Hi Grannyring,
If the power cord is not plugged in to your Dude and you have a hum already with just the interconnect, it is not a ground-loop induced hum then. Have you tried a shileded interconnect like the one from Blue Jeans cable?
What amp do you use these days? |
My Dude works fine with my low gain power amp. But when it was used with a pair of high gain tube monoblocks, I could hear some humming noises. So I got rid of the ground loop by floating the signal ground from the AC ground at the power amp, but keeping the chassis connected to the AC ground for safety. It has been quiet since then. |
I don't use cheater plugs. My method fixed the hums from a ground loop. Let me first establish a baseline. Some systems have two ground connections: one through the signal ground wire connection (interconnect) and the other through the ground pin in the AC plug. Most designers wire these two together and to the chassis. You can have a ground loop when you connect two components using an interconnect cable.
I don't use cheater plugs for two reasons: 1. I think they are usually not very good quality, and 2. I want the chassis wired to the AC ground for safety reasons. (I am paranoid...)
So you would need to decide where you want the ground point of your system to be. You want only one ground point in the entire sysetm. By ground point, I refer to the point that signal ground is connected to the AC ground. Most people think the ground point should be either the source or the preamp. I chose the preamp as the ground point because one of my sources does not use the ground pin of the AC plug.
If you choose the preamp as the ground point of the system, you may have two ground loops: one at the source and one at the amp. Typically, the hum is caused by the ground loop at the amp. So the next step is to get rid of the ground loop at the amp. Some amps have "float" switches for this purpose.
Before we go on, we need to make sure that the preamp is indeed the system ground point first. My understanding is that some TRL Dude preamps don't wire the signal ground to the AC ground. If you have this configuration, then your ground loop is from the source to the amp, which will produce even louder hums.
If you are still with me, now we can proceed to get rid of the ground loop at the amp. There are three points of interest at the amp: signal ground, AC ground, and the chassis. I would wire the AC ground to the chassis and then keep the signal ground float; i.e., not connect to chassis or AC ground.
I think my method is good and safe. I have heard some more "advanced" methods for grounding. But I think they are safety hazzards.
A remaining question is if I should get rid of the ground loops for systems that do not hum. I have a few gears to rotate and some combinations don't hum at all even they have ground loops. One school of thought is that if it ain't broke, don't fix it. The other school of thought is that even it does not hum when the sysetm is idle, it could produce ground noises when the system is not idle.
Thought? |
Grannyring,
In case it is not clear to you, I modded the amp to get rid of the ground loop. I opened the chassis and found the designer wired the signal ground, the AC ground, and the chassis all together. So I diconnected the signal ground from the AC ground/chassis.
Hope it is clearer....
PS. If you have a high voltage amp, be careful of what you are doing.... |
Al, I am very sorry that I did not see the previous posts.
Bill, you mentioned that you shorted the pin 1 and pin 3 of the XLR connectors and it would still hum. Did you just short 2 of the 4 XLR connectors? If that is the case, can you try to short all 4 XLR connectors? I mean shorting the pin 1 and pin 3 for all 4 XLR connectors.
The design of your Atlas amp looks similar to my Counterpoint/AltaVista NP100 amp by Mike Elliot. They both use 6SN7 differential gain stage and don't use switches in that area.
Let me know if that fixes your problem. |
Atamasphere, if Grannyring's Dude is like mine when I first got it, the chassis is not grounded to the middle pin of the IEC. |
Okay, I read through the whole threads and come up with another theory and idea to try. I simply cannot stand a fellow Dude owner not happy with his setup. ;-)
I still think it is a grounding issue. If I understand it correctly, it did not hum with the previous set of speakers which are electrostatics. My theory is that the set of electrostatics provided proper grounding through their AC plugs.
