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Old 11th April 2003, 04:54 PM   #11
Philo is offline Philo  United States
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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.
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Old 11th April 2003, 05:08 PM   #12
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Default Re: Gainclone help plz!!

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?
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Old 11th April 2003, 07:18 PM   #13
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Default Re: Re: Gainclone help plz!!

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
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Old 11th April 2003, 09:36 PM   #14
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Default Re: Re: Re: Gainclone help plz!!

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...
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Old 12th April 2003, 02:03 AM   #15
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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
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Old 13th April 2003, 02:41 PM   #16
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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.
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Old 13th April 2003, 02:43 PM   #17
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oops, forgot the image.
Attached Images
File Type: jpg gainclone.jpg (54.3 KB, 167 views)
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