This is the project page =
for the=20
HPDAC v0.1b2. (Updated 12/24/2006)=20
Background:=20
The problem, for me, with the available portable amps is that =
they=20
aren't really that portable. They all need batteries, and, even =
worse,=20
they all need sources which also need batteries as well as cables =
to=20
connect them. I wanted something that I could take to a coffee =
shop (or=20
the sofa) connect to my computer, and listen without a pile of =
boxes and=20
wires next to me. That is, I wanted a usb dac with a built in =
headphone=20
amp that was all powered via USB, and I wanted it to sound good. =
As there=20
seemed to be nothing of the sort available, I made it myself.=20
The HPDAC is a non-oversampled (NOS) USB digital to analog =
converter=20
(DAC) with a built-in headphone amp. The DAC is based on earlier =
work of=20
mine, though it turns out to be a very similar circuit to several=20
other =
NOS USB=20
DAC's. The amplifier section is essentially the same circuit as =
the Mini3'ified=20
version of the now discontinued Pint.
The entire system is powered via the USB supply, so there are no=20
batteries or power cords necessary. The project is also very small =
and=20
will fit comfortably into the smallest Hammond extruded case.=20
Not only are the amplifier and DAC sections of the HPDAC of =
very high=20
quality, great care has been taken to ensure that the power =
derived from=20
the USB source is clean and free of noise. The power supply =
utilizes a=20
highly efficient DC-DC boost converter to deliver enough voltage =
to the=20
amplifier and DAC. Further, this boosted power is regulated with =
high=20
quality regulators and further cleaned with ferrite beads. This=20
arrangement delivers clean strong power which translates into =
clean strong=20
sound.=20
Compared to similar projects, the HPDAC provides =
extraordinarily high=20
quality sound in a small inexpensive package.=20
=20
=20
Technical Background:=20
In order to power the entire project via the USB supply, the =
HPDAC uses=20
a DC-DC boost converter to convert the approvimate 5V input to a =
higher=20
voltage which is then filtered and reregulated. The exact voltage =
is=20
determined by the builder. This power supply scheme presents =
several=20
challenges which must be considered while building. Primarily, =
since the=20
DC-DC converter is about 70% efficient, and USB can supply about =
500mA at=20
5V, this means that at 10V you have about 170mA at most to work =
with.
Practicality means that 100 to 120mA is probably generous, and =
since the=20
TDA1543 draws up to 60mA, this is a real limit. Second, the USB =
specs=20
limit the amount of capacitance on the USB rail unless there is =
current=20
limiting. The DC-DC converter does have a slow start feature, and =
the=20
voltage regulators do limit current, but this is still worth being =
careful=20
with. It is not worth damaging your computer. That said, I have =
had no=20
problems, but prudence suggests being aware. As a DIY project, you =
are the=20
responsible party. Finally, it should be mentioned, this is a =
fairly=20
challenging DIY project. It involves a considerable amount of SMD=20
soldering and is intened for advanced DIY'ers. As such, the only =
build=20
instructions are to select the parts, and assemble from shortest =
to=20
tallest. I like to do the tricky stuff first (the PCM2707, the =
DC-DC=20
converter, and the REG101) but YMMV.=20
At the request of some car audio guys, I added one last option: =
the=20
HPDAC can be used as a source/preamp in a speaker amp setup. To do =
this,=20
you need to remove the option for the buffered ground by not =
populating=20
L12 (which is on the bottom of the board) and adding a small =
jumper=20
between J1 and J2. To reduce noise a bit, you might try using a =
ferrite=20
instead of a wire jumper, though I have not tried this myself to =
know if=20
it is a good option -- try it and see. I should warn you that =
there are no=20
output coupling caps from the amplifier, so obtaining a =
vanishingly low DC=20
offset or using a power amp with input coupling caps is essential. =
Using=20
OPA2132 opamps mine had an offset of 0.4mV on each channel. Note =
that you=20
should still be able to drive headphones with this setup, but =
perhaps not=20
quite as well, though the difference is minimal.=20
View =
the=20
schematic
View the top =
of the=20
board
View=20
the bottom of the board
Late Breaking News
There appears to be a small bug in the schematic and hence in =
the=20
board. To date, there have been no reports of problems being =
caused by it,=20
but if you are concerned, it is an easy fix. Pin 11 (SSPND) on the =
PCM2707=20
is powered while it should not be (it actually provides voltage to =
turn on=20
some DAC chips.) To disable this, you can either cut the small =
trace that=20
connects pin 10 to pin 11 (it is right between the two pads -- =
this is=20
most easily done before the board is built) or, once assembled, =
use an=20
X-acto knife to cut pin 11 off of the chip.
