[cook]

Quote:

Originally Posted by peterpan188 I am a little confused about IC3. I thought we can't really use the fixed voltage regulator, REG101UA-5, REG102UA-5, for direct USB powered option. The part list note says that, it doesn't really regulate. Instead we have to use REG101UA-A, or REG102UA-A as adjustable regulator, and regulate it down to 4.8V using R31 and R32. But at the same time, the part list tells that they are only mandatory for all configurations except Direct USB. What is right? I am planning to use the DAC always USB powered, what should I get?

I believe "direct USB" means that you take power from USB without any kind of regulation. Other option is "regulated USB" for which you will use REG101UA-A, or REG102UA-A. See top of the "Parts List" page.

Also I didn't see anywhere explanation of REG101UA-A/REG102UA-A vs REG101UA-5/REG102UA-5. Text near Vout formula only says that REG101 has higher Vref than REG102. I ordered REG101UA-5 because it was first in the list. May be a little more details on IC3 selection for different power options will help others.

 

[tomb]

Quote:

Originally Posted by cook I believe "direct USB" means that you take power from USB without any kind of regulation. Other option is "regulated USB" for which you will use REG101UA-A, or REG102UA-A. See top of the "Parts List" page. Also I didn't see anywhere explanation of REG101UA-A/REG102UA-A vs REG101UA-5/REG102UA-5. Text near Vout formula only says that REG101 has higher Vref than REG102. I ordered REG101UA-5 because it was first in the list. May be a little more details on IC3 selection for different power options will help others.

Well, I wouldn't want to get into a discussion of semantics over the use of the word "direct". Whatever the strict definition, the BOM's referenced also included R31/R32, so the intent to regulate was implicit.

As described in Alf's writeup, "Direct" USB implies no regulation, but the trick is to regulate to the regulator chip's minimum voltage drop, e.g. 4.8V. The writeup then goes on to describe the calculation and selection of R31/R32 values to accomplish this. As Cook notes, however, there was never any distinction given to which regulator.

I can see now that to those intimately familiar with selecting regulator chips, the "-5" meaning should've been obvious: it wasn't "4.8."

Hmmm - well as Mister X noted, my Black Gate order will fall through, anyway. Are there some decent coupling caps at DigiKey I can get since I need to order new regulators?

 

[peterpan188]

Thanks, I would want to regulate the USB power, so I guess I will be using the REG101UA-A, and choose the right value for R31 and R32 right?

Another question, what would be the point of using a -5 in the family for the regulator? Would it not regulate?

Peter

 

[tomb]

Quote:

Originally Posted by peterpan188 Thanks, I would want to regulate the USB power, so I guess I will be using the REG101UA-A, and choose the right value for R31 and R32 right? Another question, what would be the point of using a -5 in the family for the regulator? Would it not regulate? Peter

Regulators that have numbered suffixes indicate the voltage that they will regulate to, period - given certain requirements. One of those requirements is that the regulator needs to burn up a couple of tenths of volts to operate. So, that means a fixed "-5" regulator would need perhaps 5.2 - 5.3 volts. (This is all documented exactly in the chip's literature.)

To paraphrase slightly, the trick used by Alf is to pick an adjustable regulator, and then regulate it as close as possible to the 5V, using only the minimum required by the chip, thus: 4.8V for the USB-powered DAC. Keep in mind, the out-of-the-box PC USB voltage is unregulated. So, even though the 5V is set, in truth it can vary at the whim of the PC, spike, sag, drop out, etc. Also note that 5V was considered the minimum for the primary DAC anyway.

Hindsight is always 20-20, I guess - all this seems obvious, now.

 

[n_maher]

So, given all this discussion about which reg is the correct one is there some enterprising soul that could put out a correct BOM for a USB powered dac? It'd be greatly appreciated by those of us chugging through other projects but still wanting to build this DAC.

Thanks in advance.

Nate

 

[Tedro]

I will make a BOM as long as someone will let me buy a PPAS board off of them and or another DAC board off of them. I have already copleted one and have ordered all the correct parts before to build the DAC in a number of different configurations.

I am also working on a Step By Step build guide with pictures aswell, if someone can help me out with a board or two.

 

[Buzzerbro]

I don’t have a complete BOM for the Regulated USB Powered DAC but I think these resistors from Mouser should work in regulating the USB's 5V down to 4.8V.

R31 71-CRCW0805-37.4K (Mouser)
R32 71-CRCW0805-11.5K (Mouser)
IC3 REG102UA-A (Get from Digikey)

 

[cook]

Here is what I think is good Digikey BOM for USB-powered DAC with adjustable regulated power. Some items may be out of stock (USB receptacle in particular). This BOM have enough parts for TWO boards. For one board you may half some counts but minimum on most SMD part is 10.

Code:

[left]2PCM2702E-ND IC1 2-REG101UA-3.3-NDIC2 2REG101UA-A-ND IC3 20490-1057-1-ND L11-L18 10478-1416-1-ND C1 2P12348-ND C2 10478-1310-1-ND C11 C12 20490-1673-1-ND C14-C19 C21 C31 10478-1391-1-ND C22 C32 2P11180-ND C13 4P11180-ND C23 C33 ******************************************* 4P11180-ND CL CR These will work but there are better sounding caps ******************************************* 10311-22.0CRCT-ND R11 R12 10311-1.50KCRCT-NDR13 10P1.00MCCT-ND R14 10311-330KCRCT-ND R15 R16 10311-32.4KCRCT-NDR31 10311-11.5KCRCT-NDR32 10311-604CRCT-ND RLED optional - only if you want LED 2X030-ND X1 2609-1039-ND USBreceptacle 2HM970-ND CASE In addition you will need : 3.5mm or RCA output connectors - mandatory Soldering flux - mandatory Contact cleaner or 99% alcohol - mandatory On/Off switch - optional LED - optional[/left]

 

[Alf]

I updated the support web site to avoid confusion regarding fixed and adjustable regulators. Also Direct USB has been renamed to Unregulated USB.

Before ordering R31/R32, you should measure voltage of the USB port you intend to use. While the values specified in the part list work for most people, they might not work for you.

 

[Sinbios]

How is the USB 5v output related to the formula Vout = (1 + R31 / R32) * Vref?

 

[doobooloo]

Since the BGs I wanted were out of stock at Kyoto, I went to Sonic Craft. They were a real pleasure to deal with, and I got my shipment promptly.

www.soniccraft.com

You have to email them with your order and they'll call you for your credit card information. Kind of old school, but it works and their service is very professional!

I got a few other parts from there too, no problems.

 

[cook]

Quote:

Originally Posted by Sinbios How is the USB 5v output related to the formula Vout = (1 + R31 / R32) * Vref?

To let regulator work properly USB 5v should be higher than Vout (by 0.4V at least if I understand reg101 spec pdf right)

 

[Sinbios]

0.4V? Ouch, my USB outputs about perfect 5.0V, so I need to set the regulator output to 4.6V? Won't performance suffer quite a bit at those levels?

 

[cook]

"Note 4:IC3" says "4.5-4.8V" so I hope it will not be that bad. Either way - if you are not happy with its perfomance - with adjustable REG you can add 9V battery, bump reg to 5.4V and enjoy that overclocked PCM2702

 

[Tedro]

My usb is exactly 5.0volts aswell though I am using the adjustible regulator and drops the voltage to 4.82volts. Sounds fine. I have enough parts complete a grip of boards but only 2 boards where I should have gotten more boards!! then I can do a shoot-out on what configuration is the best.