Yamaha C-2 driving TDA7294: bad idea?

[stf92]

Hi: I have a power amplifier built around two TDA7294's, one for each channel. The circuit is such that the voltage gain is 30 dB. Hence V2/V1= 31.6. It is connected to a Yamaha C-2 preamplifier, which can put 775mV over 400 ohms. As the power amp has an input resistance greater than 100 kohms, we can say the pre is able to put 775mV at the power amp input. So, we have 0.775 V x 31.6= 24.5V as the maximum excursion the signal can make at the load. This would mean 24.5^2/2/8 = 37.5W average output power with an 8 ohms load. But the power supply is +33V/-33V and 33^2/2/8= 68W, assuming it can deliver the necessary current (the TDA7294 can deliver 80W to an 8 ohms load @T.H.D.= 1%).

So while with my 66V (33+33) I could get 68W, I must be happy with only 37.5W! The scenario would be even more ridicule if the power supply were the 40V + 40V allowed by the TDA7294, which could provide 40^2/16= 100W. What is wrong here? Is the C-2 designed for another type of power amplifier with a greater gain?

NOTE: I've been assuming the output voltage in a preamp is specified in peak volts and not rms volts, but maybe I am wrong.

 

[gmphadte]

Every AC voltage and or signal specified is always RMS value. If it is not, it will be mentioned.

http://www.diyaudio.com/forums/solid-state/259654-decibels-useful-other-info.html

Gajanan Phadte

 

[stf92]

Useful information, thanks. Applying it, now my amp delivers more power than I at first thought. Plus, the equation G= Rf/R was wrong. I am now using G= 1 + Rf/R, which gives a closer approximation, as this is a non-inverting amplifier. By the way, the Yamaha C-2 pre specification of 775mV in the output is precisely the dBu 0 reference in one of the tables in your link!