[john1970]

Dear Bryston Owners,

I am considering the purchase of a JL Audio Fathom F113 in the next couple of months, but I am concerned if it can be plugged into a 20 A (120 V, 12 gauge wire) circuit that shares my 4B SST amp. 

FACTS:
1) The Bryston 4B SST can draw 2100 W (17.5A) under full power (500 W @ 4 ohms). 
2) The JL Audio F113 is rated at delivering 2500 W RMS short-term (a few seconds).

A very basic calculation is that V=IR and P= IV, Hence, P = I^2*R.  Based on this crude model, the F113, with a nominal 3 ohm impedance, can draw up to 28 amps!  Combined with the 4B SST and the current draw will be over 40 amps. 


From JL Audio I discovered the following post regarding the F113:

1) A "15 Amp" circuit is capable of delivering well over 15 amps for short periods without danger and without tripping breakers. Usually 30 amps for well over a couple of seconds is attainable. This headroom is there to account for high on-rush current demands from appliances. This headroom gives even a Gotham enough room to operate off a standard outlet. A pair of Fathoms can trip a 15A breaker, but usually only with extended test tones at very high SPL levels. A single Fathom won't trip a breaker in our experience. We utilize highly efficient Class D (switching) amplifiers which also helps keep current demands down.

2) The "2500 watt" figure is based on the rail voltage of the amplifier referenced to the nominal driver impedance (3 ohms). Throughout most of the bass range, the actual impedance is significantly higher than 3 ohms and will not demand that much power be produced (although the rail voltages remain high and equivalent to 2500 W into 3 ohms). This phenomenon (hardly unique to our products) helps keep current drawn from the outlet at manageable levels in real world use. Were you to connect the Fathom amplifier to a 3 ohm resistive load, you would definitely run into problems... but since this is a closed system and we know its impedance characteristics, we can run things pretty close to the limit without getting in trouble.


I would appreciate any additional feedback that anyone can give.  I am not going for reference levels here.  I typically listen to music with 95 dB peaks at 2.5 meters and movies at 100 dB peaks.  Lastly, I have a Zero Surge 20 A surge surpressor hooked up to the outlet for additional protection.


Thank you,

John

[werd]

Hello John

Are you asking sonically or functionally?. Functionally it will work, you should have no problems under any condition. Sonically, i should add i have never had a 120volt 20 amp dedicated system, I would venture to say  would not degrade the performance of either component dramatically. I would recommend ditching the surge surpressor. Bryston attached inline with a surge surpessor is considered taboo around here. What you are doing is nerfing your dynamics and transients. Plug straight into the wall if possible.

Bryston addressed this issue of current demands with Torus components. Its a valid concern what your asking, having experience what my rm-20 did for my music playback. Current draw and availability is key to everything in music playback imo.

[john1970]

Hello John

Are you asking sonically or functionally?. Functionally it will work, you should have no problems under any condition. Sonically, i should add i have never had a 120volt 20 amp dedicated system, I would venture to say  would not degrade the performance of either component dramatically. I would recommend ditching the surge surpressor. Bryston attached inline with a surge surpessor is considered taboo around here. What you are doing is nerfing your dynamics and transients. Plug straight into the wall if possible.

Bryston addressed this issue of current demands with Torus components. Its a valid concern what your asking, having experience what my rm-20 did for my music playback. Current draw and availability is key to everything in music playback imo.

I am asking for functionally.  I realize that adding a Torus RM-20 would drastically improve things.  However, I need to take things one at a time and am considering the Torus in the future (within the next year).  I agree that plugging the amp directly into the output is prefered; however, i get a lot of brown outs where I live and I don't want to risk damaging a $4K amp without surge protection.

Thank you,

John

[danman]

As odd as this may sound I have a 20 amp curcuit for my audio needs and plug straight into the wall as werd mentioned. However after each listening session I always unplug! This may sound kind of labourous but until I am convinced of stable current I will continue doing this. A Torus may be in the future but I have tried some other high quality brands in the past and noticed nothing different for the price asked. I would love to experience a Torus model someday as I am a little sceptable about this area of audio probably due to the fact that I don't really comprehend it enough yet! Hoping to go to a audio show or sometning to listen for myself next year.

[richidoo]

Brown out is low voltage condition, no harm to the electronics, but they might shut off. A 20 amp circuit will have the same voltage as the 15A circuits even in a brown out. But it has heavier wire and a circuit breaker to allow more power. If you have one available, go for it, but the 15A will be plenty to run those components - functionally. The 4B power transformer is big enough to reserve energy for any musical transients. As long as the circuit doesn't trip when you turn them on, you are all set. Switch them separately, if possible.

Remember that the 15A outlets might be sharing other outlets and lights on same circuit. Each screwed or twisted wire nut connection increases the source impedance to the amp. It adds more resistance to the wire than you would have with a straight run. Looking at the surfaces of the twisted wires, the microsurfaces are not perfectly smooth, so only a very small actualy contact area. This increases resistance and impedance and constricts current flow to the amp. This is the main sonic benefit of a dedicated circuit, having a clean uninterrupted wire from outlet to circuit panel for getting a low impedance at the outlet, not so much the ultimate power handling capacity which is very rarely touched with consumer electronics. The Torus or any magnetic power conditioner regenerates the electricity and lowers the source impedance drastically, and thus spoon feeding current to the amp. It doesn't matter what kind of outlet feeds it.

The quality of the power cord connectors and the outlet itself with tight gripping contacts is also important for keeping impedance low.  There is some magic in the wire too, but the connector quality is much of the benefit.  Uh-oh, I'm rambling now.... 

[werd]

As odd as this may sound I have a 20 amp curcuit for my audio needs and plug straight into the wall as werd mentioned. However after each listening session I always unplug! This may sound kind of labourous but until I am convinced of stable current I will continue doing this. A Torus may be in the future but I have tried some other high quality brands in the past and noticed nothing different for the price asked. I would love to experience a Torus model someday as I am a little sceptable about this area of audio probably due to the fact that I don't really comprehend it enough yet! Hoping to go to a audio show or sometning to listen for myself next year.

Hi Danman

Just go get one (Torus), pure blind faith. They represent  a new generation of power conditioning. Its not a passive sounding component as ive been used to hearing from power conditioners. But more active in its ability to deliver current i think, still not really sure what is goin on yet with the improvement. I can speak for the 240 volt only, but i am sure the 120 is good too. I had a choice and picked the 240 and i would recommend anyone who can do this .... do this.