Hi,
when my power amp blows one rail fuse the output offsets to rail voltage.
Each time this has happened I have had the speakers disconnected. No damage yet.
I have read that some amps can hold zero offset when a fuse blows.
How can one recognise a schematic that can achieve zero offset?
Can a schematic be altered to achieve zero offset?
My only other alternative seems to be to add a dual crowbar to blow the good fuse on fuse failure trigger.
when my power amp blows one rail fuse the output offsets to rail voltage.
Each time this has happened I have had the speakers disconnected. No damage yet.
I have read that some amps can hold zero offset when a fuse blows.
How can one recognise a schematic that can achieve zero offset?
Can a schematic be altered to achieve zero offset?
My only other alternative seems to be to add a dual crowbar to blow the good fuse on fuse failure trigger.
Andrew,
You bring the story just as the blowing fuse is the most normal thing in the world. Oops…he did it again. 😉
A reliable amp isn’t supposed to blow a fuse unless you abuse it by either playing too loud or connecting a too low impedance load or…well…we have Cola and beer but I won’t assume this abuse for the moment.
I have no idea what amp you use but converting it is probably not the easiest task.
You could think of a DC protection but usually they are too slow and damage has been done before they kick in.
If I were you, I would ask myself why the fuse blows and if you found the cause, better fix that.
/Hugo 🙂
You bring the story just as the blowing fuse is the most normal thing in the world. Oops…he did it again. 😉
A reliable amp isn’t supposed to blow a fuse unless you abuse it by either playing too loud or connecting a too low impedance load or…well…we have Cola and beer but I won’t assume this abuse for the moment.
I have no idea what amp you use but converting it is probably not the easiest task.
You could think of a DC protection but usually they are too slow and damage has been done before they kick in.
If I were you, I would ask myself why the fuse blows and if you found the cause, better fix that.
/Hugo 🙂
Hi Andrew,
My Simple Killer Amp holds zero if it blows a fuse (output MOSFETs drains). I have to test for such things. Not easy to design for.
Having said that there may be unknown conditions where it won't but I'm still waiting for them.
Cheers,
Greg😀
My Simple Killer Amp holds zero if it blows a fuse (output MOSFETs drains). I have to test for such things. Not easy to design for.
Having said that there may be unknown conditions where it won't but I'm still waiting for them.
Cheers,
Greg😀
Hi,
I know why it blows fuses.
Each time it is when I attach a lead to the RCA input.
Presumably, it is the bad design of the connector that allows the pin to make before the ground that promotes some high frequency oscillation and instantly blows the -ve fuse.
The output goes to +ve rail. I have checked by removing the +ve fuse and output goes -ve.
This has happened twice now even though I have added an extra RF filter in front of the first stage of amplification. It already had a 50kHz (3.2uS) filter before the second LTP stage.
I normally switch off before changing cables but I short cut this process when carrying out testing. 🙁
My worry is that a careless duster might just interfere with a connector and I will lose an expensive speaker
I have four of these monoblocks which each have a relay on the output. As Netlist has said a DC detect to overide the relay will cut off but 70Vdc for 500mS is a lot of heating in a voice coil
I know why it blows fuses.
Each time it is when I attach a lead to the RCA input.
Presumably, it is the bad design of the connector that allows the pin to make before the ground that promotes some high frequency oscillation and instantly blows the -ve fuse.
The output goes to +ve rail. I have checked by removing the +ve fuse and output goes -ve.
This has happened twice now even though I have added an extra RF filter in front of the first stage of amplification. It already had a 50kHz (3.2uS) filter before the second LTP stage.
I normally switch off before changing cables but I short cut this process when carrying out testing. 🙁
My worry is that a careless duster might just interfere with a connector and I will lose an expensive speaker
I have four of these monoblocks which each have a relay on the output. As Netlist has said a DC detect to overide the relay will cut off but 70Vdc for 500mS is a lot of heating in a voice coil
If you want to know whether there's any offset when the fuse blows, why not measure and find out?🙂
Hi Peranders,
It used to have 4k7 to ground after the 10uF electro and 3k3 to 5534 in put pin.
It now has 51k to ground after 10uF and then 1k0 to input pin with 470pF to ground.
But no earthing resistor before the 10uF DC blocking cap.
It used to have 4k7 to ground after the 10uF electro and 3k3 to 5534 in put pin.
It now has 51k to ground after 10uF and then 1k0 to input pin with 470pF to ground.
But no earthing resistor before the 10uF DC blocking cap.
Hi Dnsey,
you misunderstand the problem.
The unwanted output offset is precisely why I started this thread.
I have already confirmed that it goes into offset whichever fuse is removed.
you misunderstand the problem.
The unwanted output offset is precisely why I started this thread.
I have already confirmed that it goes into offset whichever fuse is removed.
Hi AndrewT,
Is there a link to your schematic?
