Fantastic $40 WM8740-based board

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This isn't really pure DIY, more like BIY plus some tweaks, etc. but...

I just received my $40 WM8740 DAC (ebay item 190685871588) and I have to say it has far exceeded my expectations so far.

I am feeding it with a CM6631A-based USB/SPDIF board that I bought from the same e-bay seller.

Build quality, soldering, etc. are excellent on both.

The DAC board comes with an OP275 opamp in it, but I had ordered both an AD8599 and an OPA2132 because I love to have options!

After some very quick comparisons, I decided to leave the AD8599 in there for a good serious listen. The sound of this WM8740 board with the AD8599 has brought an whole new dimension to my system. Just beautiful!

Anyway, I plan to put the CM6631A board and WM8740 board into a homemade chassis, directly connect them, build the transformer in, mount the USB interface on the chassis, LEDs, switches, etc. as a DIY/BIY project. It is all that I am capable of and it will be a fun, satisfying project.

Anyone like me who cannot quite build a DAC from scratch should have a serious look at some of these Chinese boards.
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Some listening notes, which will only have meaning if you know what my previous signal chain was.

Old setup:

Ubuntu Linux (kernel 3.2.something) --> Deadbeef (direct hardware with no conversions) --> Tenor TE7022 USB/SPDIF (no 88.2!) --> HotAudio DAC Wow (WM8524) --> Shuguang I-25* --> pair of dual EL70 Planet-10 microTower "Castle".

New Setup:

Linux Mint (Kernel 3.7.6) --> Deadbeef (direct hardware with no conversions) --> CM6631A USB/SPDIF --> WM8740 DAC --> Shuguang I-25* --> pair of dual EL70 Planet-10 microTower "Castle".

The new setup (currently with AD8599 opamp in DAC) is:

- More "real" in general - perhaps more forward or less veiled. I was not unhappy at all with the "realism" of the old setup, but the new setup takes it to a new level, and it seems to get better with added wattage, not worse.

- The sound stage is both wider and narrower -- that which belongs in the centre is really, very much in the centre now, rather than in the left of the right or both... but the stuff that is far off to the right or left is more distinctly placed.

- Dynamic range is better -- bass is fuller/richer and the highs are crisper. Again, more "real".

- Subtle details in the background are much more a part of the experience now. They were just there before. Now they are essential.

- The difference between 16/44.1 and 24/96 (or 88.2) is considerably more apparent now. This varies a lot depending on the recording, of course, but really well produced stuff at high sample rates and res is just mesmerizing. "Gaucho" at 88.2/24 - WOW!

* The Shuguang I-25 is a 25 wpc EL34 PP tube amp. Currently running 4x Psvane EL34 + 2x NOS Sylvania 12AX7 and 2x NOS GE 12BH7 (I added a supplementary 3 amp filament transformer to run 12BH7 in place of 12AU7). I have some EH EL34s for it, but they are noisy as hell and lack the bass of the Psvanes.
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After work today I decided to integrate this WM8740 DAC board with my new CM6631A USB/SPDIF board.

I began by removing the superfluous components from both boards:

- Removed SPDIF-out RCA interface from USB/SPDIF board
- Removed SPDIF-in RCA interface from DAC board
- Removed USB interface from DAC board
- Removed USB/SPDIF selector switch from DAC board

Then I integrated the two boards:

- Bridged the appropriate pads to permanently select "SPDIF" input on the DAC board (in leu of the removed selector switch)
- Installed leads (green and red) in the DAC board coax SPDIF-in pads
- Connected other end of leads (green and red) to USB/SPDIF board coax SPDIF-out pads
- Used "Mighty Putty" to install/secure the USB/SPDIF board so the USB interface is aligned with the interfaces of the DAC board, ensuring that access to the opamp is maintained

I have ordered a project box that the whole works should fit into. If that fails then I will build a box.

Sorry about the photos, but all I had handy was my BB.


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The wife and I just did about 40 minutes of opamp rotations. 3 chips; OP275, AD8599 and OPA2134.

For female vocal (Chie Ado) the AD8599 had the edge for "presense" and air.

For slightly more complex (Jack Johnson) to more complex (Dire Straits, Steely Dan) the OPA2134 seems to have the edge for coherance and lack of top end harshness. We can go louder with the OPA than the AD, and the OPA has fuller bass, seemingly. Perhaps that is a slightly rolled off and less harsh top end that we are liking..

The OP275 is surely a smooth, analog sounding opamp. I can see why it was so popular back in the day. However, it sounded "distant" to us. Less real. More like we were listening to a stereo system (a good one, but still...).

This is the first really serious listen we have given to the OPA2134 since getting the new DAC, so it isn't even burned in yet.

Still not sure which opamp we will settle on as the best "all-rounder" but my gut is telling me it'll be the OPA. The AD impresses me, but it seems less refined or less controlled.

If I had to make an analogy. OP275 is like a 72 Vette, AD8599 is like a Ferrari 308 or perhaps a Lamborghini of some sort, and OPA2134 is like a BMW M5.

Which opamp is the Porsche 959?
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Yes. About 85 bucks including the opamps.

I suppose I could have bought a complete solution for that kind of money. On the other hand, this "DAC sandwich" provides asynchrous USB, true USB2Audio plug and play with my OS (Linux), an excellent DAC chip, and the option to swap opamps. Not sure if there is a product out there for less money with all these key features (for me).

The enjoyment of "building" it is very important to me as well. I just love getting soldering iron out and tinkering.
Yes, the USB board is powered by the PC.

I considered trying to go I2S directly from the CM6631A to the WM8740 but in another thread someone indicated that it would probably not work. I had a plan worked out and everything, but based on that advise, I decided to simply stick with SPDIF.

I'd love to know the details of how you achieved direct I2S.

I2S would be ideal, as it would allow me to bypass the DIR9001 on the DAC board, which limits me to 96/24. Both the CM6631A and the WM8740 are capable of 192/24.

On the other hand, 96/24 is probably way more than I will ever need and it does sound pretty damned incredible as it is, so... "if it ain't broke...."
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