TRL Dude or Joule 150 MKII for Major Pre Upgrade

Grannyring, your issue doesn't seem to me to be a ground loop issue, as it occurs even when the preamp is unplugged from the AC outlet (and with no source components connected). Therefore I'm not at all certain that a Jensen transformer would solve the problem, which I'm frankly out of ideas on.

For anyone else who may be able to contribute ideas on Grannyring's issue, it was discussed here. Note that multiple sets of interconnect cables were tried, as well as both the Dude and Lightspeed preamps. Yet the problem goes away when the inputs to the amp are disconnected, and the problem did not occur until the previous speakers, which were electrostatics, were replaced with passive speakers.

Best regards,
-- Al

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.

Vett93 , please help me understand what you did? I am not understanding your fix? Are you saying you simply used a cheater plug on the amp? If so, tried that also.Thanks

Mitch2, thanks much for the offer. I want to try what Vett93 is saying and I may take you up on your offer.

Al, you may be right or I may have a ground issue that is induced between gear thru the ic's .....don't know. I have another system I may place the amp into today to see what happens.

Back to the OP, the Joule will likely be easier to find here used (if that is your intent) than the Dude, simply because more have been made over a longer period of time. There is an LA 150 MkII for sale here now. I owned that preamp and it would be a huge upgrade over the Rotel. You would also have the option to upgrade it to the Signature Edition [LA-150 MkII SE] version in the future for $1,750. In addition to a very nice appearance, the Joule offers a couple of neat features that can have practical applications such as selectable output impedance of 400 and 1200 ohms, and selectable gain from 0 to 11 dB. The 6350 tubes used are no longer made but Joule has thousands for when you need more, and they are also available in other places...here is something I found about those tubes:

6350: This tube was mainly manufactured for IBM and other computers in the late 1950s to mid 1960s. Sylvania and GE blackplates are considered the best of all with this tube. It has a mu or gain factor of 18 so is very close to the 12AU7. These were made to tight specs and carefully quality checked, since replacement in a computer of the day was difficult and costly, and the tubes were expected to operate 24-7. These make impressive upgrades to the standard 12AU7!

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?