My finished amp

[philb]

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).

 

[philb]

pic 2

pic 2

 

[ble0t]

Nice work!

Any internal pics?

 

[philb]

pic 3

your very quick i didn't even have time to post the last pic.

here are the insides

 

[NITRO]

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

 

[Russ White]

Nice amp philb! Looks good!

 

[philb]

thanks nitro

I'll try changing some of the components, after all i did just use things that i already had. Maybe some panasonic fc caps would be a nice touch. If i get to it anytime soon i'll post back on the difference.

 

[Hugh M]

Thats a sweeet little amp. Nice work Philb.

Hugh

 

[cowanrg]

nice job. i like the incorporation of wood. its something that needs to be done more often i think. i like the organic look of some electronics.

one of my next projects is to revisit the chip amp and see what i can make of it. i like the freedom it allows you in the design aspect.

 

[Leolabs]

Internal wirings look a bit messy.Try to tidy them up

 

[Duo]

Very nice.

Lol, I've seen consumer equipment with much worse wiring sell for quite a price.

I like the wood as well. It is a nice thing to see.

 

[philb]

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

 

[NITRO]

Dear philb,
You must change the capacitance of those capacitors rather than changing the brands.Try 2,2 uF for input coupling cap and 22uF for Ci.Regards.



Türker

 

[philb]

Nirto,

The schematic calls for 1500uf, i think that you have mis-interpereted my post. The caps that i am changing are the power supply caps. These are the only caps in the amp, for i am not using a z-network or any snubber caps.

 

[elco]

It is very annoying that the amp does not have better bass output. Any other suggestions would be nice.

You are using a passive preamp. Do you have a real preamp to see if it would improve bass response? There are a few threads about bad experiences of ppl with passive preamps.

 

[philb]

preamp, what preamp.

I am playing music right out of my computer, but the lack of bass is as compared to the lm1875 amp. The lm1875 had no problems with bass. In the end i think i'll build a sub, i enjoy building things anyways.

Thanks for all the help guys.

Phil

 

[XELB]

You are my Hero I don't know how you managed to put everything in such small case Congratulations


How does it sounds ?

 

[VT67]

Nice little ampy philb. No problems with the signal cables crossing over the transformer?

Regards

 

[Mr. Triatic]

..my first thought is that it must be a relative to sir hum'alot

The hardest part must have been fitting all those parts inside that tight chassis..

very good looking aesthetics (spelling?) is it an inverting or non-inverting configuration?

 

[philb]

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.