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In Reply to: sibilance and coupling caps.... posted by dls123 on March 21, 2006 at 10:53:51:
Hi Don,I got to say this, and please accept it as constructive criticism – you’re shooting in the dark! You changed the power transformer, which changed the sound, and now you are trying all sorts of things to fix it. Your problem has to be associated with the difference between the two transformers. For example, perhaps the resistance of the high voltage winding is less in the new transformer than in the old one. I would start by making a list of all of the differences and then compensate for those differences one-by-one.
Another alternative would be to have your old transformer repaired. There are places in most metropolitan areas that will rewind motors and transformers. Look in your Yellow Pages.
Follow Ups:
Hi Dave,
No offence taken! You are right, that is precisely what I am trying to do. I realize that the only difference is the transformer. I know exactly how I am trying to get it to sound. I have had stereos in one incarnation or another for 38 years and never had a sibilance problem. Now I have one. There is some sort of peak in the upper midrange now where the sibilance lives. I have tried darkening things a bit with my stash of tubes but all I can do is make predictable changes in the tonal balance. The warm or dark tubes sound warm or darker, the bright tubes brighter, but no matter what there is sibilance. I have made sure the voltages are where they should be or were before. I have tried various filament voltages as an experiment, but can't tame the sibilance. Transformers are rather expensive so I would rather not change it out, but it looks like that is where I am headed. Rewinding the old one is not a bad suggestion, although it may have died because it could have been slightly undersized, who knows. Or maybe it's number was just up.... The current one doesn't even get warm. I was just thinking that a different coupling cap might do the trick for less money... You are right, the difference is the transformer and I am trying to compensate...
Hi Don,Here is another suggestion. Assuming that there is a peak in the upper midrange perhaps there is a resonance in the power supply.
Voltsecond has a very good article there about resonances in the power supply.http://www.siteswithstyle.com/VoltSecond/CLC_ringing/CLC_ringing.html
Dave,
Thanks for the link. Had a quick look. Very interesting article. Will have to discuss it with the amp's designer. Darn thing sounds great as long as you don't listen to vocals. Instrumentals are great. Just a hint of sibilance on vocals to drive you nuts. On the well recorded vocals there is little if any, but most pop recordings...By the way, the Philips caps are polypropylene....
With all good intentions, & meant to be constructive: in the pic alone there is a resistor blob-soldered to a metal plate, melted wire insulation from a solder iron getting too close, a circut Common Buss wrigling wily-nily thru parts, and a general mess of wiring. This *custom designer* has poor assembly skills IMO & is thus more likely a newbee hobbiest rather than a qualified EE. Re-consider what he did with the mis-matched pair OPT replacement (your present problem) before visiting him again for additional errors. With notes or not, that so-called *custom designer* guy does not know what he is doing.
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