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Basic Sound Card project?

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johnb47
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Posted on Friday, 24 October, 2008 - 07:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi.

My first post here.

Has there ever been a basic sound card project, either in Practical Electronics or elsewhere?

I mean a really basic setup, ie a two channel line input stage going through an ADC (or two ADCs?), then whatever circuitry/software is needed to allow this to be connected to a laptop via USB2. The purpose would be to allow a turntable, CD Player or Tape deck to be connected (after the pre amp stage of a amplifier) to the laptops Digital Audio Software (DAW).

Yes, I know you can buy this sort of thing but I just thought I would have fun building my own, without all the bells and whistles that tend to come with proprietary units (pre amps on the inputs, level control, mic sockets, midi, line level outputs). Also, if the design was really as basic as the one I've described, I might be able to choose really top notch ADCs for real audio quality while still keeping the overall price low.

Any ideas anyone?

Thanks.
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mikehibbett
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Posted on Friday, 24 October, 2008 - 07:53 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>Yes, I know you can buy this sort of thing but I just thought I would have fun building my own

If I had a penny for the number of times I have said this to people. I'm thinking of having some T-shirts made :o)
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steerpike
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Posted on Friday, 24 October, 2008 - 09:52 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

There is a TI chip that pretty much does it all for you. The number of it escapes me - i could look it up.
It's an analogue-to-usb or SPDIF-to-usb all in one SMIC. Software drivers free from TI website.
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johnb47
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Posted on Friday, 24 October, 2008 - 11:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks.

Mike - my version of your sentiment is, when my wife say's "we should get someone to do X or Y for us, I'd say " but I could do that". Hmmm.

steerpike - if you could get more info, i'd appreciate it. I don't now where this is going, so only if you have the time.

I did Google for some of the words/phrases you used but it got a bit heavy. I'm pretty practical but not highly techie, so I need some hand holding for this.

Thanks for the feedback.
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steerpike
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Posted on Saturday, 25 October, 2008 - 10:27 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Texas Instruments PCM2900 and PCM2902 are the ones I got hold of. (TI sent me a pack of samples)

The datasheets and application notes ought to be downloadable from their web pages.

They might be regarded as obsolete by now (2 years is a long life for a modern IC, it seems) but no doubt they will have a similar replacement.
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johnb47
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Posted on Sunday, 26 October, 2008 - 02:35 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks steerpike.

That's the first step.

I'll have a good look at TIs website and Google for related stuff but I wonder if I could find an actual circuit design using one of these things? I'm stumped otherwise - I just haven't got the design capabilities.

Perhaps some of the docs you mention will help (application notes?).

Thanks again.
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steerpike
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Posted on Sunday, 26 October, 2008 - 03:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

There's not a lot to it - a bit of audio bufferring is all that you need to think out for yourself. The TI chip does pretty much everything. The IC1 is just a voltage reference - even simpler circuit if you use an extenal power supply.
(my upload pic is on its side because this BBS doesn't accept 'wide' images)


(Message edited by steerpike on 26 October, 2008)
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johnb47
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Posted on Sunday, 26 October, 2008 - 04:43 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks. I'll get back to you if I think this is worth my progressing it. So many questions. i.e what are the little LPF Amps - would linking the inputs of those to a hi fi amp take care of that? Where are the USB connections - is that D+ and D- VBUS and GND? Where do the connections go that are indicated by an arrow (the arrows that are not filled in - do they all go to the USB GND connection?). Just interested in the practical side of things. Also, where would I actually buy one of these, how much would it cost and am I likely to build something that was better than I could buy for the price? - I see that it's a USB1.1 device for a start and most sound cards are now USB2. It occurred to me that perhaps a lot of proprietary USB sound cards would have something like this at their heart.
Thanks again.
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steerpike
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Posted on Monday, 27 October, 2008 - 01:13 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The hollow arrows are signal ground - all are connected together at the power supply.
USB plug is D+ D- Vbus and Gnd, yes.

