Krell KAS amplifier hum

Al (almarg),

I was hoping you would chime in at some point.

Them Krell amps are pigs and are power hungry when pushed hard.

I looked over what you posted and will respond tomorrow.

I noticed the OP posted after you and he tried some additional tests. One, he plugged both amps into one duplex 20 amp dedicated circuit and it didn’t make any difference. Maybe both dedicated circuits are fed from the same Line, leg.

Did you look at that Silver Circle audio, "pure power one 5.0 power conditioner?
https://positive-feedback.com/Issue33/silvercircle.htm

Jim

Rule No1: Only put these sort of amps direct into the wall.

Those Krells of yours have an incredibly "stiff" (low esr, low impedance) power supply and great output current delivery that’s why they can drive anything even the worst speaker load yet still get great controlled bass, this is only got by plugging direct into the mains.
To put any power conditioner between the Krells and the wall outlet and you introduce series resistance which lower the power supplies stiffness and that bass and ability to deliver huge current is diminished.

Cheers George

@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