Boy, my LM3886 (BrianGT kit). At first fine with 2A fuses. Then started going through them. Tried 3A then started eating those too. 4A maybe not always, 5A seems fine.
Just surprised was able to use 2A for so long.
Amp checks out fine, just current inrush at turn on. Added xformer for dual mono - really started eating fuses. Worked sometimes using 2A in dual mono amazingly. Maybe summer apartment air conditioners or something.
Used 18V + 18V, 250VA Avel Lindberg transformers, US voltage. First one then two for dual mono.
Just surprised was able to use 2A for so long.
Amp checks out fine, just current inrush at turn on. Added xformer for dual mono - really started eating fuses. Worked sometimes using 2A in dual mono amazingly. Maybe summer apartment air conditioners or something.
Used 18V + 18V, 250VA Avel Lindberg transformers, US voltage. First one then two for dual mono.
Changing to dual mono means that your inrush current has just about doubled. At time 0 the inrush current drawn by a toroid is almost entirely determined by the dcr of the winding so to prevent nuisance blowing you would need double the fuse rating or a time delay fuse.
Toroids have ridiculously high inrush current and it is not unusual to see single transformers of just a couple of hundred VA with up to 6A slow blow fuses..
You need time delay type fuses designed for inductive loads, and a 5A - 6A fuse with your 2 transformers is an acceptable choice - just don't expect it to provide much protection in the event of a component failure. Even better would be a separate fuse for each power transformer - this would provide almost reasonable protection in the event of a malfunction on one channel.
Toroids have ridiculously high inrush current and it is not unusual to see single transformers of just a couple of hundred VA with up to 6A slow blow fuses..
You need time delay type fuses designed for inductive loads, and a 5A - 6A fuse with your 2 transformers is an acceptable choice - just don't expect it to provide much protection in the event of a component failure. Even better would be a separate fuse for each power transformer - this would provide almost reasonable protection in the event of a malfunction on one channel.
Thanks glad I asked. Will try the separate fuses per side and check into soft start.
Fuses blow only on startup, no problems when in use.
Fuse is on primary side.
Used all time delay (slo blo) fuses.
Switch amp on before source a lot but it varies. Like esp if using another amp then change to gainclone amp.
Fuses blow only on startup, no problems when in use.
Fuse is on primary side.
Used all time delay (slo blo) fuses.
Switch amp on before source a lot but it varies. Like esp if using another amp then change to gainclone amp.
I have 2x 330VA avel lindberg's. Turning them on blows my 16A circuit breaker 
Use a soft-start circuit!! Much better for your rectifier/capacitors aswell, and you can get by with your 2A fuse again (also safer).
i use this one for mine. sorry that its in dutch, but the schematic is very simple and works well. Another option is this one but it is more complex and not necesarily better. Ofcourse there are other options out there aswell....
Use a soft-start circuit!! Much better for your rectifier/capacitors aswell, and you can get by with your 2A fuse again (also safer).
i use this one for mine. sorry that its in dutch, but the schematic is very simple and works well. Another option is this one but it is more complex and not necesarily better. Ofcourse there are other options out there aswell....
Thanks for the links.
Actually we're 120 volt out here but thanks still helpful.
Anyone thoughts on fusing after primaries? Is it a good idea to put a fuse before the power supply boards and the amp boards?
(i assume audiophile materials fuses if used come quite after a project been proven to be more reliable)
Actually we're 120 volt out here but thanks still helpful.
Anyone thoughts on fusing after primaries? Is it a good idea to put a fuse before the power supply boards and the amp boards?
(i assume audiophile materials fuses if used come quite after a project been proven to be more reliable)
I never fit secondary fuses, but fuses after the PSU before the amp are essential. If the PSU shorts the transformer can take a massive overload for short term, this should blow the primary fuse before anything is damaged. This is why it's so important to fuse the primary correctly and have a soft start, rather than an inappropriately big fuse to stop nuisance blowing.
Well, amps on hold, fuse holders are on the way still choosing a soft start.