The LPF-amp would be an ordinary hi-fi pre-amp, or headphone amp etc.
LPF is a Low-pass-filter, probably you can get away with just a simple capacitor, to filter out any residual digital noise.

USB2 is faster, but the speed of 1.1 is still 12MB/s, which is plenty fast enough for stereo audio.

WHERE to buy is so dependant on where you are. I got mine direct from TI in the US by mail. Best bet is to try your local TI agent, usually they will give a hobbyist / student one or two chips for free.

I DO think a self-built - IF you do it right - would be considerably better than the nasty junky computer audio peripherals that are commonly sold.
But then if the end result is to be some over compressed MP3, you may never notice the difference.

You can get *really good* sound cards, but they cost about as much a most people spend on the whole PC.
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johnb47
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Posted on Monday, 27 October, 2008 - 04:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for the excellent help with this. I'll try and find a source for one of these (I'm in the UK) before I decide whether to try building a circuit.

As I said before, if I do decide to proceed, I'll get back to you on this thread. There are bound to be many more questions.

Thanks again.
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steerpike
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Posted on Tuesday, 28 October, 2008 - 08:37 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was lazy, bought the parts and never used them (why is this the case with SO many projects???).
If you find the part & want to proceed, let me know, and I'll restart, maybe we proceed side by side.
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hamar
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Posted on Wednesday, 29 October, 2008 - 11:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Sounds like a good project to be published, I,ve been building some mini monitor powered speakers, and researching commercial DAC's units to drive them, expensive. Something like this sounds ideal.
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johnb47
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Posted on Thursday, 30 October, 2008 - 06:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for the offer steerpike. I would need help for sure. Actually I've gone onto the TI US website and managed to get them to send me a couple of free samples. That seems curious to me - I didn't lie to them or anything, I just filled in the form saying I was a hobbyist and I received an Email shortly afterwards saying they've shipped them.

Provided I can source the additional components and clarify some areas still confusing (eg there seems to be an external clock source on the diagram but I thought the chip had it's own internal one), I might well go ahead and build one of these.

I'll keep you posted with developments.
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steerpike
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Posted on Thursday, 30 October, 2008 - 07:08 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thats good news! The PCM2900/PCM2902 I thougt may have been superseded, but since you have got those, the other parts will be very easy to get.

The chip has a quartz crystal as a clock reference, as with almost every microprocessor. Is that what you are referring to ?
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johnb47
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Posted on Friday, 31 October, 2008 - 05:57 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi. I just got back from visiting friends and found that FedX had delivered two ICs, a PCM2900 and a 2904 (I'm not sure what bthe difference between them is). Very quick. I haven't really got an excuse now not to build.

Re the clock. What has me puzzled is the little symbol between tags 20 and 21 of IC in the circuit you posted, marked 12MHz. Is that an external component? I'm sure I'll have lots more questions but I need to get them all together for one post. I'll get back to you soon.

Cheers.
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steerpike
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Posted on Friday, 31 October, 2008 - 07:16 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Pin 20-21, connected by a resistor and a quartz crystal. Yes that's an external component.
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johnb47
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Posted on Saturday, 01 November, 2008 - 10:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks.

I've taken some time to look through the datasheet for the 2904 and I've realised that the 'typical circuit connexion' diagrams are just that - typical. I would need an actual circuit diagram, i.e with a clear indication of what components to use before I could start.

For example, the datasheet says things like:

"C5, C6: 10 pF to 33 pF (depending on crystal resonator)
C9, C10, C11, C12: The capacitance may vary depending on design.
IC1 : REG103xA-A (TI) or equivalent. Analog performance may vary depending on IC1."

I don't have anything near the required knowledge to be able to make decisions about things like that.

So, are you able/willing to effectively put together a project for this?

Also, now that I've looked at the ICs, I see that they are really tiny. I did some research and discovered that I'll need a '28 pin SSOP adapter' to allow me to use the IC on a typical strip board. I'll still have to be really careful when soldering the IC's tags - unless there is a different option, some sort of clip arrangement i.e where the IC is dry mounted on something like an IC socket that expands the connections to allow the socket to be soldered on a strip board?