Other late breaking news is that if a short occurs, the DC-DC =
converter=20
is susceptible to damage. The most likely cause of this is a short =
at the=20
headphone jack during insertion or removal of the headphones. As =
such, it=20
is recommended that you only plug or unplug the headphones while =
the unit=20
is powered off, or at least the volume is turned down. It might be =
that=20
this only occurs if the computer does not have a built-in current =
limiter=20
to the USB port, but I am not sure about that.=20
Ordering
Boards are sold out. As of now, there are no plans to order =
another=20
run. It is possible that another revision may appear, but not any =
time=20
soon. Thanks to everyone who ordered one and participated in this =
project.=20
=20
Samgotit's=20
comments at Head-Fi (regarding the v0.1a board with NJR4556=20
opamps)...
The first revision was a huge surprise =
considering=20
its size and power supply. I found Bass and "Weight" I have never =
heard=20
before out of the K701. This includes through all of the =
non-portable=20
gear I own! There were moments when the bass was... "concentric =
rings in=20
the water cup"... spectacular. Understand, I'm not a huge bass =
head, but=20
the new sound was very addictive.=20
Parts List
| Part |
Value/Notes |
Size/# |
| C1 |
This is the main power =
decoupling=20
cap for the DAC chip. 47uF is probably a decent value to use =
though=20
some people like to use larger. Quality counts in this =
spot, so an=20
Os-Con, Cerafine, or Blackgate is a good idea. Digikey has =
the=20
Silmic II or the Panasonic FM series which are also good =
choices. |
3.5mm pin, 8mm =
width |
| C2 (A, B, C,=20
D) |
These are the main =
power supply=20
caps. They provide some filtering, but mainly seem to =
provide=20
instantaneous power for the amplifier section. There is a =
dilemma=20
here where higher capacitance will offer better sound, more =
bass,=20
etc., but the USB standard limits the total amount of =
capacitance=20
that can be used safely The HPDAC does limit the inrush =
current both=20
with a slow starting DC-DC converter, and a voltage =
regulator that=20
limits the current. Exactly what value capacitance to use is =
the=20
responsibility of the builder to determine. 470uF is =
probably on the=20
high end, 4x47uF high quality caps is perhaps on the low =
end? I=20
would say that 4x 47uF Silmic II caps from Digikey (part=20
#604-1054-ND) is probably a decent place to start, but this =
might=20
also be a good place to experiment. You only need to =
populate one=20
position but can do all 4 if you want. |
up to 4 caps with 3.5mm =
pin, 8mm=20
width |
| C3, C4 |
C3 is the input cap for =
the DAC's=20
regulator. C4 is the regulator's output cap as well as the =
decoupling cap for the DAC. Wima MKP2 0.1uF/63V caps (or =
their=20
equivalent from other manufacturers) are recommended, but =
polyesters=20
will do in a pinch. The Mouser part number for these caps is =
505-MKP20.1/100/5 |
5mm pin, 5.5mm x =
7.5mm |
| C5, C6 |
33pF ceramic |
1206 |
| C7-C19,=20
C26 |
0.1uF (100nF) ceramic =
(but see=20
the note about C8 below in the VR3 section as in some cases =
it needs=20
to be significantly higher in value.) |
1206 |
| C20 |
4.7uF =
Tantalum
Assembly=20
Note: Tantalum caps are polarized, and unlike electrolytics =
have=20
their positive side marked. In this case, the positive side =
is the=20
one furthest from the USB jack side of the board. |
1206 |
| C21 |
.01uF (10nF) ceramic, =
but see the=20
note about this cap below in the VR3 section. |
1206 |
| C25 |
4.7uF =
Tantalum
Assembly=20
Note: The positive side is the one nearer the board's edge =
(furthest=20
from the label.) |
1206 |
| C27, C28 |
Optional, 10pF Silver =
Mica or=20
Film. In general, these should only be used if there are =
oscillation=20
problems, and then only as a last resort. The amp sounds =
better=20
without them. |
1210 |
| CR, CL, CG |
These are the AC =
coupling caps=20
that connect the DAC and the amplifier sections. High =
quality is=20
essential as the entire signal passes through them. The =
cheapest I=20
would use would be 3 x 4.7uF Nichicon ES bipolar caps which =
you can=20
get from me. You could also use 4.7uF Blackgate N series =
caps here.