Consider using a switch to short your inputs to ground, that's more convenient than shutting the amp off to change I.C.'s.
-Chris
Is there a link to your schematic?
Consider using a switch to short your inputs to ground, that's more convenient than shutting the amp off to change I.C.'s.
-Chris
AndrewT said:
The simplest solution would be to change the input connectors to the amp, so that the ground makes contact before anything else... like a BNC!! 🙂
I can't see why a momentary buzz would cause the fuse to blow, if the output of the amplifier is disconnected anyway - it shouldn't oscillate if its designed correctly, and even if it did, it shouldn't crowbar anything internally to the point that the fuse blows (unless maybe your output devices are being switched on at the same time - due to a slow driver switch-off?)
Cheers!
Clem
Hi Clem,
Amps shouldn't be unstable with open inputs. However, there are some that are. Oscillation with open inputs can happen. Nasty trait that needs rectifying. I don't think it's simple hum, but rather RF.
There are some RCA plugs that contact ground first (shell retracts). BNC's do ground first, but are a bit fussy to install behind the stereo unit. That and crimping, special wire. Heck, you would either enforce and unexpected quality in the audio world, or witness really horrible, cheap BNC's being spawned!
Turning the unit off first would be the simplest.
-Chris
Amps shouldn't be unstable with open inputs. However, there are some that are. Oscillation with open inputs can happen. Nasty trait that needs rectifying. I don't think it's simple hum, but rather RF.
There are some RCA plugs that contact ground first (shell retracts). BNC's do ground first, but are a bit fussy to install behind the stereo unit. That and crimping, special wire. Heck, you would either enforce and unexpected quality in the audio world, or witness really horrible, cheap BNC's being spawned!
Turning the unit off first would be the simplest.
-Chris
Hi Chris,
I agree, we've had some older amps we made do that, but that was before we understood the effect of living near a broadcast station... hehehe... so what I meant really was, it shouldn't blow the fuse(s) unless its a marginal design or implementation...
I suggested BNC since it's easy enough to buy, ground contacts first, and it doesn't easily get pulled out... Pretty good combination of characteristics, I think...
AndrewT should put a hand sensor at the back of his amp, so it turns off automatically whenever he reaches in! 🙂
Cheers!
Clem
I agree, we've had some older amps we made do that, but that was before we understood the effect of living near a broadcast station... hehehe... so what I meant really was, it shouldn't blow the fuse(s) unless its a marginal design or implementation...
I suggested BNC since it's easy enough to buy, ground contacts first, and it doesn't easily get pulled out... Pretty good combination of characteristics, I think...
AndrewT should put a hand sensor at the back of his amp, so it turns off automatically whenever he reaches in! 🙂
Cheers!
Clem
Hi Clem,
I like the "hand sensor". Just a field disturbance detector will do that for you. The big light on the front is labeled "GERFINGERPOKEN!" and flashes red.
-Chris
I like the "hand sensor". Just a field disturbance detector will do that for you. The big light on the front is labeled "GERFINGERPOKEN!" and flashes red.
-Chris
Nice one!
I just thought of an even simpler solution - line the back of the amplifier with some high voltage i.e. mosquito zapper, that gets powered from the amplifier switch...
🙂
Clem
I just thought of an even simpler solution - line the back of the amplifier with some high voltage i.e. mosquito zapper, that gets powered from the amplifier switch...
🙂
Clem
You could hook up the charge wires from a photocopier. That's good for about 5KV depending on brand.
Do you think there may be a liability issue here? 🙄
AndrewT, do you have a link or post we can see?
-Chris
Do you think there may be a liability issue here? 🙄
AndrewT, do you have a link or post we can see?
-Chris
There are some amplifiers, old and not so old, that oscillate when some RF is applied to the input. The mechanism is not very clear to me, but I think that some kind of positive feedback loop is estabilished, so that the amplifier radiates RF when it oscillates and that RF is picked again by the input.
I've managed to solve it sometimes by adding stonger low-pass filtering to the input, improving ground layout and ultimately increasing compensation capacitor value.
I've managed to solve it sometimes by adding stonger low-pass filtering to the input, improving ground layout and ultimately increasing compensation capacitor value.
Hi Eva,
I think it's a matter of the input picking up the HF signal from somewhere in the circuit. A low RF impedance at the input may help with this. You an only try it and see.
-Chris
I think it's a matter of the input picking up the HF signal from somewhere in the circuit. A low RF impedance at the input may help with this. You an only try it and see.
-Chris
instead of getting the high voltage warnings, may be u should fix an interlocked door/flap (covering the input connectors) which shorts the input
Gajanan Phadte
Gajanan Phadte
Too much worried that ur expensive speakers might be damaged, then design urself a fast speaker protection.
Read at
http://www.diyaudio.com/forums/showthread.php?s=&threadid=69324
Read at
http://www.diyaudio.com/forums/showthread.php?s=&threadid=69324
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