Relay delay

[Ted205]

Sorry for the newbie question.

Looking to implement a delay to the preamp output to avoid pops on start up.

I'm trying to use a simple 555 timer. I've simulated this:

An externally hosted image should be here but it was not working when we last tested it.

theory says this should work. But in the simulation doesn't.

Am i being stupid ?

 

[Nuuk]

Not sure about your circuit Ted but this one on Decibel Dungeon works fine, and you can vary the delay to suit different pre amps/buffers. 😉

 

[CJ900RR]

I seccond that. Nuuks solution works like a charm

 

[Ted205]

so the version on dd starts high and goes low after x seconds?

as this is how i have it working on bread board 🙂


the schematic of the circuit in multisim:

An externally hosted image should be here but it was not working when we last tested it.

but it does work as it does in the real world. or am i being stupid?

i want to integrate it into my psu pcb so would like to be able to sumulate and route it 🙂

 

[Nuuk]

Ted, why the PSU? 😕

 

[Ted205]

turns out it was just the software settings working ok now (set initial conditions to zero)

i want to use it in the psu to switch the power amp V+ and V- on after a short period (i.e after power has been applied to the buffer and allowed it to settle)

 

[Nuuk]

I still think that is is better to mute the audio out from the buffer until it has settled but good luck anyway. 😉

 

[Ted205]

its a work in progress, just trying to keep the signal path free 😛.

Thanks for the circuit btw.

 

[Nuuk]

But that is the point of the design shown on DD, ie it is not in the signal path. 😉

 

[Ted205]

i read it that the relay shorts the buffer output to ground for a short period while the power is applied to it. I was planning to switch the power amp section on after the buffer has settled.

 

[Mooly]

Hello Ted,
Does your preamp make any noises on switch off as well.
It's a very basic circuit is this. How about adding a diode to the IC supply and cap to suit, such that the supply to the 555 collapses immediately on switch off.

 

[Mooly]

Doesn't quite read what I mean 🙂 I mean have the supply to the 555 via diode from the AC of the tranny, maybe using CMOS timer and simple R+C+ zener.
Delays should be foolproof in that it cannot be confused by a mains interupt etc. You want it to mute instantly and go through it's full "start sequence" everytime 🙂

 

[Nuuk]

i read it that the relay shorts the buffer output to ground for a short period while the power is applied to it. I was planning to switch the power amp section on after the buffer has settled.

That's right, so no nasty offsets go through your amp, hence no nasty noise.

You could switch both the power rails but just supposing one contact of the relay sticks and you turn off just one rail?

 

[Ted205]

That would be the same thing as a fuse blowing only on one rail.

I am coming round to putting it at the buffer output as it makes life easier, and whether it makes and audible difference ...........

i like the idea mooly as on power down the transformer will be the quickest to degrate, before the caps degrate and make a small pop on the speakers the relay will have latched (maybe?) and block any signal.

 

[Nuuk]

I find that circuit acts fast enough to stop turn-off clicks anyway! 😉

 

[AndrewT]

fit the mute to the pre-amp output. Use a relay to ground as Nuuk and the others have already told you.
Arrange for delayed on and instant off.

If you want you can also add a mute the the power amp input, again with delayed on and instant off.

Finally, you can fit another relay to the speaker output of the power amp. This is the only one that has signal through the contacts while operating.

 

[john blackburn]

As a matter of interest would this circuit suit the Uno active pre from DD?

http://myweb.tiscali.co.uk/nuukspot/decdun/gainclonepre2.html

I see it's been tested with the buffer circuits but there's no mention of the Uno. I thought it better to ask than to have to stamp the flames out.

John