The Blackgates cost significantly more. They do sound =
better (more=20
detailed, less grain, maybe a little less bass but more =
balance) but=20
not necessarilly a ton better. (You can see my comments =
about these=20
caps at http://www.ecp.cc/cap-notes.htm=
l.)
My sense is if you have $200 + headphones, go with the =
blackgates,=20
otherwise don't worry about it. If you do use the Blackgate =
caps=20
here, give them minimum 100 hours to break in. I know this =
sounds=20
silly, but it took mine in this design at least that to =
develop any=20
bass at all. Both Panasonic and Nichicon make cheaper =
bi-polar=20
electrolytics that are available from Digikey/Mouser, but =
they are=20
not recommended as they sound awful. If you choose to use =
polar=20
caps, the "+" on the board is meaningless, so be sure to get =
the=20
direction right -- either by measuring or by following the=20
schematic. |
2,5mm pin 6mm case |
| L1 |
There is no L1. |
. |
| L3-L12 |
These are ferrite beads =
used to=20
help clean up the power supply. Specific parts are not =
essential.=20
MI1206K260R-10 works fine. |
1206 |
| The=20
following parts (DC1, C22, C23, C24, R5, R6, L2, D1) make up =
the=20
boost switching power supply. I have included a suggestion =
for parts=20
which provides about 9.5V and which has proved to be stable.
However, there is no substitute for reading the DC-DC =
converter's=20
datasheet.=20
|
| DC1 |
This is the DC-DC =
converter. Use=20
a TPS61040. As this is an important element of the project, =
it is a=20
very good idea to read over the datasheet.
Also note that Digikey shows this as out of stock, but if =
you add=20
it to your cart you will see that they have several =
thousand, so no=20
worries. |
TPS61040 |
| C22 (Cff on=20
the datasheet) |
100pF ceramic |
0805 |
| C23 (Co on=20
the datasheet) |
1uF tantalum or=20
ceramic.
Assembly Note: If you use a polarized tant =
here, the=20
positive side is the one furthest from the board's edge. I =
have only=20
used ceramic caps, so I can't comment on the =
difference. |
1206 |
| C24 (Cin on=20
the datasheet) |
4.7uF =
Tantalum
Assembly=20
Note: This is a very small part. The positive side is the =
one=20
furthest from the "C24" label. |
0805 |
| L2 (L1 on the=20
datasheet) |
ELJ-FA100KF |
1206/1210 |
| R5 (R2 on the=20
datasheet) |
R5 and R6 set the ouput =
voltage=20
if the DC-DC converter. The chosen values will give you =
about 9.5V.
If you want more or less, read the datasheet for how to =
determine=20
these resistors' values.
100K |
R1206 |
| R6 (R1 on the=20
datasheet) |
634K (see note =
above) |
R1206 |
| D1 (D1 on the=20
datasheet) |
MBR0530T1G, or perhaps=20
MBR0530TPMSCT
Assembly Note: D1 is polarized. The =
cathode (the=20
marked end) is the one furthest from the USB jack side of =
the board.=20
|
SOD123 |
The=20
following parts (R1L and R to R4L and R and Pot) are the =
resistors=20
in the amplifier section. If you are using an unstable =
"cranky"=20
opamp, several things need to be balanced:=20
- The gain of the amp section is determined by R3* and =
R4*=20
(R4/(R3 + 1))=20
- R1* in parallel with R2* should equal R3* in parallel =
with R4*=20
- R2* should be 10X the value if the pot
The =
suggested=20
values below are simply one such configuration. If you are =
using a=20
stable opamp (usually a FET input part) then think of the =
amp=20
section as a basic CMoy to determine part values. |
| Pot |
This is the =
potentiometer. It=20
sets the input impedence of the amplifier section as well as =
adjusting volume. 10K is the default value here. Increasing =
the size=20
of the pot means also increasing R2L and R2R which could =
increase=20
the noise level a little. Probably not enough to worry =
about, so 20K=20
or 50K is fine but 10K is preferred. EVJ-C20F02D14 is the =
default=20
recommendation.
Assembly Note: The pot has very small =
spacers=20
built in to it. Using a wire cutter, you should trim these =
off as it=20
will fit the case a little better.
