I have a problem with my latest project. I have 2 mains transformers, the transformer secondaries are center tapped. each has its own bridge rectifier and a pair of 12000 uf caps. I built the dc speaker protect, 2 soft start, one for each tranny, remote control ect. all worked fine with +60 -60 and ground for each supply. So I built the first 2 of 6 amp modules and installed them, all worked fine so i built the next 2 amps and installed them hooking the inputs to a stereo source all worked fine but now i have a low level hum so I started grounding with a saftey ground from the line cord to the chassis and a ground to the center tap of the transformers (the start of my star ground) now when powered up the fuses labeled f3,f4 smoke after a few seconds
I have pix and schematic attached. I might be in over my head here! any thoughts?
I have pix and schematic attached. I might be in over my head here! any thoughts?Attachments
You have a soft-start circuit on each transformer primary. The "few seconds" when the fuses blow, could that coincide with the soft start circuit giving the transformer full current capability?
May you have used "F" (fast) type fuses? "F"-fuses are difficult to use with large storage capacitors.
Have you tried "T" (slow) type fuses?
May you have used "F" (fast) type fuses? "F"-fuses are difficult to use with large storage capacitors.
Have you tried "T" (slow) type fuses?
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re replies
Thanks for all your replies The unit was working fine on 2 channels pushing 167 watts rms b4 the onset of clipping. I then added 2 more channels and tested them with similar results. although with all 4 amps working there was a noticeable hum with no input signal. So everything works but a slight hum thats when i decided to do some of the grounding. so I shut her down and added a star ground point. fired her up and f3 f4 smoked. Fuses are 6.3 amp type f for testing (can get over 50 w with the 6.3 amp fuses) Amps are connected to the supplies outputs. Gonna pull the ground and measure voltage between the ground wire and the stud should b 0 if i am thinking correctly. any other thoughts?
Thanks for all your replies The unit was working fine on 2 channels pushing 167 watts rms b4 the onset of clipping. I then added 2 more channels and tested them with similar results. although with all 4 amps working there was a noticeable hum with no input signal. So everything works but a slight hum thats when i decided to do some of the grounding. so I shut her down and added a star ground point. fired her up and f3 f4 smoked. Fuses are 6.3 amp type f for testing (can get over 50 w with the 6.3 amp fuses) Amps are connected to the supplies outputs. Gonna pull the ground and measure voltage between the ground wire and the stud should b 0 if i am thinking correctly. any other thoughts?
Each CT should go directly and independently to the first capacitor filter mid-point.
Have you put a meter on the supply rails to each amp module - maybe one or more amp modules is mis-behaving.
Have you done a PSUD2 assessment of your system, including transformer resistor measurements, and loading measurements, and looked at what is happening with the startup winding current levels. You can then work out what type and rating of fuse is appropriate.
PS- I think your photo doesn't show any fuses included?
Have you put a meter on the supply rails to each amp module - maybe one or more amp modules is mis-behaving.
Have you done a PSUD2 assessment of your system, including transformer resistor measurements, and loading measurements, and looked at what is happening with the startup winding current levels. You can then work out what type and rating of fuse is appropriate.
PS- I think your photo doesn't show any fuses included?
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So I learned a little something something. When testing high powered amps make sure your input wiring is solid! I was using a proto board to tie the inputs together in stereo pairs which caused the amps to oscillate and draw full current from the power supplies smoking the 6.3 amp fuses used for testing. Thanks to those that replied. Now on to the front end and mute circuit.
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