Comparing amplifier specs - gain

Rob Spence

Rob Spence

Senior
Jan 11, 2011
897
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Boston Metro North West
www.lynxaudioservices.com
So, I am feeling math challenged this morning despite the coffee so am asking for some help.

I drive my QRX212 HF (bi-amped) with one channel of a QSC PLX1602.
I have my DSP set up for this.

I need 2 more channels of amp in the rack with no available space.
I am considering the Behringer 4 ch amp as a solution but am trying to figure out the DSP gain changes I need to make for the substitution.

The specs as I could find them...

The PLX1602
Voltage gain = 40x (32dB)

Input sensitivity, V RMS
Full rated power at 8 ohms = 1.2v (+3.9 dBu) = 300w
Full rated power at 4 ohms = 1.1v (+3.2 dBu) = 500w

The INuke NU4-6000 (4 ch mono mode)
Max rated power at 8 ohms = 440w
Max rated power at 4 ohms = 860w

Input sensitivity for rated power into 4 ohms = 0.775 V (0 dBu)

Any help would be appreciated.

Sent from my iPad HD
 
Re: Comparing amplifier specs - gain

Rob Spence said:
So, I am feeling math challenged this morning despite the coffee so am asking for some help.

I drive my QRX212 HF (bi-amped) with one channel of a QSC PLX1602.
I have my DSP set up for this.

I need 2 more channels of amp in the rack with no available space.
I am considering the Behringer 4 ch amp as a solution but am trying to figure out the DSP gain changes I need to make for the substitution.

The specs as I could find them...

The PLX1602
Voltage gain = 40x (32dB)

Input sensitivity, V RMS
Full rated power at 8 ohms = 1.2v (+3.9 dBu) = 300w
Full rated power at 4 ohms = 1.1v (+3.2 dBu) = 500w

The INuke NU4-6000 (4 ch mono mode)
Max rated power at 8 ohms = 440w
Max rated power at 4 ohms = 860w

Input sensitivity for rated power into 4 ohms = 0.775 V (0 dBu)

Any help would be appreciated.

Sent from my iPad HD
Click to expand...

Max rated power at 4 ohms = 860w
58.65v =860w @ 4 ohm

Input sensitivity for rated power into 4 ohms = 0.775 V (0 dBu)

58.65/0.775=75.67x or 37.57dB

JR

[edit yes i fat fingered the dB /edit]
 
Last edited:
Re: Comparing amplifier specs - gain

860W into 4 ohms is 58.65V

58.65V / 1.1V is 53.32 or a voltage gain of 34.5 dB

So your DSP gain and limiters (if you're using them) have to be set 2.5 dB lower than they are now.

GTD

Oops, sorry, I looked the QSC sensitivity, not the B.

Running it again, I get 58.65/.775 for a gain of 75.67, which my ancient TI calculator tells me is +37.58 dB.

So gain needs to be roughly 5.5 dB lower.
 
Last edited:
Re: Comparing amplifier specs - gain

When your data is correct this would be a gain of 37,6dB.

But I wouldn't take that for granted.

My way would be to measure it and compare.
If your measurement tools aren't that good just adjust the gain to have the same reading for both amplifiers. Both will have the same error in display.
Maybe you can use a low frequency signal of about 50-60Hz, because most simple multimeters are specced for that frequency...

Edit: Glad I come up with the same amount. :)~:)~:smile:
 
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