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Old 3rd July 2004, 10:55 PM   #11
Nisbeth is offline Nisbeth  Denmark
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That looks great. Now let's see the inside


/U.


PS: If possible, can you make a pdf or something like that of the board layout (to use with phototransfer pcb-making)?
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Old 3rd July 2004, 10:56 PM   #12
roibm is offline roibm  Romania
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Is the Tuev cert genuine?
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Old 3rd July 2004, 10:58 PM   #13
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OK next up the top off! pretty much wysiwyg. Simple power supply to the right on vero board, regulators etc on main board. Beefyish 150VA traffo bought on ebay for 5 two 18v sec windings. The IV regs are LM317,337 arranged in the tracking preregulated fasion as described in the data sheet. The 5v reg is a LM340T 5v, all these run rather coolish so dont have any heatsinks. The 3.3v is an LM1086 which gets a bit warmer so I put a little heat sink I scavenged from a comp PSU on it. 4700uf of caps on each rail prior to this, very cheap nasty panasonics farnel had, still this thing sounds brilliant so im not worrying. Note the very short signal path!
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Old 3rd July 2004, 11:06 PM   #14
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WoW you guys were quick lol, yes that certificate will be genuine however I dont think what ive cooked up inside would qualify

Last photo. This is really just a close up of the various bits, first of all is the DIR1703 with the PCM1798 lurking in the corner. You can see that there is an empty DIP socket to the bottom right, this is for a PCM2902 when I get a replacement, cooked the 1st one, had the USB wires wired back to front I dont think the chip liked it too much. Next is the PCM1798, here you can clearly see the sink on the reg. And then finally the IV stage, which has OPA627 first and then AD797. Here you can also see the polystyrene caps which are bloody huge in comparison to the polyester ones used elsewhere. The grey buses (ie box shape) near the opamps and 0.1uf polyes, the close caps to the four OPA627 are 8.2nf polystye you can see the difference there.

The original pics taken by the camera look a lot better then those but unfortunately are 600k each so you see the problem lol.
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Old 3rd July 2004, 11:14 PM   #15
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Now for the slight nigle, appart from everything being great it has one small flaw. I get a small popping sound every now and again from the DAC, this is not really much of a problem but is a little annoying because it shouldnt be there. I have read somewhere else that another person had this problem and a man at TI I think said the DIR doesnt like jittery sources. Im using a Soundblaster live to drive this (it sounds MUCH better then a TEAC VRDS T1 so lets not argue why im driving this thing with crap like that haha) so it wouldnt be surprising if it was that.

Now MWP's schematic has a 47ohm resistor before the DIR on the SPDIF input, I had forgotten to add this originally and adding one made a big difference to how often it popped. Do you digi experts think making this bigger would solve the problem? Or do you think a SPDIF coupling transformer or whatever would be the ticket? If it is where do you get these things Ive only ever read about them, not seen.

Appart from the clicking brilliant.

Cheers Matt
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Old 4th July 2004, 05:33 AM   #16
MWP is offline MWP  Australia
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Is the popping being caused by interferance on the mains power supply?
As in, lights turning on/off, fridge compressor, etc?

Mine has this problem... never did have a good look at trying to fix it
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Old 4th July 2004, 01:53 PM   #17
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Quote:
Originally posted by MWP
Is the popping being caused by interferance on the mains power supply?
As in, lights turning on/off, fridge compressor, etc?

Mine has this problem... never did have a good look at trying to fix it
Nope its a digital thing I think.
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Old 4th July 2004, 05:19 PM   #18
MWP is offline MWP  Australia
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You did the modifications to the circuit i mentioned on the web page?
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Old 4th July 2004, 05:29 PM   #19
Nicke is offline Nicke  Sweden
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Default Re: My first DAC hurrah.

Quote:
Originally posted by 5th element
My version uses the DIR1703 SPDIF receiver coupled with a PCM1798 DAC chip. OPA627 perform the first pair of opamps after the DAC and then Analog devices AD797's for final shunt.

Just want to remind you about the AD797,when it is used as a follower it should have a 100ohm resistor in the feedback path.Look in the data sheet.

I have used AD797 in my old modified cdp once,and I like it a lot,especially with a JFET current source(about 2mA) connected between output and negative rail....
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Old 5th July 2004, 01:38 PM   #20
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Quote:
Originally posted by MWP


You did the modifications to the circuit i mentioned on the web page?
Aye - R23 has been removed, and im assuming that the connection to ground is also broken from pin 5 of the TL77 once this has been done. Im meaning here that it once connected via R23 and it should remain unconnected once the resistor has been removed.

And then simply add another resistor between pins 5 and 7. of the same device.

Also if the BRSEL gubbins is not used (ie the hardware sample frequency select) should the DIR automatically sense the incoming sample frequency? Mine as it stands will only work with 48k, put a 44.1k in and it doesnt detect a signal?
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