Krell KAS amplifier hum

@georgehifi

The Krell amps do plug directly into the wall outlets. Each amp has its own dedicated 120V 20 amp branch circuit.

The " Silver Circle audio, "pure power one 5.0 power conditioner" feeds the ARC preamp and the front end equipment.

All instruments are plugged into a Silver Circle audio, "pure power one 5.0, which is plugged into an existing outlet.

Pre = ARC Ref 3
Phono = DSA
Tuner = McIntosh MR 67
Transport = ML No31
Dac = ML 36s
TT = Final audio VTT-1
Tonearms = Talea and Kuzma 4pt

Existing outlet is a 120V 15 amp convenience outlet branch circuit. (More than likely 14ga wire)

The "common" 15A leg has 7 outlets, 3 of which are being used. 1 outlet in particular has my humidor plugged into it. Unplugging everything from this 15A leg yields no change.

The " pure power one 5.0" has a 5KVA isolation transformer making the unit a separately derived power system. Though the secondary 120V output is isolated from the input mains power the mains wall outlet’s safety equipment ground basically passes through the " pure power one 5.0" and connects to the equipment ground contacts of the units output duplex receptacle outlets. (The designer/manufacturer, just a guess, added filtering or what ever to/for to clean up noise that may be on the equipment grounding conductor entering from the mains wall outlet but there is nothing the " pure power one 5.0" can do about resistivity of the equipment grounding conductor from the mains electrical panel to the wall outlet.

The same mains wall outlet safety equipment grounding conductor is used for bonding,connecting, the grounded neutral conductor of the separately derived power system to the earthed grounding system of the main electrical service. (Technically because of the KVA size of the unit using the branch circuit safety equipment grounding conductor for the earth grounding (Bonding Jumper) does not meet NEC code.)

I wouldn’t be surprised if there isn’t a difference of potential, voltage, between the "pure power one 5.0" output neutral and the neutral at the 120V 20 amp dedicated branch circuits outlets for the two Krell amps.

jg2077 12-12-2019 8:59 pm EST:
... the pre is plugged into a common 15A outlet; the amps are plugged into a dedicated 20A outlet and ALL else is unplugged. I still hear the same amount of hum.

I installed a "cheater plug" between the pre and wall outlet, I hear less hum than before, about 70% less. I cannot hear hum from my listening position (10ft) away....


jg2077 12-12-2019 10:14 pm EST:
I plugged EVERYTHING as before, with one exception, there is a "ground cheater " between the pre and power distributor. The hum is 50% less than first posted.

I tried both amps on the same outlet - no change.

Am I correct in understanding that in the first of these two experiments the preamp was plugged directly into the wall outlet, without the power conditioner? If not that should certainly be tried, as Lowrider had suggested earlier.

Jim (Jea48), thanks for the link and your comments about the power conditioner. I also looked at the writeups at the Silver Circle website about the 5.0 conditioner and also at the writeup about the 5.0se. Statements in the writeup about the 5.0se confirm that the 5.0 incorporates filtering of some sort, as you speculated, with inductors being specifically referred to (that are presumably in series with some combination of the hot conductor, neutral conductor, and perhaps even the safety ground conductor, on whichever side of the transformer). Without detailed information about the design I think that all we can say is that the conditioner **might** be contributing to a ground loop issue in this application. And as was suggested the hum should be assessed with the preamp plugged directly into the wall, with its inputs disconnected, if that hasn’t already been tried.

One other thing that seems worthy of note: The OP’s speakers have very low sensitivity (apparently 83 db, although it isn’t clear if that is on the basis of 1 watt or 2.83 volts; if the latter, given its 4 ohm nominal impedance the speaker is only 80 db/1 watt). So with speakers of average or higher sensitivity the hum would be much louder than what has been described. (In saying this I’m assuming that the amount of hum doesn’t vary as a function of the volume control setting).

Best regards,
-- Al

almarg9,232 posts

12-13-2019
9:34am

jg2077 12-12-2019 8:59 pm EST:
... the pre is plugged into a common 15A outlet; the amps are plugged into a dedicated 20A outlet and ALL else is unplugged. I still hear the same amount of hum.

I installed a "cheater plug" between the pre and wall outlet, I hear less hum than before, about 70% less. I cannot hear hum from my listening position (10ft) away....


jg2077 12-12-2019 10:14 pm EST:
I plugged EVERYTHING as before, with one exception, there is a "ground cheater " between the pre and power distributor. The hum is 50% less than first posted.

I tried both amps on the same outlet - no change.

Am I correct in understanding that in the first of these two experiments the preamp was plugged directly into the wall outlet, without the power conditioner? If not that should certainly be tried, as Lowrider had suggested earlier.

