Hey guys,
I was rebuilding my 4 channel gainclone amp today using LM3875s for the tweeter amps and LM3886s for the woofers. Anyway, I keep either blowing fuses or blowing chips (I'm out now actually 🙁 Still have some lm3886 though). I've attached the schematic I'm using. Without input or output attached the chip lets out smoke. The power supply rails are +35 and -35. Power supply is filtered with 6800uF per rail.
Is it the lack of bypassing near the amps that is causing problems? My channels are located within about 3 inches of the power supply's filter caps.
Is it the massive 680uF feedback to ground cap (C1 in diagram)?
Any help greatly appreciated. The amp that I'm upgrading was previously 4 LM12 channels, I believe non inverting. I figured an upgrade to LM3886, LM3875 would help the sound a little.
Pete
I was rebuilding my 4 channel gainclone amp today using LM3875s for the tweeter amps and LM3886s for the woofers. Anyway, I keep either blowing fuses or blowing chips (I'm out now actually 🙁 Still have some lm3886 though). I've attached the schematic I'm using. Without input or output attached the chip lets out smoke. The power supply rails are +35 and -35. Power supply is filtered with 6800uF per rail.
Is it the lack of bypassing near the amps that is causing problems? My channels are located within about 3 inches of the power supply's filter caps.
Is it the massive 680uF feedback to ground cap (C1 in diagram)?
Any help greatly appreciated. The amp that I'm upgrading was previously 4 LM12 channels, I believe non inverting. I figured an upgrade to LM3886, LM3875 would help the sound a little.
Pete
Attachments
Update: I just remeasured my power supply leads. It turns out blue is negative, and red is positive... That solves one problem!
Pete
Pete
Member
Joined 2004
lm1875 on 12v 7.2AH batteries-HELP
Greetings to all inmates
It´s been a month since I started to read this forum with great interest and amusement. I learned a lot here.
Folowing Thorten´s suggestion, I decided to build a GC running on batteries.
I know lm3875´s are specified, but 1875 are far easier to obtain. So...
-Basic NIGC 1875 setup: 47k log pot, 2.2mF cap, 22k res signal-to-ground; 22k + 680 ohm res on the NFL; 1000mF caps on the power rails; no Zobel.
-Two 12v, 7.2AH batteries in series per channel; all grounds merging to the point between batteries (0 volts, I guess).
It should sound great but everytime I turned it on I got this overdrive-type distortion that ruined almost all my speakers even at low volume.
Running on common 9v batteries or even on 4,5v 3r12´s (you know the type?) it does sound great indeed, but they don´t last long enough, of course, so the circuit is well built.
Shouldn´t 1875´s accept 25v per rail (that´s 25w power) or is 7.2AH too much capacity? I plan to try 3875´s as soon as they´re available here.
What must be going wrong? Please help!
Thanks
Greetings to all inmates
It´s been a month since I started to read this forum with great interest and amusement. I learned a lot here.
Folowing Thorten´s suggestion, I decided to build a GC running on batteries.
I know lm3875´s are specified, but 1875 are far easier to obtain. So...
-Basic NIGC 1875 setup: 47k log pot, 2.2mF cap, 22k res signal-to-ground; 22k + 680 ohm res on the NFL; 1000mF caps on the power rails; no Zobel.
-Two 12v, 7.2AH batteries in series per channel; all grounds merging to the point between batteries (0 volts, I guess).
It should sound great but everytime I turned it on I got this overdrive-type distortion that ruined almost all my speakers even at low volume.
Running on common 9v batteries or even on 4,5v 3r12´s (you know the type?) it does sound great indeed, but they don´t last long enough, of course, so the circuit is well built.
Shouldn´t 1875´s accept 25v per rail (that´s 25w power) or is 7.2AH too much capacity? I plan to try 3875´s as soon as they´re available here.
What must be going wrong? Please help!
Thanks
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