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Did you ever want to hook up an external
speaker cabinet to your amp but were unsure if there was an appropriate
cabinet available, what speaker impedence would be the proper
match for your amplifier or whether it was even safe for the amp
to hook up an external speaker cabinet at all? Do you want to
know how speaker impedance relates to the amplifier output impedance?
The answer will differ depending on whether you have a solid state
amplifier or tube amplifier. The term "speaker impedance",
refers to the load which either a speaker, (or the combined load
of multiple speakers in a cabinet), presents to an amplifier.
The load will vary depending on whether the speakers are wired
in series, parallel or series/parallel.
In the case of solid state amps, there will
normally be a "Max Load" (also called "Minimum
Impedance") rating for the amp. The load plugged into the
amp should never go below the minimum impedance or serious damage
may occur to the amplifier. Maximum power will be obtained when
the speaker load matches the minimum impedance. It is perfectly
safe to use a higher impedance speaker load, but there will be
a corresponding drop in output power (i.e. an 8 ohm speaker load
will result in approximately half the output power of a 4 ohm
speaker load).
In the case of tube amps, it is best to
match the speaker load as closely as possible to the amplifier
output impedance. In theory, there is some small amount of mismatch
that will not hurt the amp, however, it is always recommended
that you match the speakers as closely as possible to the rating
of the amp to avoid potential problems. If there is a slight mismatch,
it should be at a lower ohm rating, not higher.
For wiring either in parallel or series, Click here.
The following chart will detail many
of the current and most popular Fender amplifiers, their ohm (impedence)
rating, whether or not there is an extension speaker cabinet which
will be an appropriate impedence match to the amplifier, and notes
on options.
| AMP
MODEL |
OUTPUT
RATING IN OHMS |
APPROPRIATE&
ENCLOSURE |
NOTES |
| Dual Professional |
100 watts at 4 or
8 ohms (switching jacks) |
No current Fender
enclosure is an exact match. You could rewire a 16 ohm Tone-Master
412 cabinet to 4 ohms |
Internal speaker load
is 4 ohms. Adding a 4 ohm cabinet results in 2 ohms (a mismatch),
but it will work |
| Tone-Master |
100 watts at 4,8,
or 16
ohms (switchable) |
Tone-Master 212 or
412, (both are 16 ohms) |
Set ampís switch
to 8 ohms when using two 16 ohm cabinets |
| Vibro-King |
60 Watts at 2 ohms |
Vibro-King 212 enclosure,
(4 ohms) |
Internal speaker load is 2.66 ohms. Adding the 4 ohm cabinet equals 1.6 ohm total impedance.(an intentional mismatch) |
| Prosonic Head |
60 Watts at 4, 8,or
16 ohms |
Prosonic 412 cabinet,
(16 ohms) |
Set ampís switch
to 16 ohms for one cabinet, 8 ohms for two |
| Prosonic Combo |
60 Watts at 8 or 16
ohms (switching jacks) |
Prosonic 412 cabinet,
(16 ohms) |
Internal speaker load is 16 ohms. Amp will switch itself when a 2nd cabinet is added |
| Twin-Amp |
100 Watts at 4, 8,
or 16 ohms |
Prosonic 412 cabinet,
(16 ohms) |
Internal speaker load
is 16 ohms. Plug a 2nd 16 ohm cabinet into the parallel jack,
set switch to 8 ohms |
| 65' Twin Reverb |
85 watts at 4 ohms |
No current Fender
enclosure is an exact match. You could rewire a 16 ohm Prosonic 412 to 4 ohms |
Internal speaker load
is 4 ohms. Adding a 4 ohm cabinet results in a 2 ohm total load, (a mismatch), but it will work |
| 65' Deluxe
Reverb |
22 Watts at 8 ohms |
No current Fender
enclosure is an exact match cosmetically, but you could use any 8 ohm cab like the GE112 or GE412 |
Internal speaker load
is 8 ohms. Adding an 8 ohm cabinet results in a 4 ohm total load, (a mismatch), but it will work |
| Vibrolux Reverb |
40 Watts at 4 ohms |
No current Fender
enclosure is an exact match. You could rewire a 16 ohm Prosonic 412 to 4 ohms |
Internal speaker load is 4 ohms. Adding a 4 ohm cabinet results in a 2 ohm total load,
(a mismatch), but it will work |
| Hot Rod DeVille
(410) |
60 Watts at 8 or 4
ohms (switching jacks) |
No current Fender
enclosure is an exact match, but you could use any 8 ohm cab like the GE112 or GE412 |
Internal speaker load is 8 ohms. Amp will switch to 4 ohms when a 2nd cabinet is added |
| Hot Rod DeVille
212 |
60 Watts at 4 or 2
ohms (switching jacks) |
No current Fender
enclosure is an exact match, but you could rewire a 16 ohm Prosonic 412 to 4 ohms |
Internal speaker load is 4 ohms, amp will switch to 2 ohms when a 2nd cabinet is added |
| Hot Rod Deluxe |
40 Watts at
8 or 4 ohms
(switching jacks) |
No current Fender enclosure is an exact match, but you could use any 8 ohm cabinet
like the GE112 or GE412 |
Internal speaker load is 8 ohms. Amp will switch to 4 ohms when a 2nd cabinet is added |
| Roc Pro 1000 Head |
100 Watts at 4 ohms |
GE 112 or GE 412 (both are 8 ohms) |
Optimum load of 4 ohms is achieved when using two 8 ohm Cabinets |
| Roc Pro 1000 |
100 Watts at 4 ohms |
GE 112 stacks perfectly, or use GE412 (both are 8 ohms) |
Internal speaker load
is 8 ohms. Optimum load of 4 ohms is achieved when adding an 8 ohm extension cabinet |
Stage 112SE &
Stage 100 |
160 watts at 4 ohms |
GE 112 stacks perfectly, or use GE412 (both are 8 ohms) |
Internal speaker load is 8 ohms. Optimum load of 4 ohms is achieved when adding an 8 ohm extension cabinet |
| BXR 300C |
300 Watts at 4 ohms |
BXR 115B stacks nicely,(8 ohms) |
Internal speaker load is 8 ohms. Optimum load of 4 ohms is achieved when adding an 8 ohm extension cabinet |
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