Essentials

Formulas and tables

Load-to-Power Relation in 100 V Systems

10 Ω  =  1000 W     20 Ω  =  500 W     25 Ω  =  400 W
40 Ω  =  250 W     50 Ω  =  200 W     100 Ω  =  100 W

Crest Factor

The Crest Factor of an amp represents the relation between the peak voltage and the RMS value. It can be taken as a measurement of the quality of the response of an amp.

Crest Factor   =   Peak   =   1   x   Peak
RMS √2

Resistance – Power

Ohm’s Law:   U = I x R ;   I =   U  ;  R =   U
R I
Power:   P = I2 x R ;   P =   U2  ;  P = U x I
R

Resistors in series:  Rtotal = R1 + R2 + … + Rn

Resistors parallel:  Rtotal =   1
1   +   1   + … +   1
R1 R2 Rn

Voltages in dBV und dBu

10  V     =     20  dBV     =     22.2  dBu
1.55  V     =     4.2  dBV     =     6  dBu
1  V     =     0  dBV     =     2.2  dBu
775  mV     =     -2.2  dBV     =     0  dBu
316  mV     =     -10  dBV     =     -7.8  dBu

“dB”-Relations

Voltage:   dB = 20 log10  U1
U2
Power:   dB = 10 log10  P1
P2

Conversion of THD to dB below signal level

 
THD %		   dB below
signal		  
THD %		   dB below
signal
100
10
5
1
0.5
0.25		   0
-20
-26
-40
-46
-52		 0.1
0.05
0.01
0.005
0.0025
0.001		   -60
-66
-80
-86
-92
-100

Voltage to Power

 
Volt		   Watt
4 Ω		   Watt
8 Ω		  
Volt		   Watt
4 Ω		   Watt
8 Ω
63.2
44.8
31.6
28.2
22.4		   1000
500
250
200
125		   500
250
125
100
62.5		 20
14.1
10
6.3
2		   100
50
25
10
1		   50
25
12.5
5
0.5

Pinouts

XLR   :   Pin 2 (+), Pin 3 (-), Pin 1 (Ground)
XLR unbal.   :   Pin 2 (+), Pin 1 and 3 (Ground)
6.3 mm TSR   :   Tip (+), Ring (-), Sleeve (Ground)
  • Infobox
    • Markus Ackermann
      September 2011