First post, Hi! Just posted this elsewhere, so I'm gonna copy and paste to save the time.
I have a Fender Pro Series Twin Amp, and am trying to work out how to run an external cab with it. The Twin has 2 x 8 ohm speakers wired for 4 ohm, the ext. cab has 4 x 16 ohm speakers switchable for 4 ohm, 16 ohm, or 2 x 8 ohm.
I am aware you theoretically can run an external load along with the internal in the Twin Amp (4 ohm int, 4 ohm ext, for 2 ohm etc), but just for peace of mind, I've been looking at the schems. It would appear that there is an 8ohm and 16ohm tap of the OT secondary, along with the standard 4 ohm. The 16 ohm seems to be unused, but the 8ohm looks like it's part of a negative feedback circuit.
My question is:
Is it possible to utilise the 8 ohm tap to run 2 x 4 ohm loads in series (internal 2x8 ohm and external 4x16ohm) or is the feedback circuit going to cause issues? If so, any hints on how to wire this up?
Schematic:
http://support.fender.com/schematics...Amp_SchE45.pdf
Cheers,
Matt.
I have a Fender Pro Series Twin Amp, and am trying to work out how to run an external cab with it. The Twin has 2 x 8 ohm speakers wired for 4 ohm, the ext. cab has 4 x 16 ohm speakers switchable for 4 ohm, 16 ohm, or 2 x 8 ohm.
I am aware you theoretically can run an external load along with the internal in the Twin Amp (4 ohm int, 4 ohm ext, for 2 ohm etc), but just for peace of mind, I've been looking at the schems. It would appear that there is an 8ohm and 16ohm tap of the OT secondary, along with the standard 4 ohm. The 16 ohm seems to be unused, but the 8ohm looks like it's part of a negative feedback circuit.
My question is:
Is it possible to utilise the 8 ohm tap to run 2 x 4 ohm loads in series (internal 2x8 ohm and external 4x16ohm) or is the feedback circuit going to cause issues? If so, any hints on how to wire this up?
Schematic:
http://support.fender.com/schematics...Amp_SchE45.pdf
Cheers,
Matt.
Do you want to run the amp AND an external cab? Or just the xternal cab? Oh, I guess you did spell it out.
As I guess you know, simple parallel makes a 2 ohm load, which might even work out, but isn't the best way. Series is not my favorite way to wire guitar cabs, but the simplest way would be external to the amp. I a series arrangement, one cab has neither side grounded. If you seriesed the internal speakers for 16 ohms, then run your cab at 16, then a simple parallel happens.
leave the feedback alone. The signal voltage at that tap won't change by using a different tap for speakers.
You could then add a SPDT switch selecting the 4 ohm or 8 ohm tap to your output jacks. That way a simple switch flip sets the amp chassis stock. To run the internals alone, you'd want to switch THEIR wires back though.
If you want to keep the amp wired parallel and series the cab. I'd mount a small L bracket on the sidewall with a speaker jack on it. Wire it in the hot lead to the internals, with a cutout contact completing the original path when the jack is empty. SO empty jack, normal, plug in your cab, and it inserts your cab in series with the speakers.
As I guess you know, simple parallel makes a 2 ohm load, which might even work out, but isn't the best way. Series is not my favorite way to wire guitar cabs, but the simplest way would be external to the amp. I a series arrangement, one cab has neither side grounded. If you seriesed the internal speakers for 16 ohms, then run your cab at 16, then a simple parallel happens.
leave the feedback alone. The signal voltage at that tap won't change by using a different tap for speakers.
You could then add a SPDT switch selecting the 4 ohm or 8 ohm tap to your output jacks. That way a simple switch flip sets the amp chassis stock. To run the internals alone, you'd want to switch THEIR wires back though.
If you want to keep the amp wired parallel and series the cab. I'd mount a small L bracket on the sidewall with a speaker jack on it. Wire it in the hot lead to the internals, with a cutout contact completing the original path when the jack is empty. SO empty jack, normal, plug in your cab, and it inserts your cab in series with the speakers.
Hi Enzo, thanks for the useful info. What don't you like about series wiring? Is it a speaker/amp protection thing, or a sound/speaker driving thing?
Given the above, I'm thinking of wiring up 2 switches, one to change from 4 to 8 ohm tapping, the other to change internal wiring from parallel to series. Am i correct in thinking I just take a split off the 8 ohm tap to the switch and leave it connected to the feedback section?
That way i can have:
-4 ohm tap, internal speakers parallel for 4 ohm
or
-8 ohm tap, internal speakers series for 16 in parallel with external cab at 16 ohm for 8 ohm total.
This would have the advantage of no iffy switching jacks, and I could use the existing ones without changing too much.
Thoughts?
Given the above, I'm thinking of wiring up 2 switches, one to change from 4 to 8 ohm tapping, the other to change internal wiring from parallel to series. Am i correct in thinking I just take a split off the 8 ohm tap to the switch and leave it connected to the feedback section?
