TRL Dude or Joule 150 MKII for Major Pre Upgrade

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?

Vett93 thanks for your response. Well, when my cd player is totally removed from the system by unplugging both power cord and ic's I still get a hum/buzz though the speakers. The buzz is not present with the amp and speakers only. As soon as any preamp I have here goes into the amp by ic's ( not power cord into the wall) then the buzzing begins.

My Dude is grounded at the AC inlet plug. The power supply also looks grounded, but I am not certain about the signal ground being wired to the AC ground as you say? I will ask Paul.

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....

Gentlemen, once again let me emphasize that Grannyring's issue arises even when the preamp's power cord is not plugged into an AC outlet, and when no components are connected other than the preamp, power amp, and speakers. Therefore I don't see how the problem could be due to a ground loop, because there is no loop in that situation.

The facts that the problem is not present when nothing is connected to the inputs of the amp, but is present when the preamp and interconnects are connected to the amp, would seem to suggest an issue involving emi/rfi pickup. However, as Grannyring indicated in his thread that I linked to earlier, in addition to its normal RCA and XLR inputs his amp provides separate RCA and XLR inputs that are processed through high pass filter circuitry. And when the preamp is connected to the normal RCA inputs the problem exists even if any of the other three inputs are selected on the amp. Which leaves me totally baffled, unless perhaps something is defective in the amp's input select circuitry. But that, in turn, would not seem to explain why the problem wasn't present with the previous speakers.

Vett93, regarding your otherwise excellent posts it should be pointed out that with many designs isolating signal ground from chassis and AC safety ground may involve considerably more than minor modification. For starters, the ground sleeves of RCA connectors may not be isolated from chassis. Also, it would seem possible that in many cases changing the component's internal grounding scheme might result in unpredictable sonic side-effects.

Regards,
-- Al