Its been awhile since I posted over here! I built an LM3875 with BrianGT boards a few years ago. All sorts of fancy parts too. Last spring I sold that amp and took a troubled little built-for-ebay LM3875 amp in partial trade. The thing is a mess with junky old surplus caps, a big ground loop and funky resistor values. But it works, and I'd like to make it a subwoofer amp.
The transformer the guy choose has way too much voltage for a 4 ohm load. It puts out about 36-37V rectified and under load. Rather than replace it, I decided to do something I haven't played with before. I'm going to build a regulated supply with an LM338. I know that is just over their rating of 35V, but I am going to take a chance.
My local store had a pair of versions of the TO3 package LM338s in stock, so I took them despite the price. They should dissipate some heat on their own, and I have some little AL angle scrapes (maybe 1/2 on each side by 3"?) that would fit nicely in the small chassis (which has an perforated top) to mount them. So, for the 4 ohm subwoofers (they'll be pretty efficient), I'd think of running the chips at 24-25V. But, given my lack of proper heatsinking, should I use higher rails? How high can I go and have it happily drive 4 ohm subs?
Paul
Wild Burro Audio Labs - DIY Full Range Speakers
The transformer the guy choose has way too much voltage for a 4 ohm load. It puts out about 36-37V rectified and under load. Rather than replace it, I decided to do something I haven't played with before. I'm going to build a regulated supply with an LM338. I know that is just over their rating of 35V, but I am going to take a chance.
My local store had a pair of versions of the TO3 package LM338s in stock, so I took them despite the price. They should dissipate some heat on their own, and I have some little AL angle scrapes (maybe 1/2 on each side by 3"?) that would fit nicely in the small chassis (which has an perforated top) to mount them. So, for the 4 ohm subwoofers (they'll be pretty efficient), I'd think of running the chips at 24-25V. But, given my lack of proper heatsinking, should I use higher rails? How high can I go and have it happily drive 4 ohm subs?
Paul
Wild Burro Audio Labs - DIY Full Range Speakers