Actually, the relays are also supposed to be protection devices for excess current as shown for example, on the relay driver chip app. notes for the venerable uPC1237. I haven't looked further, but presumably there are also notes for the microprocessors that replaced these ICs and added many more functions like the remote control circuits of more recent equipment.
Limiting by relays though, works as a crude, break or make output switch in overdriven conditions when the max. safe power rating is exceeded. With some music programs, it can also result in hiccups and chattering sequences or is otherwise erratic or non-functional as the timing caps deteriorate (and they often do!). However, the technique seems to be preferred by many audio enthusiasts.
Once upon a time, excess output current was controlled by electronic current/voltage sensing and limiting, which approximately followed the power transistor SOA curves (a.k.a VI limiter circuits). However, the scheme has its critics and has been unpopular in hifi applications for many years.
Limiting by relays though, works as a crude, break or make output switch in overdriven conditions when the max. safe power rating is exceeded. With some music programs, it can also result in hiccups and chattering sequences or is otherwise erratic or non-functional as the timing caps deteriorate (and they often do!). However, the technique seems to be preferred by many audio enthusiasts.
Once upon a time, excess output current was controlled by electronic current/voltage sensing and limiting, which approximately followed the power transistor SOA curves (a.k.a VI limiter circuits). However, the scheme has its critics and has been unpopular in hifi applications for many years.
Hi Ian,
Relays are a consumable. For their faults, they make the nicest way to eliminate system noise as it powers up or down, and also to protect your speaker.
The most effective non-relay protection can be found in Carver power amplifiers. Fuses are the worst protection you can think of as they cause distortion.
I-V protection is something we should return to. Don't buy speakers with stupid load characteristics and I-V protection works very well without causing distortion. The audio industry can't be trusted to make good decisions these days.
-Chris
Relays are a consumable. For their faults, they make the nicest way to eliminate system noise as it powers up or down, and also to protect your speaker.
The most effective non-relay protection can be found in Carver power amplifiers. Fuses are the worst protection you can think of as they cause distortion.
I-V protection is something we should return to. Don't buy speakers with stupid load characteristics and I-V protection works very well without causing distortion. The audio industry can't be trusted to make good decisions these days.
-Chris
Here 2000 grit sheets are about 50 Rupees, less than a dollar. After that I use diamond paste in finer grits to polish steel.
I use them to polish molds, so expense of procurement is not the issue for me, I have them lying around.
But consider the hassle of removing the relay from an old PCB, opening the cover, which might be sealed or brittle, polishing a set of contacts that is possibly pitted, and then putting the whole thing back.
Quite possibly mechanically worn too.
For a relay that costs about what a Big Mac does.
Unless it was very rare and not available, I would not do it.
And never on equipment that is outside my house or factory, it is not worth listening to criticism for a job done gratis...this is a hobby not profession for me.
In my factory or home I am the decision maker, so I simply would put a bigger relay, no issues with looks, and MOV across contacts. Bullet proof.
Worn leaf relays don't last much after servicing in my experience. Mine were in the temperature controllers, switching the heater contactors on and off.I had to replace 3 in about 25 years. I used MOVs there too to increase life.
Contactors did last, they were intended to be serviced by trained persons.
You get fine grit abrasive papers in auto paint material shops, they are used to polish paint jobs.
I use them to polish molds, so expense of procurement is not the issue for me, I have them lying around.
But consider the hassle of removing the relay from an old PCB, opening the cover, which might be sealed or brittle, polishing a set of contacts that is possibly pitted, and then putting the whole thing back.
Quite possibly mechanically worn too.
For a relay that costs about what a Big Mac does.
Unless it was very rare and not available, I would not do it.
And never on equipment that is outside my house or factory, it is not worth listening to criticism for a job done gratis...this is a hobby not profession for me.
In my factory or home I am the decision maker, so I simply would put a bigger relay, no issues with looks, and MOV across contacts. Bullet proof.
Worn leaf relays don't last much after servicing in my experience. Mine were in the temperature controllers, switching the heater contactors on and off.I had to replace 3 in about 25 years. I used MOVs there too to increase life.
Contactors did last, they were intended to be serviced by trained persons.
You get fine grit abrasive papers in auto paint material shops, they are used to polish paint jobs.
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I wouldn't bother with cleaning a relay I would replace it with a good quality relay.
I have an amplifier test bed with a DC protect relay on output.
I have had it 15 years and had a few bad amps causing relay to disconnect and it is still going strong.
I have an amplifier test bed with a DC protect relay on output.
I have had it 15 years and had a few bad amps causing relay to disconnect and it is still going strong.
