Monoblock power amps same dedicated outlet?


Hi,

Looking for input whether putting both monoblock power cables into same dedicated line outlet receptacle is ill advised.

I would rather not get a dedicated line for each monoblocks ....

But if big differences...I could....

I have pass labs 260.8 monoblocks..
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Wow, congrats, amazing monos!!

 I have ran monos off of one outlet, nary an issue unless pushing very hard.

 I use one outlet for one amp and another for other amp + Xbox,and a DVD player.

if I remember correctly, i think the wall I’m,plugged in is on the same circuit, never had an issue.

 Test it, sure, separate outlets would b better, if you can’t then don’t.

  I ran the,monos of of a Furman protector in the past, no issues.

 I’m sure others will be in soon ........

if you can play moderately loud without popping a breaker, you will be fine.
Got so tired of writing the same thing over and over for people who seem to not care or already have their mind made up and anyway this is so much more satisfying https://ultimist.com/video/2018/07/21/michael-fremers-listening-room/
skip to 15:50
Enjoy!
The only place to get your answer is from your Pass dealer or Pass engineering team. Be prepared for them to tell you that a single 20A circuit will limit the performance here.

I have a pair of CAT JL-3 amps and there is no way a single 20A circuit can support both of these. I also have a pair of BAT 600Se amps and a single 20A circuit will trip with these once they get going.

I watched the above link.  He talks about one dedicated line.  Too many systems just can not survive on one dedicated line.  The key is to have all the lines on a single phase.
Looking for input whether putting both monoblock power cables into same dedicated line outlet receptacle is ill advised.
Always best in the same highest quality outlet, as if in different ones there is a chance of creating an earth loop with the household wiring, and you may get hum or slight hum.

Cheers George
Ill advised? No. But you won’t get optimum performance into low impedance loads, even at moderate loudness listening levels.
I agree with georgehifi and the advice from Michael Fremer in the video from millercarbon, the amps should be on the same ground plane to avoid a ground loop hum.  Speaking from experience here.
The guys at Reno HiFi told me that Pass Lab amplifiers do not employ a ground reference at the speaker terminal which makes them "less" susceptible to ground loops.  Therefore, if you are running the big Pass mono block amplifiers, they recommend separate dedicated lines.  I get the argument for one dedicated line for the whole system, but some amplifiers may over tax the circuit. 
You should certainly try it both ways—amps in single outlet vs separate outlets—-and reach your own conclusions.  Each system may react a little differently. 
In my system, using tube monoblocks, the sound with separate outlets is slightly brighter, slightly leaner, slightly bigger and more spacious, slightly recessed in the mids, and slightly more exciting.  With both amps plugged into the same outlet, the tonal balance is more linear, more coherent, but also slightly smaller and less exciting.  
In past years with some different tube amps and different speakers, I preferred the sound with separate outlets.  With my present setup I hear the same types of differences noted above but overall I now prefer the single outlet.
I agree with Jafox that you should consult with Pass Labs. But FWIW let’s look at the specifics:

Gs5556 makes a good point in referring to the significance of the speaker’s impedance characteristics. And I see in one of your other recent posts that you are using Harbeth 40.2s. In terms of relevant specs the 40.2 appears to not be greatly different than the 40.1, for which Stereophile measured a sensitivity of 84.5 db/2.83 volts/1 meter, and stated that:

... the Harbeth is easy to drive in terms of its demand for current. The impedance drops below 6 ohms only in the middle of the midrange, and then only for a short while; and while the electrical phase angle occasionally reaches extreme values, this is only when the impedance magnitude is high, ameliorating the drive difficulty.

The relevant specs of the amp are:

Max power (8 ohms): 260 watts
Max power (4 ohms): 520 watts
Leaves class A at: 34 watts peak
Power consumption at idle: 3.1 amps, 375 watts

The 375 watt figure is low enough that I would have high confidence that turn-on surges will be reasonable and won’t trip the breaker, especially given that both amps will not be switched on at the same instant.

If we assume a 6 ohm speaker impedance the amp’s maximum power capability with these speakers can be calculated to be 347 watts. Given that the amps would be operating mainly in class AB at power levels approaching that amount I suspect that a safe estimate of the maximum amount of AC power each amp would ever draw with your speakers would be in the range of 800 to 1000 watts. So the total worst case draw of the two amps plus a preamp and say a couple of source components should fit within the 20 amps x 120 volts = 2400 watt capability of a single dedicated line, although without a great deal of margin if and when the amps are ever running close to full power.

From a sonic standpoint, though, the problem may be that since the amps will draw most of that AC power during just a small fraction of a given 60 Hz period, the total current drawn during those brief instants may be significantly more than 20 amps. Not enough to trip the breaker, given the short duration, but conceivably the resulting drop in line voltage during those instants could affect dynamics or have other sonic consequences, especially if the length of the run is long and/or if the gauge is not over-specified.

So the bottom line seems to be that you would probably be ok installing just a single dedicated line, which as has been mentioned would minimize the risk of ground loop issues, but it’s somewhat marginal and might not be sonically optimal, especially if you listen at high volume levels. Again, check with Pass.

Good luck. Regards,
-- Al


First of all thanks for all the detailed input.

I should have added more detail though ...my line preamp and sep phono preamp and turntable are all on a second dedicated line plugged into a synergistic power conditioner.

