[grego9198]

Ordered the y1 & y2 pcbs (along with a mini3). I'm excited to build this, but still need to source an AD8656ARZ opamp for th y2 since mouser was out of stock until October 19th. Hopefully one of these electronic suppliers near my work will have one.

This will be my first amp build. I've been soldering for a few years though so I don't think it should be very difficult and it gives me a reason to upgrade some of my equipment.

 

[Nebby]

Ordered the boards and a few other parts from amb

My Box enclosure came in today, I'm a bit surprised how sturdy the little case is! It's rather rigid for it's size.

 

[nightanole]

Im starting my BOM and are confused. What do C11, C13 and there bypass caps c12, c14 do and why do they need to be audio quality? They are also not mentioned in the build up when it comes to parts selection. I have 2 black gates for the outputs c20 and c26 but i would need one more to pop them in the c11,c13 slots.

 

[MisterX]

<deleted the redundant part now that parts list page has been updated>

C11, C12, C13 and C14 are described in the WM8740 datasheet as "reference de-coupling capacitors for VMIDR and VMIDL"

"Audio grade" caps are suggested because many people (myself included) feel they effect the sound of the DAC just as much as the output capacitors do.


And...

If I have 2 of something I would need 2 more to have 4.

 

[rds]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Nice try but.... A few comments about the link to the saved project at Mouser that was posted above: You do not need a dual row 4 position pin header when U4 is populated. You do not need U6 when either the WM8741 or WM8742 DAC chips are used. You need more then 8 positions for the female pin headers when connecting a Gamma 1 full or Gamma 1 Plus version to the Gamma 2 and little birdie suggested you may be better not ordering them from Mouser. The specified part number for the .1uF ceramic caps is: 80-C320C104K5R. Why pay 10 cents extra per part for tape and reel packaged parts when you have to mess with them instead of plugging them right into the board? The specified part number for the .01uF ceramic caps is 80-C315C103K5R. The price is the same this time but the rest of the question remains? (not like the $ total of those parts is a major problem but you may wish to consider revising your project)

If you want to post your own y1 and y2 projects I won't stop you

 

[amb]

I updated the y2 website to improve the C11, C13, C20 and C26 descriptions. Thanks for the head-up.

 

[CodeToad]

From the Gamma2 site:

"U7 should be either a OPA2365AID or AD8656ARZ. These two were chosen for their stringent rail-to-rail swing characteristics, low-noise, low distortion and high CMRR performance. Do not substitute with other opamps. OPA2365 is recommended for line-level use while AD8656 is recommended if you plan to drive headphones directly. "

I'm not entirely clear about the outputs.

1. The jack on the y1 board is the one on the front panel and it only runs from the y1 boards dac and not the y2?

2. The jack in between the rca's on the back panel comes from the y2?

3. If I run the AD8656 on the back panel jack from the y2 can I still use it at line level to a HP amp?

 

[MisterX]

1. Yes.
2. Yes.
3. Yes.

 

[CodeToad]

Are the rca's affected by the opamp or only the mini jack?

 

[MisterX]

The audio output jacks on the Gamma 2 board are connected in parallel.

 

[fordgtlover]

Quote:

Originally Posted by nightanole /img/forum/go_quote.gif Im starting my BOM and are confused. What do C11, C13 and there bypass caps c12, c14 do and why do they need to be audio quality? They are also not mentioned in the build up when it comes to parts selection. I have 2 black gates for the outputs c20 and c26 but i would need one more to pop them in the c11,c13 slots.

I used Panasonic FMs for C20 & C26 and Silmics for C11 & C13.

I'm very happy with the sound.

 

[nightanole]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif <deleted the redundant part now that parts list page has been updated> C11, C12, C13 and C14 are described in the WM8740 datasheet as "reference de-coupling capacitors for VMIDR and VMIDL" "Audio grade" caps are suggested because many people (myself included) feel they effect the sound of the DAC just as much as the output capacitors do. And... If I have 2 of something I would need 2 more to have 4.

I have 3 thanks to a generous donation from you

I just havent used them yet.

 

[Mr.Duck]

Trying to understand the output filter design. I know it is a low pass filter to loose the high frequency junk from the DAC outputs. But why fc = 100 KHz? Why not 40 KHz for example? I realize to have a corner freq at 20 KHz would be too low because it will be at -3dB.

Is the filter a 2nd order one? 12dB / octave?

Oversampling pushes the high freq junk to very high freq range, yes? Do you know what kind of frequency the audio junk will be at for the gamma2? How much will be getting through the filter? For example, the audio junk could be at -80dB, -90dB, etc.

How does the digital filter fit in to all of this? Or is it not really related to the analog filter?


Think that is all. I've been playing with FilterLab and have a rough idea in my head for my own output filter for the gamma2 (not better, just different).

 

[dumbears]

About the audio grade caps, shouldn't we pick non-polar/bi-polar caps than polarized caps?

 

[nightanole]

So would it sound odd to use my black gates in C11 & C13 and use only poly film caps for the output caps? I wanted to try that this time but the C11 & C13 caps threw me off.


As for the polar output caps. The caps are just there to get rid of the dc off set, every dac ive seen uses polar caps. Your free to use non polar ones if you wish.