Always liked th3e idea of soft start wish most things used them.
The PSU to amp board fuse sounds good.
Wondered about between amp and speakers but that's just curious about the "fuse everything" approach. Must be a little tricky to not lose sonics, fusing the speakers.
Safety before sonics though-or figure out how to, or so I keep hearing.
thanks
Always liked th3e idea of soft start wish most things used them.
The PSU to amp board fuse sounds good.
Wondered about between amp and speakers but that's just curious about the "fuse everything" approach. Must be a little tricky to not lose sonics, fusing the speakers.
Safety before sonics though-or figure out how to, or so I keep hearing.
thanks
What are you saying!Mooly said:
You are in the chipamp section, where gaincloners live, and where it is assumed that every superfluous micrometer of copper in the feedback path will influence the sound catastrophically. Imagine a fuse holder with several milliohms in that path. Shocking! But let us use science. Imagine to use an 8 Ohm speaker with the LM3886's 5,6 A of peak Ieff. Ignore the fact that the output voltage will be too high for that IC. It would be 44,8 V, clearly worse than the worst case scenario. Now let us use the most beloved feedback resistor combination of 680R/22k, giving a current of less than 0,002 A for that situation. Where do you buy fuses with that rating?
As Richie says, the fuse is the last ditch protection for the speaker. On a DC coupled amp I would always use a DC offset protection scheme. Always ! Fuses are not quick enough and give no protection against smaller but still damaging offsets.
The Zobel should be close to the output pin really.
To more fully answer your question. When the fuse is blown the feedback is removed. Almost certainly this means the IC output will swing to one of the rails and sit there. It can't oscillate anyway then, for that it needs feedback. You can add something like a 1k 1 or 2 watt resistor across the fuse. This maintains some measure of feedback if the fuse is blown. How much though depends on whats connected to the output. Does no harm anyway.
The Zobel should be close to the output pin really.
To more fully answer your question. When the fuse is blown the feedback is removed. Almost certainly this means the IC output will swing to one of the rails and sit there. It can't oscillate anyway then, for that it needs feedback. You can add something like a 1k 1 or 2 watt resistor across the fuse. This maintains some measure of feedback if the fuse is blown. How much though depends on whats connected to the output. Does no harm anyway.
Hi,
use separate T rated fuses on each primary.
Try for <T2.17A for each 250VA transformer. (250/115=2.17Amps).
You may find that the amps will work long term with T1.6A fuses.
Now, consider what is happening with your T5A feeding a combined load of two 250VA transformers.
Let's assume one channel is operating perfectly and consuming just quiescent power of ~10W.
The T5A fuse will pass 10A continuously for many minutes before rupturing.
That is 1150 Watts passing into the amp chassis.
With just 10W going to the good channel that would leave >=1140W going into the faulty channel. How hot will it get before that T5A ruptures?
I don't want to insure your house!
Fit a soft start to avoid the need for massive overfusing on transformer start up.
If you want to avoid fast charging of the smoothing capacitance, with it's enormous charging pulses flowing through rectifiers and capacitors, then also consider fitting slow start after the secondaries.
use separate T rated fuses on each primary.
Try for <T2.17A for each 250VA transformer. (250/115=2.17Amps).
You may find that the amps will work long term with T1.6A fuses.
Now, consider what is happening with your T5A feeding a combined load of two 250VA transformers.
Let's assume one channel is operating perfectly and consuming just quiescent power of ~10W.
The T5A fuse will pass 10A continuously for many minutes before rupturing.
That is 1150 Watts passing into the amp chassis.
With just 10W going to the good channel that would leave >=1140W going into the faulty channel. How hot will it get before that T5A ruptures?
I don't want to insure your house!
Fit a soft start to avoid the need for massive overfusing on transformer start up.
If you want to avoid fast charging of the smoothing capacitance, with it's enormous charging pulses flowing through rectifiers and capacitors, then also consider fitting slow start after the secondaries.
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