shadders said:
Hi,
Marantz state that for a 2volt input signal, you obtain the rated output, which is 40watts RMS. This is with an 8ohms load.
From the picture, the volume control goes from 7 o'clock which is no sound output (actually minimal) to 5 o'clock which is the maximum gain of the amplifier. This is a angular rotation of 300degrees.
Therefore, for a 2volt input signal, and with the volume control at 5 o'clock, you will obtain an output of 40watts RMS into 8ohms.
Depending on the type of potentiometer used in the volume control, whether linear or logarithmic, the 60degrees from 7 o'clock to 9 o'clock will increase the perceived sound level significantly, but the power delivered to the load will be less than 1/2 power. My statement of 1/4 was a generalisation and an estimation. You still have 4/5 of the total rotation to go, from 9 o'clock to get to 5 o'clock.
As the original poster stated, they may have turned up the bass tone control to a maximum which +10dB at 100Hz. If we assume 1/4 power at the 9 o'clock position, then this requires a power of 10x 1/4 = 2.5x more power required than the amplifier can deliver.
Regards,
Shadders.
Generally speaking the input sensitivity, 200mv in this instance, is defined as the input required for full output, this is what sensitivity means.
I don't know where you get the marantz quote from, but it is clearly an error.
Based on an incorrect premise, the second highlighted part is therefore incorrect, just 200mv is sufficient to give the full rated ouput of 40watts. This is why, when driven by the 2+volts of a digital player/dac, the amplifier gets loud so quickly.
The volume control is something of a red herring in all this, it operates entirely at the whim of the designer, about the only thing you can say for certain is that if you turn it up it gets louder, thats it. The idea that a 50% setting relates to half power (with a linear pot) or to one tenth power (with a logarithmic pot) simply is not true.
The use of the bass control causes some confusion too, it is simple a frequency dependent volume control, and adjusts the gain but only at lower frequencies. Given the power vs frequency distribution of popular music, virtually all the power is at low frquencies, so boosting the bass has pretty much the same effect on the power delivered by the amp as turning up the volume.
Ie, if you boost the bass by 10dB, you have 10dB less available on the volume, it's all about gain, you have around 26dB of gain in this amplifier, if you use 10dB to boost the bass, you only have 16dB 'left' for the volume.