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Can I use these DIP relays to switch speakers?
Old 6th March 2012
  #1
Gear Addict
 
🎧 15 years
Can I use these DIP relays to switch speakers?

I am building a monitor switcher and I used relays to switch not only the line level signal going to Genelec active monitors, but also the output of a Yamaha P2200 power amplifier which feeds NS10's and and a mono Auratone.

I am using DIP relays (Omron # G2RL-24-12VDC) with contacts rated for 8A at 120V. Will there be any problem passing the amplifier output through these?

Also, the (12V) relays get warm when the coils are driven directly by the 12V supply (they have a resistance of 390 ohms). Is the proper practice here to put a 150 ohm resistor in series with the supply that drives the coil? I tried other values, and any larger than 150 ohms causes the relay to no longer switch reliably.

Thanks for any suggestions!
Attached Thumbnails
Can I use these DIP relays to switch speakers?-switcher1.jpg   Can I use these DIP relays to switch speakers?-switcher2.jpg  
Old 6th March 2012
  #2
Lives for gear
 
LeeYoo's Avatar
 
🎧 10 years
Speaker relais are used inside amps for delayed start and speaker protection.
Not a big fan of them. I have replaced many in the past with failing contacts at low volume.
A 12 volt relais is made to run on 12 volt, and will get slightly warm.
If 150ohm works for you, put a capacitor over the resistor, e.g. 2200uF/10volt.
This will kickstart the relais.
Leo..
Old 6th March 2012
  #3
Gear Addict
 
🎧 15 years
Thanks Leo! I'll add the caps and put this thing into service. I was worried about the relay contacts adding some kind of intermodulation distortion, but now I realize that that's off-base. I'll report back in a few weeks if I have any problems with the relays.
Old 6th March 2012 | Show parent
  #4
Here for the gear
 
RBBlackstone's Avatar
 
🎧 10 years
The cap is a good idea.

Is one of the monitors your primary setting? I listen to Mon1 80% of the time. I wired the relays up where mon1 was connected in the relay 'relaxed' position. That reduced heating and saved energy. If your relay is set up that way, that might help a bit.
Old 6th March 2012 | Show parent
  #5
Gear Addict
 
🎧 15 years
Quote:
Originally Posted by RBBlackstone ➑️
I wired the relays up where mon1 was connected in the relay 'relaxed' position.
Hi RBBlackstone. That is clever. I hadn't thought of that. Thanks!
Old 7th March 2012
  #6
Lives for gear
 
🎧 15 years
Hi
The contacts CAN cause distortion so you are right to have some concern but you do not need to panic unduly. Some power relays are better suited to this application but I can't remember the various 'arguments' for which type.
As you are nearly there, go for it but if you have 'issues' in a year or so time, review the types you have used.
Using them with almost 'full' supply voltage may be better than 'just on' as the contacts may not actually pull in 'tight' and make a good connection. On some types the contacts slightly 'wipe' when they are pulled in fully, which would be a good thing in this application as the signal voltage is relatively small.
Nice engraving by the way!

Matt S
Old 7th March 2012
  #7
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S2udio's Avatar
 
🎧 10 years
Nice box .....
Some 1N4148's in flyback mode across the coils is not a bad idea.
Old 8th March 2012
  #8
Lives for gear
 
🎧 15 years
Hi
Looking at your picture, are those 6 relays the ones intended to switch the speaker lines?
If so you should not be wiring them using that perf board as the copper is too thin.
Whilst good for mounting you should connect the speaker wires direct to the relay pins (on the back of the board). A PCB version would have traces a quarter inch wide and possibly heavy copper foil and as short as possible.
The wire looks a touch thin too. It should be at least 24,0.2 or equivalent, rated at least 6 Amps.
Matt S
Are those relays really rated for 8 Amps, they look pretty small?
Matt S
Old 8th March 2012
  #9
Gear Addict
 
🎧 15 years
Quote:
Originally Posted by Matt Syson ➑️
Nice engraving by the way!
Thanks Matt! I had Front Panel Express: fabricate it. They are Home in Europe (in the remote chance that you didn't know this already)

I understand the reason for the flyback diode across the relay coils, to dissipate energy stored in the coil when the switch contacts are opened. What I don't understand is the operation of the capacitor across the current limiting resistor. I see how the cap is discharged through the resistor when the switch is opened, but how exactly does the cap help the relay close? It seems to me that upon closing the switch the cap would charge first, thus slowing the ramp-up of voltage across the relay and achieving the opposite of the desired effect?
Attached Thumbnails
Can I use these DIP relays to switch speakers?-relay-circuit.jpg  
Old 8th March 2012 | Show parent
  #10
Gear Addict
 
🎧 15 years
Quote:
Originally Posted by Matt Syson ➑️
Are those relays really rated for 8 Amps, they look pretty small?
Yep, 2 of those relays will be switching speaker lines. I did solder the 22awg wire directly to the relay and DIP header pins, and to the perf board. I double checked the relays, they are really small, and that had me concerned, but the specs from OMRON say 8 amps. It really doesn't seem possible though, I think these things would just burn up spectacularly if I put that much current through them.

I'm hoping for the best... (no melted relays)
Old 8th March 2012
  #11
Lives for gear
 
🎧 15 years
Hi
I would reduce the resistor value anyway as you want the relays to be ON with no 'messing about'. Say 10 - 15 percent of the coil resistance.
A smaller resistor is possible (although not really necessary).
The capacitor 'appears' as a short circuit before it charges up, so at switch ON of your circuit the 'full' 12 volts appears across the relay coil. After this initial 'surge' the capacitor will start to charge and eventually a steady state voltage defined by the relay coil resistance and your resistor will be established. (Ohms law applies).
Since they are 'Power' relays, they may not be suitable for 'line level' high (relatively) impedance work and may have issues related to not enough current. Relay specification is moderately complicated and the different types available are made for specific purposes. Don't worry, it will work now, just be aware and look out for possible problems.
You can do your reading up on this while listening to the music through the system!
Matt S
Old 8th March 2012
  #12
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LeeYoo's Avatar
 
🎧 10 years
Hi.
Some reading material about relais contacts.
http://relays.te.com/appnotes/app_pdfs/13c3236.pdf

And why the diode. This is only needed when the relais is switched by a transistor.
Leo..
Old 8th March 2012
  #13
Lives for gear
 
🎧 15 years
Hi Lee
Although not strictly needed all the time a diode or resistor / capacitor 'snubber' is a good idea to restrict the reverse EMF at switch off. Think of it as 'good manners'.
For the loudspeaker switching it is not important but for line or especially mic level you could introduce clicks into the audio by capacitive coupling of the 'spike'.
Matt S
Old 8th March 2012 | Show parent
  #14
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S2udio's Avatar
 
🎧 10 years
Quote:
Originally Posted by LeeYoo ➑️
.
And why the diode. This is only needed when the relais is switched by a transistor.
Leo..
As matt stated its good practice,and not always the case.....
Most dc o/c output logic chips (transistor) already have them fitted
IE ULN280* series.
As this just switches speakers no problem but old habits die hard !
A low level amp switching stage is another matter !
My diy 1k poweramps use 16A schracks ,and no coil resistor needed.
Running now for 20 yrs ..no faults
cant see any possible advantage with the cap.... only to slow the coil saturation ?,no need imho
If the coil voltage is @ or 10% below rated ....why bother,they will run warm ,if your worried read the spec sheet,
http://www.farnell.com/datasheets/419217.pdf
Seem fine to me .
and what does a diode cost !
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