Al (almarg),
Yes you are correct the OP plugged the preamp directly into the wall 15 amp convenience outlet and he did not hear any difference in hum.

He then tried the ground cheater between the wall outlet and the preamp. He lowered the hum by 70%. That tells me indeed he has a ground loop that is caused by a difference of potential between the equipment ground at the convenience wall outlet and the Krell amps 20 amp dedicated branch circuit outlets equipment ground.

Almarg said:

Without detailed information about the design I think that all we can say is that the conditioner **might** be contributing to a ground loop issue in this application. And as was suggested the hum should be assessed with the preamp plugged directly into the wall, with its inputs disconnected, if that hasn’t already been tried.

Al, that’s what I thought when I first read this statement of the OP’s.

jg2077 12-12-2019 10:14 pm EST:
I plugged EVERYTHING as before, with one exception, there is a "ground cheater " between the pre and power distributor. The hum is 50% less than first posted.

70% less hum to 50% less using the power conditioner? That don’t make any sense. Then I went back and reread what the OP said.

I plugged EVERYTHING as before, with one exception, there is a "ground cheater " between the pre and power distributor. "

" I plugged EVERYTHING as before," ........ As in all the other equipment he had plugged into power conditioner originally before he started troubleshooting for his hum problem.
Well, that’s a horse a different color.

One of these is causing the additional ground loop hum. One of them, or more, has a 3 wire cord and plug. Also I would guess the way the circuit ground/signal ground is connected to the equipment grounded chassis is definitely different than the way the ARC preamp is done. Your thoughts.......

Phono = DSA
Tuner = McIntosh MR 67
Transport = ML No31
Dac = ML 36s


Last night when the OP was trying different things and when he plugged both Krell amps into one duplex outlet dedicated 20 amp branch circuit, I wonder if he could have been able to plug the "pure power one 5.0" power conditioner into the other unused dedicated branch circuit 20 amp duplex outlet. Then plug the preamp into the pure power one 5.0. Listen for hum, then plug in the front end equipment and check for hum. That would speak volumes.......

Al, I liked your idea about using the Jensen transformers on the balanced ICs between the preamp and krell amps. Not only does it isolate the ARC preamp from the two amps but wouldn’t they isolate the two amps from one another because of the common circuit ground/signal ground connection of the ARC preamp. Your thoughts....
Jim

almarg9,232 posts   

12-12-2019  
 8:26pm  

Some thoughts that have occurred to me after reading through this thread:

1) Since these amps are huge high powered monsters which draw lots of current and require a dedicated 20 amp line for each monoblock, I’m guessing that the electrician probably installed the two lines on opposite AC legs. Jim (Jea48), some years ago you had provided us with a link to a paper by Henry Ott and Bill Whitlock which explained that powering interconnected equipment from opposite legs is conducive to ground loop issues. And of course the grounds of the two amps are interconnected via the preamp.

Al, I think this is the quote you are referring to. For what ever reason the web Link no longer works

"Less than 300 microamps of ground loop current can cause hum as it flows in an unbalanced audio interconnect cable. However, harmonics of 60Hz that are generated from lighting dimmers or switch-mode power supplies sound like Buzzz mixed with a bit of Hummm and are more easily coupled by even smaller currents. Harmonics can add together when equipment is powered from different phases, so clearly there is an advantage to specifying same-phase electrical service to power the electronics systems in most cases....

Any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference....

Power conditioners do not solve any of these common problems: Cross phase coupling (doubles hums & buzzes) .... What actually does solve them: Same phase power.

.

Split Single Phase electrical service is most commonly found in residences and smaller commercial buildings, and is commonly used to feed AV equipment. One key advantage that single phase has over three phase is that while harmonic currents are still present, it is not possible for the �triplen� components to add in the neutral. In addition, use of split single phase can result in at least a 6dB reduction in noise floor as compared to three phase if the capacitances of the connected equipment are relatively well balanced. However, any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference."
http://www.exactpower.com/elite/assets/pdfs/theTRUTH.pdf

Jim

Gentlemen, please allow me to be COMPLETELY off-topic.
I am humbled by all the thought processes and the suggestions you have provided.  Audiogon is filled with back and forth banter, so much so, that there are many recent posts about it...However, you prove that this is a site where help and assistance is given/provided, Thank you.

@jea48 - Yes, everything was was reinstalled as before.  The one exception was the ground plug installed between the pre and power distributor (hum was reduced to 50% less of when i first posted).  It would be easy to plug the 5.0 into one of the unused 20A outlet, as would be to move the Pre.  Having to Move everything would require MUCH work.  Could I use a long heavy-duty power cord plugged into one of the 20A outlet to power the 5.0 distributor where it sits without moving it?

I have a Coda 02b preamp, I will try it tonight and check for hum.

Respectfully,
Jose