If you ask the question you know the obvious answer.
Amplimo manufactures a unique LSP protection relay that is inaudible on 9 of 10 power amps, the LR(Z) relay dates back as far as their takeover from ILP in the late 1980s.
Too slow for fast BJT output power amps for my taste, for which i use two parallel 4-layer SDS relays with a delay that handle 160A peak, 40A continuous and 8000VA.
I could show you relays which are totally out of this world, completely inaudible for decades, but out of reach for both DIYer and pro amp manufacturer.
Combined with intelligent protection circuitry of proven track record, such as a NEC uPC1237, the LR(Z) relay would work like a charm with a power amp as the Fist 5.
Search Janneman (linearaudio.nl) for more on the Amplimo relay.
There are a few comparable relays from other manufacturers, not superior to the LR(Z) but more difficult to obtain.
Amplimo manufactures a unique LSP protection relay that is inaudible on 9 of 10 power amps, the LR(Z) relay dates back as far as their takeover from ILP in the late 1980s.
Too slow for fast BJT output power amps for my taste, for which i use two parallel 4-layer SDS relays with a delay that handle 160A peak, 40A continuous and 8000VA.
I could show you relays which are totally out of this world, completely inaudible for decades, but out of reach for both DIYer and pro amp manufacturer.
Combined with intelligent protection circuitry of proven track record, such as a NEC uPC1237, the LR(Z) relay would work like a charm with a power amp as the Fist 5.
Search Janneman (linearaudio.nl) for more on the Amplimo relay.
There are a few comparable relays from other manufacturers, not superior to the LR(Z) but more difficult to obtain.
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I have speaker protection in all my power amps. They are not in the signal path.
When you have a fault, you want to make sure the output has no voltage, and the power supply is switched off as fast as possible.
You might have to sacrifice your output devices and protection relays. But they are cheaper compared to good speakers.
Not for the faint-hearted.
Patrick
When you have a fault, you want to make sure the output has no voltage, and the power supply is switched off as fast as possible.
You might have to sacrifice your output devices and protection relays. But they are cheaper compared to good speakers.
Not for the faint-hearted.
Patrick
Patrick, yup, are you connected the protect relay to the AC mains? what do you think since the amp output still in parallel to the protect circuit?
No, but you will get a lot of current through the output mosfets if you don't limit the current.
So, if you still want to keep the transistors and probably the supply caps, you need to limit the maximum current.
There are many ways to do it.
One way is to switch off all the mosfets by turning Vgs to zero (short circuit).
You can do this by a transistor like Nelson did, but also by a relay.
You can also put a current limiter on your power supply.
Patrick
So, if you still want to keep the transistors and probably the supply caps, you need to limit the maximum current.
There are many ways to do it.
One way is to switch off all the mosfets by turning Vgs to zero (short circuit).
You can do this by a transistor like Nelson did, but also by a relay.
You can also put a current limiter on your power supply.
Patrick
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I find the idea of shorting the output to ground in case of failure
(and probably killing the comparably cheap output devices instead of
the speakers) very appealing. But would it be adviseable to have an
otherwise usual protection circuit wired that way (with the output
connected to ground for some seconds during turn on and connected to ground
immediately at turn off) ?
What makes me unsure is the sentence about the current limiting
"As it is, you will still be taking some chances with a shorted output".
In short, with the current limiting in place, will the output devices
survive a shorted output for some seconds on a regular basis ?
(and probably killing the comparably cheap output devices instead of
the speakers) very appealing. But would it be adviseable to have an
otherwise usual protection circuit wired that way (with the output
connected to ground for some seconds during turn on and connected to ground
immediately at turn off) ?
What makes me unsure is the sentence about the current limiting
"As it is, you will still be taking some chances with a shorted output".
In short, with the current limiting in place, will the output devices
survive a shorted output for some seconds on a regular basis ?
> connected to ground for some seconds during turn on and connected to ground immediately at turn off) ?
This is what we do.
But you better make sure you short the input before you short the output, and you release the output before the input.
> In short, with the current limiting in place, will the output devices
> survive a shorted output for some seconds on a regular basis ?
Yes, because they only see the max current you allow.
But I don't think you want to do that everyday.
I have not had a failure ever, so I can only say that in theory.
And no I am not going to try it deliberately on one of my Class A amps.
Patrick
This is what we do.
But you better make sure you short the input before you short the output, and you release the output before the input.
> In short, with the current limiting in place, will the output devices
> survive a shorted output for some seconds on a regular basis ?
Yes, because they only see the max current you allow.
But I don't think you want to do that everyday.
I have not had a failure ever, so I can only say that in theory.
And no I am not going to try it deliberately on one of my Class A amps.
Patrick
For a balanced amp, as in :
- input on both sides shorted to gnd ?
- output on both sides shorted to gnd ?
- Vgs on both sides switched to zero ?
- (switched current limiting on both power rails ?)
- input on both sides shorted to gnd ?
Yes.
- output on both sides shorted to gnd ?
No, as we don't want ground to see high current.
So Vo+ to Vo-.
- Vgs on both sides switched to zero ?
Optionally yes.
- (switched current limiting on both power rails ?)
Current limit is built-in. No need to switch.
And switch off 230Vac.
Patrick
Yes.
- output on both sides shorted to gnd ?
No, as we don't want ground to see high current.
So Vo+ to Vo-.
- Vgs on both sides switched to zero ?
Optionally yes.
- (switched current limiting on both power rails ?)
Current limit is built-in. No need to switch.
And switch off 230Vac.
Patrick