 =20
|
Panasonic EVJ |
| R1L, R1R |
1K This may be jumpered =
in some=20
configurations -- if in doubt, leave it in. |
1/8W Axial |
| R2L, R2R |
100K for a 10K pot, =
200K for a=20
20K pot, etc. (this may be optional in some configurations, =
but if=20
used it should be 10X the value of the volume pot.) |
1/8W Axial |
| R3L, R3R |
1K2 |
1206 |
| R4L, R4R |
6K2 |
1206 |
| R1, R2 |
1M |
1206 |
| R3, R4 |
These form the voltage =
divider=20
for the amp's virtual ground. 47K is appropriate. A little =
higher=20
or lower should be fine. |
1206 |
| R7, R8 |
22R |
1206 |
| R9, R10 |
1K5 |
1206 |
| RBCK, RD,=20
RWS |
These connect the USB =
receiver=20
chip to the DAC chip and are used to help clean the digital =
signal.
Anything from 22R to 100R should be fine with 22R being the =
default=20
recommended value. |
1206 |
| RIVL, RIVR,=20
REF |
These are the so-called =
I/V=20
resistors that convert the current output from the DAC to =
voltage.
Quality counts here more than usual with different =
resistors=20
offering very different sound. If you use metal film, use =
high=20
quality resistors like PRP or older Holco. Dale's are fine =
though=20
they are not my favorite as are Draloric. You can also use =
Allen=20
Bradley or Stackpole for a fuller sound. Rikens are a great =
choice,=20
though they will be very tight so must be flush with the =
board --=20
Kiwame's won't fit. There is also space on the bottom of the =
board=20
for 1206 sized resistors which might be a decent =
option.
For what=20
it's worth, my impression of various resistors follows: I =
find the=20
PRPs to be very clean and sweet sounding, but to lack a =
little bass=20
and be a little cold. They make the HPDAC sound a little =
more=20
solid-statey with a lot of crisp detail. The PRPs (and =
really any=20
metal film resistors) will sound a litle bit sheeny in the =
way that=20
a lot of high end solid state gear does. If you like that =
sort of=20
sound, then this is what you want here. Steel string =
acoustic=20
guitars sound very real to me with these. Other metal films =
like=20
Dales or Panasonics, or other generic resistors are similar =
but lack=20
the sweetness.
Allen Bradleys (and other vintage carbon=20
composition resistors) are the polar opposite. They are warm =
and=20
pillowey and very euphonic. They offer a thick warm sound. =
They are=20
a little noisier and you might hear it as background hiss at =
high=20
volumes, though there is some hiss anyway due to the PS, so =
the=20
addition is probably not noticable.. You can get these at =
various=20
places, including Handmade electronics, Nebraska Surplus, =
and a few=20
other places.
Riken Ohms are in the middle. While perhaps =
closer=20
to the ABs in tonal balance, they have all the detail of the =
PRPs=20
and also do not have the noise problems of the vintage =
resistors.
They are, however, expensive.
One last resistor to think =
about=20
are Tantalum resistors. These are my favorite I/V resistor =
offering=20
a very natural organic sound. I use them in my personal =
HPDAC=20
(though I use the ABs in my secondary one.) They are really=20
expensive, though and are available from Parts Connexion and =
Angela.
Also, the REF resistor is considerably less =
important to=20
the overall sound, so a generic metal film is okay there. =
=20
Optimal value is tricky here. This is in part because it =
depends=20
upon what voltage you give the DAC chip (I'll assume 5V =
here) but=20
also because they set the output impedance of the DAC =
section and=20
influence the amplifier section. If you are using a cranky =
high=20
current opamp, then you will probably be using a 10K pot =
which means=20
that you want the output impedence of the DAC to be 1K or =
lower.
Thus, in this case, 1K is recommended. If you are using a =
less=20
cranky opamp, then you can use a higher value pot and thus a =
higher=20
value I/V resistor. If this is the case, then you will need =
to do=20
some reading and or experimenting to find the optimal value. =
2.7K=20
for the I/V's and 1.4K for the Ref is probably a decent =
place to=20
start, though you may want 8V for this option. Anyhow, as =
noted, 3 x=20
1K work well with a 5V supply.
|
up to 1/2W Axial (lower =
W rating=20
is fine) or 1206 SMD |
| RLED |
Sets the LED current. =
Anything=20
from 470R to 1K is fine, lower will lead to a brighter LED =
and will=20
drain more power. |
1206 SMD |
| PCM |
This is the chip that =
converts=20
from USB to something the DAC chip can use (I2S). The board =
was=20
designed with the PCM2707 in mind, but the PCM2706 also =
works just=20
fine. |
PCM2707 |
| TDA1543 |
This is the DAC chip =
and is=20
supplied with the board. In theory, you could stack these*, =
but if=20
you decide to do this be very cautious about current draw.
