why use relays?

[buschfsu]

In the half dozen or so projects ive done these have never come up. I understand that they are basically electric switches but what is the advantage that would overcome the pain of having to power them??

 

[solder_city]

i can think of a couple big reasons right off the bat:

remote switching- you dont have to run the signal lines being switching up to the control panel

number of poles and switching combinations that wouldnt be possible with mechanical switches. for example try to find a 24PDT mechanical switch!
-but you can do it inexpensively with a few relays

automatic switching- power failure standby switching, output fault in an amplifier, etc
a regular mechanical switch wont switch itself

 

[[silent:arts]]

what solder_city said, and for live / on air applications: true hardwired bypass.
when the power or PSU of the unit fails, signal still goes through - automatically.

 

[JohnRoberts]

Relays are lower on resistance and much better behaved electrically than solid state switches.

A switch with a magic finger to push it.

JR

 

[SSLtech]

[quote author="JohnRoberts"]A switch with a magic finger to push it.[/quote]
But I have LOADS of unused switches here...

Can't I just buy the magic fingers on their own?

You got any spare ones for sale, John? :green:

Keef

 

[JohnRoberts]

I have spent decades thinking about a non relay based approaches to gain control for low z mic preamps and such... so far with no elegant success. I could probably do something using a lot of parts in an IC, but too much complexity for discrete designs.

I am now pondering non-liner (digital) magic.

Perhaps a combination of linear compressor VCA or mic preamp gain stage, with non-linear microprocessor to apply "if this do that" decision trees that are akward in analog domain.

or not...

JR

 

[lofi]

[quote author="JohnRoberts"]"if this do that" [/quote]

just had visions of a farmer leaning on a gate with some corn between his teeth ....

need more sleep

Iain

 

[JohnRoberts]

I didn't say "if dis do dat"....

but I do try to write in simple terms, sorry if you think I sound corny.

JR

 

[buschfsu]

ok so there a standard relay that would replace a DPDT switch. (something that everyone uses)?

 

[lofi]

[quote author="JohnRoberts"]I didn't say "if dis do dat"....

but I do try to write in simple terms, sorry if you think I sound corny.

JR[/quote]

im from farming stock (with a healthy viking influence) so my history and inexperience came to the fore, and for a split second i saw the farmer, then realised the meaning.

guess for a second i was just too simple for you :grin:

Iain

 

[solder_city]

[quote author="buschfsu"]ok so there a standard relay that would replace a DPDT switch. (something that everyone uses)?[/quote]

well, a DPDT relay is the first thing that comes to mind.

then again you could use two SPDT switched in tandem if it was more convenient in terms of physical layout- for instance, input and output switching on a PCB for signal bypass

there is no 'standard' make and model everybody uses. sorry.

 

[buschfsu]

ok how about a recommendation for a reliable brand or model number that some have found to be good for diy projects (usual suspects like wima for caps, alpha for pots, etc)

 

[clintrubber]

Relays add weight to a box and can let the front-panel control be a simpler (lighter) one at the same time. So in this age of cheap & plastic stuff, the gear now doesn't move as quickly when being operated.

 

[bcarso]

Beware of dry circuit (very low voltage) switching with relays. Or with switches for that matter.

But with some switches you can get a fair amount of wiping action. This is harder to achieve with relays.

 

[clintrubber]

[quote author="buschfsu"]the pain of having to power them??[/quote]
Also be sure to keep the audio & relay powering well separated. You can derive them from the same supply, but care should be taken to avoid plops in the audio when the relay is operated. For instance ground-currents (transients from kicking in/out the relay-coil) can lift the audio-part.

 

[Crusty2]

[quote author="bcarso"]Beware of dry circuit (very low voltage) switching with relays. Or with switches for that matter.

But with some switches you can get a fair amount of wiping action. This is harder to achieve with relays.[/quote]
I remember you mentioning this before. Does having gold plated or bifurcated contacts cure this? (I know the silver contacts need a bit of juice to keep clean...)

 

[bcarso]

Gold is good but stuff will plate out on it from the environment, sometimes from the solvent-borne residue in the varnish etc. Silver is terrible when it gets sulphates. Bifurcated helps but is not a panacea.

Mercury-wetted reeds are great but usually gravity-related position-sensitive and of course now a major baddy as an environmental no-no.

And yet there are some manufacturers who have the outgassing and sealing issues under control for normal contacts. Ap equipment uses relays successfully, but they are one of the major failure modes for what is otherwise very reliable equipment.

 

[Dan Kennedy]

The Aromat TQ series have been a very reliable, fairly inexpensive relay for me for years.

Out of maybe 20,000 in the last five years, I am aware of 2 or 3 issues.

These have been the 24v 2 form C type, some experience with the same type in 12v, take it for what it's worth.

Used in mic level and line level applications.

 

[bcarso]

Thanks for that information Dan. I think possibly the Ap uses Aromats as well, at least in the System One.

 

[buschfsu]

thanks dan, thats exactly what i was looking for. ill start playing around with some of those.

btw my mp-500nv kicks serious ass!
cheers

jason