Bypassing the preamp, output levels question

[Jack_TriPpEr]

On a solid-state guitar amp head, if I bypass the preamp by routing my guitar + stompboxes into the Effects Loop Return jack, will the output level (in Watts) from the speaker output jacks vary dependent on how the volume/output knobs are set on the stompboxes? Or no, the output level will be the full, non-varying RMS Wattage output rating for that amplifier? I've tried this set-up with the amp head hooked up to a speaker cabinet and I can audibly hear differences in volume as I tweak the volume/output knobs on the stompboxes, but I am wondering if that audible volume difference is still separate and distinct from how many Watts the amp is sending to the speaker cabinet (?) Since - at least on my amp (an Acoustic G120H head) the volume knobs for the two channels have no effect when I have bypassed the preamp in this manner - and there is no Master Volume knob on this amp head either.

 

[El Dunco]

Re: Bypassing the preamp, output levels question

I would put a volume control or line mixer at the very end so you don't get killed by the volume when you turn your drive boxes off.

 

[Jack_TriPpEr]

Re: Bypassing the preamp, output levels question

I would put a volume control or line mixer at the very end so you don't get killed by the volume when you turn your drive boxes off.

Yep, my signal path into the Return jack ends with a volume pedal.

 

[SlyFoxx]

Re: Bypassing the preamp, output levels question

Wattage always tracks with the gain/level sent to the amp and thus the resulting volume.

A 100 watt amp at whisper volume is putting out something like .05 watts to the speaker(s). At bed room volume perhaps 2 watts. At small club gig volume it might be peaking at 20 watts. At full roar the cops will be here any minute volume...well now your using all 100 watts and probably a bit more.

 

[El Dunco]

Re: Bypassing the preamp, output levels question

Instead of a volume pedal, I'd use something you can't crank by accident. Even an eq pedal at the end of the line set flat with the output volume to attenuate the signal on the way in, that's if it turns out the master volume doesn't affect the power amp and goes full blast in the effects return.

 

[Jack_TriPpEr]

Re: Bypassing the preamp, output levels question

Wattage always tracks with the gain/level sent to the amp and thus the resulting volume.

A 100 watt amp at whisper volume is putting out something like .05 watts to the speaker(s). At bed room volume perhaps 2 watts. At small club gig volume it might be peaking at 20 watts. At full roar the cops will be here any minute volume...well now your using all 100 watts and probably a bit more.

That makes intuitive sense but the second paragraph in this quote from an article by Two Notes Audio Engineering seems to state that there is no proportional relationship between Volume Level setting and Output Power. What's crazy is that in the prior paragraph they seem to state that there *is* a proportional relationship.

http://support.two-notes.com/knowledgebase.php?article=277

"The output power is related to the actual output volume of the amplifier, which is dependant on many things (amount of distortion, EQ, output level of the guitar...), but is mostly controlled by the Volume or Master Volume control. So if you keep the output volume of any amplifier low enough, no matter how powerful it is, you can make it output less than any chosen amount of power.

Of course, it is almost impossible to know what the actual output power of your amplifier is in any particular situation. In particular, please note that the power output is in no way proportional to the Volume control : when the Volume is set to 50% (12 o'clock), the output power is never half the rated power of the amplifier ! It can be 10%, 90%, or even already the maximum power."

 

[SlyFoxx]

Re: Bypassing the preamp, output levels question

That's because the volume knob number is just that...a number on a face plate. If I run a HUGE amount of signal ...like say 10 times the amount that a normal electric guitar can produce into the amp...now X on the volume knob will be much louder than it was before. (provided I don't clip the signal path with too much signal)

My example is dealing with power as related to volume. Take a typical guitar speaker that generates 100 dB at 1 meter driven by 1 watt. (very loud by the way) If you're sitting a meter away from the speaker and you hear about 100 dB of volume you can be pretty sure the amp is churning out about a watt. If that same situation nets you 70 dB you can calculate the approximate wattage as 1/1000 of a watt. If that same situation nets you 120 dB then you know your using about all a 100 watt amp has to give. Doesn't matter where any of the knobs are because I know the efficiency of the speaker and how close I am to it. So I know how much power from an amp it would take to reach those figures. Of course these are ballpark figures as a guitar signal isn't a pure sine wave. If fluctuates as you play.

 

[Demanic]

Re: Bypassing the preamp, output levels question

There also comes a point to where you ear physically compresses the signal. And when you push it past that point, you start going deaf. I think that the effect is cumulative.

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