Hi Eva,
I have never seen a relay fail to make contact when shorting out the resistor (except the thermal types strapped to the resistor). The contacts do not have large surge currents to deal with and also save the power switch or relay from the same problem. PTC parts are better suited to TV's and other devices where the current draw is more constant. A class B or AB amplifier would modulate the temperature of the part (music on, music off).
Hi Andy,
Hi djk,
-Chris
That would be me for sure! I am comfortable working on SMPS designs but I don't know enough to design one. I often refer people to you for information on that topic.
I have never seen a relay fail to make contact when shorting out the resistor (except the thermal types strapped to the resistor). The contacts do not have large surge currents to deal with and also save the power switch or relay from the same problem. PTC parts are better suited to TV's and other devices where the current draw is more constant. A class B or AB amplifier would modulate the temperature of the part (music on, music off).
Hi Andy,
Well, they are supposed to do that in a fault situation. This stops many would be techs in their tracks and tends to limit the damage. Both very good things for the units owner in my view. The metal cased, wire wound units would not be my choice. A 3W metal oxide to a 5 or 10 watt bathtub style mounted clear from the PCB is the right way to do this.
Hi djk,
Let's add Marantz as far back as 1969, Denon, Nakamichi and Denon all used this method. I'm sure many other other companies did the same thing.
-Chris
Hi Andy,
I was but a few years older, but consider that the Marantz 500 was probably designed in 1967 through 1968 for release in 1969 (discontinued in 1974). Whoever the design team members were, I feel they were well ahead of their time.
The inclusion of the soft start with speaker relay protection also was very advanced for the time. Each channel used a buffer for the input signal and three long tailed pairs in each channel. Very advanced if you ask me. Right down to buss bars for the supplies.
If Marantz did this on a commercial product starting so early, there is no reason at all why it shouldn't be standard practice on all larger amplifiers. Speaker relays are not terribly expensive compared to a woofer or two. That and the user is not greeted by a thump every time "he" * turns the amp on.
-Chris
* English usage that includes all genders.
I was but a few years older, but consider that the Marantz 500 was probably designed in 1967 through 1968 for release in 1969 (discontinued in 1974). Whoever the design team members were, I feel they were well ahead of their time.
The inclusion of the soft start with speaker relay protection also was very advanced for the time. Each channel used a buffer for the input signal and three long tailed pairs in each channel. Very advanced if you ask me. Right down to buss bars for the supplies.
If Marantz did this on a commercial product starting so early, there is no reason at all why it shouldn't be standard practice on all larger amplifiers. Speaker relays are not terribly expensive compared to a woofer or two. That and the user is not greeted by a thump every time "he" * turns the amp on.
-Chris
* English usage that includes all genders.
Once upon a time a rack with several 230V amplifiers was powered with 120V by mistake. Voltage was not enough to close the soft start relays (which never fail themselves), but it was enough for the amplifiers to work, and indeed they worked until the 10 ohm soft start resistors and and the stuff around them got cooked and failed.
Hi Eva,
Well, you haven't lived until you have seen a 120V device plugged into 208 V. Now that is burnt!
You will appreciate this Eva, a customer plugged a Carver amplifier into a 550 VAC circuit. Unfortunately it did not explode immediately, but got around to that soon enough. Unrepairable (to say the least!).
Ever see MJ15024 and 25 cases with flame cuts burned through? How about also nearby chassis parts as well? I was duly impressed. I wish I had a digital camera back then.
That was that amp.
So I would have to say that AC voltage too high is far more destructive than AC voltage too low. I have seen guys power up amplifiers too slowly with a variac and burn those parts out. No biggie to fix.
-Chris
Well, you haven't lived until you have seen a 120V device plugged into 208 V. Now that is burnt!
You will appreciate this Eva, a customer plugged a Carver amplifier into a 550 VAC circuit. Unfortunately it did not explode immediately, but got around to that soon enough. Unrepairable (to say the least!).
