Welcome Guest! To enable all features please Login or Register.

Notification

Icon
Error

markus_b
#1 Posted : Sunday, May 08, 2011 5:24:20 PM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

Hello everybody,

I am new to DIY audio (but I have an embedded systems background). I have some general questions about putting
Twisted Pear components together. I already took a look this PDF with some basics that was posted by one of the forum's users but it didn't help me much as it is focussed only on BuffaloII DAC based setups. I would appreciate if someone could give me a
starting point for my DAC/preamp setup which should fulfill following requirements:

Must:
- At least one optical and coxial input to chose from
- Possibility to insert an MCU board (BeagleBoard) into the signal chain for audio processing via I2S intefaces
- Not too much space requirement (my case has only 8x8" space available). Are there any heat/noise issues with stacking Twisted Pear boards by a distance of ~1-2"
- Unbalanced RCA output (since my current equipment is not balanced)
- A good value/cost/space ratio (e.g., Opus vs. BuffaloII?, output stages vs. no output stages?, dual mono vs. stereo DAC?)

Nice to have:
- 2 optical and 2 coxial inputs to chose from
- SPDIF output of the processed I2S data

Controlling the components will be done by the BeagleBoard and another ATMega MCU. So there is no need for other control components.
I am pretty unsure about the power supplies and also the output stages. How many transformers/power supplies do I need? Would it be possible to drive the BeagleBoard with a shared power supply together with the other digial audio boards (it requires 5V at a max. current of 1.6A) Do I need an output stage before/after the Ballsie Lite module?

I read somewhere that feeding the DACs via BeagleBoard I2S interface is possible and it has been done by someone (Russ White?) but it is seems to be somehow tricky. Unfortunately, I could not find out what the tricky part actually is. Is there a problem with different voltage levels? Maybe someone can provide some more details on that issue?

I know I have many questions but it would be really kind if someone could answer at least some of them.
Thanks in advance!

Best regards,
Markus
iprebeg
#2 Posted : Monday, May 09, 2011 4:13:54 AM(UTC)
iprebeg

Rank: Member

Groups: Member
Joined: 5/9/2011(UTC)
Posts: 1

Hi dude, how far did you get?

I'm trying to do the same with Gumstix Overo and TwistedPear...
Have you done any pin muxing?
Which pins did you connect DAC to?
markus_b
#3 Posted : Monday, May 09, 2011 6:28:22 AM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

I have not even ordered the parts at Twisted Pear Audio yet since I am still in the planning phase.
In order to be sure that everything will work together I need a starting point for a configuration that fits my needs.

Concerning the BeagleBoard I2S interfaces: I took at look at the manual to see which pins are available
at the BB's expansion header. The TI OMAP MCU provides three McBSP controllers for I2S interfacing.
One is hard wired to the audio codec on the BB and thus cannot be used. Regarding the other two McBSPs
it is not possible to mux all pins of both controllers to the expansion header at the same time.
But as far as I know you only need three pins for a stereo I2S transmission: CLOCK, DATA and DATA_SELECT.
Those can be muxed to the expansion header without conflicts. Hence, I think it should be possible
to have one input and one output I2S port available for the audio processing.

But I have some doubts about this because I heard it should be tricky to connect the DAC. But I don't know why exactly.
How far did you get?
LeonvB
#4 Posted : Monday, May 09, 2011 11:14:38 AM(UTC)
LeonvB

Rank: Member

Groups: Member
Joined: 5/23/2010(UTC)
Posts: 672
Location: Netherlands

Thanks: 2 times
Was thanked: 39 time(s) in 36 post(s)
Actually most of your questions are already answered in the integration guide. I suggest reading it. The basic setup remains the same, as are the parts required. In your setup you just replace the Volumite with the I2C header of the Beagleboard, and feed it I2S from there also like you would do with a Mux.
Feeding the Beagle from the same PSU as the DAC might not be a good idea. It might introduce noise into the circuit. In any case the default PSU you would use for the DAC (Placid) isn't capable of powering the Beagleboard, while the normal PSUs use for a Beagleboard aren't as clean as a dedicated Placid for the DAC.

