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PCM2706 USB DAC

post #1 of 49
Thread Starter 
Hello!

I wanna try to build this same DAC as is on this website that you may already know:


http://electronics-diy.com/PCM2706_USB_Soundcard.php
dphones

My question is that on the schematics it shows an inductor connected to the Vbus on the USB connector but on the part list it is not said which inductor it is. Any ideas of which one should I use?
post #2 of 49

This is almost certainly just a ferrite bead for EMI suppression. I looked at the PCM2706 datasheet, there's no inductor on the example circuits. You can probably omit it without too much of a problem, just put in a short. I see the website with the DAC schematic has a couple of beads:- http://electronics-diy.com/store.php?sel=ferrite_beads one up to 40, one 40-200MHz. You could use both in series, just thread them on a bit of thick wire and make it U-shaped like a staple.

 

Or you can clamp one on the USB cable, probably actually of more use since anything on the power wire will get on all the other wires if they run any distance in parallel.

 

w

post #3 of 49
Thread Starter 

Thank you, wakibaki! Your explanation was really helpful. I'm just gonna get the two of those that are available on the website and then I see what I'll do. You recomended clamping one on the USB cable, but for that I need to cut the USB cable and put a bead on each cable inside or just put one around the black USB cable itself? 

 

I have one other question regarding the PCB schematics on that same website. The USB type B I bought has 6 pins and the heaphone female jack has 5. According to the draw on top of the website all 6 pins of the USB should be soldered and only 3 of the headphone jack. I can understand why only 3 are connected but then when I look down to the PCB schematics I see 5 holes on the headphone place and only 2 on the USB place. Am I missing something here?

 

Don't know if I'm making a lot of sense :)

post #4 of 49
Quote:
Originally Posted by scanferr View Post
 

You recomended clamping one on the USB cable, but for that I need to cut the USB cable and put a bead on each cable inside or just put one around the black USB cable itself? 

 

You can get a split ferrite intended to go round a cable, they usually have a plastic housing that is held together with screws. You open it up, put the cable in and close it up again.

 

You can also use a toroid (ring) ferrite that is big enough for the USB plug to pass through, or pass the whole cable through before putting the USB plug on. If the ferrite is big and there is enough cable, you can put multiple turns of cable through it, which increases the effect.

 

Quote:

Originally Posted by scanferr View Post
 

I have one other question regarding the PCB schematics on that same website. The USB type B I bought has 6 pins and the heaphone female jack has 5. According to the draw on top of the website all 6 pins of the USB should be soldered and only 3 of the headphone jack. I can understand why only 3 are connected but then when I look down to the PCB schematics I see 5 holes on the headphone place and only 2 on the USB place. Am I missing something here?

All 5 pins of the headphone socket are actually connected, there is a tie between the LHS and RHS pins on the top foil pattern.

 

Pins 5 and 6 of the USB connector are partly intended for securing the connector shroud to the PCB and are also connected to ground to improve the effectiveness of the shrouding.

 

The PCB foil layouts are flipped with respect to one another. The top one on the page shows the top of the PCB, and 2 connections going to the upper 2 USB connections. This foil pattern is a mirror image and the USB port is at the opposite end from what is shown in the photo.

 

The lower pattern shows the bottom layer of the PCB. It is NOT mirror-imaged, and it shows 2 connections going to the lower 2 pins on the USB connector.

 

They should really have mentioned the mirror-imaging. The top foil pattern is mirror imaged because is intended for home etching, so that a laser print on transparency (or paper for toner-transfer) has the ink against the (resist-coated in the case of transparency) PCB.

 

w

post #5 of 49
Thread Starter 

Thanks for the explanation. I understood it now!

 

But I still have a question about the connectors. These are the connectors I bought (and I don't think they had different ones):

 

 

 

 

The USB I understood, but the headphone jack I didn't. Comparing the connector I have and the PCB holes, the pins displacement don't match. Is there any workaround for this?

Also, instead of buying SMD components I bought normal ones, is there any difference apart from having to make more holes on the PCB?

 

Sorry if I'm bothering you with my "noobness".

post #6 of 49

They come in different styles, there's no workaround.

 

Going by the pictures, I think you want one like this... ...although I have 2 different types of 5-pin 3.5mm headphone sockets right here.

