So, you are pretty sure Scott must have only been referring to the poster tier as sometimes problematic?
Don't forget a lot of the poster sessions are by students, and they receive a lot of interest, and any errors are pointed out gently. It's a great learning experience; beats being thrown in front of the lions all at once ;-)
Really, if you are in one of the convention cities (NY or LA/SF alternating), it is a very nice experience to attend a few sessions and rub elbows with the great & mighty. I think a day pass is like $ 20, well worth the experience.
Jan
Really, if you are in one of the convention cities (NY or LA/SF alternating), it is a very nice experience to attend a few sessions and rub elbows with the great & mighty. I think a day pass is like $ 20, well worth the experience.
Jan
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The point I was making earlier is that many of the AES papers I've read would be considered "gaming" their statistics for a positive. Now that's a pan-publication problem, and I see it all the time in many a major journal, so not picking on AES, but the bars for "quite rigorous" are rising.
Yes, but an exponentially decaying impulse is much easier for relay contact to interrupt than the DC arc is. BTW, I was working in circuit breaker research for 5 years, measuring phenomena during arc interruption.
What puzzles me is the fact that you and JC would blame film coupling caps (esp. polyprops??) for sound degradation and you do not care about relay contacts in series with speaker, though these contacts have non-linear contact resistance after some time of use and this non-linearity is easily measurable as rise of amplifier distortion. On the other hand, 1uF good film cap loaded with some 100k has absolutely no measurable distortion. So again audiophile stories above any sane reality. It is probably a part of a marketing hype, oriented on some apparent design school originality, which is again a part of the story.
No. I agree that interrupting a high current arc is hard to do quickly without damage to the contacts. I worked on power system of 230KV direct from Hoover dam which drew 12 " arcs that burnt holes in the disconnect contact spheres. Those use compressed air to blast the contacts open as fast as possible.
There may be, as you say, relays used in audio speaker disconnect that have contact issues. That is not a capacitor issue. So, I havent commented on it. With proper selection of relay/contacts, it doesnt have to be an issue. I too have had those relays contact trouble but only in cheap receivers that I use out in the garage.
Tweeters are especially easy to damage with the shortest high energy impulse. Not sure even a relay circuit is fast enough. But, the relay will prevent fire and then backed up by slower fuse or CB.
Possibley as an excuse for poor relay selection is not so much to protect speakers from OPS and from smoke and fire (fuses can do that) but to eliminate the annoyingly loud PA turn-on impulse to the speaker.
THx-RNMarsh
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PMA, you have gone too far. An input cap would NOT remove the need for an output relay in one of my amps. The relay protects the speaker from any problem with the amp, it sits between the amp and the speaker, not IN FRONT of the amp. A relay is a 'necessary evil' sometimes when we want cost effective protection that can be opened by a number of problems, including DC offset, amp damage, oscillation, over-temperature, and exceeding the safe area of the output devices (this is VERY IMPORTANT).
If I were to select a PP cap, I would today select a RELIABLE PPMFX 1uf (200V) cap that costs at least $5.25 ea for amateurs at a minimum. Maybe you can find a cheaper Russian made cap that will work for you. However, it would not eliminate the need for the output relay in my amps. The only way to eliminate the output relay is to vastly increase the cost of the amp, by using a balanced bridge output for example, or use a Crowbar circuit to short the output supply, or vastly reduce the power supply voltage to +/-50V or less.
I do agree that relays are not a perfect solution, as they can add to somewhat reducing sound quality due to their contacts, but they ARE practical and protect the speakers.
If I were to select a PP cap, I would today select a RELIABLE PPMFX 1uf (200V) cap that costs at least $5.25 ea for amateurs at a minimum. Maybe you can find a cheaper Russian made cap that will work for you. However, it would not eliminate the need for the output relay in my amps. The only way to eliminate the output relay is to vastly increase the cost of the amp, by using a balanced bridge output for example, or use a Crowbar circuit to short the output supply, or vastly reduce the power supply voltage to +/-50V or less.
