Is a single 20 amp dedicated circuit enough to run mono blocks

Chances are you'll be ok doing that, but not necessarily. It depends on the speaker impedance (the higher the better), the speaker sensitivity (the higher the better), and your preferred listening volumes (the lower the better).

Each of the two monoblock amps is rated as follows:

Max output power into 8 ohms: 600 watts.
Max output power into 4 ohms: 900 watts.

AC power consumption, 600 watts into 8 ohms: 1100 watts.
AC power consumption, 900 watts into 4 ohms: Not specified, but certainly a good deal more than 1100 watts.

AC power consumption, 75 watts into 8 ohms: 725 watts.
AC power consumption, 75 watts into 4 ohms: Not specified.

So if the two amps were delivering 75 watts into 8 ohms the total power consumption would be 725 x 2 = 1450 watts. 20 amps at 120 volts corresponds to 20 x 120 = 2400 watts, so you would be ok in that situation unless other things on that line drew a lot of current. But you might have a problem if the amps are required to supply power levels approaching their max capability.

Regards,
-- Al

Power Consumption (Watts)
600 watts 8 ohm 1100 watts
75 watts 8 ohm 750 watts

Note the data plate on the back says ,
120V 60 Hz 1100W
http://www.bryston.com/PDF/Manuals/7B3_Manual.pdf

It’s not a question whether you can plug them both into outlets fed from the same 120V 20 amp dedicated circuit. The question should be how will they preform? Will they be starved for power if they are pushed hard any where near their full rated available output power?

What is the distance, length, of the 20 amp dedicated branch circuit? (Up, down, over, and around.)

What size of AWG wire did you use? Bare minimum #12awg or #10awg?
If you used #10 you should be fine if the length of the branch circuit is not too long.

If the branch circuit wiring is #12awg and the length of the branch circuit is over, say 50ft or so, then when you push the amps hard playing music with a lot of dynamics you may experience fluctuations in the AC mains voltage. As the amps are trying to draw more current, amps, (in gulps), to replenish, recharge, the electrolytic capacitors in the DC power supplies the mains voltage will/may dip. A power amp’s power supply need a steady state voltage. It doesn’t like the voltage fluctuating with the beat of the music.

You could use a volt meter and watch the meter as you push both amps hard to see if the voltage is holding steady or fluctuating, bouncing all over the place. You might even try a table lamp using a 60 watt incandescent light bulb. If you see the brilliance of the lamp changing with the beat, dynamics of the music, when you are pushing the amps hard, then that tells you the voltage is fluctuating as the amps are trying to draw more current.

.

Speakers are Focus Audio FS-788,i believe that they are 10 ohoms 

New house ,using 12/2 wire at 40 feet from distribution box,,great idea with the lamp

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&u...


Ohm chart for speaker