Hey everyone,
This might not be the right forum for this but I'm installing it on my solid state amp so I figured why not.
I purchased this cheap speaker protection kit from ebay a week ago:
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
It just dawned on me that it might not be able to handle the full volume output voltage from the amplifier.
I've no schematic for the board. I was wondering if anyone here had experience of could tell me what the input handling range on this guy is.
I know my rail voltage is +/- 85V on this particular amp.
If the unit cant handle that voltage, can i replace the transistors/capacitors with higher rated units and make it able to handle?
Thanks!
Kris
This might not be the right forum for this but I'm installing it on my solid state amp so I figured why not.
I purchased this cheap speaker protection kit from ebay a week ago:
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
It just dawned on me that it might not be able to handle the full volume output voltage from the amplifier.
I've no schematic for the board. I was wondering if anyone here had experience of could tell me what the input handling range on this guy is.
I know my rail voltage is +/- 85V on this particular amp.
If the unit cant handle that voltage, can i replace the transistors/capacitors with higher rated units and make it able to handle?
Thanks!
Kris
Do you have a schematic?
How many inputs does the circuit have?
Does each input have a different set of limits for correct and reliable operation?
If you accept that condition and then discover that it does not suit your use, then you will have to spend more money.
How many inputs does the circuit have?
Does each input have a different set of limits for correct and reliable operation?
are you willing to accept this condition?
If you accept that condition and then discover that it does not suit your use, then you will have to spend more money.
The relays look far to small to handle a fault condition from such an amp as yours. They have to survive breaking the connection under a real fault condition and also under high drive (high volume). The relays say 10A DC.
Don't want to sound negative about it, just being realistic. For a switch on delay and played at normal volumes they should be fine. If an output transistor goes short in the amp then you could probably expect the relay contacts to weld together as they "try" to open.
There is a thread in this forum using solid state (FET) switches that I can confirm work very well. Depends on your DIY skills. You could probably add such devices to this circuit you have but you would need to understand and know how to implement it.
Don't want to sound negative about it, just being realistic. For a switch on delay and played at normal volumes they should be fine. If an output transistor goes short in the amp then you could probably expect the relay contacts to weld together as they "try" to open.
There is a thread in this forum using solid state (FET) switches that I can confirm work very well. Depends on your DIY skills. You could probably add such devices to this circuit you have but you would need to understand and know how to implement it.
Just to add... your ebay circuit looks to need a separate low voltage supply to power it. It looks intended to be used with a small auxilliary transformer. Probably something around 12 to 18 volts AC to feed it with. That's not a problem if you know how to generate a low voltage DC rail from your -/+85 volts although its a lot to drop dissipation wise for a linear reg suppling a few 10's of milliamps.
Mooly,
Without this board the amp naturally has no other protections so as it stands this is better than nothing. I didnt expect amazing things from this unit as it was only $9.99.
My only concern (as of before your fault condition concern) was if the circuitry could handle the AC voltage coming out of the amp.
EDIT: You are correct, It needs some AC. I just picked up a transformer from radioshack than try to drop the 85 down.
Without this board the amp naturally has no other protections so as it stands this is better than nothing. I didnt expect amazing things from this unit as it was only $9.99.
My only concern (as of before your fault condition concern) was if the circuitry could handle the AC voltage coming out of the amp.
EDIT: You are correct, It needs some AC. I just picked up a transformer from radioshack than try to drop the 85 down.
Resistors attached to the board INputs seem to be 15K 1/4W (someone check my eyes).
This will long-term take 60V steady or 90V sine-peak.
> +/- 85V on this particular amp.
Assuming you won't KEEP it in shut-down, it seems ample.
> relays look far to small to handle a fault ....10A
But relays such as this are widely used in heaters and microwave ovens which cycle many-Amp loads thousands of times; how often do we expect a dead-short fault?
I think it is a fine 10-buck gizmo.
Are our speakers worth more than $10?
I'd probably use it at home, where ANY shut-down would be instantly investigated.
Probably not in a 42-amplifier PA rack where shutdowns may go unnoticed or be re-set repeatedly.
This will long-term take 60V steady or 90V sine-peak.
> +/- 85V on this particular amp.
Assuming you won't KEEP it in shut-down, it seems ample.
> relays look far to small to handle a fault ....10A
But relays such as this are widely used in heaters and microwave ovens which cycle many-Amp loads thousands of times; how often do we expect a dead-short fault?
I think it is a fine 10-buck gizmo.
Are our speakers worth more than $10?
