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Old 19th September 2005, 10:06 PM   #1
pjpoes is offline pjpoes  United States
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Default Big cap bypasses LM3875

I finally finished building my LM3875 amp from Peter's kit, Audiosector. I initually had it setup as he had suggested, with just the 10uf cap on the negative rail, then I tried it on the positive too, I think I agree that it sounds better. However, Then I got to experimenting a bit, I had some Black Gate .47uf caps, N type I believe, N series anyway, and I they were sufficiently high enough that I figured I could probably install them as further bypass caps on the rectifier board. I tried this and have been listening today. First, however possible, as I wouldn't expect such small caps to do this, this has completely eliminated any hum what-so-ever. All that is left is a small amount of residual hiss that my system has always had, and not enough to be heard from any distance at all. This setup has less hum than my regular amp, as in none at all, maybe I will try bypassing its caps. It also sounds much better, noticably cleaner, with all the benefits of a blacker background.

I also shortened the path length of the feedback resistor by changing how I had it mounted a little, taking away maybe 1mm or so. This and the bypass cap lowered my DC Offset to about 22mv now.

Just aobut half an hour ago I placed some Panasonic FC caps rated at 4700uf, or something like that, as I had them laying around, and they seemed to add a little bit of headroom maybe, though that is sudtle, but the bass is firmer. I even tried using it to power a passive sub I had, and it seemed to work with good results. I'm inclined to try the snubberized powersupply next.

Which reminds me, anyone want to let me know if anyone has any feelings on drawbacks to this, is it just a cost issue that everyone isn't doing it. Anyway, what are the suggested cap values for this, resistor values, and any brand prefrences. I am impressed with the Blackgates so far with this project, but man are they expensive.
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