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Speaker protection pcb design

I hunted for them for a while, sent repeated emails, tried to find a suitable replacement transformer myself, etc. I finally got fed up and moved on.
 
Further digging shows that Velleman are using a Songle mains AC appliance relay with no DC breaking rating at all and a contact resistance of 100 mOhm at 1A.
There is a very good chance that this relay will fail to break a ~50V dc rail and leave your speaker connected to a rail until a fuse blows. I have recently repaired some battery backup controllers where a similar relay had burned out switching a 6V SLA battery.
Breaking high DC voltages is a hard problem, we used to use special and expensive relays to do this.
 
I always used the LS protection boards from Jims Audio in preference to the Velleman kits. Les at Avondale does his own now and that's what I'm using for my ncc300s. I'm very interested in what you come up with though David.
 
An Arduino is a little overkill for this kind of app. I started but never got round to finishing a similar module using an 8 pin PIC controller. Dead easy using its internal RC oscillator, a small delay after the amp turns on before connecting speakers, DC and overheat detection using a bicolour LED. E.g. Red - overheat fault, Orange - temp warning, Flashing Red DC fault, Green good. I could probably dig out the source code if anyone was interested.
 
My comments about breaking ~50Vdc power apply to all of these.
Breaking AC is easy as the arc quenches on the zero crossings or not more than 10ms.
These relays don't have very big gaps
 
I do some PCB design in my day job. It is one of those skills that needs regular use.
I am also one of the KiCad user forum moderators.
Making a small business out of selling boards to Europe from Malaysia is too much trouble with taxes etc for now, so I am happy to publish small projects on a user should make a donation to charity basis.
I hope to put up the Gerber plot set and Sketch soon.
 
Things I would wish for in a speaker protection design :D
- Amp switch on delay as there is often a DC thump at switch on
- DC speaker protection monitoring on the output
- Amplifier Oscillation would trip the output to the speakers, the velemans picked up a faulty interconnect (disconnected ground) once at a bake off and my amp refused to switch on showing a red light.
- Good heavy duty speaker connections in and out
- 30A relays
Alan
 
My files above updated.
I have added 6.35mm Faston connections.
Do I need resistors to ground on the amplifier side to charge output capacitors?
It would be easy to give an extra long switch on thump delay option for amplifiers with these.
 
337alant said:
Things I would wish for in a speaker protection design :D
- Amp switch on delay as there is often a DC thump at switch on
- DC speaker protection monitoring on the output
- Amplifier Oscillation would trip the output to the speakers, the velemans picked up a faulty interconnect (disconnected ground) once at a bake off and my amp refused to switch on showing a red light.
- Good heavy duty speaker connections in and out
- 30A relays
Alan
Click to expand...

I'm working on a design that not only covers all of the above but, optionally, many extra functions such as over temp cut out, over driving into clipping warning and cut out and even protection for individual drive units by being able to set the maximum output over specific frequency ranges... and... it gets around all the issues with both relays and the mosfet method! It would be expensive (>£100) and no doubt will never see the light of day (the challenge of designing stuff to at least the point where I can be certain it works well and could be put into production is the be all and end all to me) but it's going well so far. It will be self powered as IMO this is an absolute must and the most capable version will be for incorporation into the case of the amp being protected. A necessarily less capable version that can be a stand alone unit will also be designed.

ATM I'm working on doing just the normal functions in Alan's list above but avoiding the relay and mosfet issues, and it's getting there:)
 
davidsrsb said:
My files above updated.
I have added 6.35mm Faston connections.
Do I need resistors to ground on the amplifier side to charge output capacitors?
It would be easy to give an extra long switch on thump delay option for amplifiers with these.
Click to expand...

A small point... but if it's got output capacitors it can't go DC anyway... still useful as anti thump I guess
 
I have never come across an output capacitor failing short. The thump can be a nuisance. The Quad 303 output size is limited by this and does have a very audible effect on the bass ( in a good way)
 
Would there be any interest in the protection circuit fro my Sugden Au51p, which is pretty complex (to my naive eye) ?

I have good (and registered) photos of both track and components sides of a single sided PCB.

BugBear
 
My simmed unit is now about as far as I want to take it for now. Super fast reacting due to multiple order LPF, turn on delay for thumps and while it checks for DC offset, combination of mosfets and gold plated contact relays in phased switching arrangement so relay never switches or sees DC or in fact much in the way of anything.... it's there to short out any possible "sound of mosfets/silicon". Under actual fault condition another layer of protection comes in and removes power from the amplifier itself leaving it "in protect" and needing a reset by removing mains. Spare OR'ed inputs present for HF detection, over temp, and even the driver protection by frequency band. No SMD parts or any specialised ones available from just one company. Sorted and ready to be abandoned like the hundreds of other designs:rolleyes:
 
Arkless Electronics said:
My simmed unit is now about as far as I want to take it for now. Super fast reacting due to multiple order LPF, turn on delay for thumps and while it checks for DC offset, combination of mosfets and gold plated contact relays in phased switching arrangement so relay never switches or sees DC or in fact much in the way of anything.... it's there to short out any possible "sound of mosfets/silicon". Under actual fault condition another layer of protection comes in and removes power from the amplifier itself leaving it "in protect" and needing a reset by removing mains. Spare OR'ed inputs present for HF detection, over temp, and even the driver protection by frequency band. No SMD parts or any specialised ones available from just one company. Sorted and ready to be abandoned like the hundreds of other designs:rolleyes:
Click to expand...
Hi,
Why not publish the design, and let others pursue the PCB design if they want to ?.

You could do a group buy if you designed the PCB yourself, or offer the unit in the classifieds as a final solution with notes.

There have been quite a few enquiries here in the DIY section on the amplifier/loudspeaker protection circuit, whether the IC that is difficult to locate, or the Velleman kit. Another source where it is easier to discuss the solution from the designer may be preferred.

Regards,
Shadders.
 
Shadders said:
Hi,
Why not publish the design, and let others pursue the PCB design if they want to ?.

You could do a group buy if you designed the PCB yourself, or offer the unit in the classifieds as a final solution with notes.

There have been quite a few enquiries here in the DIY section on the amplifier/loudspeaker protection circuit, whether the IC that is difficult to locate, or the Velleman kit. Another source where it is easier to discuss the solution from the designer may be preferred.

Regards,
Shadders.
Click to expand...

I did consider this, for a moment.... I would want to make some money from it if I published it for a start. As with all my work I'd rather it remain vapour ware than give it away for free. I'm acutely aware that 95% of the things I design will never see the light of day or make me a penny... but I'll be damned if anyone else is going to!

I did publish a design here (in AOS first in fact but when I fell out with Marco I wanted it to be available elsewhere) for a very simple valve line stage but it seems that DIY'ers won't look at anything that doesn't have the "paint by numbers" of a silk screened PCB.... To my knowledge, two people built one and that was it... I've never seen its very existence mentioned since!

It was designed to be the non plus ultra of protection boards. Completely devoid of any effect on the sound and no issues with burning relay contacts or anything like that. That was the challenge. It is as complicated as some amplifiers. Protection circuits are a "grudge purchase" and generally people will just buy the cheapest

It would need to be breadboarded to find and remove any bugs with it and this is a weeks work probably.
 
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