[pjnad]

Just received my new( previously owned) Modwright Swl 9.0 Signature today. Hooked it into my system: using it with a Krell KSA 150 (ss) amp...replacing a ss audio research. Loud hum through both channels...certainly sounded like a ground hum. Spoke to Krell to ascertain that there was no compatibility issues; they assured me that there shouldn't be- which confirms what my research in various forums indicated. They suggested floating a ground using a cheater plug. Didn't help.
Next, spoke to Dan at Modwright, we ran through some troubleshooting, again to no avail. Tried disconnecting the source components, no good. Tightened the ground screws on the iec plug inlet as per Dan's advice, no good either.
Any ideas???
Thanks,
Paul

[Ericus Rex]

You tried a cheater plug.  But have you tried having only 1 component actually grounded?  I'd ground the amp, then use cheaters on ALL other components and see what happens.  If you still have hum then, I'd suspect a tube is the culprit.

[rollo]

  Sounds like a tube issue. Check your connections as well.


charles

[pjnad]

You tried a cheater plug.  But have you tried having only 1 component actually grounded?  I'd ground the amp, then use cheaters on ALL other components and see what happens.  If you still have hum then, I'd suspect a tube is the culprit.

I haven't...but that seems like a simple plan of attack.
The unit was played and checked out before shipping to me, and was suppossedly quiet. I did try changing out the rectifier tube and still had the same issue. The 'hum" definitely sounded like a ground hum, down around maybe 60hz.

[pjnad]

  Sounds like a tube issue. Check your connections as well.


charles

Thanks. Please see above post. And, yes I did check all my connections, and even changed the ic's running between the amp and the pre.
Someone shared a similar experience that they had and it turns out the culprit was his PS audio duet conditioner. I am using the quintet, so, when I get the unit back from Dan at Modwright, if I still have the issue, I'll try removing the ps audio.

[Ericus Rex]

Shipping can sometimes screw up perfectly quite tubes.  Bummer, that.

Keep us informed!

[pjnad]

Will do. Everything is on hold now, until I get the Modwright back from Dan. Just shipped it to him priority mail this morning.

Reconnected my audio research ss pre, and all is good. No hum. So, it's definitely something to do with introducing the Modwright into the loop.....

[Wayner]

It's probably a ground loop thru all the components' earth ground. If you have more then one path to ground, eddy currents are invited. So if all the components have a ground plug, and then we connect interconnects to all the components (now multiple paths) we have violated the single ground path rule and trouble starts. Maybe it's the PS Audio device, but I suspect that there are other problems involved. To solve this dilemma, all grounded components should be connected to a single "star point". and then that device, connected to power. And this doesn't always work because of the circuit topography of the individual component.

Wayner

[pjnad]

wayner: what do you mean by " a single star point" and what kind of device would that be?

someone else suggested floating all the grounds except one by using cheater plugs...would that be another way of doing what you are suggesting?

[Wayner]

All power connects need to be to a single point, like a power strip, then to the wall outlet. Not like plugged into several power outlets. This is what causes eddy currents as there is a difference of potential to ground from the different connecting points. When you make only one connecting point, it helps to eliminate this problem.

So as a recommendation, I suggest even a cheap power outlet (the usual 6 plex). Plug all of the components into this power strip and then into 1 outlet. If you have a big amp, this is a problem as the amp may produce high current influx at start-up and pop a circuit breaker. This is the reason all by itself that many people have ground loop hum problems.

I worked on a machine that had 4 separate modules that measured pico farads (10 to the minus 12 value) and was filled with noise, until I convinced folks that the problem would never go away unless they did a different ground scheme.

In the hifi world, the real stupidity is supplying equipment with a 3 prong plug. It's not necessary and causes lots of problems. Thank you IEC socket.