As you can see, I'm pretty green but I'm learning fast.

Cheers.
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mikehibbett
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Posted on Saturday, 01 November, 2008 - 10:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

HAve a look here:

http://focus.ti.com.cn/cn/lit/ug/sleu024a/sleu024a.pdf

Might give you some more info.
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johnb47
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Posted on Sunday, 02 November, 2008 - 12:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks. Lots more info there - presumably everything you'd need to build something.

I suppose the demonstration kit is no longer available? I might try searching the TI site.

Any advice on mounting such small ICs as these? Is the adapter I mentioned the only option if I use a standard strip board?

Thanks again.
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johnb47
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Posted on Sunday, 02 November, 2008 - 01:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Update: I found the dem kit on the TI website. $299! Looks like I'll be doing it the hard way.

Also, someone else kindly posted a link to videos on good soldering techniques, including ones covering small ICs.
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steerpike
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Posted on Sunday, 02 November, 2008 - 07:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was/am going to solder my ICs onto a conventional 'big' DIP IC socket or header, so I could plug & unplug them, as well as use a more conventional through-hole circuit board.
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johnb47
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Posted on Sunday, 02 November, 2008 - 08:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks.

Do you mean you will solder the IC to something like the SSOP adapter I mentioned earlier, then solder that to a standard size header that will plug/unplug onto a socket soldered onto the board? I'm wondering how that would be done.

I've found this type of adapter:

http://www.futurlec.com/SMD_Adapters.shtml

and this type of socket:

http://www.futurlec.com/SockIC.shtml

How would you use these (plus other items?) to achieve what you mean?

Cheers.

(Message edited by JohnB47 on 02 November, 2008)
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johnb47
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Posted on Sunday, 02 November, 2008 - 08:49 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hang on.

I've just found this:
http://www.futurlec.com/Connectors.shtml

So, you solder the IC to the adapter, then solder two strips of header under the adapter, then this combination can be pluged/unplugged into a standard socket soldered onto the board.

Is that it?
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steerpike
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Posted on Monday, 03 November, 2008 - 12:13 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)


quote:

So, you solder the IC to the adapter, then solder two strips of header under the adapter, then this combination can be pluged/unplugged into a standard socket soldered onto the board.




Thats EXACTLY how it's done
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johnb47
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Posted on Monday, 03 November, 2008 - 03:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Great. That's one small question answered.

Looking at the document that mikehebbett mentioned, I see that there are circuit board top and bottom views. I was thinking of using a standard strip board but is there a way I could use these diagrams to produce a 'proper' circuit board - using sort of etching techniques? Can anyone post a link to something that will explain the process? I'll Google myself too. It's another whole area that I need to educate myself on.

Thanks.
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steerpike
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Posted on Monday, 03 November, 2008 - 05:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I'm about to create one - a tiny PCB to convert SMS to DIP, so I'll pot the artwork when i'm done.

(Message edited by steerpike on 03 November, 2008)
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mikehibbett
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Posted on Saturday, 08 November, 2008 - 06:36 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just found this. Might interest someone as an alternative.

http://www.raccoonrezcats.com/soundcard.html
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johnb47
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Posted on Sunday, 09 November, 2008 - 08:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks.

I'm pretty well resigned to go with the current proposals (PCM2900) but this looks interesting too.

I'm preparing some questions on the circuit I'm proposing to follow (from your earlier post). Will post them soon.

Cheers.
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johnb47
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Posted on Tuesday, 11 November, 2008 - 04:50 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Me again.

I'm going to try building a Sound Card based on the diagram shown below, as shown in the document posted by mikehibbett. I'm trying to insert a jpeg here - hope it works. By the way, anyone know how to best insert a diagram taken from a pdf document? I did a very crude Print Screen then pasted it into a blank Photoshop doc and created a web sized jpeg that way - poor quality I think.

