkr a *shorting jack*... when you disconnect it, the output is shorted to ground! Believe it or not, this is better than infinity (open)... that's where you really start arcing and ruining components in a hurry. You can, however, ruin an amp by running into a short... it just takes longer (don't ask how I know).
So, again, my advice... connect the 15" to your Ext Spkr jack, leave the 2x12's connected to Spkr, and try it. You can also try just the 15", but make sure you use Spkr, not Ext Spkr by itself!
_________________
New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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Dave Grafe
From:
Hudson River Valley NY
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Posted 13 Nov 2013 11:07 pm
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| Quote: |
| Question ? What is the difference in a JBL D 140 F 15", and a D-130 F 15" ? |
The JBL D130f, K130 and E130 are guitar speakers with a usable response bandwidth of about 50 Hz to 6000 Hz; the D140, K140 and E140 are bass speakers, with a correspondingly lower frequency response curve of roughly 40 Hz to 2500 Hz, i.e. more than an octave lost at the top end. |
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John Walden
From:
Simi Valley, California, USA
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Posted 14 Nov 2013 6:13 am using 1 - 12 & 1 - 15
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Many thanks for all the wisdom guys. Dave, I now understand that a D 140F is probably not the best idea for steel. Stephen, I am not hip to the 9V battery trick. Could you tell me how to do that ? An what would happen if I just disconnect one of the 12s, and run a 15 with one 12. Would I use the ext. spkr. jack for the 15, or should I somehow connect the 15 to the 12 in use, via the spkr. jack ? Thus mantaining the 4 ohm load, using an 8 ohm 15. Sorry I am beating this horse to death, but you guys are awesome with your knowledge. I appreciate it.
J. W.
_________________
http://www.myspace.com/johnmwalden
Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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chris ivey
From:
california (deceased)
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Posted 14 Nov 2013 11:38 am
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| that's a great looking twin. i'd leave it alone. if you don't like it for steel, use your steel amp. |
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Lane Gray
From:
Topeka, KS
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Posted 14 Nov 2013 11:53 am
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The 9v battery thing? Put a 9V battery across the speaker terminals BRIEFLY. Notice which way the speaker jumps. And which way you oriented the battery. Now repeat with the other speaker, WITH THE BATTERY ORIENTED THE SAME. They should both move the same way. If they don't, then wire one speaker backwards.
The reason for brevity? Speaker wire isn't meant for DC or high current: It wouldn't take long for a mere 9V cell to fry that wire (notice it's thinner than the wire in most fuses).
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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Michael Hummel
From:
Ottawa, Ontario, Canada
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Posted 14 Nov 2013 2:59 pm
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| Quote: |
| The reason for brevity? Speaker wire isn't meant for DC or high current: It wouldn't take long for a mere 9V cell to fry that wire (notice it's thinner than the wire in most fuses). |
Sorry, Lane...a 9V cell hardly possesses enough power to fry a wire. Its internal resistance will limit any damage.
An amplifier putting out 25 watts into an 8 ohm speaker is providing voltages that peak around 10 volts all the time.
P = Vsquared / R
so at 10 volts output swing into the speaker
P = 100 / 4 = 25 watts
Mike
_________________
MSA Classic 5+4
Too many 6-strings and amps to list |
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John Walden
From:
Simi Valley, California, USA
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Posted 14 Nov 2013 3:22 pm confused
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Please forgive my ignorance, but what do you mean by brevity ? To me, it sounds like a bad idea to do this. It may not hurt anything at all, but I just don't know about that type of thing. I just want to play guitar, steel, bass, keys, sing, and record. But alas, I am drawn into understanding how to make the best of it all. Continue to educate me. Please.
J. W.
_________________
http://www.myspace.com/johnmwalden
Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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Michael Hummel
From:
Ottawa, Ontario, Canada
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Posted 14 Nov 2013 3:51 pm
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Well, when you are checking speaker polarity, you can be brief when connecting a 9V battery just to see which way the speaker cone moves when you connect it.
I'm sure it does little harm, but once you see the movement of the cone, your work is done!
