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Re hooking up Trace head to Peavey cab


surfguy13
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I was about to buy a used Trace GP7 SM head to run into an old Peavey 4 ohm  1x15 cab.  But.............I had neglected to check outputs on the Trace and I now realise that there are 2 x 8 ohm outs on the Trace head.  

Is there a way to hook up a head with 2 x 8 ohm outs to a 4 ohm cab.  I suspect not but I just wanted to be 100% before I do anything.

Many thanks!  

Edited by surfguy13
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2 minutes ago, Nobatron said:

I don't know that particular model but most likely the outputs are parallel and the head will drive a 4 ohm load into a single cab just fine. Just don't plug a second cab in.

Cheers for that.  So would I just run a lead from one of the 8 ohm outputs to the single 4 ohm in the cab?  Also, would this effect the volume?

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37 minutes ago, Nobatron said:

I'm not sure what you mean by it affecting the volume. The amp would be running it's full wattage into a 4 ohm load.

I only asked about volume because when you look at a spec for an amp it'll say something like 300 watts @ 4 ohms and 150 watts at 8 ohm.  Or maybe I'm getting confused!!

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Yeah, that's right. So the wattage an amp puts out is in relation to the load it is running. Typically amp power ratings are advertised at the number of watts they will put out at their lowest resistance. So if your amp is rated at 300 watts you'll get the full 300 watts at 4 ohms.

Assuming the outputs on your amp are parallel (which they probably are) you'll get the full power into that 4 ohm cab.

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25 minutes ago, surfguy13 said:

I only asked about volume because when you look at a spec for an amp it'll say something like 300 watts @ 4 ohms and 150 watts at 8 ohm.  Or maybe I'm getting confused!!

That's because an amp will deliver higher voltage into a lower impedance load. No matter, the difference in what you'll actually hear is slight, if any. There are a lot of factors that determine how loud a rig will go, and watts are only a minor part of the equation.

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6 minutes ago, Bill Fitzmaurice said:

That's because an amp will deliver higher voltage into a lower impedance load. No matter, the difference in what you'll actually hear is slight, if any. There are a lot of factors that determine how loud a rig will go, and watts are only a minor part of the equation.

 

No, the voltage will remain the same but the current will increase into a lower impedance load. This assumes that the power supply is large enough (electrically not physically).

Edited by Chienmortbb
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Thanks guys so much.  Impedance tends to go over my head, I haven't really ever understood it and just followed the basic rules.  However, being faced with 2 x 8 ohm outputs when I use an 4 ohm cab is slightly disorientating.

So..........do I need to establish that the 2 x 8ohm outputs on the Trace are parallel before I do anything?  Or, can I use the outputs regardless?  I assume I just use one of the outputs direct into the cab?

Edited by surfguy13
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38 minutes ago, Chienmortbb said:

 

No, the voltage will remain the same but the current will increase into a lower impedance load. This assumes that the power supply is large enough (electrically not physically).

Quite right. What I meant to say is that with lower impedance the cone will move further with the same applied voltage, and the further the cone moves the louder the sound. Current goes up, which causes power to go up, but the downside to that is too low a load impedance draws more current than the amp can comfortably deliver, both with respect to the power supply and the output devices. What's key to the oft mentioned 'I want to get all the watts out of my amp' is that to sound twice as loud requires ten time the power. At maximum output the average amp will only deliver 1.7 times the power into 4 ohms versus 8 ohms.

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Just waded through a PDF I found online courtesy of americanmusical.com which seems to be a generic manual for a number of Trace combos and heads.  All I found that seemed like it might be relevant is the following:

"Trace Elliot amplifi ers are designed to deliver their rated RMS output power into 4 ohm speaker loads. Therefore each amplifi er can drive 1x 4 ohm cabinet or 2x 8 ohm cabinets (in parallel).

Driving a single 8 ohm load will deliver between 50% and 60% of the rated power. Never connect your amplifi er to a speaker load lower than the rated 4 ohms. This will result in over heating of the amplifier and it shutting down into protect mode."

I don't know whether this shines any light on the issue but it seems to suggest that all the amps listed can either drive 1 x 4ohm cab or 2 x 8ohm cabs in parallel.  I can provide the link to the manual if anyone wishes to see it.

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1 hour ago, Merton said:

That’s standard of the vast majority of solid state heads. The speaker outputs on the amp are wired in parallel, so you can connect your one 4 ohm cab to either output. Just don’t connect any more cabs.

Many thanks for confirming that @Merton  I will go ahead and grab this head as it seems there is no doubt that I can safely use one of the 8 ohm outputs on the Trace to connect to the 4 ohm cab.  Big relief!

Really appreciate all the above help and advice.

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