Am I going to damage my amp ???? - Jemsite
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post #1 of 12 (permalink) Old 04-10-2003, 02:27 PM Thread Starter
 
Join Date: Apr 2003
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Am I going to damage my amp ????



Hi folks,

I recently bought a 1x12 Mesa Boogie cabinet to use as an extension speaker to my Laney LC15R amp. I intended to use them together but found out that this is only possible if I keep the cable inserted only half-way inside the amp "To External Speaker" output.

The amp's speaker has an impedance of 8 ohm

The cabinet's speaker impedance is 8 ohm as well

The "External Speaker"output says 8-16 ohm

If I insert the plug all the way down, only the cabinet works. If I have it inserted half-way, amp and cabinet work together.

Do you guys know if this procedures can damage my amp ? Or my cabinet ?

I would really appreciate any feedback,

best regards
Marcus Vinicius (ToneZoner)

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post #2 of 12 (permalink) Old 04-10-2003, 02:43 PM
 
Join Date: Apr 2003
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Are you using a speaker cable or instrument cable?

NEVER use shielded instrument cable from an amp to a cabinet. ALWAYS use unshielded speaker cable. You could fry your output tranny.

It almost sounds like your using a stereo instrument cable.
Dan D Mahnn is offline  
post #3 of 12 (permalink) Old 04-10-2003, 02:46 PM Thread Starter
 
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Hi Dan.

now I'm getting really scared. I use a regular instrument cable. My God...I will fry my equipment...

Where can I find this specific kind of cable ????
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post #4 of 12 (permalink) Old 04-10-2003, 03:29 PM
 
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Just your local music store.

Make sure its unshielded, 1/4" speaker cable.

Theres not much here for quality. If you want quality with speaker cable the rule is the thicker the gauge, the better. Its not a big difference.


You were using a stereo plug right? On the tip it has 3 seperate metal sections instead of 2. Right? Make sure you dont do that by accident again. Very not good.
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post #5 of 12 (permalink) Old 04-10-2003, 03:31 PM Thread Starter
 
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Hi Dan,

if I'm not confusing things, the cable has 2 stripes at the tip, not 3...it's a regular Spectraflex...
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post #6 of 12 (permalink) Old 04-10-2003, 03:38 PM
 
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If the stripes your refering to are thin and black then it is a stereo cable.

I am refering to the metal portions of the plug tip.

On a stereo plug there will; be 3. A tip and 2 sleeves.

Understand? Is that what you have?
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post #7 of 12 (permalink) Old 04-10-2003, 03:41 PM Thread Starter
 
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I guess that's exactly what I have.

I can't believe it...

If I don't use a stereo cable, but a standard instrument cable, will the risk still be around ?
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post #8 of 12 (permalink) Old 04-10-2003, 03:52 PM
 
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Yes. Its still very bad. Guitar/instrument cable is designed to handle a certain current/ amount of signal. Its very faint. If you plugged a guitar striat into a cab you wouldnt hear anything. Now the signal that comes out of your amp head is very large.

Is that making sense?

The importance of whether its a stereo cable or not is that that may be why you only get a signal when plugged half way in. Some combo amps are made to bypass the internal speaker when an extension cab is plugged in. Im not familiar with Laney at all. Never owned one. Get yourself a speaker cable and try it then.
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post #9 of 12 (permalink) Old 04-10-2003, 03:52 PM
 
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Posts: 111
For starters, definitely get a proper speaker cable! A instrument cable wont do, because the shielding around the central wire cannot cope with the current that flows through the cable. You want something like 2-core mains cable (2 cores, unshielded) with jacks on either end, shouldnt cost more than a few bucks

It sounds like you're pushing the jack in far enough to make a connection, but not far enough to trigger the switching part of the socket (ie the bit that switches off the internal speaker). Although this isnt really advisable (the jack could get pulled out easily, which wouldnt be good), it wont necessarily damage the amp..

You cant really say whether this will damage it or not without knowing how the speaker outputs are wired - if theyre in parallel (most likely), then youre running a load of 4ohms. Seeing as the ext. speaker jack specifies 8ohm minimum, this could cause damage (hard to tell for sure, have a look in the manual for some data about the output transformer)

Best bet is to get in touch with Laney and ask them.. If theyre not too keen on you "cheating" their system then try asking how the speaker jacks are wired (series/parallel), and if the output transformer can cope with a load of 4ohms
rilla is offline  
post #10 of 12 (permalink) Old 04-10-2003, 03:58 PM
 
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I checked the manual at Laneys website. It sounds like its wired so that if you plug in an extension speaker, the internal speaker cuts out. Its normal.

Just make sure you have yourself a speaker cable before you plug into it again.
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post #11 of 12 (permalink) Old 04-10-2003, 04:02 PM
 
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Yeah, but i thought he was trying to get it so that both worked at the same time...

I suppose you could wire the two up in series (giving 16ohms total), and plug that into the ext speaker socket... its a bit messy tho
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post #12 of 12 (permalink) Old 04-10-2003, 04:04 PM
 
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I agree with Rilla too. Call Laney. Personally I wouldnt just leave the cable hanging halfway in. If it falls out and you have the amp cranked, thats when things can get bad.
Dan D Mahnn is offline  
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amp head , combo amp , extension cab , local music store , mesa boogie , music store , speaker cab

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