universal chip pre-amp project

[cancerkazoo]

Originally Posted by tent

PS: cancerkazoo is now your buzz away? no hum any more (I mean by powering from the kitchen)?

It is very very low now, but I can still hear it with my ear up to the horn. (klipsch). It also increases when the interconnect is removed from the source.

But I have a feeling it will be a little better when in an enclosure and a chassis ground (and resistor?) is used.

I need to track down the mains power issue (6v between neutral-ground and 30v between hot-ground)and there is no ground behind the wall plate there.

[digi01]

Originally Posted by tent

what would be a good gain setting with this preamp? You say preamp has gain 10, I have a LM3886 with gain 33.. would it be ok, just design correctly my attenuator with resistances? or probably better change amp gain?
tent:wq

i think you need not change the gain.you can adjust the levels with attenuator.the preamp with gain 10 is a average value.
for low gain setting,you have to apply deep feedback to the opamp that is no good.
the UCP preamp was designed for work under tough applications.it is not only for driving chip based power amp but also for driving solid & tube based power amp.some power amp have an low or nonlinear input impedance so that usual sources can not drive the input perfect.the preamp allows use of such devices without worry about impedance issue.

can you test below configuration?
(1)CD player ->attenuator->LM3886 poweramp
(2)CD player ->attenuator->UCP preamp->LM3886 poweramp
(3)CD player ->UCP preamp->attenuator->LM3886 poweramp

the outputs on a source are often lower sound quality than fixed outputs.some sources have nonlinear output impedances which are not perfect for driving a power amp directly.


Zang

[digi01]

Originally Posted by cancerkazoo

That would make sense, I was under the impression that this was a unity gain preamp. ( I thought I read that somewhere)
Is there a way to make this unity, or less? as my TV output is higher than what I want for my amp.

yes,the preamp with gain 10.
you can modify the gian via adjust R5,R7,R6,R8.the preamp is a two stage device,voltage gain + buffer stage.for make this unity gain,set R7,R8 as 0ohm is a simple way.

[st3al]

Good project. How much is the cost of the finished unit?

[cjkpkg]

Well,

I just ordered the board, the parts to stuff the board from mouser, and the stuff to stuff a PSU board I had left over from a gainclone project - basically the Carlos Filipe circuit.

The board was $20
Components to stuff UPC and PSU(including 2 OP2227P) $35

still need a xformer, and misc jacks, plugs, fuse holders etc along with enclosure, pot, and anything else I neglected to mention. probably another $100 or so.

All in all I am looking forward to this project for about $155...maybe less if I can repurpose an enclosure I have kicking around.

[tent]

Hi all,
I finally got some time to continue this project.. now populating my 6 channel pre amp with three of those pre-amps using LMs...
The attenuator is in good shape now..
Currently I'm struggling not having Hum and noise.. unluckily I do not know if I'm doing some earth ground wiring wrong or my implementation with PSU and toroids is wrong......

Anyway what I wanted to ask was: I was thinking also about putting a headphone jack in the box... ))) Do you have a suggestion on how I could implement a headphone in this implementation? Something not too complicated..

Thanks,
tent:wq

[jleaman]

I knew you were still on here DIGI!

Glad u are still here, are you making boards for this project ?

Jase

[cjkpkg]

VERSUS



The PSU board I have leftover from my chipamp.com project is the one I want to use for the UCP. I notice that there is a difference in the Carlos Fillipe circuit with the chipamp.com version having a +PGND and a -PGND.

How would I properly hook up the UCP to this PSU board?

[cjkpkg]

OK,

After studying the layout of the LM3886 amp board it looks like the +PGND and the -PGND are not isolated from each other. Would it be as simple as just twisting the +PGND and -PGND together and connecting them to the ground of the UCP?

[ratza]

Yes, it is really that simple.