I'd probably use it at home, where ANY shut-down would be instantly investigated.
Probably not in a 42-amplifier PA rack where shutdowns may go unnoticed or be re-set repeatedly.
It will handle the voltage as the "input" to this kind of circuit is an integrator.
The problem is that a large speaker presents itself as an inductance at DC.
Switching a resistive load at 110 or 240 vac doesn't generate an arc as the contacts open in the same way that even 12 or 24 volts dc would into an inductive load.
How often do you get a short... it happens when you see how many ask for help with blown up amps on here.
Not so sure that would work tbh. A DC arc is "sustained" as the contact opens unlike an AC arc.
On small contacts it doesn't take much to weld them together as the actual forces "the spring force in the relay" is to small to pull it apart.
On an amp with -/+85 volt rails and a half decent PSU and there is a huge amount of energy available via reservoir caps.
Found this on youtube which illustrate the problem. Appears to be just a bulb (so low current, highish resitance load) and you can see how it arcs,
120Volts DC Arc - YouTube
Even when all the theory is thrashed out the bottom line is that no one ever "tests" their protection on a real speaker. By that I mean sticking a screwdriver across the output transistors etc (please don't !)
The best you can hope for on a large amp is that the system will isolate a speaker such as to prevent it catching fire and it will almost certainly be damaged by the huge cone excursion even if the applied voltage were only present for a few milliseconds at most.
Be under no illusions of how hard it is to protect a speaker against an instantaneous DC fault with a rapid rise time (as opposed to a slowly rising DC offset).
I was curious as to what they seller would say so I asked them. They said that kit in my original link was good for 150W/channel amplifiers. So I asked if they had one that was suitable for 250-500watt/channel amplifiers. The said to look at this:
2-channel Stereo Speaker protection board LED assembled | eBay
This makes me wonder what protections--if any--are installed on my higher end amps... I have some high power Crown amps and some hefty vintage Kenwood 600s...
2-channel Stereo Speaker protection board LED assembled | eBay
This makes me wonder what protections--if any--are installed on my higher end amps... I have some high power Crown amps and some hefty vintage Kenwood 600s...
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The amp in question here is a 1980s Bose 1800 Series I. It has an enormous 40 pound transformer fueling the massive capacitors. When I got the amp, only one channel was working. I just used it as a center channel amp for a few years until it started throwing 2-3V of DC every now and again at the speakers. It didnt hurt them or anything. I recently started repairing the bad channel. I decided that I'd like to have some form (even if minimal) protection from DC.
I installed the aforementioned kit last night and was testing it out. I'm not quite finished with the bad board (waiting for parts to arrive) so it will still occasionally throw + rail voltage out the back then return to normal. The protection board reacted quickly in shutting down.
I'll do a more detailed investigation later when I have access to more measuring devices.
I came across a website of a fellow that did some significant work on an amp similar to the 1800. He used a similar speaker protection set that I bought:
ls_protect.jpg
It looks like he used this:
Velleman, Inc.
ls_protect.jpg
It looks like he used this:
Velleman, Inc.
The relay in your other ebay link looks a lot more substantial but I certainly wouldn't like to say that it would interupt a speaker connected across 85 volts without failure.
No easy answer I'm afraid, and rather you than me in connecting speakers to an amp with a known DC fault
It might be worth you searching some old service manuals of high powered amps and seeing what relays etc they use.
No easy answer I'm afraid, and rather you than me in connecting speakers to an amp with a known DC fault
It might be worth you searching some old service manuals of high powered amps and seeing what relays etc they use.
The relay in your other ebay link looks a lot more substantial but I certainly wouldn't like to say that it would interupt a speaker connected across 85 volts without failure.
No easy answer I'm afraid, and rather you than me in connecting speakers to an amp with a known DC fault
It might be worth you searching some old service manuals of high powered amps and seeing what relays etc they use.
It does look more substantial.
I wont be connecting up any speakers until I've repaired the DC fault. I've already toasted two small junk test speakers I had laying around. Ive spend about a month tracking down problems on the other amp board. I'm currently waiting for a large batch of replacement parts to replace some defective units.
I plan on fully testing the amp before loading it down with real speakers. I was planning on using a meter with logging to observe DC offset over a long time period with a dummy load installed. Once I'm satisfied the DC fault has been repaired it will go back in service.
The protection board serves a few purposes other than just DC protections. It provides a nice soft start for the speakers, and disconnects the speakers from the amp once the amp is turned off. When it was running with just one channel it would keep outputting to the speakers even if the power was turned off. It would output until the main caps were drained.
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