Tuesday, 3 May 2011

More F4 parts and update on TU882 Kit

Having looked around at the different suppliers and options for the source resistors for the F4, I think that the Mills MRA5 0R47 option would be the best. The Caddock MP915 requires a heat sink, and their other range of higher power resistors that do not require heat sinking, like the MV261 series are not easily found. Having made a personal note to avoid Parts Connexion, I have sourced Michael Percy for them, and will put together an order, along with the Nichicon KG that they stock.

Other information of note. The transformer selection for 2 channels of the F4 requires a minimum 300VA transformer, with two 18V secondaries. In my design, since each channel gets its own PSU, I will aim use a 250VA to 300VA transformer per channel. This should provide adequate headroom and maybe keep the load lighter, and thus the core cooler. From this, I can deduct 5A rated choke should be adequate, one for each of the positive and negative rails, instead of the parallel 0R47 resistors. The Hammond 159ZJ should do nicely. Now I need to get four of them. It also appears that amps with large farads of filtering capacitors may have a problem with the power on thump. So I will look into a soft start arrangement, and try to keep that to the primary side of the transformer.

I also contacted Victor about the hum and noise issue, and he suggested that I revert the amp back to the standard configuration, using the supplied pot and PCB to see if this problem can be removed. Smart idea. I will do that when I get the chance.

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