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The GrubDAC - Page 14

post #196 of 1062
Yes it's a USB mouse. I have a decent 5V linear supply here that I can try. Do I need to desolder the USB power pin to try out the external PSU?
post #197 of 1062
Thread Starter 
I wouldn't try and use an outside power supply. Yes you could desolder the power pin on the USB jack and attach the outside power supply, but per the spec sheet, the HOST pin of the PCM2707 is supposed to go high when attached to the bus. That will happen before as the way I did the board, it is attached to power (with no switching). So it may or may not work. I would try some other USB ports first.

Also curious what kind of amp you are running and at waht gain?
post #198 of 1062
Anyone have two spare PCM2707s on them?
post #199 of 1062
Just noticed the Wolfson WM8524GEDT is on back-order at Mouser.
According to them, backordered items are free delivery to UK, but when I try
to buy, it still comes up with a £12 ($19) delivery charge !
Anyone had any experience with this ?
post #200 of 1062
I think they mean that if something is backordered, they'll sent everything else (for the appropriate fee) and then when they get the other items they'll send them out free of charge. I could be wrong but I can't imagine why they would ship everything for free just because something is backordered.
post #201 of 1062
Quote:
Originally Posted by cobaltmute View Post
I wouldn't try and use an outside power supply. Yes you could desolder the power pin on the USB jack and attach the outside power supply, but per the spec sheet, the HOST pin of the PCM2707 is supposed to go high when attached to the bus. That will happen before as the way I did the board, it is attached to power (with no switching). So it may or may not work. I would try some other USB ports first.

Also curious what kind of amp you are running and at waht gain?
though it would be interesting to see/hear improvements with battery power w/ grub & carrie. How high does HOST pin go cant be more than what usb can provide 5v 500ma?
post #202 of 1062
Quote:
Originally Posted by Juaquin View Post
I think they mean that if something is backordered, they'll sent everything else (for the appropriate fee) and then when they get the other items they'll send them out free of charge. I could be wrong but I can't imagine why they would ship everything for free just because something is backordered.
Yes, that's right quote from mouser below. I'm not sure whether they do this for international orders though:

In an effort to reduce shipping costs to our customers we pay for the first pound of UPS Ground or FedEx Ground on backordered shipments if there has been one or more previous shipments on the order. If your order is not scheduled to ship UPS Ground or FedEx Ground or if the freight is being billed directly to your UPS or FedEx account number and you would like us to update your ship method so that you can take advantage of this service, please let us know by replying to this e-mail and specifying how you would like it shipped.
post #203 of 1062
Clear as mud !
It seems the `free shipping` refers only to the back-ordered items when a multiple order is made.
So, if, like me, your only after 1 item (on back-order) you have to pay $19 postage for a $2 part that could take weeks/months to be despatched.
I`ll keep looking.
post #204 of 1062
Thread Starter 
Quote:
Originally Posted by keyid View Post
though it would be interesting to see/hear improvements with battery power w/ grub & carrie. How high does HOST pin go cant be more than what usb can provide 5v 500ma?
The HOST pin should be attached to Vbus (5v) when the USB cable is attached. From the datasheet:
Quote:
Host detection during self-powered operation (connect to VBUS).
So you can jumper it right to the 5V from the USB cable. You'd need to ensure that pin 4 is grounded (PSEL). On the production boards PSEL will be high to tell the PC that the board could draw up to 500ma (when attached to a Carrie or other item).
post #205 of 1062
Thread Starter 
As we are really close to sending the board out to production:


Revision F = Final

So what changed from the original proto to now?

The board layout changed. This was driven by a couple of items. First, to make it compatible with the Bantam, the output holes were adjusted to nearly match the Bantams, but the grubDAC's were kept on 0.1" centers. The mounting holes were moved to match the Bantam's exactly. The LED was moved to be near the USB connector.

You may notice that there are cutouts on the board as well. These are there so the board can fit into a Hammond 1551H case without modification to the board or the case. With the right choice of electrolytics, the board will fit in the case and mount cleanly on the PCB mounts. All you have to do is cut slots in the case for your input and output wiring. Makes it very simple to build a cable dac.

Yes, with the physical changes, the board still does fit into a 1455C case for mounting with the Carrie.

Schematic-wise, there were two changes. First, a change was made to the post-DAC RC filter. In the original, a SMT ceramic capacitor was spec'ed. The new default is a Wima film capacitor, but the option still remains to the ceramic on the bottom of the board. The second change has to do with the timing for the PCM2707. With the layout changes, I felt that the crystal would have to be placed too tight to the PCM2707 to allow a user to work on the chip if required. To move the crystal around, I thought there would be problems with trace lengths so I changed the crystal for an oscillator. It gets fed with its own RC filtered supply from the rest of the board.

These last refinements have taken a while to get down, given that every change has taken 3 weeks for a BatchPCB run, but the production board is finally here. Now we just have to wait to get it made.
post #206 of 1062
Yep - hope to order the production versions this week.

I built a couple this weekend using the latest prototype that Erik pictures above. These were built with the PCM2706, a pin-compatible alternative to the PCM2707. They sound great - lots of detail, great midrange and a surprisingly impactful, resolute and tight bass. It's really a wonderful little DAC!!





As Erik noted, these fit the little Hammond 1551HTBU perfectly, only requiring a slot to be cut on both sides under the lid for the wiring. Once the CableDAC is assembled with cable and RCA outputs, simply lay the assembly into the Hammond box, screw down the two #2 screws and attach the lid. Since the box is translucent, the LED shines through without having to pop a hole in the lid.

Kudos to Erik for coming up with the idea for the case - also for his patience as I pestered him to death to make the changes to fit the case so nicely. We'll probably be ordering them from Hammond in volume with the slots pre-cut on the sides for the wiring - so you'll have nothing to do but screw the board in, and screw on the lid.
post #207 of 1062
Quote:
Originally Posted by tomb View Post
Yep - hope to order the production versions this week.


Looks like I'll wait Tom ....
post #208 of 1062
... and I was hoping to stop ordering stuff from out of europe for a while
post #209 of 1062
are these going to be priced the same as the proto boards?
post #210 of 1062
Quote:
Originally Posted by pistolsnipe View Post
are these going to be priced the same as the proto boards?
No, but when they're already priced at the cost of potato chips, we think you'll agree that the increase will still be trivial.
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