Comments for my PCM2702 DAC layout? - Page 8

TomB, Apart from the board and the Panasonic Cap are you planning to carry any other parts at Beezar?

No, The BantamDAC is still strictly USB input, by design.

You'll have to look elsewhere to have those features in a DAC.. but it wont come at the same price :P

Yes - I will be carrying the Wima caps, the Box Enclosure cases and the USB pigtail cables. I may also carry the United ChemCon low-ESR gel cap. There's nothing special about any of those except the cases are only in stock at Newark or directly from Box Enclosures themselves. Allied also carries them, but they're normally a special order, I think. The USB pigtails are available at Mouser, but I'd like for everyone to be sure to select one that's shielded. The Wimas and the United Chemcon gel cap are also at Mouser, but Beezar has a lot of international customers where Mouser's shipping is prohibitively expensive.

USB specifies a shielded cable, so you shouldn't really have to worry about that, an unshielded cable is not compliant and can't use the name.

Good of you to carry the other stuff though, especially the enclosure (DigiKey carries the rest and has good shipping to a lot more places than Mouser).

Sub-channel vs. full-rated makes the difference. You can select one or the other at Mouser and DigiKey. A sub-channel USB cable is not required to have shielding. There are other differences, too. I think we're better off with full-rated.

Which type BG and what value did you used here?

Regards

BG NX-HiQ, 47uf 6.3V.

Alright, well then everyone is going to have to excuse my ignorance, please... but what is the cable dac mod going to do then?

Instread of having a USB connector on the borad, the usb cable will be directly conneccted to the dac. less coneections so sound should be a lil better and more convenient since you will not need a usb cable.

I see, thanks for the quick reply!

Ask a question -

The BantamCableDAC is a variation on building the BantamDAC. Essentially, the USB Type B jack is left unpopulated. The selected case, Box Enclosures #RX2KL07-S, is very small - 2.48x1.10x0.63" inside dimensions - and light. This allows one to wire the case directly into the ends of a USB cable and to terminate the other side with standard leads and RCA jacks. In one fell swoop, you've eliminated any plug-in connection to the BantamDAC board, and eliminated any patch cords in connecting the BantamDAC to an amp.

I drilled the Box Enclosure in seven places:

• Four holes for 4-40 screws on the bottom of the case for the board mounting holes
• Two 1/4" holes on both ends at approx. mid-height on the case, and
• One 3mm hole for the LED in the case lid.

The case itself is closed up with four tiny Phillips screws at the four corners on the top (provided with the Box Enclosure). On the ends, I put a rubber grommet in each hole to act as a strain relief. The cables on both ends are extremely tight. My guess is that the case will crack before the cables will pull out, despite any lack of hard clamp on the interior side of the grommets.

Wiring the USB cable into the board is a piece of cake. USB wiring is an international standard - all wiring positions are defined down to the color:

(Note that the BantamDAC board is the same as the diagram for "B". A Type B jack simply turns those wire positions 90 degrees.)

The trick becomes wiring the board with the cables routed through the grommets on the ends. Pulling slack was not too difficult, but taking the slack back out while pushing the board back down into the case onto the mounting screws was a bit difficult. Smaller wiring on the RCA Jack side would probably make this easier. Also, there's a 1/6" nylon washer underneat each mounting hole. This corrects for the thickness of the C8 SMD cap on the bottom of the board, which is the thickest part on the bottom of the board (you don't want to stress the board by clamping down over that SMD cap in the middle).

Finally, mark the hole in the lid for the LED (after soldering the LED at the proper height) and screw the lid on. Voila - BantamCableDAC!

Here are some results of RMAA testing for the BantamCableDAC with BG's versus an Alien DAC w/BG's (one of my Penguin Mint Tin Aliens):

RightMark Audio Analyzer test: comparison of BantamCableDAC with the Alien DAC (both with BG NX-HiQ's on output)

Keep in mind that my setup is far from ideal. I have a bunch of wireless powering my keyboard, mouse, and other items. Cable differences and location of the test can make huge differences. In addition, it's fairly easy to game certain aspects of RMAA, IMHO. Depending on how you set levels, you can vary distortion relative to signal-to-noise. However, the comparison is valid because the test for both DACs was made under the same conditions.

The only purpose for posting the results of the test is to demonstrate that the BantamDAC is functionally equal to the AlienDAC, perhaps a tad better in some respects.

Well there's a good answer

That looks very do-able, looks great as well! I was thinking of trying to stick this DAC in with my Millett Starving Student, but I think the CableDac looks good, plus I'd be able to use it with more than one amp.

Ok, I was wondering why the results were so bad... Amb measurements of the Alien are far better and so were the measurements of the usb dac I designed with Guzzler.

Yes, well, not many of us have the extent of AMB's equipment. It's fairly easy to game certain aspects of RMAA, IMHO, too - which is why I felt that comparisons are what's important. As evidence, these are much better measurements than most of the RMAA results posted by users in the Alien DAC thread. In particular, the AlienDAC got a bad rap from some of our more experienced members as having a steep roll-off at 15KHz. One can see that this is not true. It's also easy to see that the BantamDAC is a functional equivalent of the Alien, if not a tad bit better in some aspects.