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Guitar Amp Dummy Load for 1 of 2 cabs...
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NickH
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#1
26th August 2007
Old 26th August 2007
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Question Guitar Amp Dummy Load for 1 of 2 cabs...

Hi,

A quick question; Can I make dummy load for a guitar heads that will act as a replacement of one 4x12 in a two 4 x12 setup?

My reasoning is this, if I run the head at 16 ohm with one (16 ohm) 4 x12 to get the nice output stage distortion I end up pushing the volume up past a level where the cab is happy (or sounding good) I am basically pushing it too hard.

Now if I connect two 16 ohm 4x12 cabs up to the head & run it at 8 ohm, I can get the nice distortion I am after and it’s not pushing ether cab too hard, so they are sounding much better.

However I am only micing one of these cabs, the other is there only to suck power if you like, if I could replace that cab with a dummy load without damaging the head or compromising the sound I would love to... Less volume flying round the live room, less coming though the wall etc, etc..

Can this be done without screwing the amp head up the sound of the other cab? The main head I will be doing this with is 120watt, if it’s not a totally flawed idea, what resistors should I get to make this box? Anything else I should know about this?

Many Thanks

Nick
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27th August 2007
Old 27th August 2007
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There are devices called hot plates or power soaks that do exactly what you are talking about (more or less).

There is a reason that 35w and 50w (and even 15w) amps are popular. The 100w guitar head was made for a large venue before PA's were good.




-tINY

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27th August 2007
Old 27th August 2007
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Quote:
Originally Posted by ArtGarceau View Post
Shit...even that 5watt Valve Jr. is loud as hell. I used a 300watt Randall Warhead which didn't have nearly the same amount of volume as my old 50 watt JCM800 that I used to have. Why are lower wattage tube amps so powerful? Maybe I used a broken Warhead?
It's because loudness and watts are not a 1:1 ratio. For example, a 10 watt amp is not twice as loud as a 5 watt. It takes a ten-fold increase to effectively double an amplifier's loudness.

-SD
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28th August 2007
Old 28th August 2007
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I always used the 4x to double the loudness.

But, if you change speakers, there can be a huge shift in efficiency. 300w driving a 85dB/1w speaker is about as loud as 50w amp driving a 92dB/1w speaker.

And remember that you increase your efficiency by about 3dB when you double the number of drivers.

100w head and a full stack - Yikes!.



-tINY

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28th August 2007
Old 28th August 2007
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Quote:
Originally Posted by NickH View Post
Hi,

A quick question; Can I make dummy load for a guitar heads that will act as a replacement of one 4x12 in a two 4 x12 setup?

My reasoning is this, if I run the head at 16 ohm with one (16 ohm) 4 x12 to get the nice output stage distortion I end up pushing the volume up past a level where the cab is happy (or sounding good) I am basically pushing it too hard.

Now if I connect two 16 ohm 4x12 cabs up to the head & run it at 8 ohm, I can get the nice distortion I am after and it’s not pushing ether cab too hard, so they are sounding much better.

However I am only micing one of these cabs, the other is there only to suck power if you like, if I could replace that cab with a dummy load without damaging the head or compromising the sound I would love to... Less volume flying round the live room, less coming though the wall etc, etc..

Can this be done without screwing the amp head up the sound of the other cab? The main head I will be doing this with is 120watt, if it’s not a totally flawed idea, what resistors should I get to make this box? Anything else I should know about this?

Many Thanks

Nick
It would work... but I've always felt it make the sound coming out of the speakers sound stiff and hazy. never was happy with any product that does what you're saying. and I've tried quite a few.

-steve
NickH
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28th August 2007
Old 28th August 2007
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Quote:
Originally Posted by hangman View Post
It would work... but I've always felt it make the sound coming out of the speakers sound stiff and hazy. never was happy with any product that does what you're saying. and I've tried quite a few.

-steve
Even though it would be just acting as a load instead of the second cab? Would the first cab really be affected?

I could see why an attenuator between the amp & the speakers would do this, but this is just taking one cab out of the equation & replacing it with a dummy load...

If as tINY says that I get a 3db increase by adding the second cab, when the second cab is replaced by a dummy load the actual volume in the room should drop by 62.5% (that was off the top of my head & it’s late, so probably BLX) compared to both cabs running... But how would it affect the sound of the first cab? That should sound the same as it did with both real cabs going shouldn’t it (apart from the room sound of the other cab of course...)

Cheers

N
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29th August 2007
Old 29th August 2007
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Quote:
Originally Posted by NickH View Post
If as tINY says that I get a 3db increase by adding the second cab
actually it depends on whether it is in series or parallel. Adding another cab changes the load. Drop the impedence and it gets louder. What he said applies more to, given the same speakers, 1x8ohm vs 2x16ohm(changing the speaker surface area at a given load) or 1x8ohm vs 2x8ohm(changing load to either 4 or 16ohm and surface area).

If you want a quieter amp, you need an attenuator between the head and cab. Or you can install a post phase inverter master volume.
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