Ultimate noise rejection
I'm in the process of making an integrated dual mono amp with circuit boards care of ESP.
As the design of the beast in question entails there to be 3 toroidal transformers inside the same box as the pre-amp and power amps I want to employ internal shielding as well as earthing the case.
I've already decided to shield the pre-amp in it's own aluminium box inside the main case as this is probably the most prone to interference. I'll also be using a "zero volt line" - as described on the ESP website.
One final thing I was wondering about was sheilding the toroids?
Would it be benificial for me to source individual boxes for them for inside the main case or could I wrap foil around them or would this break the continuity of the lux lines?
Any help would be appreciated, also ideas how to reduce any kind of interference.
Be careful about how you box the toroids. Most toroids mount with a bolt through the center and a large metal washer on top. If you put the thing in a box, and the box and the bolt connect to a conductive chassis, you are making a very low resistance, shorted, 1-turn secondary and it will blow fuses (assuming you use them- you are going to aren't you?) or destroy the transformer.
Make sure there is no way the bolt can come into electrical contact with the shield box.
Use of Toroids
Better use two chamber or split bobbin transformers in the preamp. I have researched this in my DAC and preamp and the latter type of transformers gave better sound. Not a day and night difference but worth the effort. To mininise hum pickup I placed the trannie for the preamp in a separate box. In the DAC hum is not a issue. The twochamber transformers have much <I><B>lower interwinding capacitance</B></I> making transfer of hash and garbage from the mains to the circuit more difficult;)
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