Gainclone help plz!! - Page 2

Philo · 11th April 2003, 04:54 PM

Olle,
The whitepaper is online at http://www.national.com/ds/LM/LM3875.pdf. I also recommend going back through the "Not just another Gainclone" thread for suggestions and recommendations. There is way to much info there to be repeated in another thread.

Peter Daniel · 11th April 2003, 05:08 PM

Quote:

Originally posted by TedPolzin
Hi I am having some problems with my attempt to build gainclones. I have sucessfully built 4 clones. I am also having trouble with others. I get full voltage on the output. This has happend with 5 chips. I an getting frustrated since they may be cheap but not that cheap. I have looked at the chips and have no idea why this happens. The bad ones are identical to the good ones. I take my time and it still does it.

Please do you have any ideas??

thanks

Ted

What exactly is the problem? You've built 4 amps that are OK and the other you've built are not working?

TedPolzin · 11th April 2003, 07:18 PM

Quote:

Originally posted by Peter Daniel

What exactly is the problem? You've built 4 amps that are OK and the other you've built are not working?

Ok I have built 4 that work fine (I later fried one .. but that was my fault.) I have also built 5 that seem to have full voltage on the output. I have no idea why. I follow the same building techniques and have double and triple checked all my connections but it seems a crap shoot whether it will actually work or give not. When I say full power on the output I mean with no signal it will give 15 volts on the output pin when I put a volt meter across the output. (from output to ground). I have no idea why this is happening and am hoping someone can give me some direction as to what I am doing wrong.

Does that make any sense?

Thanks

Ted

pinkmouse · 11th April 2003, 09:36 PM

Quote:

Originally posted by TedPolzin

Ok I have built 4 that work fine (I later fried one .. but that was my fault.) I have also built 5 that seem to have full voltage on the output.
SNIP
I have no idea why this is happening and am hoping someone can give me some direction as to what I am doing wrong.

Hi Ted

The only thing I can think of is that maybe you have a batch of dodgy chips. Do they all have the same lot number? I have built about a dozen amps using the LM chips, ( I am just in the middle of building another 5 channel system for a mate's HT system), and the only problems I have had were down to user error...

TedPolzin · 12th April 2003, 02:03 AM

Hmm I may have solved it. I think some how my bench supply was causing it. I hooked it up to my amp power supply and worked good. Tried it with my bench supply and +15 volts. I also tried another one same result. Now I need to figure out what my bench supply is doing

.

On another note what reisitor do I need for the mute on a 3886 with +-35 rails?

Thanks

Ted

Matttcattt · 13th April 2003, 02:41 PM

i have made a mono gainclone (one channel) with the OPA548 and i looked at the datasheet and got the pinout. i have built this circuit (see image) and i get -20v (supply voltage) at the output. i am using a bench power supply so this could be the cause but i dont think so.

Matttcattt · 13th April 2003, 02:43 PM

oops, forgot the image.

11th April 2003, 04:54 PM	#11
Philo diyAudio Member Join Date: Jul 2002 Location: Ever sunny San Diego	Olle, The whitepaper is online at http://www.national.com/ds/LM/LM3875.pdf. I also recommend going back through the "Not just another Gainclone" thread for suggestions and recommendations. There is way to much info there to be repeated in another thread. __________________ Philip "If you didn't make it with your own two hands, its not really yours".

13th April 2003, 02:41 PM	#16
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	i have made a mono gainclone (one channel) with the OPA548 and i looked at the datasheet and got the pinout. i have built this circuit (see image) and i get -20v (supply voltage) at the output. i am using a bench power supply so this could be the cause but i dont think so. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

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12th April 2003, 02:03 AM	#15
TedPolzin diyAudio Member Join Date: Oct 2002 Location: Drayton Valley, AB	Hmm I may have solved it. I think some how my bench supply was causing it. I hooked it up to my amp power supply and worked good. Tried it with my bench supply and +15 volts. I also tried another one same result. Now I need to figure out what my bench supply is doing . On another note what reisitor do I need for the mute on a 3886 with +-35 rails? Thanks Ted