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Post subject: Disassembling Mustang GT 40 / Adding an External Speaker Out
Posted: Wed Nov 14, 2018 12:10 pm
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Does anyone have any experience disassembling the Mustang GT 40? If so, did you run into any surprises once you opened it up? Or was it fairly straightforward? Is there a repair guide or anything similar out there?

And, because I know someone will ask, I want to add an external speaker(s) output to run the amp through a 2x12" cab. Ideally, I'd install a pair of switched jacks that disable the internal speakers when plugged in. It all depends on what it's like in there… I guess I could also run some cables out the bass port on the back to avoid drilling any holes.

Anyway, just thought I'd ask before I crack this sucka open!


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Wed Nov 14, 2018 12:41 pm
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Try the Mustang v1/v2 forum. Chances are the construction is about the same and I know several people posted about similar projects there.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Wed Nov 14, 2018 12:59 pm
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ghost_of_strings wrote:
Try the Mustang v1/v2 forum. Chances are the construction is about the same...


I don't know… the GT is a completely different design than original Mustang. Plus the GT 40 has stereo speakers. Any work done on the original Mustang is likely not applicable to GT model.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Wed Nov 14, 2018 2:41 pm
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I think GT 40 speakers are 8 ohms total resistance,
4 ohms for each 6.5" speaker. If you keep your new speakers
in that ohms range, there shouldn't be any problem.

If you go for higher ohms, the speakers might not get
acceptable power to drive them the way you hope for.
So be prepared to experiment, if possible.
Cheers


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Wed Nov 14, 2018 5:05 pm
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guildorf wrote:
I think GT 40 speakers are 8 ohms total resistance,
4 ohms for each 6.5" speaker...


That's awesome! Thanks for the info. Just curious, how did you find that out? (We might be having the conversation in two different threads). Did you open yours up? Do you have any pics of the internals? Easy to access in there?


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 5:10 am
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sambot wrote:
ghost_of_strings wrote:
Try the Mustang v1/v2 forum. Chances are the construction is about the same...


I don't know… the GT is a completely different design than original Mustang. Plus the GT 40 has stereo speakers. Any work done on the original Mustang is likely not applicable to GT model.

So the original question was about disassembling the amp. Should be a whole lot of glue holding that cabinet together. Glue plus more glue. We'll call that a complete guess then.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 6:06 am
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https://www.youtube.com/watch?v=HKFYEcOEz0I

This fellow replaces a knackered headphone jack
with a 1/4 inch jack. It's a Mustang 1, but his
issues, blunders and tools may prepare you somewhat
for your project. You might consider sacrificing
some of Fender's weird shaped particle boards,
and put the GT control panel in a rack case,
or greatly simplied wood/plastic case.

A proper heat gun, might soften some glued
joints for you. Or use a steaming pressure cooker,
with rubber tubing on the vent, aimed at the joints.
Glove, gloves, and gloves.
Cheers


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 6:14 am
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ghost_of_strings wrote:
Should be a whole lot of glue holding that cabinet together.


Well, it will be weekend project, I guess.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 6:15 am
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guildorf wrote:
Or use a steaming pressure cooker,
with rubber tubing on the vent, aimed at the joints.


That's a great hack!


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 2:12 pm
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Found it in a carpentry forum, woodworkers/luthiers
have some great ideas. Saw this cool mod over in the
elder Mustang forum:

https://forums.fender.com/viewtopic.php?f=27&t=110800

Image[/quote]


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 3:38 pm
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Quote:
I think GT 40 speakers are 8 ohms total resistance,
4 ohms for each 6.5" speaker. If you keep your new speakers
in that ohms range, there shouldn't be any problem.


Ahem, in a stereo amp, the speakers are not connected in parallel. There are two separate power amp each with a 4 ohm speaker.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 3:45 pm
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Location: England
Quote:
Does anyone have any experience disassembling the Mustang GT 40? If so, did you run into any surprises once you opened it up? Or was it fairly straightforward? Is there a repair guide or anything similar out there?

And, because I know someone will ask, I want to add an external speaker(s) output to run the amp through a 2x12" cab. Ideally, I'd install a pair of switched jacks that disable the internal speakers when plugged in. It all depends on what it's like in there… I guess I could also run some cables out the bass port on the back to avoid drilling any holes.

Anyway, just thought I'd ask before I crack this sucka open!


I've had my GT 100 apart. No surprises there. Yes, you could add an external speaker jack feeding two 8ohm speakers in parallel. With a GT 40, you have two amps (it's stereo) so you have to go into two speaker cabinets with combined resistances of 4ohms - 2 x 8 ohms in series or 4 x 16 ohms in series. I don't know of any 2 ohm speakers. If you drive 8 ohms, you are effectively halving the output power. You could put 2 x 4 ohms into one cabinet but you would need two separate pair of cables.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 6:00 pm
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I've read that using 2 ohm speakers in a 4/8/16 ohm setup would
be a strong enough short circuit to eventually damage the amp electronics.
Once the GT40 is opened, is there any technical problem in just
using one of the power amps, aside from losing the stereo speaker?
I only use headphones, so a stereo jack, and get stereo effects through daw/plugins
as desired.
Cheers


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 6:28 pm
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guildorf wrote:
I've read that using 2 ohm speakers in a 4/8/16 ohm setup would
be a strong enough short circuit to eventually damage the amp electronics.
Once the GT40 is opened, is there any technical problem in just
using one of the power amps, aside from losing the stereo speaker?
I only use headphones, so a stereo jack, and get stereo effects through daw/plugins
as desired.
Cheers


No not one 2 ohm speaker, two in series but I've never seen a 2 ohm speaker.

It's not a good idea to run an amplifier without a speaker attached. All that (20) wattage has to go somewhere. You might be able to find or make a 'dummy' load. A 4ohm/20 watt resistor (or combination of 4 x 16 ohms or 8 x 32 ohms) in parallel – but it's going to run hot and will need a heat sink. Google 'speaker dummy load'.


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Post subject: Re: Disassembling Mustang GT 40 / Adding an External Speaker
Posted: Thu Nov 15, 2018 7:22 pm
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Roadie
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Joined: Mon Apr 10, 2017 2:19 pm
Posts: 270
Does using the headphone jack bypass that need for load?
Thats the only way i use the Mustangs. How does the Mustang V
deal with that, does it have some resistor wired to the cab jack
that gets bypassed when a cab cable pin has been inserteded?

I read where some early Line 6 amps fried because some people only
connected one of two cabinet jacks, and info was lacking at the time
as to what was actually needed for safe use when used just for recording,
or with a single mono cab, and if using a resistor on the secondary cab jack
was necessary.
Cheers


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