That way i can have:
-4 ohm tap, internal speakers parallel for 4 ohm
or
-8 ohm tap, internal speakers series for 16 in parallel with external cab at 16 ohm for 8 ohm total.
This would have the advantage of no iffy switching jacks, and I could use the existing ones without changing too much.
Thoughts?
I think that was an option I mentioned. You're gonna need a 4/8 switch no matter what, I think.
Speakers are wired in series all the time, like in a 2x12 or 4x12 cab. But when we have two cabs in series, we start to get too many things in series fr my taste. it will work, but I'm just not into it. But my main objection is that I don't like special situations or situations I have to keep something unusual in mind, like not allowing anything on my cab to touch ground. I also avoid like the plague any connection in my system that requires a special cord. If I use a special cord and it breaks or gets lost, then I cannot just grab another cord from the bin. Imagine f you had one cab wired backwards and had to use one special reverse phase speaker cord with it, and had to remember that every time you set up. Not for me.
So it is my outlook, not like something would be "wrong".
As to the speakers, you could wire up a series/parallel switch for the internals, but really, how often would you use it? If your cab can be 4 or 16, why not pick one? If you have lots of cabs of various impoedances, then maybe.
I don't consider switching jacks iffy, they have been on the inputs of amps for 60 or more years without causing trouble. This is not a complex circuit for a jack, it is the exact same circuit as the main speaker jack on the schematic, or most any input. It shorts tip to sleeve until something is plugged in.
Speakers are wired in series all the time, like in a 2x12 or 4x12 cab. But when we have two cabs in series, we start to get too many things in series fr my taste. it will work, but I'm just not into it. But my main objection is that I don't like special situations or situations I have to keep something unusual in mind, like not allowing anything on my cab to touch ground. I also avoid like the plague any connection in my system that requires a special cord. If I use a special cord and it breaks or gets lost, then I cannot just grab another cord from the bin. Imagine f you had one cab wired backwards and had to use one special reverse phase speaker cord with it, and had to remember that every time you set up. Not for me.
So it is my outlook, not like something would be "wrong".
As to the speakers, you could wire up a series/parallel switch for the internals, but really, how often would you use it? If your cab can be 4 or 16, why not pick one? If you have lots of cabs of various impoedances, then maybe.
I don't consider switching jacks iffy, they have been on the inputs of amps for 60 or more years without causing trouble. This is not a complex circuit for a jack, it is the exact same circuit as the main speaker jack on the schematic, or most any input. It shorts tip to sleeve until something is plugged in.
I'll usually be using it without the cab, just occasionally for some extra low end.
I ended up doing the 2 switch thing which seems to work fine. I stuck the tap selector in the chassis and the series/parallel switch on a bracket in the cab. I like options, and being able to play with different combinations with the flick of a switch is great.
Thanks again for your help!
I ended up doing the 2 switch thing which seems to work fine. I stuck the tap selector in the chassis and the series/parallel switch on a bracket in the cab. I like options, and being able to play with different combinations with the flick of a switch is great.
Thanks again for your help!
I'd put the internal speakers in series, plugged into the 16ohm tap.
Then, using the external cab as 16ohm, you have the option to put both cabs in parallel on the 8ohm tap. Should keep everything happy, but you'll need a splitter on the 8ohm output.
Chris
Then, using the external cab as 16ohm, you have the option to put both cabs in parallel on the 8ohm tap. Should keep everything happy, but you'll need a splitter on the 8ohm output.
Chris
Hi,
For equal power to each driver, rewire the combo
in series and connect it to the 8 ohm tap.
Connect the 4x16ohm as 16 ohm to the 16 ohm tap.
(4 ohm and 4 ohm tap will not be as good.)
I assume 2 ohms is a no-no and the current external
speaker socket disconnects the internal speakers,
you will need to change this.
rgds, sreten.
For equal power to each driver, rewire the combo
in series and connect it to the 8 ohm tap.
Connect the 4x16ohm as 16 ohm to the 16 ohm tap.
(4 ohm and 4 ohm tap will not be as good.)
I assume 2 ohms is a no-no and the current external
speaker socket disconnects the internal speakers,
you will need to change this.
rgds, sreten.
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Hi Matt,
Which amp do you have as the schematic link didn't work.
Pro Series Amps from Fender's web site shows a few of them
listed as Twin Reverb Amps.
Fender Products
Which amp do you have as the schematic link didn't work.
Pro Series Amps from Fender's web site shows a few of them
listed as Twin Reverb Amps.
Fender Products
He has the Twin Amp - Pro Tube
http://support.fender.com/schematics/guitar_amplifiers/Twin-Amp_schematic.pdf
http://support.fender.com/schematics/guitar_amplifiers/Twin-Amp_schematic.pdf
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