LM1875 power on POP problem

[AndrewGM]

Just asembled an LM 1875 GC,
At start up / power on there is a POP and the speaker cones
move back and forth.

It sounds great and am happy with it but am a little worried
about damage to the speakers.

Is there anything I can do to prevent this happening.

Thank you

Andrew

[Minion]

I believe this is caused by a momentary DC offset that happens as the PSU and Caps are chargeing and voltage is stabilizing ...

It won"t hurt your speakers but it is anoying , to eliminate it I believe you would need a soft Start curcuit ....

Most of my amps have that turn on thump and it hasn"t caused any problems and the initial noise doesn"t bother me .....

if you do a search arround here for a soft start curcut you will probably find one ....


Cheers

Some of my amps have a turn off thump accept the thump happens about 1 min after I turn it off .....

[AndrewGM]

Minion thanks.

I'll search around for this and investigate.
I also read a thermistor may slow the current inrush down
a little but would prefer more protection, so I'll take your advice.

Thank you for the info

1 minute for yours ?
That's a long time :-)
Your amps are large and surely not small Gainclones ?

Andrew

[Minion]

Hi, No problem , Actually they are chip amps , this one in particular is a TDA7293 100w chip with 40,000uF In the PSU , when the caps are finally fully discharged the amp pops and goes quiet .......

Cheers

[Uncle Olaf]

Hey Andrew,



I also built an amp with this IC. Mine makes the same noise upon powering up and as the power supply caps discharge. I am using a regulated supply with mine, and it makes most of its noise as the supply caps discharge. Like mentioned before, its of no consequence to your speakers, but if you were to use it with an active system, I would recommend using a series cap with the tweeter. Another solution to get rid of the noise upon powering up is to have a relay based muting circuit. There are a couple of these offered as boards or complete kits. Velleman and Rod Elliott (sound.westhost.com) offer them.

They do sound nice, don't they?


Cheers, Jon 'Uncle Olaf'

[jb74]

Here's a link to a circuit that is working for me with a DIY stereo amp using LM1875's:

http://www.epanorama.net/circuits/ampdelay.html

When the amp is turned on, there is a short
delay of a second or so before sound is heard
from the speakers.

When the amp is turned off, sound from the
speakers stops with no delay.

Result - no pops, etc., at either turn-on
or turn-off using LM1875 chips.

[Uncle Olaf]

Hey Jb,



Thats a neat little circuit. Thanks for sharing it. I'll give it a try.


Cheers, Jon 'Uncle Olaf'