Wayner

[pjnad]

I do have a fairly "big" amp, a Krell Ksa 150. It is plugged directly into the wall, as per Krell's recommended use. My pre, dac, and transport are then plugged into the ps audio quintet which then goes to the wall, same outlet as the amp.
Would your method still work if I ran the three units into a power strip and then into the ps audio conditioner, leaving the krell in the wall? What if I was able to use a separate wall outlet?
I hate the idea of giving up even the decent power conditioning that the ps audio provides...as it does make a definite sonic improvement.

[pjnad]

Wayner: by the way, the hum only is present after turning on the krell and it passes out of it's initial protection circuit.

[Speedskater]

My basic troubleshooting procedure:
a] Unplug and disconnect every wire and cable.
b] Connect the speaker wires and plug the amp directly into the wall outlet. Turn it on ,does it hum?
c] Using a cheap power outlet plugged into the other half of that same wall outlet. Plug in the pre-amp and use Plane-Jane interconnects. Turn on the pre and then the amp. Does it hum?
d] Continue one unit or item at a time until it starts to hum.
Then start the real troubleshooting.

[Ericus Rex]

Wayner: by the way, the hum only is present after turning on the krell and it passes out of it's initial protection circuit.

That's a bit like saying 'my car makes this funny engine noise, but only when it's running.'  The hum wouldn't be sent to your speakers until the amp is up and running.

Hey Wayner, electrically speaking, isn't your suggestion the equivalent of just pulling the outlet out of the wall a few feet?  Unless you have a cheater plug on the power strip (and the grounded amp plugged into the wall) you'd still have the loops between ICs and power cables.  Am I wrong about this?

[pjnad]

That's a bit like saying 'my car makes this funny engine noise, but only when it's running.'  The hum wouldn't be sent to your speakers until the amp is up and running.

I guess that 's a big duh on my part...that should be obvious.
My "power strip" the ps audio does have an isolated receptacle for an amp, so if I am following Wayner's suggestion I could plug everything into that, including the amp, correct???

[Speedskater]

I believe that Wayner wrote:

So as a recommendation, I suggest even a cheap power outlet (the usual 6 plex).

The PS Audio unit doesn't meet that qualification.

[pjnad]

Correct, speedskater...but I was thinking that he meant that as a way to 'test' what was going on. I was hoping that theoretically the ps audio could do the same thing, i.e. serving as a single star point.

[Speedskater]

Well yes the best thing about the PS Audio is that it acts as a star ground.
As Bill Whitlock wrote:

"In reality, many of the benefits often ascribed to “power conditioner” schemes are simply
due to plugging all system equipment into the same outlet strip or dedicated branch
circuit. For obvious reasons, this is always a good idea!"

But still the PS Audio has all kinds of pieces and parts while the outlet strip is only wire and connectors. I still would start with the outlet strip until the main problem is solved.

[Wayner]

Unfortunately, this problem arises here at AC quite often and there is no one fix that fixes all. All systems are unique to their own inherent problems. Yes, cheater plugs may be in order, and there is no fear of getting a shock or electrocuted as the system is still a class II. Sometimes it's as simple a mistake as having a 6 pack with preamp and small amperage devices connected to that going to the top side of a duplex outlet, and then the amp going to the other half of the duplex. The real problem is that the interconnect shields are going to bridge those neutrals and eddy currents start to move. It doesn't take much, but it will be that horrible 60 cycle domain, and will sometimes have even order harmonics sympathizing with it, like 120, 240, 480 until it diminishes.

I don't have all the answers, but I do know some of the causes, and there are many. Hopefully, there are enough folks here with intelligent input, to help solve the problems that otherwise would be someone's private and incurable nightmare.

Wayner

[pjnad]

Hey All,
If I haven't said it already, Thank You! It's a wonderful thing to have interested, experienced, intelligent folks who are willing to take their time to help others here....one of the nice things about this hobby, and also the least expensive!
I don't really have a local, knowledgable audio shop here in the uppper Hudson Valley, so these and other forums have been great.

So, the preamp should arrive back at Modwright by Friday, and Dan will have a look...
by the way, did I mention that when I went back to using my audio research ss amp, I have no issues?