Gainclone help plz!!

[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

 

[RAYSIMMONS]

can you post a schematic or a photo of your wiring?

 

[Cradle22]

Hi!

I had the same prob on my first attempt because I was using a LM3876 instead of a LM3875, but wired it exactly the same way like a LM3875, so I also got full voltage at my (supposed) output pin... but the pins are all aligned in another way than with the LM3875.

Don't use the "standard" schematics with anything else than a LM3875. You will have to adapt the schematics ton anything else.


Bye,

Arndt

 

[Olle Bard]

how about the lm3886. does it have the same pinout as the LM3875?

if it doesn´t ive got some unsoldering to do

 

[UrSv]

how about the lm3886. does it have the same pinout as the LM3875?

if it doesn´t ive got some unsoldering to do

So you didn't check the datasheet before building it...

 

[Olle Bard]

you can timagine how silly i feel when im saying this: no

i thought national had some standard they used on all their cihps(would be quite good).


which pins should i connect to?
the +, -, gnd, mute(to gnd via resistor), in+, in- and the output?

 

[UrSv]

you can timagine how silly i feel when im saying this: no

i thought national had some standard they used on all their cihps(would be quite good).


which pins should i connect to?
the +, -, gnd, mute(to gnd via resistor), in+, in- and the output?

The answer is in the scriptures:

http://www.national.com/ds.cgi/LM/LM388.pdf

 

[TedPolzin]

can you post a schematic or a photo of your wiring?

I can post a pic when the digital camera gets back from Germany tomorrow. It is a 3875 using Peter Danials schematic

Thanks

Ted

 

[UrSv]

I can post a pic when the digital camera gets back from Germany tomorrow. It is a 3875 using Peter Danials schematic

Thanks

Ted

So that means that oscillations might very well be the reason for the sound...

 

[Olle Bard]

does anyone have a product sheet for the lm3875?

 

[Philo]

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]

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]

Re: Re: Gainclone help plz!!

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]

Re: Re: Re: Gainclone help plz!!

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]

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]

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]

oops, forgot the image.