Ever see MJ15024 and 25 cases with flame cuts burned through? How about also nearby chassis parts as well? I was duly impressed. I wish I had a digital camera back then.
That was that amp.
So I would have to say that AC voltage too high is far more destructive than AC voltage too low. I have seen guys power up amplifiers too slowly with a variac and burn those parts out. No biggie to fix.
-Chris
The relay failure is easily guarded against by using one of these thermal fuses that you find in everything from deep fat friers to toasters... place in heatshrink and clamp to the body of the resistor. They pass 10A i think.
There's also those ones you can bolt to the chassis, but as I understand it, most of those have a live case
There's also those ones you can bolt to the chassis, but as I understand it, most of those have a live case
some where you have to stop.
these thermal things cost and the customer will only pay so much
to protect the protection.
more parts for staff to fit wrong and inrush issues.
also if you use a resetable one the inrush will kill it.
the ntc down side is when it is hot, and then the wall braker may trip but the amp will tsill work (do the gig)
the customer will understand that point
also the problem with the hot ntc is not one that customers ever complain about,thay do not switch amps on off on off in practice
andy
these thermal things cost and the customer will only pay so much
to protect the protection.
more parts for staff to fit wrong and inrush issues.
also if you use a resetable one the inrush will kill it.
the ntc down side is when it is hot, and then the wall braker may trip but the amp will tsill work (do the gig)
the customer will understand that point
also the problem with the hot ntc is not one that customers ever complain about,thay do not switch amps on off on off in practice
andy
If you use NTC in place of resistor in relay bypass soft start, it will cool down a few seconds after switch on because it's no longer passing any current. So the switch on/off cycle is not a problem. I've been using this way for a while now as I just wasn't happy with the attendant problems of simple resistor, I'll have the design up on my website very soon, it's very simple.
"and indeed they worked until the 10 ohm soft start resistors "
Which is why BGW was smart enough to put "a fuse in series with the resistor". If the relay failed to pull-in the fuse would open if you tried to operate the amplifier.
"you haven't lived until you have seen a 120V device plugged into 208 V"
Been there, done that. Replaced all the fuses in all the equipment and everything worked. Had to replace the 450V caps in a guitar amp a week later (they developed shorts). Everything else was fine long term. Magnetic circuit breakers are worth the extra money! All the 500W frenels blew, but the 1KW PAR64s were all fine.
On the other hand, 277V caused some problems with another stage set-up. They had thermal breakers and everything was fried pretty good. I eventually got it all fixed, very expensive.
"the Marantz 500 was probably designed in 1967 "
Used a 2 ohm 50W resistor with three relays, one for the AC, one each for the L and R channels, ±91V on the front end, ±82V on the outputs.
Which is why BGW was smart enough to put "a fuse in series with the resistor". If the relay failed to pull-in the fuse would open if you tried to operate the amplifier.
"you haven't lived until you have seen a 120V device plugged into 208 V"
Been there, done that. Replaced all the fuses in all the equipment and everything worked. Had to replace the 450V caps in a guitar amp a week later (they developed shorts). Everything else was fine long term. Magnetic circuit breakers are worth the extra money! All the 500W frenels blew, but the 1KW PAR64s were all fine.
On the other hand, 277V caused some problems with another stage set-up. They had thermal breakers and everything was fried pretty good. I eventually got it all fixed, very expensive.
"the Marantz 500 was probably designed in 1967 "
Used a 2 ohm 50W resistor with three relays, one for the AC, one each for the L and R channels, ±91V on the front end, ±82V on the outputs.
Hi djk,
Hi richie00boy,
Hi Andy,
Anything that reduces the cost of the warranty program is pure bonus in my book. Those costs are higher than anything I know of.
-Chris
I have some affection for those amplifiers. It's nice to see someone else knows them well. The only problems I ran into with those were other technicians. They seemed to be extremely reliable. I would love to rebuild one today with new parts. They sound great once gone over and set up properly.
