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How to install a second input for a cabinet
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t.olsen
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PostPosted: Wed May 19, 2010 8:28 am    Post subject: How to install a second input for a cabinet Reply with quote

I am playing at home with my Gretsch G5222.The amp is completely modified with an alnicomagnet kit,the 6" speaker inside has gone for a weber 8".The speaker is connected inside to the speaker input.



Normally the back is closed.I can reach the plug but it's a little tricky.The idea was to install a second input outside to connect my cabinet easyly with the amp.There should be a switch as well to cut the internal speaker when it is connected to the cabinet.I installed a second input,visible right beside the volume knob.



The second socket is parallel to the first one,the 2 cables are only bridged from one socket to another.
When I connect the cabinet to the new input everything works fine.When I switch to the weber speaker inside I have much less volume and a kind of distortion,scratching,not sounding good.Seems that I cannot only install a second socket absolutely parallel to the first one.Any idea to solve would be welcome
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JohnA
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PostPosted: Wed May 19, 2010 8:49 am    Post subject: Reply with quote

With a valve amp you need to make sure the impedance of the output transformer is matched to the speakers. I don't know what the impedance of the internal and external speakers you are, are they the same? If so you should only run either one or the other, not both at the same time.
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t.olsen
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PostPosted: Wed May 19, 2010 8:56 am    Post subject: Reply with quote

That is the reason why I installed the switch : with cabinet the internal speaker is switched off,without cabinet I play over the internal speaker.But when I use the internal speaker,the cable to the cabinet is not connected,only the internal speaker is active.And scratching like hell...
The internal speaker has 4 ohm,same for the cabinet
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t.olsen
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PostPosted: Wed May 19, 2010 9:03 am    Post subject: Reply with quote

As soon as I cut off the cable between both sockets,I can plug in the internal speaker and it sounds normal.Same with the cabinet.Only with both sockets parallel it doesn't work
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JohnA
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PostPosted: Wed May 19, 2010 9:42 am    Post subject: Reply with quote

t.olsen wrote:
As soon as I cut off the cable between both sockets,I can plug in the internal speaker and it sounds normal.Same with the cabinet.Only with both sockets parallel it doesn't work


Strange! So you are saying even without a speaker connected to the second output it still affects the sound? This sounds like the +ve connection is finding its way to ground, or a possible ground loop issue, try un-screwing the second output from the chassis, or using an insulated socket like a cliff socket rather than the switchcraft style, and see if you have the same problem.

Any chance of a picture of how it's wired up from the inside?
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t.olsen
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PostPosted: Wed May 19, 2010 9:53 am    Post subject: Reply with quote

Hi John,It is a switchcraft socket..too late for pics,I changed the mods back to one socket only but I use the outside socket now,not the one I just cannot reach inside.I take the cable from the internal speaker out now through a hole in the backplate if I need it.Most time it is connected to the cabinet but when I take the amp to another place I will use the weber inside.I only have to think about always connecting one speaker to the output not to destroy the amp.But I still don't understand It
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JohnA
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PostPosted: Wed May 19, 2010 10:12 am    Post subject: Reply with quote

t.olsen wrote:
Hi John,It is a switchcraft socket..too late for pics,I changed the mods back to one socket only but I use the outside socket now,not the one I just cannot reach inside.I take the cable from the internal speaker out now through a hole in the backplate if I need it.Most time it is connected to the cabinet but when I take the amp to another place I will use the weber inside.I only have to think about always connecting one speaker to the output not to destroy the amp.But I still don't understand It


I would definitely try a cliff jack (like on marshall amps) that is insulated from the chassis, the switchcraft jack is grounded because it is metal which means the output transformer is grounded in two seperate places, I think this could be the problem.
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t.olsen
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PostPosted: Wed May 19, 2010 10:40 am    Post subject: Reply with quote

I will try it with a plastic washer to isolate it from the ground.just to make sure that is the reason and go for a better socket then
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JohnA
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PostPosted: Wed May 19, 2010 10:55 am    Post subject: Reply with quote

t.olsen wrote:
I will try it with a plastic washer to isolate it from the ground.just to make sure that is the reason and go for a better socket then


A plastic washer might not work as the socket could still touch the chassis where it goes through the hole, give it a try though it might just fix it!


Good luck
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t.olsen
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PostPosted: Wed May 19, 2010 11:13 am    Post subject: Reply with quote

Most important is I did not kill my amp
I will check it but it is strange..
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JohnA
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PostPosted: Wed May 19, 2010 4:33 pm    Post subject: Reply with quote

t.olsen wrote:
Most important is I did not kill my amp
I will check it but it is strange..


Yes killing an amp through tinkering is never good!! Report back if you have any luck!
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t.olsen
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PostPosted: Thu May 20, 2010 9:11 am    Post subject: Reply with quote

I had another try...took the new input completely out of the amp and connected the pins only with 2 wires with crocodile clamps to make sure not to have ground connection.By the way,the original socket is fixed at a place where the paint has been removed for a good ground connection,so seems that is needed.Anyway,the result is the same : when connection the internal speaker to the normal input it sounds as it should,when connecting to the new input scratching distortion and volume loss.
No idea why
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JohnA
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PostPosted: Thu May 20, 2010 9:30 am    Post subject: Reply with quote

You got me beat!! How is your switch wired? You could use a double pole switch to totally disconnect the second socket when using the internal speaker.
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t.olsen
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PostPosted: Thu May 20, 2010 9:54 am    Post subject: Reply with quote

This is what it looks like



A double switch would help but first I have to find out why one of 2 parallel inputs is working fine while the second is not.I have to know to avoid sleepless nights
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JohnA
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PostPosted: Thu May 20, 2010 10:13 am    Post subject: Reply with quote

Is that a stereo socket?
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