Delayed power up when using buffers

[Nuuk]

It is a good idea when using a buffer circuit with a GC (or other amp) to power the buffer up first before powering the GC (or amp).

There are various ways to do this; eg using a delayed start that uses a timer and relay. Or you can use speaker protection modules that incorporate a delay before they connect the speakers.

I wondered if the following would work (and I hope you can understand the rather rough diagram )



The idea is that when SW1 is closed power is fed to the buffer PSU. A feed is taken from the output of that supply and connected to a momentary push button switch. When that switch is closed, a relay allows mains supply voltage through to the amp PSU.

A feed taken from that PSU then keeps the relay closed after the momentary button is released.

If the mains fail, the power amps will not be reconnected until the push button is pressed.

I am not saying that this is a better solution (or even that it will work). It's just an idea that I had and wondered what the more electroncially educated think of it.

Flack jacket on.

[Upupa Epops]

Whatabout to use delayed relay on output of GC ( with immediate fall down by switch off ) ? Is not this "clear " solution ?

[Sheldon]

I use a relay such that the buffer output is connected via the normally closed terminals (NC) to ground when the power is off. Upon power up these contacts open up so that the relay switch is out of the circuit altogether. Capacitance is used in parallel with the relay to delay the switching of the relay after power up. This way the buffer and circuit is fully powered and stable before any signal goes to the amplifier chip. The delay required in my case is less than a second (I'm using Pedja's discreet buffer).

The current setup is a 115v dc relay, powered through a DB104 rectifier bridge, with two 47uf capacitors. You can increase the delay by increasing the capacitance. I also use two 2.2k resistors in series with the relay coil to reduce the voltage across the relay and caps below 100v (the relay coil is 15k ohms). Whole setup cost about $3.50.

Sheldon

p.s. I don't know if other buffers would cause noise when the ground is removed, but it's easy to test by just manually grounding the buffer output with the unit on.

The above approach would also solve the power off problem in most cases. It's possible that a break in power could be shorter than the time required for the relay to close (it's delayed just like the on cycle) but longer than required to discharge the main power supply caps. In that case, you might get a "thump".

[JojoD818]

Nuuk,

Almost all of my GC amps (including Joe's Hybrid) includes a delayd relay for speaker swithing. My opamp buffered GCs needed less time while the tube buffered takes a lot longer before connecting the output. However, when the power switch is turned off, the relays are switched off within milliseconds which is another useful feature.

However, I think your circuit is a very clever one but if power is the one to be switched, the GC section (amp side) must absolutely be "thump-free" when switched on.

Cheers!

[Nuuk]

Thanks for the feedback guys.

My aims were to avoid relays on the output of the amp and remove the problem of capacitors not discharging quickly enough in the event of a momentary power cut.

Whatabout to use delayed relay on output of GC ( with immediate fall down by switch off ) ? Is not this "clear " solution ?

Do you mean like I have on my Velleman speaker protection modules?

Sheldon, your solutions sounds neat. Do you use just one relay, or one for each channel?

Jojo, I agree about the different length of delays needed for different buffers. The valve buffers take longest while I have found the opamp and discrete buffers need only a second or two to 'settle down'. I appreciate that my suggestion does not deal with the problem of power up thump (although I don't get that with my 'smaller' PSU).

[Sheldon]

Originally posted by Nuuk
Thanks for the feedback guys.

Sheldon, your solutions sounds neat. Do you use just one relay, or one for each channel?

One two pole relay.

I apologize for not providing schem. I don't have a program to make them. Any suggestions for something with a short learning curve?

Sheldon

[Nuuk]

I apologize for not providing schem. I don't have a program to make them. Any suggestions for something with a short learning curve?

I have just about learned to use Circuit Maker (Student version that is free).

I can't remember where I got it but I think that JR posted a link to it on one of these threads within the last week!

[Nuuk]

Found it! (with thanks to JR)

Click here Sheldon.

[Sheldon]

Thanks Nuuk,

That learning curve ain't gonna be short enough for today, though. Here's a crude attempt at a one pole switch. Couldn't find an AC source and don't know how to delete the annoying device labels.

Sheldon

[pete.a]

If anyone's interested, i can get 24v dc coil single pole relays with contacts rated @240v / 7A...

We throw away photo cell sat work that use these, and it's never the relay that goes faulty ,only the electronics that control them !

(Cells are used to switch your street lights off and on)