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I am finally getting around to building a proper box/chassis for my RAKK DAC circuit (it's currently fixed to a piece of plywood in breadboard stage). My circuit consists of an LL1683, 1689, 1685, and a Hammond choke.
My new chassis consists of a wooden box with 4 sides of thick cocobolo and a (much thinner) top plate that is 2 copper sheets sandwiched between a layer of fiberglass (probably intended as a PCB at one time).
My question:
Is it beneficial to mount the transformers and chokes to the copper sheet of my chassis (for chassis grounding) or does it make a difference? I seem to recall reading that the core of the transformers is connected to the metal mounting plate and will therefore benefit from the connection to the chassis.
My preference is to mount the iron to the (much thicker) wooden sides of my chassis for damping reasons. If I connect the iron to the thinner copper plate, it will no doubt cause some flexing of the plate (and a larger amount of mechanical vibration).
Thanks in advance,
Chris
I have done non-extensive testing of a whopping 5 types of transformers, so my experience is most limited. I have noticed, in some xfmrs, that the high frequency behavior is affected by the grounding of the core with grounded source and/or load. I assume this has to do with the stray capacitance of any particular winding to said core.
The Lundahls I have found to be particular with core grounding; that is, they preferred to have their cores grounded. With the complex winding arrangements, it pays to experiment with the connections to optimize the low, mid, and high frequency behavior. Just my $0.02. I use the LL1689AM/PP, as well as LL1692A, and believe this to be reliable advice. Experiment! Once you find the optimal winding arrangement, nothing beats a Lundahl.
That being said, I think it foolish to not ground the cores of mains transformers and PS chokes, for safety. You can still mount everything to the wood chassis (that's what I do), but I also use conductive adhesive foil tape a la McMaster Carr to bond the core to the chassis ground. Works great, and you can keep the benefit of wood mounting.
In the unlikely case that a wire from a HT coil comes into electrical contact with the frame, it could pose a safety hazard mounting on wood. The frame would have no path to ground, if you touched the frame, you could provide that path. What I do, is mount it on wood, and run a wire underneath the mounting screw, but in contact with the frame, and solder the other end to my star ground. That way if a wire ever comes in contact with the frame, it makes a path directly to ground (short circuit), and blows the fuse in the amp.I know this is pretty anal, but being trained in the electrical field, I know these things, although highly unlikely, have occurred. This is a simple precaution that you might consider.
twystd
Edits: 05/22/09
I doubt that screwing the transformers down to the copper/fiberglass panel will have any positive effects that outweigh attaching them to the wood sides.
Kevin Carter
K&K Audio
www.kandkaudio.com
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