I know this is a very old post, I have been reading through this.
Why do we need two pairs of diodes to the two rails? With the SS relay circuit, seems like you need one pair of diodes to go to the two rails between the speaker and the SS relay only. Why do you need another pair of diodes to the two rails at the output of the output power transistors? That would be redundant. The pair of diodes that are in between the SS relay and the speaker already prevent the inductive kick from the speaker already, there will be no inductor kick at the output of the power amp.
Besides, if you have EF push pull output stage, one side of the transistor will be able to handle any kick from anywhere!!! They are emitter followers with very low impedance and they can drive many amps.
I look at this design, on the surface, it looks simple and works. But where do you get the extra 10V above the rail? You have to get an extra power supply. This make the Avago V621 a better choice.
Hi Mooly
I already bought the V621 and layout into the pcb already. I am just reading through the thread getting info on the turn off time of the MOSFET and ran across this. I my opinion, photovoltaic coupler is much better, who wants to put in an extra supply just for the sake to be different!!
I know the spec said the MOSFET turn off time delay is 0.4mS, but I put two output of the V621 in series, that's the reason I am looking for the time delay for the MOSFET to turn off.
Hi,
Are you doing this to test or to you it must work this way and won't require testing?
I have been looking at such switches, both for rail and output muting, but I haven't tested, so I'd be interested in test results and what comes out of it, making perhaps different choices and why.
Are you doing this to test or to you it must work this way and won't require testing?
I have been looking at such switches, both for rail and output muting, but I haven't tested, so I'd be interested in test results and what comes out of it, making perhaps different choices and why.
I am not doing it for testing, just want an amp that is better than my Acurus and enjoy. I already put into my pcb, I just want to get more info. I want to protect my speaker. Burning the amp is not even that big a deal.
So this means as it is, this is considered a viable and fully functioning method that doesn't require any further tweaking. Is it?
On my part, I would want to try to protect both the speakers and the amp, if at all possible. With rail switches, there is a better chance for the amp to survive, or at least limit the damage.
Often the danger comes from what comes in the amp's input, so I would also add a muting on that amp's input.
Doing it all solid state and avoid mechanical relays is definitely a plus.
Did you read this post,
http://www.diyaudio.com/forums/solid-state/191449-output-relays.html#post2661555
I have been out of touch for an overly long time, so I haven't kept up with all the threads. So, no, I had not read that, and thank you for pointing me, and others to it.
I have a work in progress amp design that is in a "stalled" status for now, which I will reactivate as soon as I can, and the main focus on that design when I was last working on it was to replace all mechanical relays by solid state ones, adding a mute on the input and possibly have some type of automatic compression on the input applied just before the amp would clip, to try to limit the effects of saturation.
My goal is to aim for an almost indestructible amp, as much as possible, as well as making sure it is never any threat to the speakers.
For one thing, although the use of crowbars on the output might somewhat insure the speakers would never be harmed, I don't like that idea because it also kind of makes the amp a sacrificial part.
I also don't like it when an amp goes into some protection mode and stays that way even if the fault has gone.
I would like to add some logic that looks at various things to assess the fault and take steps to eventually bring back the amp online if the fault's origin was only temporary, if the symptoms causing the amp to go into protection mode have gone (overdrive, overheat, temporary short...).
The show must go on, unless the fault is permanent.
If you're not careful you can soon find all the protection circuitry of an amp becoming more complex and involved than the amp itself.
Is indestructability really that important when its your own amp used at home ?
Products in the hands of the public at large, and used under goodness knows what operating conditions are more likely candidates for complex protection imo.
Is indestructability really that important when its your own amp used at home ?
Products in the hands of the public at large, and used under goodness knows what operating conditions are more likely candidates for complex protection imo.
A small microcontroller can make a complex sounding design fairly simple. http://www.diyaudio.com/forums/solid-state/264313-how-build-21-st-century-protection-board.html
Crowbar designs sound scary to me as well. I'm playing with a design that opens the power rails at the supply with a fault detection so there's no waiting for the supply caps to dump into a damaged or overheated amplifier.
I can see the desire to have a commercial amplifier restart itself, but in a domestic amplifier if the safety circuit is activating there is something wrong. If it's overheating there is a design issue that should be addressed. If there's a short, there's a wiring/operator issue that should be addressed. If there's DC or overcurrent, there are other issues that should be addressed. In all cases there's problems that should be corrected before the amp restarts itself(drunk idiot playing with speaker wires included). I prefer to need to manually restart the amp.
Crowbar designs sound scary to me as well. I'm playing with a design that opens the power rails at the supply with a fault detection so there's no waiting for the supply caps to dump into a damaged or overheated amplifier.
