My finished amp

philb

Member
2004-02-16 7:58 pm
Canada
Here are some pictures of my new amp, it uses the national semiconductor lm3875 chipamp. It is the second amp i build and find that the bass response on this amp is not nearly as strong as the lm1875. Why is this? the schematic is the same as the brian gt ones, no z-network or snubber caps. The supply caps are 2200uf for each board and i am using a bridge rectifier and a 150VA torroid transformer that I modified slightly to get the proper supply voltages.

Anyway hope you enjoy the pictures. Oh yeah this amp cost nothing to build beside the shipping on the lm3875's, i had everything lying around already, and even borrowed from an old broken sony tuner (The speaker jacks).
 

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philb said:
it uses the national semiconductor lm3875 chipamp. It is the second amp i build and find that the bass response on this amp is not nearly as strong as the lm1875. Why is this?


I encountered same situation too.First i build a 1875 amp then a PA100 with LM3886.Both amps builded same as with national semi's datasheets included.Suprisingly LM1875 amp (with a tiny 30 VA transformer) sounded basses powerful and deep instead of PA100.Then i changed some component values (input coupling caps and especially feedback caps called Ci in datasheet) and finally amp sounded good.

Türker
 

philb

Member
2004-02-16 7:58 pm
Canada
caps

Thanks for the support guys!!!

The internals are messy because i didn't have a lot of room to work with. It certainly could of had been better, i just wanted it finished.

I tried changing the caps on the boards. I have tried three different typres of caps all 2200uf, and find that all give a slightly different sound, but none give better bass. I have yet to try the panasonic caps. It is very annoying that the amp does not have better bass output. Any other suggestions would be nice. Would resistors make a difference in the sound quality? I know that the briangt boards can be built with premium resistors.

Thanks
 

philb

Member
2004-02-16 7:58 pm
Canada
Thanks XELB

No probs with the signal cables, but the amp does pick up RF signals sometimes, this was easily fixed with a ferrite bead.

The amp is identical to the briangt amps, and therefore is non-inverting.

I am looking into building a pair matching speakers, and have done some sucessful tests in sheilding a pair of 4" JBL speakers. They can be placed within 3 inches of my screen without any distortion whatsoever.