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Technical Question Re: Speakers

 
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BobK
Guitar God


Joined: 10 Mar 2008
Posts: 176
Location: Kent, England.

PostPosted: Mon Jun 01, 2009 9:36 am    Post subject: Technical Question Re: Speakers Reply with quote

Have a Marshall AVT 412 speaker cabinet (8 ohms).

Can I run any head through it provided it is '8 ohms' as well?

Bob
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colinhotrod
Guitar God


Joined: 19 Jul 2008
Posts: 195
Location: Fife, scotland

PostPosted: Mon Jun 01, 2009 9:55 am    Post subject: Reply with quote

you are correct in thinking that, Alot of heads have the option of impedance outputs, my marshall is either 4, 8 or 16 ohm

This is from my manual,

15. SPEAKER Outputs
There are 5 speaker outputs available on the
rear panel. They are labelled according to the
intended impedances:

16 ohms: connect any 16 ohms guitar cabinet to this
jack.

8 ohms: connect a single 8 ohms guitar cabinet or
two 16 ohms guitar cabinets.

4 ohms: connect a single 4 ohms guitar cabinet or
two 8 ohms guitar cabinets.


WARNING, although the JVM amplifier has 5
speaker outputs never attempt to connect more
speakers than rated. The safe combinations are
1x16 Ohm, 1x8 Ohm, 1x4 Ohm, 2x16 Ohm or
2x8 Ohm. Any other speaker configuration may
stress the power amplifier section and in
extreme cases may lead to valve and/or output
transformer failure.
HINTS & TIPS
Factory Reset
This will erase all the MIDI presets and set MIDI
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JohnA
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Joined: 02 Mar 2007
Posts: 4176
Location: Leicester UK

PostPosted: Mon Jun 01, 2009 9:56 am    Post subject: Reply with quote

In short, Yes

A valve head will be OK as long as the output is 8 Ohms, a transitor head would be OK as long as the impedence is at most 8 Ohms. i.e. you can run a transistor head rated at 4 ohms in to a cab rated at 4 or 8 Ohms, but a valve head & cab should be matched.

Mis-matching impedence on valve amps you run the risk of danaging the output transformer.
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BobK
Guitar God


Joined: 10 Mar 2008
Posts: 176
Location: Kent, England.

PostPosted: Mon Jun 01, 2009 1:10 pm    Post subject: Reply with quote

Thanks guys.

Bob
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Skybone
Guitar God


Joined: 04 Dec 2001
Posts: 504
Location: South Yorkshire, UK

PostPosted: Tue Jun 09, 2009 8:18 am    Post subject: Re: Technical Question Re: Speakers Reply with quote

BobK wrote:
Have a Marshall AVT 412 speaker cabinet (8 ohms).

Can I run any head through it provided it is '8 ohms' as well?

Bob


It'll also depend on the actual wattage of the cab too. Generally, most cabs are fairly "robust" in terms of their power handling capabilities, most 4x12 cabs are designed to handle 100w heads, so that the sum of all 4 speakers will be greater than the power they need to handle.

For example, 4 Vintage 30 speakers can handle a loading of 120w, easily enough for most amps @ the right impedance (be it 4, 8 or 16 Ohms).
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JohnA
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Joined: 02 Mar 2007
Posts: 4176
Location: Leicester UK

PostPosted: Tue Jun 09, 2009 8:46 am    Post subject: Reply with quote

Totally agree, but Just to be picky
A Celestion Vintage 30 despite it's name has a power handling of 60W
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