Aleph30 vs LeachAmp: PS Fusing - diyAudio
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Old 12th July 2002, 10:51 AM   #1
swede is offline swede  Switzerland
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Default Aleph30 vs LeachAmp: PS Fusing

Hi,

I recently built a Leach Amp, which works fine. It is all mounted in a nice case and everything. This morning I finished mounting the last parts on my second PCB for Aleph 30. Yesterday I was trying to learn how to simulate the Aleph circuit in Spice, which took a lot of time, since I'm not very experienced in simulations.

Now I started to think on the differences in the schematics (HUGE) between the Leach Amp and the Alephs, and what attracted my eye is the fusing of the powersupplies.

Look at the Leach Amp powersupply:

Click the image to open in full size.

Compared to the Aleph 30 (and other Alephs as well), there are fuses on the Leach Amp powersupply on the DC rails right before the amplifier boards.

I read in another thread last night (and now I cant find it) about some guy who disconnected his V- from an Aleph 2 (or some other aleph) to do some measurements. This caused his output transistors to blow, since he claimed them not to handle the voltage very well, using only one rail.

So, is it a bad thing to fuse the DC-lines in an Aleph? Should I use a "small" fuse on the mains instead (only), as Mr Pass suggest in his schematics (bad question)?

Why does Prof. Leach urge the use of fuses on the DC-rails in his design?

As I said before, I don't have too much experience in this field, but I do want to learn as much as possible.

Best regards,
//magnus
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Old 13th July 2002, 03:21 AM   #2
swede is offline swede  Switzerland
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Ok,

I'll try to clarify myself.

Is it a "no no" to fuse the DC rails, or is it a good thing to do?

I'd really like to know.

Best regards,
//magnus
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Old 13th July 2002, 03:56 AM   #3
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It is certainly not a no no and generally I would fuse multiple places in the power supply to account for all failure modes and avoid a fire. Fuses on the DC rails are fine but dont remove fuses from elsewhere in the circuit. The mosfets in the Aleph 2 you read about died because those mosfets can only withstand 20V Vgs and this was exceeded under said conditions. Fuses wouldnt have helped in this case because current was not exceeded, voltage was.
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