Hi richie00boy,
What problems were you having? I like the idea that the resistor goes open when the outputs fail. Stops the inevitable further damage from others.
Hi Andy,
I think these are good value and will reduce the cost to the customer long term. This extends power switch life and makes for a dignified power up sequence. I'm sure it may extend capacitor life by reducing a wicked surge current to sane levels on first cycles. Personally, the customer that can afford the larger amplifiers would be annoyed that these measures are not taken. They just don't consider what happens when things go horribly wrong when they are making the purchase. There have been many retrofit requests over the years and no real reason for this not to be included. The case work is still the major cost here (and certification in all markets sometimes), and don't forget the cost of shipping.
Anything that reduces the cost of the warranty program is pure bonus in my book. Those costs are higher than anything I know of.
-Chris
Hi Chris
Switch life is important and despite the ntc the switch is chosen with hi inrush rating.
the crest 7001 amp takes 16 ish hours to build,my own H class 3kw is less than two hours.
the answer is smt and automation.
people like crest would not invest in this so became uncompetative,and biuld quality sufferd du to large labour content.
andy
Switch life is important and despite the ntc the switch is chosen with hi inrush rating.
the crest 7001 amp takes 16 ish hours to build,my own H class 3kw is less than two hours.
the answer is smt and automation.
people like crest would not invest in this so became uncompetative,and biuld quality sufferd du to large labour content.
andy
I can see where you are coming from with the resistor offering protection under certain circumstances. But I'm just not happy with anything that is a possible fire or smoke risk in equipment I design or build. I'm rigorous on correct fusing etc so these would blow (or some other protection come into play) for me in the case of bad output stage.
one off a musician's tools can be an amplifier, the fuse is his worst enamy
the gig stops
The amp must do the gig i have seen hundreads of fuses blown.
sorry mate 20 quid the fuse has blown.
the reason may be that he had a brief short on the amp
the "gig is over"
resetting every whare and one mains fuse
andy
the gig stops
The amp must do the gig i have seen hundreads of fuses blown.
sorry mate 20 quid the fuse has blown.
the reason may be that he had a brief short on the amp
the "gig is over"
resetting every whare and one mains fuse
andy
Hi Andy,
I agree.
Mind you, the pro sound market is very price conscious. Not a market I would like to compete in unless my assembly costs were very low. The warranty program on abused amps needs constant supervision. Smt and automation is the only way to go for any mass produced item. I don't believe China is a sustainable option here.
Hi richie00boy,
Advanced shut down is the only thing that will prevent smoke in my experience. Fuses are typically too slow and are commonly replaced for larger ones (or foil). A little smoke from this one resistor can be a good thing. They will not generally emit a flame, but might under extreme overload. All the more reason to use them, put them in a metal "U" bracket. You can use this to support wires or the relay (making a module that you can supply complete.).
-Chris
I agree.
Mind you, the pro sound market is very price conscious. Not a market I would like to compete in unless my assembly costs were very low. The warranty program on abused amps needs constant supervision. Smt and automation is the only way to go for any mass produced item. I don't believe China is a sustainable option here.
Hi richie00boy,
Advanced shut down is the only thing that will prevent smoke in my experience. Fuses are typically too slow and are commonly replaced for larger ones (or foil). A little smoke from this one resistor can be a good thing. They will not generally emit a flame, but might under extreme overload. All the more reason to use them, put them in a metal "U" bracket. You can use this to support wires or the relay (making a module that you can supply complete.).
-Chris
Hi Andy,
Yes, I know there are like children when they are upset. The things that upset them are generally their fault. Young musicians with a record deal drive me nuts. The older guys tend to be more realistic in their expectations.
-Chris
Then he needs a better sound man. You can't allow stupidity to continue - or you shouldn't.
Yes, I know there are like children when they are upset. The things that upset them are generally their fault. Young musicians with a record deal drive me nuts. The older guys tend to be more realistic in their expectations.
-Chris
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