I do agree that relays are not a perfect solution, as they can add to somewhat reducing sound quality due to their contacts, but they ARE practical and protect the speakers.
I thought they were to protect the speaker from faults not morons (the welsh for carrot)
It's not clear what the problem with relays would be if they are normally switched at or very near zero current, assuming they are suitably designed for such use. In the rare instance of shorted output transistors, maybe the relay should be replaced at the same time as other damaged parts?
Haven't they used SodiumHexafloride breakers to do that for quite some time? Since the 70s?
At work I rank relays just below fuses as the least desirable components to use. I mostly work with 24VDC PLCs, which control either 24VDC or 120/230VAC.
Lampload testing of relays shows they have poor failure standard deviation (very broad failure curve) and suffer from high infant mortality.
At work I rank relays just below fuses as the least desirable components to use. I mostly work with 24VDC PLCs, which control either 24VDC or 120/230VAC.
Lampload testing of relays shows they have poor failure standard deviation (very broad failure curve) and suffer from high infant mortality.
Relays are often considered a 'necessary evil' to protect high power amp designs. It is almost impossible to do without them, but it can be managed. I built a custom 250W/ 8 ohm amp about 35 years ago that did not use output relays, but it used a dual circuit breaker in the DC power supply instead. As PMA well knows, there are serious limits on the circuit breaker DC voltage, due to arc-over. I only got away with this with regulated DC supplies and a balanced output (which halved the DC voltage for a given amount of output power) and this cost more to make. Today, this amp would cost $20,000 minimum for me to build one today of the same or better quality. The output stage might have up to 10 output pairs in each channel, as well, to maintain operation in the safe area of operation and also supply very high peak current. My original design only used 8 output pairs, but I would at least double it today, because I ran out of current drive for difficult loads with this 35 year old amp. I also used air blown heat sinks, that are generally impractical and tend to be noisy. Yet, I would have to use some super passive heatsink like Richard Marsh uses today for best performance, to remove the fan noise contribution.
I would like to point out that almost every sort of permutation and combination of protection has been tried over the decades. Most either effect the sound by firing while music is playing, like the early E-I electronic protection used by Crown and just about everybody else for years. Or fuses that are naturally non-linear at all times, but seem to be marginally OK in the DC or AC power supplies. The Crowbar protection circuits are very traumatic in operation, because they have to 'instantly' discharge the power supply to ground, to keep the amp from self-destruction. As you see, nothing is easy or perfect to use.
I would like to point out that almost every sort of permutation and combination of protection has been tried over the decades. Most either effect the sound by firing while music is playing, like the early E-I electronic protection used by Crown and just about everybody else for years. Or fuses that are naturally non-linear at all times, but seem to be marginally OK in the DC or AC power supplies. The Crowbar protection circuits are very traumatic in operation, because they have to 'instantly' discharge the power supply to ground, to keep the amp from self-destruction. As you see, nothing is easy or perfect to use.
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Another cheap relay at the Amp input can take care of any moron ;-)
Good tip.
many cheaper relays only give ac current rating for the contacts....... better specs include DC contact rating. Note also that the DC rating is a lot lower than the ac rating.
Note also how contacts are rated.... into resistive load. An inductive load (speakers) you would derate the ac resistive contact rating by 50%.
So, it is the designers job to select the correct relay spec for his amplifier.
I generaly use relays designed for automotive apps. They are reliable for zillions of cycles and designed for good, reliable contact performance under high DC currents.
Even so, I put an arc suppressing series R+C across the contacts.
THx-RNMarsh
Note also how contacts are rated.... into resistive load. An inductive load (speakers) you would derate the ac resistive contact rating by 50%.
So, it is the designers job to select the correct relay spec for his amplifier.
I generaly use relays designed for automotive apps. They are reliable for zillions of cycles and designed for good, reliable contact performance under high DC currents.
Even so, I put an arc suppressing series R+C across the contacts.
THx-RNMarsh
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