Prototype gainclone, pls comment/criticize ;)

[mAJORD]

Well after blowing one chip up (suspect) , trying to probe with a meter while on.. i managed ot finsih my proto..


details are..

18+18V toriod, 2 bridge rectifiers 1 per winding to be snubberd still. , filtering:, 2x1000uF 25v caps (yes im right on the limit of the rating there, is this a problem?) .

feedback is 100k+5.1k , u used the national app example to arive at these , even tho id calulated others for a higher gain, i thought id start with a pretty standard 20gain, that should at least have the freq range im after.

IC is an LM3876 , which i think ive determined is identical to a 3875 only with muting.

optional components, ive used a 0.2R resistor ins eries with the load.




this should show where ive mounted Rf, power connections are 1.25mm thick solid copper 'extentions' on the end of the pins going through the veroboard to the +v and -V points . Ri goes through the veroboard to the start earth point underneath, which you can see in the next picture.....




im new to the concept of star earthing, so laugh if u like , long as you give me pointers afterwood .... IVe run everything destined for ground to this point, including the return for speaker, ground for input socket, ground on pot,




http://members.optusnet.com.au/~majj...010013-sml.jpg


cheers

[Nuuk]

I've seen a lot worse

Make your power star ground point between the two 1000 uF caps (yes you are pushing the rating - they should be rated for 35 volts).

Make a separate earth star and then connect that to the power star with a short piece of wire. That should tidy things up considerably.

I wouldn't be too happy about that PCB with the two caps on it stressing the legs of the chip so it would be a good idea to make some sort of support to take the strain!

Finally, I am not too sure what TL would say about that 0.22R resistor

[mAJORD]

Thanks Nuuk

i could find only had 25 or 50v caps, and i had read that using higher than needed voltage caps was bad for SQ. but could be an internet myth , so ill find some better quality, 35v ones from elsewhere i guess.


that picture doesnt show it to well , but the star point actually is in between the caps,


+ ------( |---X---( |------ - , X= star earth


is that ok do you think?. ill

[mAJORD]

:S dont know what key i hit then but it posted before i was finsihed..


I was going to say, in my final deisgn the PCB will be supported properly, and the star earth neatend up as u suggested,

also whats wrong with my resistor?

[Nuuk]

As regards capacitor ratings, there's nothing worse than one exploding and while I wouldn't encourage people to use vastly over-rated types, I would strongly urge them to use the rule of the cap being rated at 1.25 times the actual voltage across them.

In your case the 18V secondaries will produce around 25 volts DC on the rails. Multiply that by 1.25 and you get 31 so 35 is what you should go for.

However, if you have a good quality cap rated at 50 volts, you are not going to hear the difference between that and one rated at 35 volts.

The 0.22R resistor is a cheap wirewound type and you may notice an improvement by trying something better. Or you may get away with not using one at all!

[mAJORD]

ahh cheers, well the caps are pretty ordinary quality wise, so I dont think ill go 50v in that brand, hopefully they dont explode in the meantime :P

ive since removed the 0.2R resistor and tried it again.. result being good enough for me to throw them out the window.

[Nuuk]

result being good enough for me to throw them out the window.

Never do that You never know when you might need even the most obscure part sometime in the future. File it away carefully