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PCB Group Buy for the "DAC + headphone amp" Project

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Geek

Geek

Member
Joined 2004
Hi doobooloo,

doobooloo said:
Geek -

Am I still in the confirmed 25 list? If so, do I have one or two boards reserved? I'm fine with either, especially if there will be a second batch that I can source more boards from if I decide to build a few variations.

I tried emailing you, but seems like you have it turned off. Sorry for posting this here.
Click to expand...

I have you confirmend for one. if one of the other "1 or 2" guys go for only 1, you can have the second. The reson is the PCB maker will only do them in lots of 25 per run. We also might have a few "fall off" in the process, in which case more will be available for the confirmed buyers.

So far three have been paid for. When the majority of the the rest are in, the PCB maker will hit the "Go" button :)

As for the email, I have no idea. I have had all my email addresses "whitelisted" at the ISP/host server level and have any and all incoming filters turned "off". If your email didn't get through, it could be on the Spamcop.net blacklist, in which case I have no control over because that's done at the bandwidth provider level.
 
gmarsh

gmarsh

Member
Joined 2004
Geek said:
Gmarsh - I've found perhaps a suitable sub?

Allied Electronics ( http://www.alliedelec.com ) part# 689-3636 or 689-3638 which is Qualtek numbers 771W-X2/02 and 770W-X2/12 respectively. They are $1.05 and $0.50 in single lot.
Click to expand...
Those are snap-mount parts, and they require more PCB space which isn't available. I'd buy the 100 from Digikey.

doobooloo said:
I was going to put it in the 53mm case anyway...

What about the Lansing cases? Will they have similar clearance issues?
Click to expand...
I never knew a Lansing case existed until now. :D I'm looking at them now.
 
gmarsh

gmarsh

Member
Joined 2004
Re: Last minute request ?

argofanatic said:
Is there a possibility of adding 4 jumper pads between the OPA4134's and the TPA6120 ?

That way we could use the DAC as designed as a headphone amp, or we could connect a couple of XLR connectors and turn it into a general purpose DAC.
Click to expand...

If soldering to SMT pads doesn't bother you, you can leave the TPA6120 out and solder four wires to the pads for the TPA's input resistors.

Only thing is, there's quite a big DC offset at this point - the output of the OPA4134 has a -4.4V offset with zero audio, and a peak swing from -1.7 volts to -7.1 volts. If you run this voltage to an XLR connector, you'll want to make sure that the receiving end can handle this offset.
 
A

argofanatic

Member
Joined 2005
Re: Re: Last minute request ?

gmarsh said:

...
Only thing is, there's quite a big DC offset at this point - the output of the OPA4134 has a -4.4V offset with zero audio, and a peak swing from -1.7 volts to -7.1 volts. If you run this voltage to an XLR connector, you'll want to make sure that the receiving end can handle this offset.
Click to expand...

Does anyone have a suggestion on how this offset could be tamed ? I have just enough analog knowledge to be dangerous, but this is beyond my capacity to deal with.

Thanks.
 
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