Anyway, I'm wondering about the Schottky diode mentioned (RB520S-30) - I can't seem to source this anywhere. Can anyone suggest a retailer, or maybe an equivalent? Like some of these perhaps?

http://www.futurlec.com/cgi-bin/search/search.cgi

I have lots of other questions but let's see how this one goes first. Thanks
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johnb47
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Posted on Tuesday, 11 November, 2008 - 04:57 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Sorry - the futurelec link I gave strangely doesn't work. It's supposed to be the results of searching for 'schottky' on futurelec.com Then I couldn't edit the post. Anyway, I hope you get the idea.
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amr_bekhit
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Posted on Tuesday, 11 November, 2008 - 05:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi John,

Have a look at this Farnell part: http://uk.farnell.com/rohm/rb520s-40te61/diode-schottky/dp/1525501

It's exactly the same diode except it has a larger maximum reverse voltage.

--Amr
Helm PCB - My personal site.
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johnb47
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Posted on Tuesday, 11 November, 2008 - 09:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks. The site you linked is currently down for maintenance so I can't see what you mean. For now, how can you tell that "It's exactly the same diode"? Just wondering how to identify equivalents. Also, is the fact that it has a larger reverse voltage a problem? Thanks again.
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steerpike
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Posted on Tuesday, 11 November, 2008 - 10:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I think ANY Schottky diode will work there. The main point is the forward voltage drop is much lower than that of a silicon diode. You might even be able to use a germanium diode.
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johnb47
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Posted on Tuesday, 11 November, 2008 - 10:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks. Perhaps I'll go for a schottky diode from my chosen supplier. More questions to follow.
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amr_bekhit
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Posted on Tuesday, 11 November, 2008 - 10:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

When I compared the diode on the site to the one you were looking for I compared the Absolute Maximum Ratings (AMRs) to make sure the replacement at least met the AMRs of the old one. Since the replacement diode is actually made by the same company as the old one and has the same part number (except for the suffix - RB520S-40 vs RB520S-30) and has the same package, I assumed they'd be (for all practical purposes) identical.
Helm PCB - My personal site.
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johnb47
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Posted on Wednesday, 12 November, 2008 - 12:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

That seems very logical to me. Thanks for explaining.
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johnb47
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Posted on Wednesday, 12 November, 2008 - 08:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi. Another question for you. I want to see if I can do away with the output/input OP Amps in the circuit I attached earlier. I believe that I can use my HiFi amps PreAmp to perform both of these functions, controlled by a switch on my Amp. If we assume that that is possible, would it be OK to simply connect PCM2900 pins 15/16 (VoutR and VoutL) through the 10 microF/16V elect capacitors directly to the output mini jack tip/ring? Similarly to connect pins 12 and 13 via the same value capacitors directly to the input mini jack tip/ring? (I might actually use RCA connectors instead of mini jack). Would I need any additional circuitry? My reasons? Well, to keep the circuit simple and also to utilise my HiFi Amps higher quality PreAmp (Audiolab 8000A), compared to what I presume would be fairly LoFi OpAmps. Thanks.

Edit: I suppose it all depends if the output direct from the PCM2900 is high enough to be fed directly into a Hi Fi preamp. Any views on that?

(Message edited by JohnB47 on 12 November, 2008)
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johnb47
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Posted on Wednesday, 12 November, 2008 - 08:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Oh, another question. This one concerns the link or jumper block (I don't know the correct terminology) called CN002, at top centre of the diagram posted earlier. I'm presuming that I will insert links to connect through the SEL1, SEL0 and REG-Vcc leads but I believe the S/PDIF functionality is not available on the PCM2900, so should I insert the links for S/PDIF Out and S/PDIF In, thereby grounding them? Or should I leave those links out - or not even bother to connect pins 24 and 25 of the PCM2900 to the link block in the first place? Thanks.
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steerpike
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Posted on Wednesday, 12 November, 2008 - 11:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I think you need to retain the on-board op-amps; they are acting as anti-aliasing filters, and recovery filters, on the input, and output repectively. Without them you will get nasty sampling artefacts. You could search out a better op-amp, but I suspect TI have recommended ones that are a close performance match to their D/A converter.
I would probably use NE5534AN or the dual NE5532 in that position - it's my favourite audio chip, but there are people that have different tastes in the 'sound' of op-amps, so that's only my taste preference.

