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Old 18th January 2009, 01:07 PM   #1
cdfr is offline cdfr  United States
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Default Music Server with Improved Apple Airport Express

Hi,

I'd like some advice on building a quiet power supply that could deliver 1.2A in 3.3v and 0.7A in 5v.
This is a project to improve the Apple Airport express as an Audio Source. On the web you can find that the Apple Airport Express has been used apparently very successfully to work as a High End wifi audio source. For instance Apertura Rosita is a modified Airport express (http://www.larosita.eu/english/). The modification seems related to the Power supply, the clock and some caps or dig output of the pcm 2705.

My objective is to use the AE Dig output to High end dac (Studer D424) and I can envison a project in 3 phases:
- 1) improving the power supply
- 2) convert the optical output to a SPDIF coax or AES/EBU output (the PCM2705 has SPDIF output)
- 3) Improve the clock (Apparently without trying to make any publicity Selectronic has a good clock)

Phase 1: Power supply.
From what I can gather the AE I have 802.11g has a power switching power supply that can deliver 5V 0.7A and 3.3V 1.2A.
This stock power supply is noisy and a quiet one should improve a lot the Analog and dig out.
Link to a dissected AE: http://www.vonwentzel.net/ABS/Dissec...ess/index.html
I am looking for something more advanced than the std LM317, and I found the two schematics in old magazines (LED):

-Schematic A

- Schematic B

However I have some questions:
- Can any of those schematics with a LM317 and a transistor handle up to 1.2A with 3.3V and 0.7A with 5V?
- What reference of transistor should I use?

Any advice/help on this is welcome.
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Old 18th January 2009, 01:08 PM   #2
cdfr is offline cdfr  United States
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Default With Schematic B

Attaching the Schematic B
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Old 29th January 2009, 08:57 PM   #3
cdfr is offline cdfr  United States
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Default Values for the supply

I think I am going to try schematic B as I think I was able to calculate the right values.
If I understand correctly the schematic B, the transistor is a pre-regulation stage then the IC1 is the regulator.
I plan to use a 30VA Transformer with 2x 9v on the secondary. 1 secondary will be used for the 5v 0.7A and the other for 3.3v 1.21A.
So here are the values that I have calculated:

For 5v 0.7A
PR1 6A 600v
C1 0.1uF63v
4 caps for the rectifier 10nF 63v
C6 4700uF 40v Electrolitic
C7 0.1uF 63v
Z1 Zener 9v1 1.3W
R1 82 Ohm 1/2 Watt
T1 TIP31C
C8 10uF 25v Tantal
C9 1uF 25v Tantal
Rv1 Variable 1KOhm 1/4 Watt (Set at 706 Ohm)
IC1 LM317T
D1 & D2 1N4001
R2 240 Ohm 1/4 Watt
C10 47uF 25v Tantal
C11 1uF 63v

For 3.3v 1.21A
PR1 6A 600v
C1 0.1uF63v
4 caps for the rectifier 10nF 63v
C6 4700uF 40v Electrolitic
C7 0.1uF 63v
Z1 Zener 6v8 1.3W
R1 82 Ohm 1/2 Watt
T1 TIP31C
C8 10uF 25v Tantal
C9 1uF 25v Tantal
Rv1 Variable 1KOhm 1/4 Watt (Set at 386 Ohm)
IC1 LM317T
D1 & D2 1N4001
R2 240 Ohm 1/4 Watt
C10 47uF 25v Tantal
C11 1uF 63v

I have included the schematic in attachment.
I'd appreciate if anybody can confirm that my calculations are correct.

Thanks,

cdfr
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Old 29th January 2009, 10:10 PM   #4
glt is offline glt  United States
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I think the zener pre-regulator is of no use for the regulator. The end noise figure is determined by the regulator which in the case of an LM317 is in order of tens of uV. What DAC are you going to use? (Sorry, I can see what DAC you are planning on using).
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Old 30th January 2009, 06:32 AM   #5
WT is offline WT
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cdfr You are a brave one. Mind to show how you open the airport espress? I did not see how other than break them.

You can try Teddyreg.

http://www.pinkfishmedia.net/forum/s...ad.php?t=39990

http://www.acoustica.org.uk/t/teddyreg.html

Set up voltage like you set up LM317 plus extra couple volts for the gyrator to work. It is explain well in the web. I try it with my dac and like it.
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Old 30th January 2009, 03:18 PM   #6
Pano is offline Pano  United States
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Well it's interesting to know that the AE uses the good old pcm2705.

