J
jonnyc
New member
The two v30's I got are 8ohm speakers and the celestions in my 4x12 are 16ohm. It's a typical 1960a model with the stereo switch and 4ohm and 16ohm jacks. Is there anyway to wire this up so it'll work or no?
B
boingoman
New member
What is your end goal?
Zaphod B
Raccoons-Be-Gone, Inc.
What boingoman said..... 
Also, are you saying that the individual speakers in your 4X12 are 16-ohm speakers, or that the whole cab is rated at 16 ohms?
Also, are you saying that the individual speakers in your 4X12 are 16-ohm speakers, or that the whole cab is rated at 16 ohms?
Zaphod B
Raccoons-Be-Gone, Inc.
Never mind, I found a wiring diagram for a 1960A cab. Pretty cool, I didn't know they had all those options.
So, again, what are you trying to do?
So, again, what are you trying to do?
G
ggunn
Crystal Flavolian
Zaphod B said:
It sounds to me like he wants to swap out two of his 16 ohm speakers for 8 ohm ones in his 1960 cab.
Zaphod B
Raccoons-Be-Gone, Inc.
Oh. Well, then, the quick answer would be no, not if you want to maintain exactly the same functionality.ggunn said:
First case: If you throw those 8-ohm speakers in there, both on one side, then in mono mode the 4-ohm jack becomes 2.66 ohms and the 16-ohm jack becomes 12 ohms. In stereo mode the impedance on the side with the new speakers would become 4 ohms rather than 8 (the other side would still be 8 ohms.)
Second case: If you put the new speakers in with one on the left side and one on the right, then in mono mode the 4-ohm jack becomes 2.65 ohms and the 16-ohm jack becomes 10.6 ohms. In stereo mode both sides would become 5.3 ohms rather than 8 ohms.
I've been told that most tube amps are very tolerant of impedances that are not right on the money, particularly if the speaker load is a bit higher than the rated output load from your amp. So in the first case, using the 16-ohm jack (which is now 12 ohms) with a corresponding 8-ohm output from the amp would be safe. In the second case, using the 16-ohm jack (which is now 10.6 ohms) with a corresponding 8-ohm output from the amp would also be safe, and even more closely matched.
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ggunn
Crystal Flavolian
Zaphod B said:
Yeah, but the 4 ohm mode at 2.65 ohms (and thanks for doing the math; I didn't have time to do it) would be a bit risky.
Zaphod B
Raccoons-Be-Gone, Inc.
Absolutely correct. You want to keep away from those low impedances.ggunn said:
As long as you re-label your outputs and take care hooking stuff up, it should be fine.
J
jonnyc
New member
Zaphod B said:
So if I throw them both into the same side and run thru the 16 ohm jack I'll be ok? I just don't want to blow anything up.
rayc
retroreprobate
There seems to be some resistance to sitting in the lotus position & chanting Ohm.
Zaphod B
Raccoons-Be-Gone, Inc.
If it were me I'd put one on the left, and one on the right, and use your amp's 8-ohm output into the 16-ohm cabinet jack (which would now be 10.6 ohms) in mono mode.jonnyc said:
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jonnyc
New member
Zaphod B said:
Do you think this would be the safest bet? I just don't want to blow my head, I've lost one already and I don't want to lose another.
Zaphod B
Raccoons-Be-Gone, Inc.
I think it's the most sensible solution. Jonnyc, as long as you are running the amp into an impedance that is higher, rather than lower, than the amp's rated output impedance (at a given amp output jack), you will be fine. You don't want to run into too high of an impedance, though, since you will have to push the amp harder to attain a given volume level and you may also affect the tone.
That 10.6 ohm impedance is very close to and slightly higher than 8, so it should work fine.
That 10.6 ohm impedance is very close to and slightly higher than 8, so it should work fine.
M
Micter
No Title
jonnyc said:
Then don't mess with the speaker load. Although running the load higher often doesn't cause a problem that all depends on the output transformer. I personally don't mess with impedence.
J
jonnyc
New member
Micter said:
Great advice.
Zaphod B
Raccoons-Be-Gone, Inc.
You have to remember that a quoted speaker load is only nominal, and its value also changes as a result of the frequency it is presented with. So your amp is continually running into a variable load, depending on what you are playing on your guitar.
Just to give you an idea, a Peerless 8" audio speaker that would be used for a woofer-mid in a 2-way system, nominally rated at 8 ohms, has a minimum resistance of 6.6 ohms at 188 hz, and a maximum impedance of around 20 ohms at the upper end of its useable range. All audio speakers (with voice coils) exhibit the same characteristic rise in impedance with increased frequencies because the voice coil is a ... coil, or inductor if you will. Inductors exhibit low impedance at low frequencies (almost nothing at DC, which is why you should never hook up a speaker to a DC source, as overcurrent will cook the voice coil) and high impedance at high frequencies.
The whole point is that amps are designed for dynamic impedances, and higher impedances won't hurt them.
Just to give you an idea, a Peerless 8" audio speaker that would be used for a woofer-mid in a 2-way system, nominally rated at 8 ohms, has a minimum resistance of 6.6 ohms at 188 hz, and a maximum impedance of around 20 ohms at the upper end of its useable range. All audio speakers (with voice coils) exhibit the same characteristic rise in impedance with increased frequencies because the voice coil is a ... coil, or inductor if you will. Inductors exhibit low impedance at low frequencies (almost nothing at DC, which is why you should never hook up a speaker to a DC source, as overcurrent will cook the voice coil) and high impedance at high frequencies.
The whole point is that amps are designed for dynamic impedances, and higher impedances won't hurt them.