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Re: DC Filaments

5/26/2003 1:46 PM
anonymous Re: DC Filaments
One thing to keep in mind is that p-p power stages should be somewhat hum cancelling if designed and assembled correctly.  
So, whether you employ it in the front end or power stages, DC heater circuitry is primarilly a single-ended hum cancelling technique IMO.
5/26/2003 4:30 AM

even w my high gain stuff, i use AC heaters. easy, and if the layout and lead dress is good, then no problems. but i expect a bit of noise w the super high gain stuff, so.....  
hows the l"siana? anymore squiters?  
5/26/2003 7:04 PM

It's not trivial to make a low ripple heater supply. The Mesa versions I've seen don't work at all. There are a number of ways to do it well but it will generally involve weight, heat, and/or SS components that make an otherwise simple part of a guitar amp into a complicated and unreliable part. Nonetheless, I've been using an amp for about six months that has a regulated 3.4A/12VDC supply I got from Mouser for all the heaters. It also runs a quiet little fan I got from Antique Elec Supp. As someone above said, the regulation is actually unnecessary, but the thing only cost about $50. DC heaters help with hum in the preamp more than the power tubes, but they do make a noticable difference in the power tubes. For an amp thats only going to be on stage its overkill, but for a studio or practice amp low hum is nice. Its cool to hear nothing when you're playing nothing.
5/26/2003 9:48 PM
I'm with WoodyC. If you don't mind a little noise, regulated DC is not necessary. If you design a very high gain amp and want it to be completely free of noise, then it is a must. Why would companies like CAE bother if it didn't make a difference. It's not very difficult to build a quiet supply for the heaters, only about $20.00 in parts and some time but the results are well worth it. BTW, I have tried the method that Steve A suggests and in a high gain amp there is still noise. There is still some residual ripple even with a large filter cap. A regulator will not only give you pure DC, but a steady, stable voltage as well.  
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