My latest subwoofer - a bridge opa549 built onto a piece of plexiglass - Page 3

thomas997 · 27th December 2004, 10:57 PM

Quote:

Originally posted by soundNERD

I have also tied the ref to current limit, then connected them both to ground. Be sure the pcb connection is good (use a multimeter on resistance mode, touch to the main gnd trace and touch the other side to the ref and current pins). I spent about an hour trying to figure out why another amp I built using an OPA549 wouldn't play anything. The trace on the PCB had split (small enough to not be visible easily), and the chip was stuck in off mode.

Are you using a split or single supply?

Im using a split supply at +/-25 VDC, but I have another transformer that has +30V only, but a bit more VA.

I will recheck all the ref and current connections, it does sound as if the chip is in off mode because there is no static at all coming from the speaker.

Thanks

thomas997 · 29th December 2004, 11:14 PM

ok I have found the problem... the Enable Status pin was grounded, which turns the amp off.

After fixing that the amp sounds great. It seems to have less noise (with no input) than the LM series. Seems to not be as affected by ground loops(?), I just had it all hooked up in a mess with zero 60hz hum.

The datasheet also shows how to build a variable current and voltage supply, which would be quite usefull.. Ill have to try it out soon.

Richie V6 · 13th January 2005, 01:27 PM

Where can I find the "AN-1192 schematic"? I found a national page but i thought this was a TI chip.

soundNERD · 13th January 2005, 07:56 PM

The one you found is correct. I used the one provided by National.

I just used TI chips. The schematic isn't specific to their brand only, as any op amp can be used.

I used the OPA549 chip because it has more power than the LM series, and I find it more suited to bass use than the LM chips.

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29th December 2004, 11:14 PM	#22
thomas997 diyAudio Member Join Date: Feb 2004 Location: Vancouver	ok I have found the problem... the Enable Status pin was grounded, which turns the amp off. After fixing that the amp sounds great. It seems to have less noise (with no input) than the LM series. Seems to not be as affected by ground loops(?), I just had it all hooked up in a mess with zero 60hz hum. The datasheet also shows how to build a variable current and voltage supply, which would be quite usefull.. Ill have to try it out soon.

13th January 2005, 01:27 PM	#23
Richie V6 diyAudio Member Join Date: Nov 2004 Location: In my dreams	Where can I find the "AN-1192 schematic"? I found a national page but i thought this was a TI chip.

13th January 2005, 07:56 PM	#24
soundNERD diyAudio Member Join Date: Sep 2003 Location: Illinois	The one you found is correct. I used the one provided by National. I just used TI chips. The schematic isn't specific to their brand only, as any op amp can be used. I used the OPA549 chip because it has more power than the LM series, and I find it more suited to bass use than the LM chips.