DACKit complete, but a few issues!! - diyAudio
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Old 30th November 2003, 06:56 PM   #1
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Unhappy DACKit complete, but a few issues!!

Hi All (and hopefully Scott is reading, too!!),

well, I have just finished my DACKit and have fired it up using a 12v 7.5 ah gel battery. The batt had 11.5V when we started.

I was sad to hear lots of fuzz, and the music very quiet in the background. Our houseguest re-connected everything and turned on the system again when I was out of the room. Much excitement as music filled the room! Hurrah!

Anyway, I left the CD on overnight to burn the dac in. This morning, the fuzz was back. Hmm.

However, the batt voltage was down at 6.5!!! I recharged it today, and it was steady at 13-ish. OK, now to re-connect.

Still fuzz, then I remembered something about the order of when to switch on the source and the dac. I had the CD on and then powered up the dac. It worked !

Happy that I thought I had solved the problem, we listened to some Annie Lennox (Album Bare, track 5 "Wonderful"). No problem here, sounded very nice. Then, only occasionally, the sound would drop out. Once the loud part of the song kicked in, the system went dead. Hmm.

I turned everything off, back on, and the fuzz had returned.

Does anyone have any ideas? I was as careful as I could when I assembled the dac, but I think I have missed something here.....

Anyway, here are some pics. This is my first project, and it will not be complete until I can enjoy those sounds.

BTW, compenents are 0.1% resistors, BG and Wima caps, teflon coated silver wire etc etc.

CHEERS

Jon
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Old 30th November 2003, 06:58 PM   #2
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Thumbs up More pics

Here is the open case......

Jon
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Old 30th November 2003, 07:00 PM   #3
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I was hoping my work would be neat enough.......

Jon
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Old 30th November 2003, 07:05 PM   #4
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Are you sure you soldered the electrolyics in the right way ?? I don't see that you made errors with grounding but it is not always clear what one sees on a picture. to my eyes the DAC looks OK.

Did you double-check the resistor values and did you measure as well ? Did you doublecheck solder joints ? Did you measure the voltages at the DAC chip and receiver ? I had once trouble with dropouts caused by too large film caps at the input of the CS8412 receiver. I also read once that a forum member used the 7808/9 for the receiver and the 7805 for the DAC chip ...

Maybe it is wise to mail Scott himself for support !?!?! Although I never bought anything from him he always helped me with things I wanted to know.
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Old 30th November 2003, 07:24 PM   #5
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Hi JP,

I will check all the joints etc. The resistors have the values written on them, so I did not bother to measure them. However, I have not checked the voltages at the dac and receiver. I have a multimeter, so I'll give it a go tomorrow.

The film cap sizes are within the ranges specified, but I was experiencing drop-out, so I will have another look at them.

I soldered in the electros with the short leg as negative. Some were NP, but the polar ones had a gold "-" vertically on the side.

I'm glad you think it looks ok though - I'm really pleased with it (apart from the glitches!!)

Thanks for your thoughts!!

Jon
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Old 30th November 2003, 07:27 PM   #6
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Wink Missing LEDs

I forgot to mention that the LEDs are not installed as I coudn't make up my mind which one to specify.

Of course I want blue but when I look at the LEDs available and work out the 330R resistors into the equasion in the Maplin cataloge, the figires don't quite add up (or I will get a very soft blue???).

I am learning tons as I am going thought this!!

Jon
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Old 30th November 2003, 07:51 PM   #7
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Jon, please check current draw of those fancy blue LED's first ! Not being one with much experience with blue LED's ( it is more original to use plain read and green ones nowadays with every pc or amp having blue LED's )

I recall they have a Uf of 4V and draw more current than their red/yellow/green/orange collegues. AFAIK the LED's on DACkit are fed directly from the CS8412 that has a current limit. Please check CS8412's datasheet for that value. You might have a chance that a switching transistor has to be added.

I leave the googling for the blue LED current draw and the maximum current output of the CS8412 for you.

The series resistance is calculated as follows: R = ( Ubat - Uf ) / I led. I led is the desired current through the LED of course. Ubat is 5V and Uf is the forward voltage of the LED in question and depends on the colour of the LED.

Still waiting for fancy purple LED's ....
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Old 30th November 2003, 08:49 PM   #8
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Cool Purple!!!

Now there's a thought!!

Maplin do an Ultra-Violet LED - new product.

That could look good with a bit of engraved, painted lettering on a thick Acrylic fascia!!

I'll report back with my voltage readings tomorrow eve.

Cheers!

Jon
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Old 30th November 2003, 09:48 PM   #9
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Default Pretty work Jon!

fuzzy frizzy huh? Double check PLL filter values, 1k and 0.047 should work for sure. Then shorten and untwist and separate the input lead to the receiver. If you need the length, use a miniature 75 ohm coax, but it's bad form to twist that pair. Good lookin' dac there, I'd say.
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Old 30th November 2003, 09:54 PM   #10
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Default LED

The receiver goes low to trigger and the LED anode is pulled high through the +5 rail. Most any normal (ie: non-super brite or high current) LED is fine. I use blue, green, red whatever and never have had an issue, unless I doubled up on them.
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