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-   -   Standby mode and speaker turn on delay together? (http://www.diyaudio.com/forums/chip-amps/218865-standby-mode-speaker-turn-delay-together.html)

TiGeRGuY 1st September 2012 07:44 AM

Standby mode and speaker turn on delay together?
 
Hi everyone!

My goal is to build an integrated stereo amp based on the LM3886, that will include a soft switch (that activates a relay witch connects the main transformer to the mains) , and a DC protection circuit with a turn on delay.

I relized that i can't use the same 12VDC power rail for the soft switch and the speaker protection together, because the soft switch transformer will have to be always on, and the DC protection circuit will have to be switched on when the main transformer is switched on, for the turn on delay to occur.

so how can i combine those two circuits together? do i need to use separate transformers or maybe use a voltage regulator to lower the voltage from the main transformer (about 30VDC for the LM3886) to 12V for the protection circuit? wouldn't it be wasteful?

I always wondered how does it designed in commercial amps?

tnks for the helpers ;)

AndrewT 1st September 2012 11:11 AM

A separate small transformer to power the start up control circuits.

You can run the delay trigger from either the main transformer, or from a tapping on the soft start trigger output.

The delay circuit itself can be powered by either transformer. It's the trigger signals that need to be sequenced.

TiGeRGuY 1st September 2012 03:30 PM

Hi Andrew! I think i understood your second option, you ment that the softstart output will activate 2 relays, something like this:
http://img440.imageshack.us/img440/3356/diagramwd.png
I didn't understand your first option though, the main voltage is 30V and the DC protection circuit voltage is 12V

AndrewT 1st September 2012 04:55 PM

Use an lm7812, to cut the 30Vdc to 12Vdc.

TiGeRGuY 1st September 2012 06:09 PM

Witch option do you recommand using? is a regulator commonly used for this purpose?
and also i would like to know if using the 12V from the regulator will be ok for an active tone control?

tnks alot Andrew :)

TiGeRGuY 4th September 2012 07:42 PM

Guys a little help please?
I need to know how this is supposed to be done, i don't really want to use the LM7812 becuse 30V is it's limit.
if you can refer me to a project where a similar thing has been done, it will also help.

tnks again :)

AndrewT 5th September 2012 08:40 AM

lm317 as a pre regulator.

CharlieLaub 5th September 2012 04:19 PM

Quote:

Originally Posted by TiGeRGuY (Post 3152136)
Guys a little help please?
I need to know how this is supposed to be done, i don't really want to use the LM7812 becuse 30V is it's limit.
if you can refer me to a project where a similar thing has been done, it will also help.

tnks again :)

You can also use a LM7824 as a pre-regulator (use it first and send its output to the input of the LM7812). The LM7824 has an input voltage limit of 40V.

-Charlie

TiGeRGuY 5th September 2012 07:50 PM

tnks for your answers! i read that linear regulators are very inefficient, is it the best option i have?
Based on what you say, if i'll open my old yamaha AV reciever i should find a regulator for this purpose?

i am very confused, i searched the web for weeks to find how this thing works and i just can't find anything.

i was also counting on using the "after turn on" 12V rail for a sound control (some little opamp's), and i always hoped it will run from a pure 12V rail.

if you say this is the method manufacurers use, i will go for it.

AndrewT 6th September 2012 07:55 AM

build something simple and get it working. Then expand your knowledge and try some simple experiments.
Then you should be ready to try working out what you need and how to implement the sequencing.

Trying to develop a specification before you know what can be done is almost impossible.


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