You may not be able to buy a suitable replacement from local suppliers that is pin-compatible with an unusual product or maybe suits a 1980's dinosaur that someone wants to keep alive. If it's your own amp, chances are you can wait as long as it takes but if you're a repairer, you could earn yourself a bad rep. if it resulted in more than a couple of weeks turnaround. Then, the only sensible way forward may be just knuckle down and do that cleaning work.
Of course I know contactor contacts and large relay contacts can be cleaned but the relay type as used in audio is simply best replaced as it often has a thin layer of either gold or silver (or a mix of metals). The gold ones are simply wrong for speaker protection. The gold ones can certainly not be sanded/cleaned as one then removes the thin layer. Also the relay may have suffered from aging.
The Nemo seems to use quite common relays. Sanding relay contacts of such relays never has given me the desired results as the problems return, then one has to open a device twice. The success rate of the amplifiers that got new relays fitted is way higher in my experience. In fact I almost never see them back after that.
The Nemo seems to use quite common relays. Sanding relay contacts of such relays never has given me the desired results as the problems return, then one has to open a device twice. The success rate of the amplifiers that got new relays fitted is way higher in my experience. In fact I almost never see them back after that.
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The very first thing i would do is replace the relays with trench mosfets. Perhaps mounted inside the relays cases to preserve esthetics.
If there is pitting on the contacts, the relay can't be repaired by machining the surface because the platings are very thin. Any grit or cutting compound based cleaning of a switch or relay contact is doomed to fail fairly quickly no matter how fine the grit is. Microscopic particles get embedded in the soft metal plating or base metal of the contacts and cause local arcing on make and break which results in premature failure.
A high contact resistance causing audible noise and distortion does not necessarily imply pitting; there can simply be fine corrosion products on the surface of the contact. That's when DeoxIT chemical contact cleaner on stiff paper is the go. The DeoxIT dissolves metal oxides and sulphides whilst the fibres of the paper burnishes the contacts without leaving contaminants behind.
A high contact resistance causing audible noise and distortion does not necessarily imply pitting; there can simply be fine corrosion products on the surface of the contact. That's when DeoxIT chemical contact cleaner on stiff paper is the go. The DeoxIT dissolves metal oxides and sulphides whilst the fibres of the paper burnishes the contacts without leaving contaminants behind.
Hi johnmath,
There are many zero residue cleaners that do the same, but even better results. Anything that leaves any kind of residue on speaker relay contacts is the incorrect product. You could follow up your cleaning with a zero residue cleaner to get rid of the crud that your cleaner leaves on the contacts. That way you can still claim you used whatever audio darling cleaner is at the time. The real cleaners that do a good job are things audio people have never heard of. Mine comes from an aerospace supply firm. It isn't cheap, but man it does a great job. Also, use any chemicals sparingly. They are tools like anything else and too much cleaner is generally not good, or it may get into places where you really, really don't want it to go.
Turn the brain on, put it in gear before you press down on the nozzle!
-Chris
There are many zero residue cleaners that do the same, but even better results. Anything that leaves any kind of residue on speaker relay contacts is the incorrect product. You could follow up your cleaning with a zero residue cleaner to get rid of the crud that your cleaner leaves on the contacts. That way you can still claim you used whatever audio darling cleaner is at the time. The real cleaners that do a good job are things audio people have never heard of. Mine comes from an aerospace supply firm. It isn't cheap, but man it does a great job. Also, use any chemicals sparingly. They are tools like anything else and too much cleaner is generally not good, or it may get into places where you really, really don't want it to go.
Turn the brain on, put it in gear before you press down on the nozzle!
-Chris
Ha ha very funny post! I was using Cramolin® and had the entire kit of vials and hypodermics of red and blue in different strengths plus all the applicators in a suitcase that cost an arm and a leg back in the 1980's when I was sound master and technical manager for a multi-venue performing arts complex. That kit was standard issue for the aerospace industry.
Hi johnmath,
That kit was not standard issue. Certainly not in the labs areas, that is for darned sure. They may have claimed that, but ti wasn't true at all. It was very popular in audio, but it wasn't the only cleaner to be used and a non-residue cleaner was even more critical. If you were caught with your kit in a calibration lab they would escort you out immediately!
Don't read "white papers" and other propaganda. They are just ads with more technical jargon.
Now that, was a funny post! LMAO!
That kit was not standard issue. Certainly not in the labs areas, that is for darned sure. They may have claimed that, but ti wasn't true at all. It was very popular in audio, but it wasn't the only cleaner to be used and a non-residue cleaner was even more critical. If you were caught with your kit in a calibration lab they would escort you out immediately!
Don't read "white papers" and other propaganda. They are just ads with more technical jargon.
Now that, was a funny post! LMAO!