It's a good chip, but will not do anything over 48Khz - 16 bit.
For the most part our music is 44.1/16, so no worries. But can you force iTunes and/or the OS to send 44.1 and not resample to 48K? Maybe on a Mac or Vista?

Funny to see that the AE, which has a USB port, uses a USB DAC. Hmm.....

Cool project - have fun! I'll be interested to know what you come up with.
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Old 30th January 2009, 10:51 PM   #7
cdfr is offline cdfr  United States
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Hi, thanks for the comments. I'll try to provide some answers...

glt:
what I read was that the pre-regulator with the zener would actually help reducing the noise. I made sense to me on the "Garbage in, Garbage out" principle. If the regulator input is less noisy than its output should be a bit better. But true it does not change the fact that the LM317 will provide at best 80db ripple rejection.

Schematic A which I think is a Sultzer could be better but I am not sure how to calculate the values for 3.3 & 5v as well as not sure if it can wistand 12.A draw.
From looking at the forum, Jung redulator would be even better but there again the complexity increases and I could not find if actually i works for 3.3v.

WT:
You have to break the AE to open it. It is sealed no other way. I cut it with a dremel at the seam between the 2 half. Be careful though not to cut too much. You can find plenty of explanations on how to do that. I don't have a link handy just google it.

Your idea of the Teddyreg seemed appealing, but I read that it is for small current. 1.2A is not small. I do not think it will work well.

panomaniac:
Apparently itunes does not resample PC or Mac. I have used both. The AE I have which is a 802.11g version has the 2705 so as you said limited to 16/44.1. However the newer ones support 802.11n and use a Marvel chip, not sure of their capabilities but supposedly better...

There is a lot of buzz on this rosita and db system modified AE:
http://www.db-system.fr/bd_system/Ai...ee_-_WiFi.html
http://www.homecinema-fr.com/forum/v...747&start=1335
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Old 16th March 2009, 10:55 PM   #8
cdfr is offline cdfr  United States
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Default Update on AE Mod

I just wanted to post some updates on this project.

I completed Phase 1 (Power supply)
- The results were very good on both analog output and surprisingly on the digital output. It gave a sound with more detail, more subjective dynamic and wider soundstage. All in all much better than the original.

I have not started phase 2.

I also completed phase 3
- This turns out to be a big disappointment so far. I am not sure why but removing the built in crystal and replacing it with a low jitter clock (10ps 1ppm; suposedly as good as tent's clock) has not provided any positive results. I cannot compare with phase 1 anymore but it seems worse, still better than the original AE but....
May be the input wire is too long? I used a separate transformer, rectifier and a 1000uf cap just for this clock which is then regulated with a low noise regulation circuit (150db ripple). Any hints, advice welcome here.

A picture is attached.

So far the CD drive (Studer D730) is still a far better source.
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Old 17th March 2009, 05:56 AM   #9
glt is offline glt  United States
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Hi, very nice. Regarding your previous post, theory says that the zener will help reduce the noise of the 317 if you use it in the adjust pin (see TNTaudio). But you already have it running.

I also plan to upgrade the PS of my AE. How easy was to remove the casing? Did you have to destroy it?

Since my dac can take I2S (TwistedPear Opus). I plan on tapping the USB inteface an feed that to a PCM2707, thus bypassing the internal USB to SPDIF (at least that was how the old AE was configured)

If possible, can you show the DAC chip in your AE? Thanks...
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Old 17th March 2009, 04:57 PM   #10
cdfr is offline cdfr  United States
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Hi glt,

>I also plan to upgrade the PS of my AE. How easy was to remove the casing?
cdfr: Not very hard with a dremel, but you have to be careful not to go too deep.

> Did you have to destroy it?
cdfr: Yes you basically destroy the casing since it is welded.

>I plan on tapping the USB inteface an feed that to a PCM2707, thus bypassing the internal USB to SPDIF (at least that was how the old AE was configured)
cdfr: Ok so if I understood you well, instead of the std pcm2705 of the AE 802.11g you want to put a pcm2707 which can deliver I2S. Keep me posted on your progress.

For the pictures I refer you this link:
http://www.vonwentzel.net/ABS/Dissec...ess/index.html
http://www.vonwentzel.net/ABS/Dissec...SCN8883-pp.jpg
http://www.vonwentzel.net/ABS/Dissec...SCN8884-pp.jpg

This is the same model as the AE I am using (i.e. the old one 802.11g). If you find pictures of the new AE 802.11n, let me know I am interested to find out more.

My immediate worry for now is how to get the expected results from the clock, and adding the phase 2 (AES 110 Ohm output).
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