21-05-2011, 01:47 PM
DAC90As are noted for background hum Rob, and generally, it's the UL41 that's on its way out, partly due to heater/cathode leakage. I have a DAC90A in which I'd replaced the UL41 as the output was low and the set hummed, then although the smother/reservoir caps had reformed nicely and showed little leakage, the set still hummed, so at last year's NVCF, I bought a new dual cap from the BVWS stall. It made little difference, so I've kept the original cap for a spare. Neither does it sem to make any difference whether or not C22 - the 0.1 cap which is a mains suppressor is removed or replaced. As it's directly across the mains, it should be replaced not with a yellow polyester cap, but with an X Class cap, which - if they fail, they fail safe, and are self healing.
So much has been written about DAC90As that there's little more that can be said. On mod that many have made, which is said to improve the tone by giving it more treble, perhaps more suited to today's listening, is to replace the tone corrector cap, C17 - a .003uF, with a 390pF.
Hope that helps a bit Rob.
Best of luck with the DAC90A - eveery home should have one!
David
So much has been written about DAC90As that there's little more that can be said. On mod that many have made, which is said to improve the tone by giving it more treble, perhaps more suited to today's listening, is to replace the tone corrector cap, C17 - a .003uF, with a 390pF.
Hope that helps a bit Rob.
Best of luck with the DAC90A - eveery home should have one!
David