Personally, I wouldn't do it. Also, don't put the chip in a =
socket.
Considerable attention has been paid to layout such that =
the=20
digital signal to the chip is as clean as possible. The =
socket is=20
counterproductive and will audibly degrate the sound =
quality.
*=20
Some people think this sounds better, though I don't. It =
seems to=20
trade some midrange magic for greater extension at the =
frequency=20
extremes. The idea is that on any given bit a DAC can make =
an=20
error. By stacking chips you increase the chance that there =
is some=20
error on any given bit, but decrease the amount of that =
error. |
8 pin DIP |
| OP1, OP2 |
These are the opamps =
for the=20
amplifier section. OP2 provides voltage gain while one half =
of OP1=20
creates a virtual ground while the other half buffers the =
ground. In=20
general, since there are no buffers, at least for low =
impedence=20
headphones, you want high current opamps. This typically =
means=20
something that has some amount of instability.* The amp =
section is=20
designed to handle this instability in all but the worst =
cases.
Thus, opamps like the NJR4556 of the LM6172 are =
appropriate. (For=20
what it is worth, I have found the NJR4556 to have very good =
bass=20
and dynamics but to be a bit harsh on the top end. =
Conversely, the=20
LM6172 is very smooth and open on the top end but does not =
have=20
quite as much bass slam, though there is plenty for most =
purposes.)
The default recomendation is thus the LM6172. It is cheap =
and=20
sounds very very good. My sense is you should have a good =
reason for=20
using something else, but then, it is your amp so you maybe=20
shouldn't listen to me. For headphones that do not need as =
much=20
current, less cranky opamps (OPA2132, AD8620) may work well. =
Also,=20
if you plan to set this up as a preamp (this is a note to =
the car=20
audio guys!), using a less cranky fet input opamp like the =
OPA2132=20
or AD8620 might be a good idea as the offset should be =
slightly=20
lower.
* A full vetting of this topic is well beyond the =
scope=20
of this parts list. The amp section is based upon the =
Mini3'ified=20
version of the now discontinued Pint amp. However, while =
those amps=20
concentrate in the AD8397, that particular part draws enough =
current=20
that its use here might be problematic. If you want to use =
it, be=20
sure you know what you are doing. I have not tried it, so I =
can't=20
really offer any advice. I have, however, tried the AD8397 =
in other=20
circuits and to my ear the LM6172 is the better sounding =
opamp=20
anyway. The high current opamps (the ones mentioned above) =
that are=20
perhaps more appropriate here are a bit more stable than the =
8397=20
making them a little easier to work with. |
2x Dual 8 pin SMD |
| VR1 |
This is the voltage =
regulator for=20
the amplifier section. My suggestion is that you want =
something that=20
limits current to avoid damaging the USB bus in the computer =
either=20
due to the inrush of C2 or due to a short somewhere. You =
also want a=20
LDO regulator so that it can be as close to the output of =
the DC-DC=20
converter as possible to avoid wasting voltage. So, if you =
used the=20
suggested values for R5 and R6, then an 8V LDO regulator =
with 150mA=20
current capability is perfect here. TL750L08CLP works quite =
nicely.=20
|
TL750L08CLP |
| VR2 |
This is the voltage =
regulator for=20
the TDA1543. The part you use will depend on a number of =
factors. =20
First, you must give it a high enough voltage on the input =
to work=20
and it's output voltage must fall within the range =
specified by the=20
TDA1543. This means that the output must be between 5 and 8 =
volts.
It also means that, depending upon where you set the DC-DC=20
converter's output you might need a LDO regulator here. =
While high=20
voltage does change the sound of the TDA1543, it is not =
necessarilly=20
for the better, though it is not necessarilly for the worse =
either.
