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PCB Group Buy for the "DAC + headphone amp" Project

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#108
MattN said:
Got my boards too, thanks.

I've put one of them together. It worked first time, which was nice. First impressions are good.

Matt
Click to expand...

Excellent! I wasn't expecting another amp to be alive this fast, especially without a barrage of "why doesn't it work?" e-mail. 😀

Depending on your headphones, you may want to manipulate R22/R23 to adjust the output gain of the amp. I'm using 1820 ohms for my Grado 125's.
 
#109
gmarsh,

I'm populating my boards now and I have a couple of quick questions....
1. The crystal does not have solder tabs that protrude...does it solder direct, and if so, how do you be sure it flows under the tabs? I use solder paste for all my smd work, and it works well, but I've never done a crystal before.

2. I am curious about the numerous small vias you placed adjacent to some of the component solder pads.....are those just test points?

Thanks, Robert
 
#111
To solder the XO I wet the pads on the device with blobs of solder, wet the pads on the board the same, place the device on the board and then solder to the board. The XO ends up lifted a small bit off the board, but it works fine.

There's no test points on the board. I've doubled up vias in a couple of places (ground vias, etc) but every via you see has an electrical function.
 
#112
C11 12 14 15 Value?

The DigiKey part number for C11 12 14 15 is actually for a 220uf cap instead of the 330uf listed. Would using the 220uf degrade the performance of the PSU in any significant way?

For gmarsh:
I'm nearing completion of my first board and wanted to ask if you could explain the goal in re-programing the ATMega8L. I have a programmer and I got your code from the other thread. I also read your original description of its function as a digital volume control using the attenuation register of the PCM172; and its function as an input selector by cycling back and forth between inputs until it locks.

But my programming knowledge is limited, so I don't know how it will function without re-programming, and what exactly the programming is meant to accomplish? If I know what the goal is, I can find my way through it a bit easier I think.

Thanks! Man...those 0603 SMDs are small!! I'm glad I have a microscope.

Robert
 
#115
Re: C11 12 14 15 Value?

rjkdivin said:
The DigiKey part number for C11 12 14 15 is actually for a 220uf cap instead of the 330uf listed. Would using the 220uf degrade the performance of the PSU in any significant way?

For gmarsh:
I'm nearing completion of my first board and wanted to ask if you could explain the goal in re-programing the ATMega8L. I have a programmer and I got your code from the other thread. I also read your original description of its function as a digital volume control using the attenuation register of the PCM172; and its function as an input selector by cycling back and forth between inputs until it locks.

But my programming knowledge is limited, so I don't know how it will function without re-programming, and what exactly the programming is meant to accomplish? If I know what the goal is, I can find my way through it a bit easier I think.

Thanks! Man...those 0603 SMDs are small!! I'm glad I have a microscope.

Robert
Click to expand...

220/330 shouldn't matter in the PSU. The Mega8L microcontroller chip comes unprogrammed, you'll have to program it for the DAC to function...

Geek said:
I have just got a report that the spec's of Gary's DAC are similar to this:

http://www.benchmarkmedia.com/dac1/

Does anyone have one for a side-by-each listening comparison?

You guys saved a ton for money! 😀
Click to expand...

they're not completely the same... analog bits are different:

Benchmark DAC1: CS8416 -> AD1896 -> AD1853 -> (I-V stage?) -> BUF634 headphone output.
My DAC: CS8416 -> AD1896 -> PCM1792 -> OPA4134 I-V -> TPA6120 headphone output.

Also, I'm doing digital domain volume control - IIRC, the Benchmark does volume control on the analog side.

I've listened to the DAC-1, it sounds good. Mine? well, it sounds alright too. Haven't listened side by side, but I hope y'all are pleased with how the DAC turned out.
 
#116
Programming

GMarsh,

I am using Atmel's Studio 4 (4.12) software and their AVR ISP mkII in-system programmer (USB version).

I tried assembling in Studio 4 from your C Code, but I get about 26 errors that I do not understand, so cannot debug.

So I loaded the hpa hex file directly instead and it steps through that just fine with all green lights, displays it in its 'Dissassembler' and seems to be ready to program. I cannot actually program yet because I am waiting for the 70010 transformer (last part needed) that has been on back order from DigiKey for a while now, so the ATMega 8 has no power, and is not recognized by the ISP.

But I had a few more questions:

I was wondering if your 'makefile' needs to be used somehow also, or does the hpa hex file take care of everything? I can also successfully load the makefile into Studio 4 and it seems to ready it for programming.

Also, for the Int RC Osc 4MHz fuse set, it offers 6CK + 0ms, +4ms, or +64ms as three choices.....which is best?

Any other fuses to set? The pop-up Fuses screen defaults with Boot Flash Section Size = 128 words, and Brown-out Detection Level at Vcc = 2.7v. Keep these?

It also calls special attention to Serial Program Downloading (SPI) Enabled? Should it be?

Thanks for any guidance you can offer,
Robert
An externally hosted image should be here but it was not working when we last tested it.
 
#117
You can't do anything until you install that missing transformer.

The Makefile doesn't need to be used, it's for compiling the C code into a new hex file, if you modify the C code. The hex file is all you need.

Here's the process:

(1) under the Program tab, select ATMega8 as the device type.

(2) Under the Fuses tab, make sure the fuses are programmed as follows and hit Program:

[ ] Reset Disabled
[ ] Watchdog timer Always On
[X] SPI downloading enabled (if it's grayed out, ignore)
[ ] Preserve EEPROM
[X] Boot flash size = 128
..
[ ] Boot Reset Vector Enabled
[ ] CKOPT fuse
[X] Brown out at 2.7V enabled
...
[X] Int RC Osc 4MHz, 6CK + 4ms

(3) Under the Program tab in the Flash area, point that at your .hex file and hit Program.

If all goes well, your headphone amp should come to life.
 
#118
Programming

gmarsh said:

Here's the process:
(1) under the Program tab, select ATMega8 as the device type.

(2) Under the Fuses tab, make sure the fuses are programmed as follows and hit Program:

[ ] Reset Disabled
[ ] Watchdog timer Always On
[X] SPI downloading enabled (if it's grayed out, ignore)
[ ] Preserve EEPROM
[X] Boot flash size = 128
..
[ ] Boot Reset Vector Enabled
[ ] CKOPT fuse
[X] Brown out at 2.7V enabled
...
[X] Int RC Osc 4MHz, 6CK + 4ms

(3) Under the Program tab in the Flash area, point that at your .hex file and hit Program.

If all goes well, your headphone amp should come to life.
Click to expand...

Thanks! That should do it if I didn't screw anything up .

The components and solder pads are so small that I checked all my soldering under a microscope, and verified continuity of the passives to their end traces with my handy Fluke.

I'll post as soon as I get the transformer and get it installed, and finish the programming.
Robert
 
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