The Beagleboard is one of the options I considered as it has I2S/I2C connectivity, and one should be able to get it to work at least up to 192/24. As I understand, using I2S & I2C from the board does require one to hack a bit in the code and recompile to get it functioning (hence the tricky bit).
In the end not having a true dedicated network port (it's USB based) or SATA to connect a HDD/SSD made me look for other options. I'm waiting for the USB interface to be able to hook the DAC to a low power Atom based board which wil also act as a small NAS server.
Note: You will definately want the Beagleboard-XM, as that one has an I2C header and exposes the McBsp2 interface, which offers better buffering.
markus_b
#5 Posted : Tuesday, May 10, 2011 2:43:46 PM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

Thanks LeonvB for your reply. You're right, my questions were partially answered by the PDF guide.

Concerning the BeagleBoard xM: I already own a Rev C4 board and want to use it for that. So unfortunately, BeagleBoard xM is not an option for me. But thank your for that hint!
But if 96/24 via McBSP1/3 is possible, I'm happy. If the tricky part is just related to the software then I'm sure I will find a solution.

In order to make my questions concerning the other parts more concrete I linked a figure at the appendix depicting my currently planned layout of the usable inner area of my enclosure. It's an aluminium profile enclosure with 210*230*80mm usable space (I know it's a little bit small but hopefully it will do for me).

Some questions:
-Does anyone see a general problem with combination of these components this way (e.g. stacking of the IVY3+Buffalo+4:1MUX-RECEIVER)?
-I saw some discussions concerning issues with stacking transformers but without a convincing statement saying it is or is not a problem. So once again, is it a problem to put the small transformer on top of the bigger one? Do I have to put something inbetween to make magnetic interaction of both as small as possible?
-The user interface and control of components will be done by the BeagleBoard and another custom designed ATmega board mounted to the front panel. Currently, there is no power supply included in this layout for both. Either I will find some place on the front panel for that or it will be external (not so nice).

Thanks for your answers!


markus_b
#6 Posted : Thursday, May 12, 2011 3:00:50 PM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

I've done some updates concerning my planned layout (see attached figure). In order to make it more clear which components shall be interconnected I've drawn some lines between them. The major difference is the vertical mounting of the BeagleBoard which saves a lot of space so I can avoid stacking transformers. Morerover, I have some more space for a sepparate power supply to drive my BeagleBoard and the front mounted board with ATmega, LCD, IR, incremental encoder etc.

However, I would still appreciate if someone could have a quick look at my setup. Are there any concerns doing it this way?
What about putting the mux-receiver board between the Buffalo2 and the IVY3? I thought it would make sense because of the identical dimensions and for sake of short I2S cables. Moreover, the Buffalo2 needs some more headroom due to the AVCC module, right?

For wiring of the components I plan to use follwing bulk cable from SommerCable.com since I think very good shielded cables could be important when putting them so close together.
SPDIF/I2S/I2C: http://www.sommercable.c...terware/2__520_0051.html
Balanced/Unbalanced phono signals: http://www.sommercable.c...terware/2__800_0104.html
Power: http://www.sommercable.c...re/2__700_0101_0315.html

BTW, do you think it could be necessary to put any iron sheets for shielding anywhere?

Concerning the process of ordering in general. Some products are regularly out of stock and the Buffalo2 needs to be even pre-ordered ,right? How should I proceed if I want to place an order for all my required components and to get them in a single shipment?



Cheers,
Markus
Russ White
#7 Posted : Thursday, May 12, 2011 3:30:03 PM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,569
Location: Nashville, TN

Thanks: 20 times
Was thanked: 64 time(s) in 58 post(s)
I think your plan is sound. I have used the beagleboard to do I2S output with no issues. But that was long ago, and honestly I don't even remember much of what I did. This is one of those thing you just have to take a step at a time and figure out each bit one by one.
LeonvB
#8 Posted : Thursday, May 12, 2011 3:33:13 PM(UTC)
LeonvB

Rank: Member

Groups: Member
Joined: 5/23/2010(UTC)
Posts: 672
Location: Netherlands

Thanks: 2 times
Was thanked: 39 time(s) in 36 post(s)
Quote:
What about putting the mux-receiver board between the Buffalo2 and the IVY3? I

The BII is better stacked on top of the IVY. Keeping those lines short and of equal length is even more important than short I2S cables. Those can be 10cm easily.
Side mounting the Mux could be considered.
Russ White
#9 Posted : Thursday, May 12, 2011 3:39:48 PM(UTC)
Russ White

Rank: Administration

Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,569
Location: Nashville, TN

Thanks: 20 times
Was thanked: 64 time(s) in 58 post(s)
I would probably go MUX/IVY/Buf from bottom to top, but there are other ways that would work just as well.
thomaspf
#10 Posted : Sunday, May 15, 2011 2:58:19 PM(UTC)
thomaspf

Rank: Member

Groups: Member
Joined: 12/24/2008(UTC)
Posts: 101
Location: Seattle, WA

I had looked at a BeagleBoard a while back to add an Ethernet port to my latest Buffalo DAC. Somehow digital audio did not seem to be a strength or focus of that board.