So, Bill, can you try the following and see if it fixes the hum? The idea is to provide grounding at the source. So find any of your source equipment that has the signal ground wired to the ground pin of the AC plug. I don't know what source equipment you have. But you can measure the source's output RCA ground and the the ground pin of the AC plug. If it reads close to zero ohm (meaning there is a connection), then the signal is grounded to the AC line. You can use that equipment as the source.
Then connect the source to the Dude and select the right input. Connect the Dude to the amp. Turn them on and see (or hear) if you still get a hum.
Please let us know. Thanks. |
Bill, in your earlier post today, you said that the chassis was not wired to anything, which was similar to my experience. Then you said it in your most recent post that the chassis was wired to the middle pin of the IEC. So I am a bit confused. Can you use your ohm meter to measure the chassis and the ground pin of the IEC socket?
Did you send your Dude back for re-work? I got my Dude after reading your review a few years back. Being an engineer, I opened it up to review its design as soon as I received it. I found that the chassis was NOT wired to the AC ground. I sent it back to Paul and specifically asked him to do so later on.
I still think you should try my latest suggestion: find a source equipment that has its signal ground wired to the AC ground pin. Then see if it still hums... |
Granny,
I don't think my explanation is clear to you. My point is that the signal ground has to be grounded at one location for the entire system. Otherwise, the whole thing is floating. It seemed to me that your electrostatic speakers provided a grounding point. You lost the grounding point by switching to a set of passive speakers.
If you still use the same CD player as the one you used when we talked last time (a Marantz, I think), it does not provide a grounding point. If you look at the IEC socket of a Marantz CD player, there is no ground pin there.
To test my method, you will need to find a CD player that uses the AC ground pin, and plug in AC power cord to the wall and use the interconnect too. This is so that the CD player can provide a grounding point for you. I don't think you followed my explanation. |
Also, you will need to short pin 1 and 3 for the XLR connectors when you try my suggestion. I think it will work for you... |
Granny, can you explain what you meant by "my CD player is grounded to the chassis by the power cord middle pin"? Did you use the multi-meter to measure the chassis and the power cord middle pin and then concluded that?
On the CD player, can you measure the ground of the RCA connector and the power cord middle pin, if you have not done that already? By the "ground" of the RCA connector, I refer to the outside surface area of the RCA connector.
On the power amp, can you also measure the ground of the RCA connector and the power cord middle pin?
Atmasphere, I think it is a system issue. The whole thing worked well previously with the electrostatic speakers. If the only change is the speaker, the only possible cause is the change of grounding. |
Atmasphere, my understanding is that Granny is now using a pair of passive speakers. There should not be power supply for it.... |
Granny has put an integrated amp in place of Dude preamp and Atlas amp, with the same CD player, ICs, power cords, and speakers. It was quiet. No hum.
The Atlas amp has balanced differential input gain stage and followed by driver and output stages in bridged configuration. We measured the RCA ground to the IEC ground pin to verify that signal ground is connected to AC ground.
We also tested the RCA and XLR inputs and concluded they are correctly wired, by measuring the resistance of pins to the ground and RCA center to XLR Pin-2. We got new XLR connectors, short pin 1 and 3, and connect them to the amp.
Then we use a pair of RCA sockets to simulate inputs. First, we shorted the RCA sockets. With ICs between shorted RCA sockets and amp, the system was quiet. So we changed the RCA sockets from being shorted to being loaded with 1K ohm resistors. This was to simulate if the amp could pick up noises and then hum/buzz. But it was quiet too.
Then strange thing happened as soon as we connected anything else to it. They don't even need power cords to cause hum. We also measured Dude preamp and concluded that it was also wired correctly too. On the Dude preamp, if we adjust the volume all the way down, it is like shorting the output. (We verified it by measuring the output with a multimeter and got 0.3ohm.) But the system would still hum, without power cord. This was extremely bizarre to me...
What was even more bizarre to me was that we connected CD player to the amp directly, without any preamp. One channel was humming loudly and one was humming a little. When we switched cable the hum pattern stayed. |
