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What's my amp's actual output wattage to my speakers?

spankjam

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Hello there,

I'm trying to figure out how much wattage my speakers are actually receiving at full output from my Bryston through the Lynx Aurora (n)?

Speakers: Amphion One 18s
DAC: Lynx Aurora (n) at +20 dBu
AMP: Bryston 3B-ST Pro with trim fully counterclockwise

So the speakers apparently have a sensitivity of 85 dB @ 2.83V/1m

My DAC (Lynx Aurora n) is set to +20 dBu.

The Bryston 3B-ST runs XLR in balanced mode, which according to the manual has a gain of +23 dB (I'm not really able to make sense of the 23) with the front input trim fully CCW at -13 dB which is then obviously 4.5 times less energy, 1 volt equalling 6.3 volts to 5 watts and 8 ohms vs fully CW, 1 volts input equal to 28.3 output voltage, corresponding to 100 watts at 8 ohms. Don't understand though where the 5 watts are coming from 100 down.

Do the 28.3 volts output actually mean my converters output voltage peak to peak, which actually is 21.01 volts peak to peak in my case at 20 dBu or 22.2 dBu, which equals 28.3 volts?

I want to know, in case I set the output volume in the Aurora in the Mixer to 0 dBfs, which is a full output of +20 dBu, and the Brystons front panel trim pots completely counter click-wise (-13 dB), with which wattage I would hit the speakers at full power and whether it'd be safe given it's input sensitivity.

I already leave some headroom by turning the trim poti down (input to the amp resistor level trim) so they amp wouldn't distort but I have no clue how much +20 dBu for the Bryston is, whether it is in safe level and and I'm not already clipping with 20 dBu full output and how that translates to wattage given the speakers sensitivity and then what the actual wattage to the speakers is.

I used to be better at this but need some help to refresh my memories.

I've added all the spec docs to this post.

The reason why I wanna know this is because working with digital output control is funky and sometimes you end up going full volume out of the converter accidentally, which then has to be for me a safe error zone the speakers can take.

Thanks in advance guys.

Screenshot 2021-11-03 at 19-11-03 create_productsheets_one_18_euen_0117 pdf.png

Screenshot 2021-11-03 at 19-24-55 Lynx Aurora User Manual - Auroran-Manual-2020 03 18-Web pdf.png

aurora-n-top-wide-1-1400x850.jpg

bryston trim.jpg

bryston series.jpg

bryston specs 2.jpg

bryston specs.jpg
 

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spankjam

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If I remember this correctly, then 1 volt (I hope they mean rms) equals +2.2 dBu at 100 watts output, it would mean 120 watts would be 1.22 volts, which is +4 dBu studio standard? Which then at 120 watts the amp is made for?

Having always run it at full trim down -13 would put it at 7 dBu? Which equals to which wattage put out?

Is my math correct?
 
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spankjam

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Or does anyone know what the supposed input level for the amp is? I'm going in symmetrical over XLR which according to the manual is +23 dB of gain right? I couldn't find which voltage headroom this gain level takes except on an SST manual, which said 2v, which I suppose is rms not Peak to peak? Or is it dBv?

The only reference given is 1 volt to 28.3 volt output equalling 100 watts.

Like what's the input voltage / dBu recommended for this amp.

Screenshot_20211106-183233_Chrome.jpg
 
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DVDdoug

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I'd suggest you set-up a spreadsheet. I've got a spreadsheet set-up for converting back-and-forth between dB and voltage, and between dB and power. I've got another for calculating power (Wattage) but of course that doesn't have to be a separate spreadsheet.

It looks like you already know how to calculate dB, right? And, you know there are different formulas for power and voltage, right? (+6dB is double the voltage but 4 times the power.)

The specified voltages would be RMS.

0dBV is 1 Volt and 0dBu is 0.775V.

For calculating power the most-handy formula is Voltage squared/Resistance (or Voltage squared/Impedance).
(It can also be calculated as Voltage x Current or Current squared x resistance.)

And while were at it... Ohm's Law says Current = Voltage/Resistance. ;)
 

solderdude

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The 3B can deliver 120W in 8ohm.
Your speaker is rated for amps up t0 150W so this will be fine.
To reach 120W you will need 2.2V = +9dBu = +6.9dBV n the balanced input with the control set to max sensitivity so no issue for the Lynx.
 
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spankjam

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The 3B can deliver 120W in 8ohm.
Your speaker is rated for amps up t0 150W so this will be fine.
To reach 120W you will need 2.2V = +9dBu = +6.9dBV n the balanced input with the control set to max sensitivity so no issue for the Lynx.
So having the front panel input trim down full CCW (-13 dB it said in the manual) and going out at +20dBu out of the Lynx into the Bryston would put me where output wattage-wise? Thanks so much for the answer Been a decade and forgot most of the formulas along the way.
 

solderdude

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Lynx set to +20dBu = 7.7V

3B set fully CCW = 10dB gain = 3.1x7.7V = 24V in 8 ohm = 74W.
3B set fully CW = 23dB gain = 14x7.7V = clipping at 120W.

So the 3B should be set somewhere in between these settings.
 

Head_Unit

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Uh, wow that's a lot of calculations, but in the end I don't trust anything but a good AC voltmeter at the outputs to double-check those calculations.
safe error zone the speakers can take.
Well, that's not just one number. It depends a lot on the signal to the speaker. 100W sine wave at 400 Hz? Probably OK at least for a while. At 10 kHz? zzzzttttt is the sound of the tweeter frying like an egg on a Dubai sidewalk in summer. It's perhaps more important to work through this to set up your gain structure so your amp doesn't clip-THAT is a killer. Square waving the outputs can nearly double the power to the speaker but worse the treble peaks can crash through at far higher levels than normal, again killing the tweeter.
 

solderdude

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The solution is simple.
Dial the volume control down when sound gets 'ugly, gritty, distorted or coarse'.
 
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