You just want to make sure all of the speakers you are driving move the same way when you connect them to your amplifier. One way to do this is to use the 9V battery technique. When you put the + terminal of the battery to the tip of the speaker connector, all speakers should move in the same direction.
Mike
_________________
MSA Classic 5+4
Too many 6-strings and amps to list |
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Lane Gray
From:
Topeka, KS
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Posted 14 Nov 2013 5:18 pm
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I was told it's not the voltage that poses a problem, but the current. Into a dead short (and I think 4 ohms is close, no? Been too long since I've used Ohm slaw¹), a 9V cell can put out enough current to kill a fuse. I know if it shorts across a dime in a pocket, the heat can get extraordinary quickly, but I don't know if that comes from current or from the rapidity of the chemical reaction.
¹Autocorrect. Turning formula into salad.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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Lane Gray
From:
Topeka, KS
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Posted 14 Nov 2013 5:27 pm
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Sorry, John. Brevity is the adjective form of "brief."
You could also say "briefness," but that word hits my ears funny.
(The saying "brevity is the sole of wit" means that it's hard to be funny and long-winded at the same time. Even the funny bit of a shaggy dog story is in the last sentence)
So, Michael, it's not so much as harmful as pointless to leave it longer? I'd always been told otherwise, and believed it.
_________________
2 pedal steels, a lapStrat, and an 8-string Dobro (and 3 ukes)
More amps than guitars, and not many effects |
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John Walden
From:
Simi Valley, California, USA
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Posted 14 Nov 2013 6:30 pm
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Thanks for the info, Lane and Michael, and all that have help me understand more about speaker electronics. I guess it might be a good idea to unplug the speakers from the amp before doing the 9volt batt. test. I assume that I would be able to see what I am looking for from the back of the speaker. No need to remove them. I came across some folks in Danbury Ct. DSR Audio. Speaker repair folks. Looks like they know what they are doing. Any comments on these folks ? Somewhere I read that there is a certain percentage of loss in the magnets over the years. This amp is easy 40 years old. How would I tell how much loss I have myself ? ( OK, I just tried to stick a tool to the back of the JBL, and I got nothing. Same tool stuck good to the Black Shadow in the Mesa Boogie ). Does the JBL back cover prevent an accurate test ?
Thanks, J. W.
_________________
http://www.myspace.com/johnmwalden
Rains SD-10
Emmons SD-12 PP
Sho-Bud LDG
Fender Twin w/ JBL's
Mesa Boogie Mark IV x 2
Peavey 112 w/Knob-Guards x 2
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 14 Nov 2013 10:09 pm Re: using 1 - 12 & 1 - 15
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| John Walden wrote: |
| Stephen, I am not hip to the 9V battery trick. Could you tell me how to do that ? |
Some others have chimed in by now... but yes, you unplug the amp and touch the two terminals to the 1/4" plug coming from the speakers or cabinet. Three reasons for 'brevity':
1.) Holding the battery on there doesn't help, you want to see which way it jumps when the contact is made. Either feel the cone with one finger (from the back) or watch through the grillcloth with a flashlight (from the front)
2.) A DC voltage is bad for speakers... the voice coil doesn't get to have its normal impedance, it's just a resistance at DC. Connecting a battery will definitely heat up the coil... you just want to touch it to see it jump.
3.) It wears out the battery!
| Quote: |
| And what would happen if I just disconnect one of the 12s, and run a 15 with one 12. Would I use the ext. spkr. jack for the 15, or should I somehow connect the 15 to the 12 in use, via the spkr. jack ? Thus mantaining the 4 ohm load, using an 8 ohm 15. |
You could certainly do that... you could use the Ext Spkr jack to do that, and disconnect one 12". This only works because they're all in parallel... if this were a series connection this wouldn't work. But as I mentioned, the impedances are similar enough that disconnecting one 12" is not necessary. You can try it first... then if you like it, and want to run that way, you can disconnect a 12 for a perfect 4ohms. In fact, you can put 1/4" plugs on each 12, and run both out of the jacks, or run one internal and the 15 external... the jacks are just paralleled together like the 12's are. I kinda like that idea, actually...
_________________
New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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