Wow, an intersting read even if I didn't understand all of it!
So,if I understand correctly, the supply needs to be 1.7 volts more than the relay requires, ie 13.7 volts for a 12 volt relay.
So,if I understand correctly, the supply needs to be 1.7 volts more than the relay requires, ie 13.7 volts for a 12 volt relay.
Yes and no, you can use a higher supply to compensate for the losses, but usually, your relay will clamp at a lower voltage than the rated one.
If you look at your relay specsheet, the coil operating range is 70%-150% or for the 12V version 8.4V to 18V. Any voltage in between those two will suffice to make the relay clamp.
I never really used the NE555 to drive the relays directly, I always buffer them with a transistor or a mosfet. This allows the coil to see practically the full swing of the power supply, especially with the mosfet solution. This way I can use a 12V supply and the relay will have it's rated 12V.
Hope this helps!
Sébastien
EDIT: More info here:
http://home.cogeco.ca/~rpaisley4/LM555.html
If you look at your relay specsheet, the coil operating range is 70%-150% or for the 12V version 8.4V to 18V. Any voltage in between those two will suffice to make the relay clamp.
I never really used the NE555 to drive the relays directly, I always buffer them with a transistor or a mosfet. This allows the coil to see practically the full swing of the power supply, especially with the mosfet solution. This way I can use a 12V supply and the relay will have it's rated 12V.
Hope this helps!
Sébastien
EDIT: More info here:
http://home.cogeco.ca/~rpaisley4/LM555.html
Update
I have now built and installed the circuit shown at the start of this thread and it works! No noise at all on power up (or power down). 🙂
I get a delay of about 3 seconds using a 47 F cap. Adjusting the trimmer doesn't seem to make any difference to the delay so I guess it is to do with the voltage that the relay is triggered at. Perhaps Sébastien could confirm that if he is still around. 😉
The circuit is powered from the buffers supply (15 volts) and I have used a 12 volt relay.
In my buffers, I have 15 volt rails, R3 is 120R and the output series resistor is 75 ohms. With BC547's there is no problem. I did wonder if higher currents were involved whether it would be a good idea to use an additional resistor between the output and ground.
Anyway, at last I am pleased to be able to turn on the power amps and buffers at the same time (with the same switch!) and not get any nasty noises. 😀
I have now built and installed the circuit shown at the start of this thread and it works! No noise at all on power up (or power down). 🙂
I get a delay of about 3 seconds using a 47 F cap. Adjusting the trimmer doesn't seem to make any difference to the delay so I guess it is to do with the voltage that the relay is triggered at. Perhaps Sébastien could confirm that if he is still around. 😉
The circuit is powered from the buffers supply (15 volts) and I have used a 12 volt relay.
In my buffers, I have 15 volt rails, R3 is 120R and the output series resistor is 75 ohms. With BC547's there is no problem. I did wonder if higher currents were involved whether it would be a good idea to use an additional resistor between the output and ground.
Anyway, at last I am pleased to be able to turn on the power amps and buffers at the same time (with the same switch!) and not get any nasty noises. 😀
I have just noticed that I forgot the protection diode on my delay circuit. But which way does it go? 
An externally hosted image should be here but it was not working when we last tested it.
Is the above correct please?
Hi Russ, as I said, the circuit works fine without the diodes but it's better to have them to protect the NE555.
If you want to order the parts, then go ahead and don't forget the IN4148 and IN4002 diodes too! 😉
When you build the circuit leave room for the diodes. The IN4148 could be soldered underneath the PCB across the legs of the relay.
No:
1) no current may pass trough the relay due to your 1n4001
2) 1n4148 diode cannot withstand relay back-emf. If it does not burn at 1st use, it will for sur burn one day or another. Since diodes tend to burn as short-circuit, relay will not be operated, but ne555 will burn. It may burn as a short-circuit vs. supply, which won't like it at all, etc. My guess is that you don't really want that experience
Cure:
1) remove or reverse your 1n4001
2) use a 4001 instead of 4148.
A 1N4148 is quite enough for a freewheeling diode. The coil current is less then the diode current rating.
Parameters to have in mind is that the diode must be able to take used voltage, like > 15 volts, times 2 or 3 at least and in case it's 75 volts.
The current for the diode must be at least 0.25 times the relay current and in the case a 10-25 mA would be enough but good engineering pratice would be to choose a diode with at least the same current rating as the coil and that wouild be in this case 30-50 mA. A 1N4148 has 100 mA as limit, note continuous current limit
Parameters to have in mind is that the diode must be able to take used voltage, like > 15 volts, times 2 or 3 at least and in case it's 75 volts.
The current for the diode must be at least 0.25 times the relay current and in the case a 10-25 mA would be enough but good engineering pratice would be to choose a diode with at least the same current rating as the coil and that wouild be in this case 30-50 mA. A 1N4148 has 100 mA as limit, note continuous current limit
Thanks for your help chaps! 
I found a circuit using the IN4148 and that's what I copied. As I have IN4002's in my parts box that's what I will use. And as it's easier to order one type rather than two, I'll suggest IN4001's on Decibel Dungeon. 😉
I found a circuit using the IN4148 and that's what I copied. As I have IN4002's in my parts box that's what I will use. And as it's easier to order one type rather than two, I'll suggest IN4001's on Decibel Dungeon. 😉
Diodes for relay coils are very unsensitive. You can use almost anything as long as the voltage rating is enough.
Nuuk said:
If your preamp has 100 ohms at least as output impedance and this is accomplished with a resistor, it's safe to just short the output. If you aren't sure add 100-220 ohms to have in series.Nuuk said:
The relay contact should ge between the power amp input and ground. The extra series resistor should go between the preamp and the power amp.
Check how I have done the mute of my DAC
http://home5.swipnet.se/~w-50674/hifi_pics/hifi_100pr/dac_pics/dac_schema_sida_4.pdf
Nuuk, if you output IS short circuit proof, it's no harm to brutally short the output to ground. If you aren't sure,100 ohms extra in series is nothing compared to the rest.
Check how I have done the mute of my DAC
http://home5.swipnet.se/~w-50674/hifi_pics/hifi_100pr/dac_pics/dac_schema_sida_4.pdf
Nuuk, if you output IS short circuit proof, it's no harm to brutally short the output to ground. If you aren't sure,100 ohms extra in series is nothing compared to the rest.
I'm a bit confused!
If you add 100R in series with say the 68R on the output of the transistor buffers that I am using, doesn't that change the characteristics of the buffer by limiting the output current? If not why is 68R specified and not 168R (or 150R)? 😕
You must also consider the load in th other end. If it is 10 kohms 68 or 168 ohms will make not much difference but if you have 68 ohms, this will be enough I think for current limiting at startup.
Did you check how I have done my muting?
Did you check how I have done my muting?
IF I understand it correctly, you short the outputs of the OPA627s to ground after the 51R resistors.
OT: Nuuk, I don't get any pop at all when I switch on the buffer or my gc. I builded a similar gc for my brother, and he gets loud pops. Why is that :?:
Edit: Now that I come to think about it, I have used 8 ultrafast diodes in my gc, while my brother's uses a standard bridge. In my buffer I use 8 byv27-150.
Edit: Now that I come to think about it, I have used 8 ultrafast diodes in my gc, while my brother's uses a standard bridge. In my buffer I use 8 byv27-150.
Do you have your power amps switched on when you power up your buffer? Or do you power up both together? If the latter, are you using an LM3886 or similar chip with a muting function?
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