The default choice would be the LM78L05 as it is stable and =
easy to=20
use and cheap. However, some people swear by the AN8008 and =
AN8005=20
Vregs for the position next to the 1543. My own experience =
is that=20
these do indeed sound pretty good. However, they are only =
rated for=20
50mA and the 1543 datasheet says that it can draw up to =
60mA, so=20
they might not be the best choice. On the other hand, they =
might be=20
worth considering. |
LM78L05ACZFS-ND |
| VR3 |
This is the voltage =
regulator for=20
the PCM2707. There are a couple of ways to set this up. =
The=20
PCM2707/2706 has built in internal voltage regulators. They =
are=20
enabled by supplying the Vbus pin with 5V. When this is =
done, then=20
the other power supply pins need to be decoupled externally, =
and=20
have a measured 3.3V on them whic his internally supplied.
Alternatively, you can diasable the the internal regulators =
by=20
supply 3.3V to the Vbus pin and then supply 3.3V to all of =
the power=20
pins youself.
So, there are 3 ways to set this up:=20
- The simplest (and cheapest) is to use the PCM's =
internal=20
voltage regulator. To do this, do not populate C7, C8, =
C21, L6,=20
and L10. Instead of using a regulator for VR3, simply =
jumper from=20
the input to the output pins.=20
- To supply 3.3V externally, use a 3.3V REG101 for VR3 =
and=20
populate C7, C8, C21, L6, and L10 as per the normal =
instructions.=20
- If you like to live on the edge and want to use dual=20
regulation of the PCM, you can use a low dropout voltage=20
regulator for VR3 to supply something on the order of 4.5 =
to 4.75V=20
(the choice may depend on what voltage your USB supplies). =
In this=20
case you should populate C7, C8, and C21 according to the =
voltage=20
regulator's datasheet, but you should not populate L6 and =
L10 as=20
you will be using the PCM's internal regulators. =
The=20
$20,000 question here is, does this make any difference, and =
the=20
answer is, I have no idea. I have been using the 3.3V REG101 =
option=20
as my default, but the simple cheap option seems fine even =
though it=20
is theoretically noisier. I have not tried the 3rd option, =
so I have=20
no opinion there. |
SOT23-5 foot print |
| LED1 |
Any 3mm LED should be =
fine. This=20
part can be left out if you don't like LED's. It only =
indicates=20
that usb power is connected, not that anything is=20
working.
Assembly Note: The anode (the longer lead) =
goes=20
closer to the "RLED" label. |
3MM |
| Q1 |
The 12MHz crystal =
oscillator for=20
the PCM2707. Part number MP120 (CTX058-ND) from Digikey is =
fine=20
here.=20
| HC49 |
| USB |
Part #571-7877801 from =
Mouser is=20
suggested. I have tried a lot of USB jacks and these have =
become my=20
favorite as the USB plug clicks in and stays stable. |
571-7877801 |
| OUT |
CP1-3513-ND (SJ1-3513) =
from=20
Digikey is the best option. However, 161-3507 from Mouser =
also fits,=20
though it it a little crooked. I was also at Radio Shack the =
other=20
day and noticed that they have a jack that should fit -- it =
looked=20
the same as the Digikey jack to me. |
CP1-3513-ND |
| Case |
The board was designed =
to fit in=20
a Hammond 1455C802. Digikey seems to have some of these in =
stock,=20
but if they run out Mouser stocks them as well. |
1455C802 |
| Knob |
You will probably want =
a knob of=20
some sort. Smaller is better here as otherwise it will =
extend beyond=20
the edge of the case. Digikey has a bunch to choose from.=20
(226-1025-ND, 226-1029-ND, 226-1033-ND, 226-1041-ND) |
. |
Some build notes and options:
- In general, this project like most PCB based projects should =
be=20
built from shortest to tallest parts. In addition, I have found =
that a=20
good order is to first add the most difficult parts (the =
PCM2707, the=20
REG101, the DC-DC converter, and the opamps), then add the smd =
parts on=20
the top of the board, and then add the rest of the surface mount =
parts=20
to the bottom, then do the tall stuff.=20
- If desired, one can build this project as only a NOS USB DAC =
leaving=20
off the headphone section. In addition, CG should be left out =
and the=20
output ground should be from true ground. There will be no cap =
bleeding=20
resistors on the output, so the next stage will need resistors =
(10K to=20
100K) from input to ground (usually a volume pot.)
Special thanks go to Tangent without whose Pint this project =
would not=20
have happened, at least not in the form it happened in. Similarly, =
Amb and=20
Morsel's modification of the Pint and work on the Mini3 proved =
very=20
helpful. It is probably worth looking at the Pint=20
project page for understanding the issues with the amplifier =
section
though since I suggest you stay away from the AD8397, some of =
those=20
issues are not that important.