My third dedicated line is just for the pair of REL subwoofers.

Late last nite I changed it so each monoblock on different dedicated line...but second outlet for each monoblock has REL sub....i figured less current draw more headroom for monoblock albeit not ideal same circuit as sub.

The sounds seems more open and bass still fantastic....maybe faster bass ?

I did reach out to Pass and Kent already emailed me back stating that one dedicated circuit is fine for both monoblocks that the power consumption is not that much ....unless you aee meters fluctuating a lot you not taxing amps nor line. He gave no opinion about sound but they claim power cables have little affect on sound and that is not my experience.

I was not thinking could blow something...maybe i should have....but just whether at loud volume would get more lively sound....seems to be the case but might be perception bias....will see over time over more records it still prefer this way...

Anyone think bad idea sonically to mix one dedicated outlet for left monoblock amp and left sub...I have REL set at low output and a low crossover so sub are very modestly involved.

I have another non dedicated outlet that could get another dedicated line but feel 3 dedicated lines enuf for now.....my SR atmosphere tweak goes into non dedicated line...

Lastly I did try running the subs into the power conditioner but felt somehow sound waa a little less big and live....the monos def prefer not going through power conditioner....SR says no power limits and my other system the stereo amp sounds better into their power conditioner but its a far less powerful amp
Anyone think bad idea sonically to mix one dedicated outlet for left monoblock amp and left sub...I have REL set at low output and a low crossover so sub are very modestly involved.
Well, to give a highly technical and esoteric answer I would say that if it sounds good it is good :-)

BTW, assuming you are connecting the sub inputs at speaker level, as you no doubt realize (but I'll mention just to be sure) the black wire from each sub should be connected to the white signal ground terminal on the rear of the corresponding amp. With the red and yellow wires being connected to a positive output terminal of the amp.  

Regards,
-- Al


Since you and I share the same amps but probably not the rest of the chain I will share what I did. 
I was told by .the Nordost rep it is best to power your system off one dedicated 20 amp circuit. So that's what I did  fortunately for my situation the breaker box is 20' away from my listening area.
Here is my rig
Dehavilland UV3 preamp
CEC TL2 X
Rega Saturn R as DAC/. backup CD player
Lumin D2 streamer
Rythmik Audio F12 subs
Pass Labs 260.8 monoblocks
My power distribution is like this a single run of marine grade 1000volt insulation 10 guage wire ,and Hubble hospital grade outlets. I distribute the outlets so as the amps are the first and then I distribute the components.
Never a problem no noise no hum or ground loop extremely low noise floor.
You don't need a nuclear power plant  for those amps
Happy Listening
Mark
I have two 20a  breakers to the back of my system. Two separate outlets. They go the same distance to the breakers probably 40’ of cable. More than enough power for this room size. While I was waiting for the electricians to change out the main power to the pole , i was running my whole system , everything off of a 50’ 10ga extension cord.  Thats three mc2300 amps and a mc2150 , mac c46 , nad m51 , bluesound node2 , and a 75” sony 4k . All off of one 15a. Breaker. Never had it trip . The plug was 6” from the panel so that helps . Even after a loud party no breaker trip. Thats 70a. Worth of fuses on just the amps . 
Moral of the story is that 15a. Plug can produce a hell of a pile of sound in a 2000 sq ft room with people in it. I’m still amazed by it. I know now that my two 20a breakers are way over kill. . One would work . 
As long as you are running a awg 12-10 gauge Copper 15-20 amp  breaker circuit then no sweat your amps and preamp should be on the same line anyway to prevent ground loops  no way you will trip a breaker unless you have super low impedance speakers blasting in the 100+ db spl region. I owned a Audio store for years and rarely seen issues with big amplifiers speakers unless very unfriendly loads to 2-1 ohm like the old Apogee ribbons your amps have plenty of capacitor storage capacity to have plenty of reserves on demand just  make sure your dedicated line is a awg12 or lower, lower # = bigger gauge.
I am experimenting for optimal sound as I am confident that I will not trip a breaker....I am not hearing any hum or ground issue in any of the configurations....

I am trying to see if a sonic difference if each monoblock is on a separate dedicated line or not.....

its not apples to apples since one line is 4 feet shorter than the other and has a different SR outlet too (yeah I know that is a controversial tweak) .....I cannot even say that the electrician used the same wiring but the gauge was the same .....

I am not sure there is a difference but my initial feeling was a bit more headroom when monoblocks were separated on different dedicated lines.....this could be some sort of bias....but if there is no hum or other negative that develops will probably stick with it.

I also tried putting subwoofers on a non dedicated line to separate it from the amp but that sound was less pleasing....not surprising since it is a nondedicated line and has a much higher gauge too....I really didnt hear any improvement in the sound of the midrange and treble with the monoblocks separated from the sub.....

I am assuming that the REL S/5 SHO taxes the dedicated line less than the monoblock but that might be wrong.....I will say I listen to the monoblocks a lot louder than the sub (the sub volume is ten clicks from minimum and the crossover is 9 clicks from minimum so essentially has only a modest output somewhere under 50hz,,,,the speaker claims goes down to 35hz +-3 but my guess in my room peters out in the 40s

You can with a dmm and an spl meter leave the realm of guessing....