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Newbie checking in, K-12G pics.
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Author:  cmetzner [ 08 Nov 2010, 18:56 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Thanks for the offer. Here is a pic of the assembly. I welcome any criticisms of my construction.

Author:  Suncalc [ 08 Nov 2010, 19:48 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Your build looks very clean :up:, so I would begin looking for a ground loop problem. The return signal paths should never from a loop of any kind. And the signal ground should only connect to the chassis ground at one point. In this way you keep ground currents to a minimum.

I did notice one thing that looked suspicious. It looks like your circuit board ground is tied to the chassis at two separate points but I can't be sure because the one wire is obscured by the transformer primary wire.

I cannot emphasis enough the need for careful grounding when working with voltages this high. I speak from (a bad) experience. :worried:

I would begin looking for places where you could have ground loops. Some common examples are shield leads with the shields tied to ground at both ends, grounded input jacks, grounded output jacks, potentiometers cases tied to signal ground, using the chassis as a power supply return, etc. I think you should get the idea. Also look at where you mounted the circuit board to the chassis and make sure that one of your screws doesn't unintentionally carry the signal ground back to the chassis.

I hope this helps. Your amp interrior looks very good, it could be just one or two wires giving you the problem.

Author:  cmetzner [ 08 Nov 2010, 19:58 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Matt -

Thank you for the comments. I know nothing about this. I just followed the directions. So, I connected one lead from each output transformer to the PCB at the points indicated in the directions with the kit. Your arrows do point to the two separate connections I used. If you say that the two wires should be connected at one point, I will do that.

I also used a ground loop interrupter on the input cables but it made no difference.

Thanks again I will keep working on it.

-- Chuck

Author:  DisasterArea [ 19 Nov 2010, 17:39 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Similar question: I'm mounting my transformers on the top of an aluminum chassis, should I then only ground ONE of the transformers to the PCB and make that my single ground connection from chassis to pcb to avoid ground loops... this should ground all three transformers if they're all mounted on the aluminum chassis, correct?

Author:  Suncalc [ 19 Nov 2010, 20:41 ]
Post subject:  Re: Newbie checking in, K-12G pics.

A good way to think of transformer end bells and frames is as a chassis to protect the circuit portions of the transformer. They shield the transformer in the exact same way that a metal chassis shields the internal parts of the amp. As such, transformer end bells and frames should be grounded to the chassis ground. The circuit grounds should all be tied to a signal ground. Then the chassis ground and the signal ground should be tied together at one and only one point. This will prevent chassis ground loops.

Make sense? :?:

Author:  cmetzner [ 20 Nov 2010, 09:54 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Thanks Matt for that explanation.

One thing that I wondered about this kit. In the stock build on a breadboard, each of the frames on the output transformers have a ground wire running to the PCB but there is no ground from the frame of the power transformer. I just figured it was OK like that. Then, I was told by Mark on this board to add a ground for safety - (thank you, Mark)

So, now with your explanation, Matt, it seems that I should tie together the grounds from the chassis and xfmr frames. I guess S5 Elec had the grounds running to the PCB because there is no chassis in stock form. I assume that all the grounds on the pcb are connected. So, hooking up the grounds as they instruct combines chassis and signal grounds? I will rerun the grounds and see if it eliminates the hum.

-- Chuck

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