@amirm :
Consider that the 50 Ohm is low LCR so it can handle MHz to GHz.
Headphones all will show a very high impedance at 1MHz so just using wirewound resistors for headphone loads is very realistic.
Of course, for e-stats it is different. I can understand you want the load to be resistive though over the entire spectrum but for headphones and speakers this is not realistic.
Honestly, I don't understand this stuff very well. I'm doing my best. I'll take your info at face value. But what about 1/4" and XLR4 being the same output? Again, Violectric (and owners of this amp) say volume and output should be louder on the XLR4 out. So what's up?
I'll try to explain to FourT6and2 the bit about balanced a bit more elaborate.
All amplifiers have a voltage limit
and a current limit. voltage x current = power.
When one wants to double the voltage one can put those amplifiers in series.
This doubles the voltage but NOT the current.
When one wants to double the current one must put the amplifiers in parallel.
To illustrate look at the O2 schematic, it has op-amps in parallel to double the output current.
This, however, doesn't double the voltage only the current.
When an amplifier is bridged (used balanced) there basically are 2 amplifiers
in series.
This means double the voltage but
not double the output current.
When one takes a look at output voltages of balanced and RCA output DAC's as an example. The RCA out is 2V then the XLR is 4V. As there is as good as no load at line level these voltages always double.
NOTE: The example is
not using actual values of the discussed Violectric amp but is an example.
Now comes the output power part, there is a lot of confusion about this.
Lets assume the amplifier in question has unlimited current (for argument sake) and can put out max 10V in SE and 20V in balanced.
some calculations for impedances.
'single ended' = 10V and 'balanced' = 20V
8 Ohm = 12.5W(1.25A) and 50W (2.5A)
16 Ohm = 6.25W(0.625A) and 25W (1.25A)
32 Ohm = 3.125W(0.313) and 12.5W (0.625A)
64 Ohm = 1.56W(0.156A) and 6.25W (0.313A)
128 Ohm = 0.78W(0.078A) and 3.125W (0.156A)
256 Ohm = 0.39W(0.039A) and 1.56W (0.078A)
512 Ohm = 0.19W (0.019A) and 0.78W(0.039A)
It is evident the output voltage is doubled and as a result of power = voltage x current (and current being voltage divided by resistance) is (voltage x voltage)/resistance. This means power is 4x higher in balanced mode.
What is also clear is that lower impedances require a lot more current than higher impedances.
Now comes the more difficult part in this story. The amplifiers are current limited. This means each amplifier can deliver 10V max and 250mA (0.25A).
In balanced mode these are in series so the output voltage can be double (and power quadrupled) as
long as the current limit is not reached.
The amplifiers are in series so max. current remains the same in SE and balanced mode. Power = (current x current) x resistance.
same table but now current limited at 250mA = 0.25A (with infinite output voltage): ‘single ended’ and ‘balanced’
8 Ohm = 0.5W(2V) and 0.5W (2V)
16 Ohm = 1W(4V) and 1W (4V)
32 Ohm = 2W(8V) and 2W (8V)
64 Ohm = 4W(16V) and 4W (16V)
128 Ohm = 8W(32V) and 8W (32V)
256 Ohm = 16W(64V) and 16W (64V)
512 Ohm = 32W (128V) and 32W(128V)
As can be seen high voltages are needed when high power levels are needed in high impedances.
Now to figure out how much power there is when the amp is voltage
and current limited all we have to do is look for the highest voltage the amp can put out (10V in single ended and 20V in balanced) in the above current table.
So for single ended (max 10V) and balanced (max 20V) we can see at certain impedances ,and 250mA current limit, voltages above 10V and 20V respectively are required but are not available.
8 Ohm = 0.5W(2V) and 0.5W (2V)
16 Ohm = 1W(4V) and 1W (4V)
32 Ohm = 2W(8V) and 2W (8V)
64 Ohm =
4W(16V) and 4W (16V)
128 Ohm =
8W(32V) and
8W (32V)
256 Ohm =
16W(64V) and
16W (64V)
512 Ohm =
32W (128V) and
32W(128V)
For voltages we can look in the table below that belong to the impedances and max currents (thus power). Here too there is a limit which in this case is 250mA both for single ended as well as balanced. Every level above 250mA (0.25A) thus is not possible.
This means we can strike out power levels requiring currents above 0.25A.
8 Ohm = 12.5W(1.25A) and 50W (2.5A)
16 Ohm = 6.25W(0.625A) and 25W (1.25A)
32 Ohm = 3.125W(0.313) and 12.5W (0.625A)
64 Ohm = 1.56W(0.156A) and 6.25W (0.313A)
128 Ohm = 0.78W(0.078A) and 3.125W (0.156A)
256 Ohm = 0.39W(0.039A) and 1.56W (0.078A)
512 Ohm = 0.19W (0.019A) and 0.78W(0.039A)
Now due to the impedances being stepped in factors of 2 the power levels that can be reached differ a bit in current and voltage.
Below the ‘borders’ once more.
32 Ohm = 2W(8V) and 2W (8V) versus
3.125W(0.313A) and
12.5W (0.625A)
64 Ohm =
4W(16V) and 4W (16V) versus 1.56W(0.156A) and
6.25W (0.313A)
128 Ohm =
8W(32V) and
8W (32V) versus 0.78W(0.078A) and 3.125W (0.156A)
So the limits are somewhere between these values because there is current
and voltage limiting in these amps.
For low impedance headphones the power is limited by current (which is the same for both amps so below a certain impedance the max. power is the same as shown in the current table BUT the voltages associated with that voltage can not be reached.
For high impedance the max power is determined by the output voltage so above a certain impedance the output voltage can be up to 2x higher in the balanced (20V) version.
8 Ohm = 0.5W(2V) and 0.5W (2V) = current limited
16 Ohm = 0.5W(2V) and 0.5W (2V) = current limited
32 Ohm = 2W(8V) and 2W (8V) = current limited
64 Ohm = 1.56W(10V) = voltage limited and 4W (16V) = current limited
128 Ohm = 0.78W(10V) and 3.125W (20V) = voltage limited
256 Ohm = 0.39W(10V) and 1.56W (20V) = voltage limited
512 Ohm = 0.19W (10V) and 0.78W(20V) = voltage limited
As can be seen above a certain impedance the power quadruples and below a certain impedance the power is actually the same with a small transition between same power and quadruple power between 32 Ohm and 128 Ohm and peaking somewhere around 64 Ohm in this case.
At 10V and 250mA one can calculate the maximum power as being
2.5W for which one needs 40 Ohm.
At 20V and 250mA the max power is
5W for which one needs 80 Ohm.
Again... these are NOT the numbers for the Violectric.