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Post by jefferym on Mar 15, 2011 19:40:42 GMT -5
Hello,
I have a Splawn Nitro and I am thinking about buying a Rivera Rock-crusher attenuator.
Currently I have the amp set to 1/2 power and I am running the amp at 8 ohms into a Marshall 16 ohm cabinet. If I buy a attenuator and it has a switch for 8 or 16 ohms what is the correct setting to run the attenuator if my amp is set to 8 ohms running into a 16 ohm cabinet?
thanks
Jeffery
jm@spe.midco.net
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Post by banenis on Mar 15, 2011 20:42:58 GMT -5
If you keep running at half power then set the amp at 8ohms, the Rivera at 16ohms and go to the 16 ohm cabinet.
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Post by metaltronixmike on Mar 16, 2011 11:31:58 GMT -5
Mind if I jump in here? I've owned and used practically every attenuator on the market. Currently using a Faustine Phantom DX2 which is by far the cleanest, most transparent unit ever. Question; if you intend on using an attenuator, why run 1/2 power? Tone? Saturation?
A couple of important points; First, when running an amp at 1/2 power, you must reduce the ohm by 1/2 of it's current setting. Example: Full power 16 ohms = 8 ohms 1/2 power. Full power 8 ohms = 4 ohms half power.
Second, every attenuator I have ever used is always matched to the ohm setting of the amp regardless of whether you running 1/2 or full power. Be very careful with this. The attenuator is is taking signal direct from the head. If it isn't properly matched with the head, you can burn caps, trannys, etc.
Finally, the ohmage of your amp/attenuator should be equal to, or LESS than the ohm setting of your cabinet. NEVER more. You can safely run a tube amp at a less ohm setting than your cab. You CANNOT safely run the opposite. Hope this helps, good luck.
MM
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Post by banenis on Mar 16, 2011 19:54:21 GMT -5
This seems an important contradiction that should probably be sorted out.
Your amp does not care if your putting it into a load box or a speaker cabinet. Tin half power mode it wants the output resistance setting to be half that of the load, not half of the eventual cabinet. If you're running at half power you should set the impedance to be half of the rating of whatever load you're putting on the amp, whether that's a LB or real speakers.
If I'm wrong, you'll have to explain why.
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Post by splawndude on Mar 17, 2011 8:45:21 GMT -5
Edit: I stand corrected. Banenis is correct. ;D
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Post by banenis on Mar 18, 2011 8:09:00 GMT -5
From Scott this morning.
Jake
I use two different half power circuits. The first is for the 100 watt heads
that have four power tubes. When you switch to half power on these models,
two of the output tubes are bypassed so you are running on two tubes. The
output transformer still thinks that there are four tubes running, so you
have to set the amp to half of the load of the cab that you are using to
match the impedance.
The other circuit is for the 50 and 40 watt amps that only have two power
tubes. This is a pentode/triode circuit, which rewires the tube. You do not
have to change the impedance on these models because the transformers is
still running two tubes even in half power.
Thank You God Bless
Scott Splawn
Splawn Amplification
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Post by banenis on Mar 18, 2011 8:10:27 GMT -5
Long story short. Set your head to half the load box or speaker cabinet rating if it's a hundred watt head.
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Post by splawndude on Mar 18, 2011 12:50:51 GMT -5
banenis - You are correct. I just looked at my head again and it is set at 4 ohms (8 ohm cab). I should have checked first before calling you out. I guess I just had a brain fart. Josh at Splawn also confirmed this. I'll edit my post.
Carry on,
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Post by banenis on Mar 18, 2011 16:36:23 GMT -5
No prob. Just wanted to make sure we're all on the same page and no one is doing anything to hurt their gear.
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