RCA connecters are a definite performance upgrade over those nasty 3.5mm phone plugs!

On the 2900, pin 24 *must* be grounded, 25 *must* be unconnected. So that determines what the SPDIF pins on the CN002 header must be connected to.
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johnb47
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Posted on Thursday, 13 November, 2008 - 11:57 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks, steerpike, for the clear reply. I'll go with the op-amp specified. I'll also go with your advice re pins 24 and 25. Now I'm wondering what is the purpose of the CN002 header. I'm presuming that it's intended to be used in a simple link arrangement, where, for example, the OUT (pin2) of the Regulator is linked to the anode of the schottky diode. But why have a link - why not just hard wire it through? Is it intended as a test point? If not, when would you want to remove the link?

Thanks for the help. I'm slowly putting together a stripboard layout while I order the various parts I'll need - it's my first time so it's a real brain teaser, but facinating at the same time. It will look a real pigs breakfast but hopefully it'll work.
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steerpike
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Posted on Thursday, 13 November, 2008 - 09:19 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The right-most jumper of CN002 is in reference to this:
"A 3.3-V IC regulator is mounted on the board to provide power for analog circuitry and optionally for the codec."

This jumper lets the codec be powered either from the discrete 3.3v regulator chip, or from the PCM2900's own internal voltage reference. HOW the two differ in performance, the notes don't seem to say, but since its an evaluation board, presumably you're supposed to 'evaluate' it yourself!

The other jumpers are there for the PCM2902 - which interprets the status of pins 24 and 25 to enable or disable the SPDIF data stream.

And power and ground on this header may be useful if you want to use a Toslink fibre-optic cable to an amplifier or CD player; the Toslink interface/plug needs a separate power source to power its IR diode.
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johnb47
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Posted on Friday, 14 November, 2008 - 10:40 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks again steerpike, I understand.

So the bottom line is that, if I was to wire this header as per the circuit diagram, I would have every link in place except the left hand one (S/PDIF Out).

My next question will be about how to choose a USB socket and how to work out which tags to connect each of the four wires to. I'll do some investigating myself first, then will ask for help if I need it.

Cheers.
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steerpike
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Posted on Friday, 14 November, 2008 - 12:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

>>> would have every link in place except the left hand one (S/PDIF Out).

Yes, I'd agree there.
MAYBE "REG-Vcc" open as well - you might want to experiment with the performance.

USB sockets come in different flavours depending on whether they are host or client ends. And then there are different sizes. If you have something like a USB scanner or printer, look at, and buy, the type of socket on that (NOT the type of socket on your computer)

(Cameras and music players seem to have idiotically tiny usb sockets that no adult can work with. Give me a bakelite McMurdo or Bulgin plug anyday!)

There are lots of web pages that show USB pinouts and socket styles.
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johnb47
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Posted on Friday, 14 November, 2008 - 04:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

"MAYBE "REG-Vcc" open as well - you might want to experiment with the performance." Yes, interesting idea.

I think the USB socket I need is called a type B - sort of square, rather than rectanular. I'm sure I'll find something suitable. The ones I've seen so far fit directly on the pcb. That might suit but it may be more flexible to have one that somehow fits on the side of the case and is simply wired to the pcb.

I agree with you about tiny usb sockets. I think the plethora of different leads/plugs/sockets that largely do the same thing is mainly a marketing ploy. But then I'm an old cynic.
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steerpike
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Posted on Friday, 14 November, 2008 - 09:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

My AKG headphones came with a plug on them (4-pin XLR) that is bigger than a whole mp3 player. That's my sort of plug - it'll last for 50 years no matter how often I plug/unplug it. And I can step on it by accident - no harm done.

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