 

http://www.ebay.com/itm/5-Pcs-3-5mm-5-Pin-Stereo-Enclosed-Socket-Headphone-Jack-PCB-Mount-Connectors-/360630235972?pt=US_Audio_Cables_Adapters&hash=item53f73cb344

 

This is the other style...   http://www.ebay.com/itm/10X-5PIN-3-5mm-Stereo-Socket-Headphones-Jack-PCB-Panel-Mount-HY-317C-15-12-10mm-/160976938518?pt=US_Audio_Cables_Adapters&hash=item257af92616

 

You can surface mount leaded components by bending the leads around underneath until they contact the pads, if there's enough room.

 

w


Edited by wakibaki - 9/17/13 at 4:49pm
post #7 of 49
Thread Starter 

I'll need to get one of those you mentioned then, with the 5 pins in a straight line.

And it shouldn't be that hard then to solder the leaded components, just by bending the leads a bit, like you said. Next step is getting the PCB from somewhere as I don't know any place here that makes them and if they do online is quite expensive...

 

Thanks, wakibaki!

post #8 of 49

It's not too difficult to make your own PCB, if you can get access to a laser printer. It's best to use the kind of paper recommended, but it is possible to use regular printer paper if you have to use a printer in a library or school, and you cannot put in your own paper. You will have to take a lot of care if using regular paper and go very slowly removing it and then repair any gaps in the toner with an etch-resist pen. You can get an etch-resist pen from ebay. 

 

If you google 'toner transfer' you will see many articles about using the toner transfer method for making PCBs, in many cases suggesting using commonly available chemicals, hydrochloric (muriatic) acid and hydrogen peroxide. You have to be careful because these chemicals can be dangerous (skin burns, encourage fires), but the total cost is quite small.

 

You need to take care that the prints you make with the laser printer are exactly the right size by comparing them to the printout (from the PDF on the project website). You can change the size of the printout in software, sometimes the printer stretches the image in the horizontal or vertical, which can make a difference for the surface mount PCM2706 in particular.

 

I have drilled PCBs with a regular, full-size pillar drill. If you need to use a drill which is too small for the chuck, you can wrap the shank by rolling a strip of thin paper round it to make it thicker, with a bit of care the drill will not run off center to the point where you cannot use it.

 

w

post #9 of 49

Here is a thread where we were talking about toner transfer.

 

 

post #10 of 49
Thread Starter 

That proccess seems way faster, Avro. Many thanks!

 

Still have a couple of questions:

 

1- On the website I'm following they give the schematics for both sides of the PCB. But do I really need to use both or one side is enough? If so, can I, for example, print one side and then drill the holes on it and then print the other side? This way I would know that the holes would match and nothing would be out of place, because it seems to me that I need to use both sides otherwise theres free connections there.

 

2- I've been searching and most people use ferric chloride. Is it ok to use?

post #11 of 49

 

1.You need both sides

 

Sometimes I just color one corner of the board black, on the outside edge

so I can remember which way it goes.

I have never done a double sided board by toner transfer.

I usually use photo etching.

A thread about that is here.

 

2. Yes 

post #12 of 49
Thread Starter 

But in both processes isn't it a bit hard to match the holes and all the circuit on both sides? I'll try to buy the PCB tomorrow and see if they have double sided PCB. Will also try to print the schematics in a paper shop.

 

Maybe I will try toner transfer one side and remove the paper but not the ink. Then I drill the holes and toner transfer the other side. After this I use the etching solution. Does it sound bad?

post #13 of 49

 

What you are talking about are known as "registration marks".

They can be anything from a couple of holes drilled in the board

to marks on your artwork and board.

 

I had the words "top" and "bottom" in the corners of my artwork

and colored the edge of the board where the words should be.

I also cut the board the exact size it should be and also had

lines on my artwork the exact size of the board. It's kinda scary

the first time you try it...and you might get it wrong once or

twice, but it's pretty easy once you get the hang of it.

post #14 of 49
Thread Starter 

I will try to get it done right, will try to buy tomorrow 2 PCB's big enough for the job : )

 

Also, I have one question regarding the paper. Which one should I use? Normal photo paper (glossy)?

post #15 of 49

Dextrin paper is the best to use.

You can even make your own.

There are many articles on how to do it.

Here is one.

 

Fred_Fred2004 uses toner transfer, I switched

to Photo etching then OSHPark.

You can check out what he uses in the toner

transfer thread. Maybe he will even chime in

in this thread (hint, hint).

 

OSHPark has good quality and is

dirt cheap for prototyping or small

quantities.

 

Good luck with your project!

We'd love to see the progress.

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