What preamp should i build for my 3886 GC??Tube?MOSFET?OPAMP?Bipolar??

[thomgun_lc]

The 3d models of 3875 INV

[thomgun_lc]

The 3d bottom model

[h_andree]

I have not tried different feedback values.
The minimum gain is 10. Carlos has tried various
combinations.

The total gain should be considered. For my
DAC output a gain of 20 is sufficient. My DVD
needs higher output for movies.

I have not build or tried reclocker. The CD output
should have no grain. If you are using an external
DAC make sure you're using a digital cable. The
impedance of the cable has to match. Any decently
build digital cable should work. Grain can come
from many sources: Poor power supplies, noise,
cabling, etc. I suggest you solve one item at a time.

I find grain very anoying and thought it was associated
with solid state amplification. I was wrong. Both
solid state and class T amps can sound without
grain. The high resolution requires everything to
be of top quality.

My DAC was $2500 new. I bought it used for $300.
This is a very good DAC (Theta basic). I also have
an PS Audio Superlink 2 (Ebay used $180). This
is also a very nice sounding DAC. Start with something
like this. Get digital cables. Use a high qulity interconnect.
I found many of them to filter out high frequencies.
My homegrown audio have only 10pF capacitance while
some well build shielded interconnects have 400pF
capacitance. This reduces detail.

[thomgun_lc]

thx harry i will try the best combination for Rfeedback/Rin. And what ur comment about my 3875 inv PCB??
What is ur 3875Ni Schematic??

[h_andree]

About the bypass. I haven't done a careful
testing.

However, I predict this is not an easy answer. It
probaly on the sources of noise. If you use
high quality large caps you probably need them less.
Low impedence caps are recommended. If you
have clean power in your house it probably makes
less of a difference. I put 0.047 uF MKT caps
on 47uF Nichicon low esr on the pins and
1500 uF Nichicon low esr ofter the regulators.
That works well. So do blackgates on the pins
(However they are very expensive).

I am experimenting with line filters. I think
they are recommended. I just put one into
the pre-amp. It sounds good. I'm considering
building a power noise reducing outlet.
Essentially external line filters in a shielded case.

I'm now convinced that the goals with these chips
is to reduce noise and distortion to a minimum while
providing power supplies that make all parts work
as much as voltage sources as possible.

Harry

[h_andree]

It looks good. I do not have caps in the signal path.

My schematic is very simple: It follows the datasheet
exactly:

For the BPA:

I'm using a DRV134. I set input impedance to 47k.
On the output I connect them through a 1K resistor
to the input. No caps on the inputs (I measured
the DC of my sources). The I use a 21kOhm feedback
resistor. A 1k from-Vin to gnd. I use DC blocking
caps: 4.7uG BG and 2 x 47uF Nichicon.