I can see the desire to have a commercial amplifier restart itself, but in a domestic amplifier if the safety circuit is activating there is something wrong. If it's overheating there is a design issue that should be addressed. If there's a short, there's a wiring/operator issue that should be addressed. If there's DC or overcurrent, there are other issues that should be addressed. In all cases there's problems that should be corrected before the amp restarts itself(drunk idiot playing with speaker wires included). I prefer to need to manually restart the amp.
That's true. And some have even gone as far as using a microcontroller and a bunch of sensors all over the place. I wouldn't go quite that far.
It is to me, because I am making amps not only for myself, but for others, and my own amps can end up in other's hands, so they do need to be well protected. Plus my usage doesn't end at home, it's also used in P.A and outdoors sometimes.
Full protection is a must for me, and the speakers also must be fully protected against the amp's failures and abuse from those using them.
So do my amps.
Interesting, I will look at this.
Actually I would consider eventually using an Arduino, because once the logic starts getting complex, using a microcontroller can actually reduce that complexity on the electronics side, while providing even more flexibility in the functions, with more intelligence.
I think it's brute force and not so smart. It's like driving a tiny nail with Thor's hammer!
I use my amps in P.A occasionally, and unless an amp is really dead, the show must go on and if possible uninterrupted. If I loan my stuff to others, which can happen, I want to make sure they can't kill my amps.
Part of the beauty of the Arduino is you can quickly change the operation of the control/protection circuit. If you want it to monitor for safe restarts and reactivate the amplifier, it can be written into the software. If you want to change it to a domestic operation, safer software can be loaded on in a couple minutes.
Another bonus is the ability to manage all aspects of the amplifier control. Softstart, delayed start, remote start, ect. are simple once integrated into a controller. The design I'm experimenting with came about because to original designer was building some Hybrid tube/SS amplifiers and needed to start multiple power supplies in the correct order at the right time in order to stop dangerous amplifier operation while the tubes warmed up. It's been a great asset for us when experimenting on the test bench We can push test devices beyond their limits only to have everything shut down before any damage occurs.
I totally agree! Using a microcontroller in that case can add features while reducing the circuitry complexity.
Actually one of my main project is a set of amps for a 4 way system, all integreated into one big cabinet, per side, with auto-shutdown, active filtering, noise gate, etc... and I think using a microcontroller for all this would be a big plus.
Yes, I read it many times, that was a very useful post.
I was just explaining why I dug up this post to look for this specific answer and I got it. Thanks.
I was just raising questions when I read the other design that need an extra supply to do the job. To me, the argument of photovoltaic is slower doesn't hold water in my book. We are talking about power dissipation...that takes time. a few mS is not going to hurt. If they are worriers, do it just like me!!! I parallel two pairs of MOSFET that are 4.5mohm on resistance!!! The lower resistance, the less voltage drop across and less power. Two in parallel, you have double amount of bonding wires inside the MOSFET and it's like a bigger fuse inside.
But from reading the thread, I am starting to think about the power on "pop" that I should avoid. I have a circuit board to turn on the relay with the output voltage settle to 0V. I wonder whether this will cure the pop as the relay will not turn on until the output settle to less than 0.7V from ground.
0.7 volts isn't much per se but it will create a very loud pop from the speakers.
You need a fixed turn on delay at power on together with an instant disconnect at power off. The circuit must also reset instantly so that even a brief interruption enables the full start cycle to commence.
That's exactly how I feel. I am not going to put a microprocessor into the power amp!!! Not that I don't know those, designing microcontroller was part of my job in my career. The point is where are you going to draw the line.
In my case, I use 5 pairs of MJL3281/1302 huge transistor with 40V rail. I am going to use only 4 to 6A fuse. Chances are I am going to blow the fuse before thermal causing the power transistor to fry.
When something goes wrong with the amp, you are going to have to open it up to fix it. Some protection of the power transistor is plenty. To me, I have a pair of JM Lab 913, protecting them is of utmost importance, that's what I am doing.
You keep thinking about ALL possibilities of the amp burning and try to protect it, the protection circuit is going to be as big as the real circuit. AND the worst is if the protection circuit gets in the way of the signal path, compromise the pcb layout, that defeat any purpose of coming here to design the best amp!!! there is a lot of truth about less is more and there is truth that some high end amps do not even put in protection.
Would just controlling the speaker relay enough to avoid all these?
I have a separate pcb to drive the SS relay. If the output relay is good enough, I can add say a 555 timer or something to keep the relay from turning on for 5 seconds.
I have not stuff this board yet, just as easy to chuck this board and relayout a new one. It's less than $30, not even worth adding onto this.
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