I recently came across this board

i.MX53 Quick Start Development Board

which appears to have a direct S/PDIF output. It is pretty new so there are not many success stories. The S/PDIF lines are only available on the extension connector togehter with two I2C ports. It also has a USB client port so with the right software you should be able to turn this into a DLNA renderer, straight CIFS/SMB client as well as a USB sound card device.

I am tempted to buy one to play with it.

Cheers

Thomas
thomaspf
#11 Posted : Sunday, May 15, 2011 3:41:37 PM(UTC)
thomaspf

Rank: Member

Groups: Member
Joined: 12/24/2008(UTC)
Posts: 101
Location: Seattle, WA

However, after downloading and reading the Linux package documentation I learned that the S/PDIF driver for the board is limited

21.2 S/PDIF Tx Driver

The S/PDIF Tx driver supports the following features:
• 32, 44.1 and 48 KHz sample rates. MX53 START board only support in-accurate 48KHz sample rate.

Which makes me wonder.

Russ, what sample rate did you manage to get with the BeagleBoard?

Cheers

Thomas
markus_b
#12 Posted : Sunday, May 15, 2011 4:15:46 PM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

Thanks to everybody for comments!

@Thomas:
The Freescale board you linked seems to be very promising for audio applications. Maybe the BeagleBoard is not the ideal board for that kind of stuff but since Russ said it is possible and I already own a BB I will at least try to use it. Once I have gathered some experience I will share my knowledge about potential issues, limitations with the BB etc. here.

About the ordering. There are some items I need that are out of stock:
-Buffalo2 DAC board
-IVY3 board
-Mux/Receiver board

I would like to place an order with my complete items list in order to receive them in a single shipment when all items are available.
It's not about time (okay, it would be nice to know at least approximately when they will be probably back in stock).
Can anyone tell me how to proceed?

BTW, is there anyone from Germany who has some recent experiences with customs and taxes applied when ordering electronic parts and DIY kits from US? How much do I have to expect to be added to the price calculated by the shopping cart. I used the forum search but could not find details on that.

Cheers,
Markus




LeonvB
#13 Posted : Sunday, May 15, 2011 9:54:01 PM(UTC)
LeonvB

Rank: Member

Groups: Member
Joined: 5/23/2010(UTC)
Posts: 672
Location: Netherlands

Thanks: 2 times
Was thanked: 39 time(s) in 36 post(s)
Both the Beagle and the Freescale board have I2C and I2S output. Exactly what you need for volume control and streaming data to the DAC. The Freescale board does have both outputs, but they are only available on the external connector which would require one to build a daughterboard to gain access. The original Beagle did not have the required pins connected to an external port, but the XM does, and it's a much simpler connector. Some developers have had the beagle running 24/192, but it requires modification in the source.
markus_b
#14 Posted : Friday, May 20, 2011 2:01:40 PM(UTC)
markus_b

Rank: Member

Groups: Member
Joined: 5/8/2011(UTC)
Posts: 6
Location: Germany

markus_b wrote:

I would like to place an order with my complete items list in order to receive them in a single shipment when all items are available.
It's not about time (okay, it would be nice to know at least approximately when they will be probably back in stock).
Can anyone tell me how to proceed?

BTW, is there anyone from Germany who has some recent experiences with customs and taxes applied when ordering electronic parts and DIY kits from US? How much do I have to expect to be added to the price calculated by the shopping cart. I used the forum search but could not find details on that.


Could anyone please tell me how to place my complete order (including parts currently out of stock)? Or is there a way to get notified when parts are available again? I don't want to check the website for the availability status each day the next weeks. I could not find any information about this on the website.

Thanks,
Markus
Rss Feed  Atom Feed
Users browsing this topic
GuestUser
Forum Jump  
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.