High Performance WM8741 Upsampling DAC New Version build thread (show 'n tell too) - Page 4 - diyAudio
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Old 26th January 2012, 05:37 AM   #31
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For the IC packages, the 8741 only comes in one package, and the 2707 only comes in one square package.

For the others, since you know the header pins are on 1/10" centers, you can come up with a scale, and measure the parts.

Doing this, the IC's are SO14, the little gates are DBV.

The watchdog only comes in one package, and the voltage regs only come in one 5 pin package.

Randy
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Old 26th January 2012, 05:49 AM   #32
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Thanks!

I don't have the board yet so it is kinda difficult to get the right package

Ciao!
Do
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Old 26th January 2012, 01:25 PM   #33
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Default Latest BOM for Digikey

I've added everything in detail in the BOM but cannot find the Sanyo Oscon anywhere... You could get the Organic Polymer Caps which are essentially the same...

The Wolfson DAC and receiver are at Mouser as well as the two 100pF and 220pF Wima FKP caps... Digi had no stock on equivalent product.

The BOM contains the Wolfson Receiver, Level Converter and MiniDAC parts.

Ciao!
Do
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Old 26th January 2012, 03:46 PM   #34
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I figured out my question about load caps and crystals.

Crystek app note for load caps

Fox has a similar app note, but it gives a fixed approximation for the Cin and Cout capacitance, which is this case is based on the PCM2707. The PCM2707 datasheet does not specifiy, so I used 5 pf.

Based on 5 pf for the PCM2707, and 3 pf for trace capacitance, if you use 30 pf caps on the crystal, load is 20.5.
To get a load capacitance of 18, you need to use 25 pf caps. Problem is that it looks like 25 pf caps are special order from Mouser, not sure about digikey.

So, 30pf may be as close as you can find that is in stock at a distributor.

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Old 26th January 2012, 04:38 PM   #35
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Yet another update!

Based on calcs done by randytsuch, I've got the closest match available for 0805 ceram caps.

Both caps on Wolfson receiver and MiniDac have changed to accomodate this.

On MiniDAC, removed 33pF and changed to 27pF
On receiver, removed 22pF and changed to 27pF

Both Crystals are 12Mhz 10PPM 18pF

@randytsuch, do you have a Mouser BOM to share?

Ciao!
Do
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Old 26th January 2012, 05:50 PM   #36
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Quote:
Originally Posted by pinnocchio View Post

@randytsuch, do you have a Mouser BOM to share?

Ciao!
Do
I am building a "custom" version, so my BOM wouldn't really help.

I decided to delete the headphone amp (I have better ones already), and to use a different output stage, so I deleted that too.

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Old 27th January 2012, 01:39 PM   #37
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Quote:
Originally Posted by randytsuch View Post
I am building a "custom" version, so my BOM wouldn't really help.

I decided to delete the headphone amp (I have better ones already), and to use a different output stage, so I deleted that too.

Randy
The output stage obviously is the weak link here. +5V opamp delivering (I think?) a 2vrms signal is going to be relatively high THD I am afraid. Shouldn't we use a dual supply opamp to combine the differential signals, get the cmrr and possibly lose the output cap? Thinking somehow using the headamp spots for a better analog stage.

The datasheet shows a nice output stage but doesn't name the opamps, also there is the balanced to unbalanced line level transformer approach to consider.

I guess I didn't buy this as a mini-dac, more for the software control and I think potential to meet the reference performance with a few mods.
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Old 27th January 2012, 02:05 PM   #38
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Guys, I'm all for a better output stage!

Anyone willing to take the lead on this?

I have two of those transformers at home http://www.lundahl.se/pdfs/datash/1545a.pdf
I'm guessing I could surely try them out?

It would be interesting to see what can be done. I couldn't care less about the headphone amplifier in this circuit.

Ciao!
Do

Last edited by pinnocchio; 27th January 2012 at 02:08 PM.
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Old 27th January 2012, 02:16 PM   #39
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I'd agree with you by bypassing the headphone amp.

Look here for transformer output from the dac....

Passive output

It would look pretty similar to the Nekko Audio DAC ( http://www.nekoaudio.com/ ) with the transformers in there.

Last edited by merlin2069er; 27th January 2012 at 02:21 PM.
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Old 27th January 2012, 02:20 PM   #40
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Quote:
Originally Posted by merlin2069er View Post
I'd agree with you by bypassing the headphone amp.

Look here for transformer output from the dac....

Passive output
Looks pretty simple to me. However, that Lundahl LL1674 is on the expensive side. I paid 85$ per 1545A and never got to use them... It is a shame!
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